Chapter 206. Leishmaniasis and Other Protozoan Infections

Epidemiology1

Leishmaniasis, a truly ancient disease,2 was recognized on Amerindian pottery drawings dating back to the first century ad.3 It was named after W.B. Leishman who identified organisms in smears taken from the spleen of a patient who died from “dum-dum fever” in India in 1901. The disease burden remains important in the twenty-first century with up to 2 million individuals developing systemic disease annually and accounting for around 70,000 deaths per year.4

The various types of leishmaniasis are confined primarily to the Mediterranean basin, Southern Europe, Central Africa, and parts of Southern and Central Asia [Old World (OW)], and Central and South America [New World (NW)]. The infection is endemic in 88 countries, 72 of which are developing countries.

In Western countries, the incidence is increasing due to human immunodeficiency virus (HIV)-Leishmania coinfection, military appointment, and tourism in endemic countries.5,6 New Zealand, Antarctica, and the Pacific islands are Leishmania-free. Australia was thought to be devoid of Leishmania species until 2004, when it was discovered in red kangaroos that had developed ulcers over their limbs or ears, raising the possibility of imported species becoming endemic, or of a current still unrecognized human form of the disease.7

More than 90% of localized cutaneous leishmaniasis (LCL) cases occur in Afghanistan, Algeria, Iran, Iraq, Saudi Arabia, Syria, Brazil, and Peru.8 In the United States, most LCL cases are imported; however, the Southern and Central parts of Texas are considered endemic for Leishmania mexicana.9,10

The World Health Organization (WHO) has classified leishmaniasis as a category 1 disease (emerging and uncontrolled). The recent geographic spread is attributed to massive rural-urban migration and agro-industrial development projects that bring nonimmune urban residents into endemic rural areas. Other incriminated factors include natural disasters, cessation of malaria spraying leading to increased sandfly population, reconstructions, control programs, global warming, wars, and deforestation.

Risk factors for contracting the disease include residing in an endemic area and in a ground floor, the design and construction material of the house, and the presence of domesticated animals. The prevalence of the disease increases until the age of 15 then seems to stabilize, probably reflecting development of immunity.11 In general, males have greater likelihood of developing the disease. This can be explained by behavioral differences in exposure as well as by hormonal modulation of disease susceptibility or resistance.12

See Box 206-1 for various forms of leishmaniasis and their abbreviations.

Etiology and Pathogenesis13

Etiology and Life Cycle

The genus Leishmania consists of parasitic protozoa of the phylum Sarcomastigophora, order Kinetoplastida, and family Trypanosomatidae. At least 21 species are pathogenic for humans and all are essentially transmitted by the bite of an infected female phlebotomine sandfly.4 Cases of venereal14 and vertical15,16 transmission, as well as transmission from infected blood transfusion17 or needles18–22 have, however, been reported.

Leishmania are dimorphic parasites; in the gut of the sandfly or in culture, they exist in the spindle-shaped motile (single anterior flagellum) promastigote form (10–20 μm). In the cells of the host reticuloendothelial system, Leishmania exist in the oval nonmotile amastigote form (2–6 μm) that has a relatively large basophilic nucleus and a smaller rod-shaped kinetoplast of extranuclear DNA at the base of the lost flagellum.23 Infected macrophages are ingested by the fly during a blood meal and the amastigotes are released into the stomach of the insect where they immediately transform into the promastigote form. The latter migrate to the alimentary tract of the fly, multiply extracellularly by binary fission, and in few days, reach the esophagus and the salivary glands of the fly where they change into infective metacyclic promastigotes, which will be released into the skin at next bite. They are then phagocytosed by host macrophages where they transform into amastigotes that multiply by binary fission and get released following cellular burst to infect other macrophages (eFig. 206-0.1)

Reservoir Hosts24,25

Leishmaniasis is mostly zoonotic, being incidentally transmitted to humans from wild and domestic animals (primary reservoir hosts) (Table 206-1).24,26–29 However, visceral leishmaniasis (VL) caused by Leishmania donovani and OW-cutaneous leishmaniasis (OW-CL) caused by some Leishmania tropica strains are anthroponotic diseases (i.e., humans are the primary reservoir hosts).

Insect Vectors30

The insect vector of leishmaniasis, the female phlebotomine sandfly, is grouped under the Suborder Nematocera of the order Diptera. Three genera [(1) Phlebotomus in the OW, and (2) Lutzomyia and (3) Psychodopygus in the NW], and around 70 species are implicated as vectors.31 They are widely distributed and have predilection to intertropical and warm temperate zones. Only the female sandfly is hematophagus. Phlebotomine sandflies are less than 3 mm long, and do not fly far from their breeding site. Their activity is mostly crepuscular or nocturnal while the host is asleep. They rest during the day and lay their eggs in dark, cool, humid, and organic matter-rich places such as rodent burrows, bird's nests, and house wall fissures. Being exophilic and exophagic, they prefer to rest and to have their meal outdoors, which limits their control through house spraying.

Pathogenesis31

The resulting disease depends on the fate of the phagocytosed amastigotes. This in turn is function of numerous parasite- and host-related factors, as well as other factors that may account for geographical differences.8,32

In general, parasites interfere with the signaling pathways, intracellular kinases, transcription factors, and gene expression of macrophages, compromising their ability to generate leishmanicidal substances. In addition, they impair dendritic cell activation, migration, and ability to secrete T helper 1 (Th1) cytokines.

Parasite-Related Factors33

Sandfly saliva is increasingly recognized as an essential element in the pathogenesis of the disease. Besides containing vasodilators, anticoagulants, and immunomodulators, it may also increase the inoculum size and the diameter of the lesion.34 Intraspecific variations of sandfly saliva may even affect the overall clinical outcome of Leishmania infantum-induced disease by shifting the adaptive immunity from a Th1 to a Th2 immune response. The development of anti-saliva antibodies after exposure may account for the decline with age of susceptibility to the infection in endemic areas.11

Other parasite-related factors include infectivity, pathogenicity, virulence, and tissue tropism.35–39 These differ from one species to the other. For example, lipophosphoglycan and gp63 are two important promastigote virulence factors that impair infected cells’ overall functions with the former being clearly involved in Leishmania major disease but absent in L. mexicana.11

Although viscerotropic species tend to spread to the reticuloendothelial system, they may become dermotropic as a consequence of treatment such as seen in post-kala-azar dermal leishmaniasis (PKDL).40 Similarly, L. tropica, classically dermotropic, may cause visceral disease.41,42

Host-Related Factors11,31,43

Malnutrition, immunosuppression, and host genetic background influence host susceptibility as well as resistance to the disease. The output of acquired T cell immunity, which depends on the net effect of the opposing Th1 and Th2 responses, largely determines the course and the therapeutic response of the infection. A dominant Th1 response resulting in the production of interferon-γ (IFN-γ) and nitric oxide leads to a leishmanicidal state of macrophages, and accounts for subclinical infection or self-healing LCL and the positive Montenegro skin test (that assesses delayed-type hypersensitivity to leishmanial antigen). A dominant Th2 response accounts for progressive disease such as diffuse cutaneous leishmaniasis (DCL), and is characterized by anergy to leishmanial antigen (negative Montenegro skin test). Mucosal leishmaniasis patients will have both Th1 and Th2 responses, with slight predominance of Th2 immunity, explaining persistence of the disease. To summarize, T-cell immunity would be intact in LCL, defective in DCL, and pathologically exuberant in mucocutaneous leishmaniasis (MCL). Humoral immunity seems to play little or no role in determining the course of the infection. High titers of anti-leishmanial IgG correlate more with chronic, nonhealing, and visceral disease.

Clinical Findings

The clinical spectrum includes cryptic infection, LCL, and other forms including disseminated infection [DCL, MCL, VL, VTL (viscerotropic leishmaniasis), PKDL, leishmanid].31

Cryptic Leishmaniasis

Both cutaneous and visceral infection can remain subclinical or manifest with mild, nonspecific, and transient symptoms.8,31,44,45

Localized Cutaneous Leishmaniasis46

LCL constitutes 50%–75% of all incident cases. It is the mildest form of Leishmania diseases and the one that prevails in the OW.3 It can be caused by all Leishmania species. Most cases heal spontaneously within 1 year and are characterized as acute LCL. Disease lasting more than 1 year is termed chronic LCL.

Acute LCL

Old World Localized Cutaneous Leishmaniasis

OW-CL (Aleppo boil, Baghdad boil, Oriental sore, leishmaniasis tropica, Biskra button, Delhi boil, Bouton d'orient, Lahore sore, Rose of Jericho, Kandahar sore, the little sister) is caused mainly by L. major, L. tropica, Leishmania aethiopica, and to a lesser extent L. infantum (Table 206-1).24,26–29 Two major types, (1) the moist type (caused by L. major) (Fig. 206-1) and (2) the dry type (caused by L. tropica), are identified (Table 206-2).47–50 Both types may coexist in the same patient.40

L. aethiopica may cause a similar cutaneous disease to L. tropica but carries a higher risk of evolving into DCL in up to 20% of affected individuals.47 L. infantum, the causative agent of Mediterranean VL in children, may cause a self-limited skin disease in adults.51–53 Species identification cannot be made clinically and requires biochemical/molecular techniques.

The morphologic spectrum of OW-LCL is wide. Lesions start as erythematous papules that enlarge over few weeks to form nodules/plaques and often ulcerate and become crusted (Figs. 206-2, 206-3, and 206-4; eFigs. 206-4.1 and 206-4.2). The “volcanic” noduloulcerative morphology is characteristic and consists of painless crateriform ulcer with a rolled margin and a necrotic base that is often covered with an adherent crust (Fig. 206-5). Other presentations include “iceberg nodules,”54 and eczematoid, psoriasiform,50 erysipeloid,55,56 zosteriform, paronychial, chancriform, annular, palmoplantar,57 verrucous, and keloidal58 lesions. Satellitosis (Fig. 206-6), regional lymphadenopathy, localized lymphadenitis,59 sporotrichoid lymphatic spread (eFig. 206-6.1), subcutaneous lymphatic nodules,54,60 and localized hypoesthesia61 may occur. Mature lesions may be elongated and oriented parallel to skin creases.54 Secondary bacterial infection is common.62

New World Localized Cutaneous Leishmaniasis (NW-LCL)

NW-LCL (valley sickness, Andean sickness, white leprosy, chiclero ulcer, uta, pian bois, and bay sore) is caused by L. mexicana and Leishmania (Viannia) braziliensis complexes mainly (Table 206-1). Infection with L. mexicana or Leishmania (Viannia) guyanensis causes only cutaneous disease in contrast to infection with L. (V) braziliensis and Leishmania (Viannia) panamensis, which may, in 40%–80% of the cases, progress to MCL. Pure cutaneous disease is very similar to OW-LCL and isolated ulcers in exposed areas are the most common presentations. The progression of the lesions gives rise to a characteristic scar consisting of thin pale skin at the ulcer site with a hyperpigmented border.3 About 50% of the lesions caused by L. mexicana heal within 3 months, whereas those caused by L. braziliensis persist much longer and are often associated with lymphadenopathy.63,64 L. mexicana, however, is the causative organism of chiclero ulcer, a chronic mutilating infection of the pinna of the ear of forest workers in Mexico and Central America. (Fig. 206-7) Lutzomyia flaviscutellata is the major vector. In Brazil, the lower limbs are commonly affected, causing the typical Bauru ulcers.3 Uta, the Andean cutaneous form of leishmaniasis, is caused by L. braziliensis and predominantly affects exposed areas in children. Its principal vector is Lutzomyia peruensis. An atypical nodular form of NW-CL caused by Leishmania d. chagasi has been reported from Honduras65,66 and Nicaragua.67 Unusual clinical pictures have been reported, especially in immunosuppressed patients.3,68

Complications of LCL

Common complications include permanent scarring, disfigurement, and social stigma. Autoinoculation or koebnerization following trauma, tattooing, or surgery have been reported.69 Major complications of LCL include chronic LCL, DCL, and MCL (in NW-LCL). Acute immunodeficiency syndrome (AIDS) and other immunosuppressive conditions increase the risk of mucocutaneous and visceral dissemination,70–73 and of recurrence following therapy.74 Disseminated cutaneous leishmaniasis, defined as more than ten pleomorphic lesions in noncontiguous areas of the body, has been reported in increasing frequency to complicate NW-LCL and HIV-associated OW-LCL.69

Chronic LCL

Typically, the lesions evolve from papules to chronic disfiguring indurated nodules/plaques that are larger than average acute LCL lesions and may exhibit variable degrees of scaling, ulceration, verrucosity, and scarring. (Fig. 206-8) The diagnosis may be challenging because of the paucity of organisms seen on histologic examination.

Leishmaniasis Recidivans

Leishmaniasis recidivans (LR) is a rare form of chronic LCL and accounts for 3%–10% of all LCL cases. It is caused mostly by L. tropica in the OW, and less commonly by L. (V) braziliensis in the NW as well as Leishmaniasis amazonensis, L. (V) panamensis, and L. (V) guyanensis. Erythematous scaly papules, often with apple jelly appearance, at the borders of a completely or partially healed CL lesion, are characteristic. It may complicate vaccination with a live strain of Leishmania75 and usually occurs in the setting of hyperactive T-cell immunity and low antibody titers. Reactivation of dormant infection (up to 15 years after apparent resolution) after an unknown stimulus such as trauma or topical corticosteroids, rather than reinfection with different strains, is believed to account for most of the cases. In fact, several studies have demonstrated persistence of the intracellular living organisms in “healed” Leishmania lesions, this being more likely to occur if therapy was incomplete or deficient.76,77

Lupoid Leishmaniasis

Lupoid leishmaniasis shares similar etiology and clinical picture with LR; however, the former is not a recurrent lesion.62 The lesion characteristically occurs over the face and may resemble clinically lupus vulgaris or discoid lupus erythematosus.78 In the absence of molecular identification of parasites, the diagnosis may be delayed for several years leading to mutilation (Fig. 206-9).79

Other Forms of Leishmaniasis

Diffuse Cutaneous Leishmaniasis

DCL, also called pseudolepromatous leishmaniasis, is an anergic rare form of cutaneous leishmaniasis that occurs in the setting of deficient cell-mediated immunity and mimics clinically and histologically lepromatous leprosy. It is usually caused by L. aethiopica in the OW and by L. amazonensis and L. mexicana in the NW. Immunosuppressed patients, especially HIV-infected individuals, may develop a severe form of DCL (>200 lesions) with no species-specific relation.4,80,81 Following a classical LCL lesion, dissemination occurs (immediately in 30% of cases but up to 11 years in others)47 in the form of nonulcerated and parasite-laden nodules (eFig. 206-9.1) with predilection for exposed areas of the body such as the face, where lesions may coalesce leading to leonine facies. Viscera are not involved. A progressive/chronic course with relapse after therapy is classical.

Mucocutaneous Leishmaniasis

MCL may complicate up to 10% of LCL patients and is characterized by the chronic and progressive spread of lesions to the nasal, pharyngeal, and buccal mucosa; lesions appear 1–5 years after resolution of the primary lesion(s), or less commonly while they are still present. It is often a complication of NW-LCL caused by L. (V) braziliensis, L. (V) panamensis, L. amazonensis, and L. (V) guyanensis. Ninety percent of cases occur in Bolivia, Brazil, and Peru.82 In the OW, similar mucosal lesions caused by L. aethiopica may be seen but have a better prognosis.4,83,84

MCL results from direct extension or hematogenous/lymphatic spread to the upper respiratory tract, and rarely ocular and genital mucosa, and liver.40 Bony structures are usually spared. Stuffy nose, epistaxis, coryza, hyperemia, and nasal septum crusting and ulceration are frequent presenting symptoms and signs. If untreated, the disease evolves into either septal perforation with resulting collapse of the nasal bridge and free hanging nose (tapir nose or parrot beak) or partial/total naso-oropharyngeal mutilating ulceration (espundia) (Fig. 206-10). In rare cases, the lips, cheeks, soft palate, or larynx are involved.11 Lymphadenopathy is common in L. braziliensis-induced disease and may be associated with hepatomegaly and systemic symptoms.4

The major causes of mortality are secondary infection, pharyngeal obstruction, and respiratory failure. Cure rates decrease with advanced disease.4

Visceral Leishmaniasis3

VL (Sikari disease, Burdwan fever, Shahib's disease, tropical splenomegaly, kala-azar, death fever, dum-dum fever) is endemic in the tropical and subtropical parts of the world. Ninety percent of cases occur in Bangladesh, Ethiopia, India, Nepal, Brazil, and Sudan.82 The causative agents are L. donovani and L. chagasi/infantum and to a lesser extent L. amazonensis, and Leishmania (Viannia) colombiensis. Infection with L. donovani occurs in the OW (India and Sudan), is anthroponotic and highly endemic, and involves Phlebotomus argentipes as a vector. Other infections are zoonotic and dogs are the major reservoir hosts. L. infantum afflicts mainly malnourished children in China, Africa, the Middle East, and the Mediterranean basin.

Hematogenous dissemination of the parasite to the reticuloendothelial system follows skin inoculation. However, congenital (transplacental) transmission may occur.16 Most infections remain subclinical. The incubation period and the duration of the disease are variable. The cardinal features of VL are persistent high undulating fever, leucopenia, anemia, splenomegaly, and hypergammaglobulinemia. Other findings include emaciation, burning feet (peripheral neuropathy), hepato-gastrointestinal disturbances, epistaxis, thrombocytopenia, and lymphadenopathy. Skin lesions develop later in the course of the disease and consist of ashy hyperpigmented patches on the temple, around the mouth, and on the abdomen, hands, and feet in light skin-persons; hence, the name kala-azar (in Hindi, black sickness). Other findings include hair and skin depigmentation (in Kenyan patients),40 cutaneous nodules and mucosal ulcers (in Sudanese patients),40 trichomegaly (Pitalugo's sign), petechiae, and jaundice.40

Without treatment, the fatality rate in developing countries approaches 100% in 2 years with the major complications being cachexia, secondary infections, enteritis, and pneumonia. Hemolytic anemia, acute renal damage, and severe mucosal hemorrhage are less common.

VL/HIV Coinfection.85

Most coinfection cases have intravenous (IV) drug use as a common denominator86 and represent diagnostic and therapeutic challenges, since VL precipitates the onset of AIDS and HIV increases the risk of VL. The problem is mostly described in Spain, Italy, France, and Portugal.82,86–89 L. infantum is the major causative agent; however, other Leishmania species that do not normally visceralize have been isolated.80,81,90 MCL-, PKDL-, and DCL-like pictures may result91 and cutaneous lesions are highly variable.71 Multiple dermatofibroma- and Kaposi's sarcoma-like papulonodular lesions may occur,86 and should be differentiated from parasitic colonization of Kaposi's sarcoma.92 The presence of amastigotes in atypical locations tend to correlate with the degree of immunosuppression.93 People with both conditions have worse prognosis, shortened survival time, higher relapse rate and inferior response to treatment compared with HIV-negative patients. VL is now being proposed to be integrated in the Centers for Disease Control and Prevention (CDC) clinical category C as an AIDS-defining illness.3

Post-Kala-Azar Dermal Leishmaniasis94

PKDL is extremely rare in the NW and is mostly seen, in two major forms, in Sudan and India (eTable 206-2.1). As the name implies, it is a cutaneous manifestation of VL that usually develops months to years after resolution of VL, and rarely during its treatment.96,98 In India, PKDL is the most common skin manifestation of leishmaniasis (eFigs. 206-10.1 and eFigs. 206-10.2). Affected patients are the major reservoirs of the infection.98 High blood concentration of the immunosuppressive cytokine interleukin-10 in VL patients is predictive of PKDL development. The parasite count is low and detection of organisms is not always possible. With polymerase chain reaction (PCR) technique, however, Leishmania parasites are recovered in skin lesions in up to 83% and 94% of Sudanese and Indian PKDL, respectively. The development of skin lesions in PKDL is closely linked to Leishmania-specific lymphocyte reactivity, or in HIV patients, to immune reconstitution during HAART treatment. The reason behind the two major clinical forms of PKDL remains essentially unclear.94

Viscerotropic Leishmaniasis41

Caused by L. tropica, this variant has been described among American veterans of Operation Desert Storm. Visceral infection manifests as fever, malaise, and variable hematologic and hepato-gastrointestinal findings. Classic signs of VL are absent and the skin is usually not involved; however, a recent report in a young Afghani refugee living in the United States demonstrated cutaneous lesions.99 Positive culture from bone-marrow aspirates and good response to antimonials are typical.

Leishmanid

This term refers to an id reaction consisting of a diffuse, asymptomatic, and symmetric papular eruption in the setting of acute LCL or LR.100 It typically resolves within 8 weeks of its appearance. Leishmanid may develop during treatment and is not an indication to withhold therapy.47

Diagnosis101,102

Given the potential treatment toxicity, confirmation of the diagnosis is always mandatory. Even when smear, histology, and culture results are combined, the parasite may not be detected in 10%–20% of cases.40,54 The diagnostic challenge is often greater in NW disease and in chronic lesions.63,103 The sensitivity of both tissue smear and culture approaches 90% when specimens are taken during the first weeks of infection.3 The best approach is to use several diagnostic methods.

Taken from the infiltrated margin, a skin biopsy may be divided into three parts: one for an impression smear, one for histological examination, and another one for culture.

Several smear techniques may be used with a success rate ranging between 50% and 80%.40 They are obtainable from fine needle aspirates or tissue scrapings, air-dried, fixed with methyl alcohol, stained with Giemsa stain, and viewed under oil-immersion microscopy. Impression smears, made by gently pressing the skin biopsy against a glass slide 2–5 times, provide better sensitivity than H&E examination.104

The histopathologic examination of early lesions of LCL reveals a dense and diffuse mixed inflammatory cell infiltrate composed predominantly of histiocytes, and scattered multinucleated giant cells, lymphocytes, and plasma cells105 (sometimes with intracytoplasmic homogenous eosinophilic immunoglobulin material called Russell bodies). The hallmark of the disease (in around 70% of the cases) is the presence of numerous extracellular and intracellular (within histiocytes) amastigotes (also known as Leishman–Donovan bodies) (Fig. 206-11A).40 Giemsa stain stains the parasite nonmetachromatically and the kinetoplast bright red. The organisms may also be highlighted by the Wright and Feulgen stains. Monoclonal antibodies such as G2D10 can identify amastigotes and promastigotes in smear, biopsy or culture specimens, constituting a rapid screening test for leishmaniasis.106 The histologic differential diagnosis includes diseases characterized by parasitized macrophages. The presence of halo surrounding the yeasts in Histoplasmosis, safety pin-like encapsulated Donavan bodies in Granuloma inguinale, and Mikulicz cells in Rhinoscleroma distinguishes these conditions from Leishmaniasis. Other considerations are blastomycosis, paracoccidiomycosis, toxoplasmosis, and trypanosomiasis. As the lesion evolves, the number of amastigotes per section decreases and the histology approaches that of chronic LCL where the predominant histologic pattern is nodular/diffuse noncaseating tuberculoid granulomatous dermatitis (Fig. 206-11B). Epidermal hyperplasia and ulceration are variable. Scarring with marked loss of elastic fibers may be seen.

In DCL, a diffuse infiltrate composed of vacuolated macrophages with numerous intra- and extracellular amastigotes is characteristic. The major differential diagnosis is lepromatous leprosy. In MCL, the histopathologic findings are similar to those of LCL but organisms are usually sparse. In PKDL, Pautrier-like epidermal microabscesses and a dense lymphoplasmacytic infiltrate with papillary dermal edema (in early lesions) are characteristic.47

Culture (at room temperature), by means of a biphasic medium such as Novy-Mac-Neal-Nicolle (NNN) or chick embryo medium, is the gold standard of diagnosis, but with a sensitivity of only 50%.40 It can be performed using aspirates, scrapings or fresh skin biopsies.69 Promastigotes often appear after several days but occasionally may take few weeks. Species identification is not possible based on their morphology.

Molecular techniques using species-specific oligonucleotide probes for kinetoplast DNA may be used on all specimens. PCR methods are particularly useful and offer superior specificity and sensitivity in the diagnosis of cutaneous leishmaniasis, MCL, and VL, especially in cases where organisms are scarce.107–111 Their widespread use, however, is hindered by cost as well as by the technical expertise they require. False-positive reactions and species identification in NW-CL may be at times problematic.11

Isoenzyme analysis is currently considered to be the gold standard for Leishmania speciation. It consists of enzyme electrophoresis of cultured promastigotes and is based on the fact that morphologically similar promastigotes of different species have different enzyme profiles; however, it is lengthy and costly.

Serology in cutaneous leishmaniasis is not useful due to its low sensitivity (antibodies present in low titre112) and specificity (due to cross-reaction with leprosy, malaria, and other trypanosomal infections).

The Montenegro skin test (Leishmanin) is analogous to the tuberculin test and consists of phenol-killed promastigotes injected in the dermis.3 This allows the detection of exposure to Leishmania without distinguishing between past and active infection.113 Up to 50% of people living in endemic areas may test positive without a history of previous or active disease. The test is positive once crusting has developed, and negative in anergic states such as DCL and PKDL or often in lesions (less than 3-months-old).

Laboratory animal inoculation (xenodiagnosis) is useful when the parasite load is low.40 Electron microscopy offers no advantage over light microscopy and its use is limited.40

In VL, microscopic detection and/or culture of parasites in tissue aspirates from spleen (sensitivity >97%), lymph nodes (sensitivity 60%), or bone marrow (sensitivity 55%–97%) is diagnostic. However, as these techniques are invasive, several serologic and molecular methods have been developed. Anti-K39 antibody based on a recombinant antigen from L. chagasi has high sensitivity and specificity. It is an immunochromatographic strip test using finger prick blood and is helpful in resource-poor regions. As a last resort, PCR of peripheral blood or tissue aspirate can be done and is extremely sensitive.114

Differential Diagnosis

(Box 206-2)

Prognosis and Clinical Course31

The clinical course is disease dependent. In general, lifelong species-specific immunity follows drug-induced cure or natural resolution.115 Cross-species immunity may also develop.116 Sterile immunity does not occur and persistent tissue infection seems to be the rule even following adequate therapy.39,117–119

Treatment120–123

Given the clinical diversity of leishmaniasis and the lack of adequately controlled therapeutic trials, each case needs to be individualized based on the parasite species (Table 206-3), extent of the disease, host immune and nutritional status, presence of intercurrent diseases, geographic region, and cost, availability and toxicity of the various therapeutic options. In general, NW-CL tends to be more severe and progressive than OW-CL. In addition, NW-CL caused by L. braziliensis may eventuate into “espundia,” thus necessitating systemic therapy. As a rule, patients should be monitored until the lesions have completely healed. Follow up at 6 months is appropriate.

Since most lesions caused by L. major and L. mexicana heal spontaneously within 4 months, an expectant approach is favored as it may confer protective immunity. Multiple, persistent, progressive, deep, sporotrichoid, and secondarily infected lesions should, however, be treated as well as lesions on cosmetically or functionally important sites such as joints.

Local therapy (Box 206-3) is appropriate for small, noninflamed and localized lesions that are not at risk to progress to MCL. Topical imiquimod alone is ineffective.141 Systemic therapy is reserved for complicated CL such as DCL and CCL, MCL, VL, relapsing disease, or disease complicated by HIV coinfection. In general, OW-CL requires shorter courses compared to NW-CL. Systemic therapies used for leishmaniasis are summarized in Table 206-4. Sodium stibogluconate and meglumine antimoniate are pentavalent antimony derivatives with slightly differing antimony concentrations and comparable efficacy and safety profiles. They are the mainstay of systemic treatment.178 Indian VL is treated with 20 mg/kg/day intramuscularly or IV once daily for 40 days versus 28 days if the disease is contracted elsewhere. Antimony resistance is a serious issue in India and in Iran.179–182 Resistant cases may benefit from combining antimonials with pentoxifylline,156 allopurinol,183–186 paromomycin,187,188 azithromycin,189–191 IFN-γ,192–194 granulocyte-macrophage colony-stimulating factor,195 and topical imiquimod.196,197

Prevention and Vaccines

Essential to prevention is the promotion of personal protective measures through the use of protective clothing, insect repellents containing 30%–35% DEET, permethrin-treated bed nets and clothing; the avoidance of endemic areas; and staying on higher floors of buildings in the evening.198 One way of reservoir control of L. major was achieved by destroying burrows made by the rodent host. In endemic areas where dogs could be hosts of parasites, a dog collar coated with deltamethrin could be a useful way to control transmission.11 Targeting anthroponotic foci that are at the origin of deathly epidemics, suspecting leishmaniasis in persons with skin lesions or febrile illnesses returning from endemic areas, and deferring prospective blood donors from donating blood for at least 1 year after their return are other measures. Control of HIV in Southern Europe where leishmaniasis is closely associated with HIV has generated positive outcome.114

New diagnostic tests, drugs, and vaccines are in development.116,199,200 Vaccine development for tropical diseases is often limited by the lack of financial return.201 “Leishmanization,” the self-inoculation of the live parasite in inconspicuous areas of the body, has been practiced in endemic areas to prevent disfiguring facial lesions, but was later abandoned due to its complications. Killed promastigotes vaccines with and without adjuvant BCG seem to be useful in some endemic areas.116,202 Adjuvants such as BCG are important to prime a Th1 response. Attenuated live parasites- and plasmid DNA-based vaccines using leishmanial antigens have shown efficacy in mouse models.116 Experimental vaccines containing a component of sandfly saliva proteins appear to be promising.203 Despite being experimentally successful, a safe nonliving prophylactic vaccine has not yet been able to confer significant protection in humans.204 The recent sequencing of the Leishmania genome might lead the way to new ways for prevention, control, and treatment of the condition.205–207

See references 208 and 209.

Epidemiology

African trypanosomiasis (Af-T) afflicts humans (sleeping sickness) and cattle (nagana), and affects up to half a million people every year in the middle latitudes of Africa, where the vector is found. Fatality rate is close to 100% in untreated patients. The disease is very rare in the United States.209

Etiology and Pathogenesis

Trypanosoma brucei, a unicellular organism, enters the bloodstream of a mammalian host via the bite of a blood-feeding infected male or female tsetse fly of the genus Glossina. Other ways to contract the disease, although uncommon, include placental transmission, blood transfusion, and sexual contact.210,211

The tsetse flies are attracted by dust clouds of moving objects and animals, as well as black and blue colors. They bite most during early daylight and at dusk, and ingest trypomastigotes from infected blood meals (eFig. 206-11.1).

Trypomastigotes have a glycoprotein-coated surface that has a protective role against lytic factors found in human plasma. Furthermore, the extensive antigenic variation of the glycoprotein present on the parasite's surface allows evasion from humoral immunity. This also explains why a vaccine targeting trypanosomes would be extremely difficult to develop.212

Clinical Findings

Af-T presents in two distinct forms. West African or Gambian trypanosomiasis (GT) (caused by Trypanosoma b. gambiense) is a chronic predominantly anthroponotic disease present in rural areas west of the Rift Valley. East African or Rhodesian trypanosomiasis (RT) (caused by Trypanosoma b. rhodesiense) is an acute fatal disease (within weeks, if untreated) that infects mainly livestock/game animals east of the Rift Valley, and sporadically herdsmen, hunters, photographers, and tourists.213–215 Water requirements of the palpalis group of tsetse flies and the savannah habitat of Glossina morsitans determine the geographic distribution of GT and RT, respectively. This ecological separation, however, is not as strict as it was in the past with an overlap of the two forms of the disease in Uganda.212

In RT, a painful chancre develops at the site of the tsetse bite and resolves within 1–3 weeks leaving no scar. It consists of a circumscribed, rubbery, indurated, 2–5 cm dusky red nodule, often with a central eschar (Fig. 206-12). In GT, however, the initial lesion consists of a single nonspecific nodule that is often mistaken for an insect bite or a folliculitis.3

Afterward, Af-T will evolve in two stages: (1) the hemolymphatic or early stage and (2) the meningoencephalitic or late stage. In contrast to the late stage, when the skin is not involved, cutaneous changes may be seen in the early stage and are more commonly observed in RT and in light-skin patients. Perhaps for this reason, skin lesions are rarely reported in native Africans.

The hemolymphatic stage occurs 3–10 days after the initial bite development with the parasites entering the circulation and causing irregularly spiking fever. Hepatosplenomegaly, constitutional symptoms, normocytic anemia, thrombocytopenia, and pruritus (especially presternal) develop, and may be related to circulating immune complexes.3 Local lymphadenopathy progresses to generalized lymphadenopathy in virtually all African natives and in about half of Europeans patients. Involvement of the posterior cervical (Winterbottom's sign) and supraclavicular lymph node (LN) is characteristic only of GT. The disease is more severe in RT where severe parasitemia, myocarditis and rarely, fatal disseminated intravascular coagulopathy develop.209 Trypanids are distinctive eruptions that develop 6–8 weeks after the onset of fever in approximately half the light-skin patients, and consist of poorly defined, centrally pale, evanescent, annular, targetoid, or blotchy erythematous macular, hemorrhagic, urticarial, or erythema nodosum-like lesions, commonly on the trunk.216 These lesions might be due to a type III hypersensitivity reaction.3 A sensation of formication may be associated. The eruption waxes and wanes over weeks with accentuation upon exposure to cold, heat, or sweat. Painless swelling of the face (imparting a sad look), and of the hands and feet may occur. Other findings include ichthyosis, acroparesthesias, icterus, petechiae, and generalized flushing.

The late stage is characterized by central nervous system (CNS) involvement weeks to months after exposure in RT, and months to years after exposure in GT and occurs when parasites cross the blood–brain barrier. Severe headache develops then chronic meningoencephalitis, somnolence, coma, and death ensues. Delayed bilateral pain out of proportion to a sharp squeeze applied to soft tissues, known as Kerandel's deep delayed hyperesthesia, is characteristically found in European patients but is uncommon in African patients.217 Patients may also develop behavioral changes, psychosis and focal neurologic symptoms. Marked weight loss can ensue.212

Diagnosis

Diagnosis of Af-T is via detection of trypanosomes in blood film or Giemsa-stained thick smears, chancre/LN aspirate, buffy coat, bone marrow, or CSF. Histologically, long, thin trypanosomes are best seen using Giemsa stain, in the midst of a perivascular lymphoplasmacytic infiltrate. Because of antigenic variability, serologic tests lack sensitivity and specificity.213 Differentiation of RT from GT is usually based on epidemiology. PCR is the method of choice but cost limits its use in African countries.218 New diagnostic tools are being developed.219–221

Control of Af-T in endemic areas is highly cost-effective and entails case detection and treatment, keeping tsetse populations at low levels,221 and mass screening of at-risk populations.

Treatment

A lumbar puncture is essential for the differentiation between the early and late stages because treatment will vary accordingly.216 Four registered drugs are currently provided free of charge by the WHO.141,164,165,206 Suramin and pentamidine are the drugs of choice for early-stage RT and early stage GT, respectively. Melarsoprol, an arsenical, is a powerful trypanocide able to cure both RT and GT in all stages; however, due to its toxicity mostly on the central nervous system, its use is restricted to late-stage disease of both forms. Eflornithine is cytostatic and can only be used in GT. Of concern, HIV-positive patients receiving treatment for RT may succumb to full-blown AIDS.218 Other drugs that can be used for late stage disease include nitrofurazone and difluoromethylornithine.3 Combination therapy of the available drugs was investigated and all trials showed better results than monotherapy. Of note, combination therapy containing melarsoprol leads to severe drug reactions. A multicountry study comparing nifurtimox (registered for the treatment of Chagas disease) and eflornithine to eflornithine alone was undertaken for late-stage GT. The combination therapy resulted in fewer infusions, shorter treatment duration, and fewer adverse effects.222,223

See reference 224.

Epidemiology

American trypanosomiasis (Am-T) is a zoonotic disease caused by Trypanosoma cruzi and transmitted to humans by blood-sucking triatomine bugs (kissing bugs, assassin bugs, reduviid bugs). It is endemic in many rural areas of Central and South America and Mexico. In the United States, up to 300,000 individuals are affected and up to 45,000 have the clinical disease.225,226

Etiology and Pathogenesis

Triatomine bugs are large (3–4 cm), “cone-nosed” bedbugs that thrive in poor housing conditions and become infected with T. cruzi by feeding on contaminated blood. An infected triatomine bug takes a blood meal usually at night, and releases trypomastigotes in its feces near the site of the bite wound, usually a mucocutaneous junction. Human infection occurs when mucous membranes especially the conjunctiva or skin breaks are contaminated with the feces upon rubbing/scratching (eFig. 206-12.1). Other reported ways of transmission of the disease seem to be via the intake of reduviid feces-contaminated fruits and fruit products.3 Congenital (transplacental) transmission227 and transmission by blood transfusion and organ transplantation224,228–230 may also occur.

Clinical Findings

Am-T progresses in three stages (Box 206-4).

Diagnosis

Diagnosis and treatment are problematic. In the first stage, diagnosis involves microscopic demonstration of trypomastigotes in blood specimens especially thin smears, hemoculture, or xenodiagnosis. Thereafter, detection of organisms becomes difficult, and diagnosis relies more on serologic testing or PCR. The WHO recommends using at least two antigen detection tests for confirmation of the disease.237

Treatment

Treatment is indicated for acute infections, congenital infections, patients who are immunosuppressed or children with chronic disease.237 Both drugs that are available, benznidazole and nifurtimox, are toxic238 and most effective when given during the first stage of the infection or in congenital infections. Because of their toxicity, potential carcinogenic risk, decreased efficacy in chronic disease, and the presumably autoimmune nature of the latter, treatment of chronic disease has long been considered controversial. Later studies, however, revealed the persistence of the parasite in heart muscle as well as digestive tissue in patients with the chronic condition.235,239 In addition, patients with chronic cardiomyopathy who were given benznidazole had less clinical deterioration a decade later as well as lower serologic titers. Therefore, chemotherapeutic intervention at any stage of the disease is currently recommended.240 Allopurinol and itraconazole have also been tried for chronic disease.3

Preventive measures are aimed to eradicate the vectors, improve diagnostic tests, develop less toxic and more efficient drugs, and implement serologic screening of organ donors and recipients. Control programs have reduced the incidence of Am-T by 70% in some countries of South America.241

See reference 242.

Epidemiology

Entamoeba histolytica, of the class Sarcodina and genus Entamoeba, is a pathogenic ameba that can cause intestinal and extraintestinal diseases. Amebiasis is the second leading cause of death from parasitic diseases. Higher incidence is reported in Mexico and in developing tropical countries.243 In developed countries, risk groups include male homosexuals, travelers, immigrants, and institutionalized patients.

Etiology and Pathogenesis

Entamoeba exists in two forms: (1) the capsuled cyst (10–15 μm) or infective stage, and (2) the mobile trophozoite or tissue-invasive stage. Both forms are passed in the feces. Human beings are the only natural hosts and infection generally occurs by ingestion of mature cysts in fecally contaminated food, water, or hands. Anal sex and contaminated enema equipment are other modes of transmission.242

Trophozoites have marked phagocytic, proteolytic, and cytolytic capabilities, releasing proteases, collagenase, hyaluronidase, N-acetylglucosaminidase, phospholipase-A, and secretagogues.244 They can therefore invade human colonic mucosa, and occasionally penetrate through to the portal circulation, reaching the liver and other organs, and causing fatal lesions. Some mammalian cells are resistant to trophozoite adherence.242 Most cases of asymptomatic noninvasive “luminal amebiasis” are caused by Entamoeba dispar, rather than E. histolytica.245

Clinical Findings

Depending on the extent of invasion and the transmission mode, the clinical spectrum includes three major presentations:

1. Invasive intestinal disease (dysentery, colitis, and amebomas).

2. Invasive extraintestinal disease (liver abscess, peritonitis, and pleuropulmonary abscess).

3. Cutaneous disease can be either primary or secondary:

   • In primary cutaneous amebiasis, an extremely rare condition, the skin is affected without underlying intestinal or extraintestinal disease. It is thought to be secondary to direct inoculation from scratching with contaminated fingers in areas with poor hygiene. Penile lesions are often acquired through anal intercourse with infected individuals.243,246
   • In secondary cutaneous amebiasis, the skin can be infected following extension from an underlying/contiguous intestinal or extraintestinal abscess, draining catheter, fistula, colostomy or laparotomy incision.243,246,247 Trophozoites can also spread through contaminated stool to the anogenital skin. This is often seen in children with diarrhea following direct and prolonged contact with infected feces in their diapers.244,248 Autoinoculation via contaminated hands may account for more distal lesions.249–251

Both types of cutaneous transmissions are rare and result in rapidly progressive, foul smelling, and painful punched-out ulcers with glairy, hemopurulent, raw beef-like base; necrotic, cordlike and undermined borders; and surrounding erythema (Fig. 206-13). Lesions may reach up to 20 cm in diameter and are often destructive if untreated. Chronic urticaria may be associated252 and local lymphadenopathy is common. Without prompt diagnosis and treatment, the prognosis is poor. In rare cases, even primary cutaneous amebiasis has a fatal outcome.246

Diagnosis

The diagnosis relies on identification of cysts and/or trophozoites in infected stool, mucosa, or skin. This method, however, cannot distinguish between E. histolytica and E. dispar. Enzyme-linked immunosorbent assays are useful in this regard. Stool culture and PCR are only available as research tools. Serology may be helpful but false-negativity may occur in early infection. Skin biopsy reveals ulceration, mixed inflammatory cell infiltrate, and areas of necrosis where trophozoites may be identified as round or oval cells (20–50 μm) with basophilic cytoplasm, an eccentric nucleus with central karyosome, and often displaying erythrophagocytosis (sign of pathogenicity).253

Treatment

For symptomatic intestinal or extraintestinal disease, the drug of choice is oral or intravenous metronidazole (250–800 mg every 8–12 hours for 10 days), followed by treatment with one of the luminal agents iodoquinol, paromomycin, diloxanide furoate, dehydroemetine, or chloroquine.123

Epidemiology and Etiology

The free-living amebas belonging to the genera Naegleria, Acanthamoeba, Balamuthia and lately described Sappinia are ubiquitous in air, soil, and water; they rarely cause disease in immunocompetent patients; reported presentations include acanthamebic keratitis (in contact lens wearers) and primary amebic meningoencephalitis (caused by Naegleria fowleri). Immunocompromised AIDS and organ transplant patients are at risk of disseminated disease254 as well as at risk of developing granulomatous amebic encephalitis, a rare gradually progressive fatal neurologic disease caused by Acanthamoeba species.255–259 Free-living amebas can also harbor bacteria, such as Legionella, Mycobacterium avium, Burkholderia spp., Escherichia coli, and Vibrio cholerae, possibly serving as vectors of bacterial infections in humans.260

The portal of entry of the amebas is usually the nasal mucosa, from which they can reach the CNS. They can also enter through a skin break or through the respiratory tract with subsequent hematogenous dissemination to the CNS.257

Clinical Findings

Cutaneous lesions have been mainly reported in Acanthamoeba-induced disease, mostly in HIV-positive patients. Balamuthia mandrillaris-related skin involvement, however, is being increasingly reported. In HIV-positive patients, skin lesions are the most common (75%–90% of the cases) and sometimes the sole manifestation of disseminated disease.255,261 The extremities (lower more than upper) and the face are commonly involved. Numerous widely distributed papules, plaques, nodules, pustules, as well as cellulitis, nonhealing ulcers with rolled borders, eschars, and palatal ulceration have been described. Lymphadenopathy may be present.262 An asymptomatic plaque over the central face with possible satellite lesions along with neurologic symptoms is a characteristic presentation of B. mandrillaris disease.3

One study suggested that the immunologic state of the patient determines the clinical outcome of cutaneous acanthamebiasis. Unexpectedly, immunocompromised patients were found to develop multiple subacute skin lesions without CNS involvement and to respond better to therapy. On the other hand, immunocompetent patients had a worse prognosis with slowly progressive cutaneous lesions and more CNS involvement.262

Diagnosis

Histopathologically, a dermal and/or subcutaneous predominantly neutrophilic infiltrate is present, sometimes with vasculitic, and granulomatous changes.255,263 The identification of 20–30 μm trophozoites with abundant vacuolated cytoplasm, and central nuclear karyosome is diagnostic but may be difficult because of their macrophage-like appearance.255 Gomori methenamine silver and periodic-acid-Schiff stains may highlight the organisms. B. mandrillaris may occasionally exhibit more than one nucleolus distinguishing it from Acanthamoeba. Definite diagnosis and speciation is possible using indirect immunofluorescence, culture or PCR.3

Treatment

The disease is often fatal but early treatment using a combination of IV pentamidine and oral fluconazole, sulfadiazine, isethionate, or 5-fluorocytosine may improve the outcome. HIV patients may benefit from antiretroviral therapy.254

See references 264–267

Etiology

Toxoplasmosis, caused by the parasitic protozoan Toxoplasma gondii (class Sporozoa), is one of the most common human infections worldwide. The main reservoirs of T. gondii infection are members of the cat family (Felidae), which become infected by carnivorism; dogs and rabbits can also host the parasite. Viable organisms invade the feline intestinal epithelium where they undergo an asexual cycle followed by a sexual cycle and then form oocysts, which are excreted in large numbers and are resistant to harsh environmental conditions and disinfectants. Human infection results mainly from ingestion of cyst-containing undercooked meat or milk, but can also result from ingestion of the oocytes from fecally contaminated hands or food, organ transplantation,268 blood transfusion,269 or transplacental transmission.270 The parasites become tachyzoites and form tissue cysts, mostly in skeletal muscle, myocardium, brain, eye and placenta, and may remain asymptomatic. Invasion of the reticuloendothelial/endothelial systems results in suppuration and granuloma formation.

Clinical Diagnosis

Three major clinical forms are identified:

1. Congenital toxoplasmosis occurs in 1 per 1,000 live births in the United States. The risk of transmission is highest in the third trimester; however, the disease is more severe if transmitted in early pregnancy.3 Approximately 10% of affected newborns will have chorioretinitis and blindness, and 20% will have generalized or CNS disease. Infection may manifest as abortion,270 stillbirth, microcephaly, tram-track intracerebral calcifications,271,272 deafness, hydrocephalus, mental retardation, or seizures. Skin lesions include purpura, jaundice, blueberry muffin lesions (dermal erythropoiesis), and erythroderma. Untreated subclinical infection may reactivate during the second to third decade of life, mostly in the form of retinochoroiditis.273

2. Acquired toxoplasmosis in immunocompetent persons is often asymptomatic in 80%–90% of cases.274,275 However, 10%–20% of patients, preferentially including pregnant women, develop cervical or occipital lymphadenopathy and a flu-like illness. Rarely, myocarditis, pneumonitis, encephalitis, and polymyositis may occur. Cutaneous manifestations are protean reflecting the heterogeneous immune responses to the organism,264 and include among others dermatomyositis-like syndrome276–281 and pityriasis lichenoides (Box 206-5).275,282–285 Toxoplasmosis should be sought in patients with an acute dermatomyositis-like picture. Both conditions share a common underlying pathogenic mechanism related to the expression on muscle fibers of human leukocyte antigen class I as well as production of certain cytokines.3

3. Toxoplasmosis in immunodeficient patients is often secondary to reactivation of latent infection and presents as disseminated disease. Toxoplasmic encephalitis is the most common cause of intracerebral lesions in AIDS patients. Disseminated papular/nodular eruption may occur.85,264,294–296 Rare cases of graft-versus-host disease-like rash have been reported in patients who underwent hematopoietic stem cell transplant. Histology may not be helpful in differentiating between the two conditions.297 A high degree of suspicion of toxoplasmosis and molecular confirmation are important to distinguish between the two conditions.298

Diagnosis

Diagnosis is routinely made by serology. Protozoa may be identified in bronchoalveolar lavage or LN specimens, or skin biopsies. Tachyzoites, visualized with Wright or Giemsa stains, are crescent-shaped and have a prominent, centrally placed nucleus. The most common histologic finding is subacute histiolymphocytic vasculitis with demonstration of trophozoites within macrophages.293 Epidermotropic infection and neural infiltration may occur.299 Immunoperoxidase stains are specific and are particularly helpful when small tissue specimens are submitted. PCR-based testing has a high diagnostic value in acute disease and has become the preferred method of diagnosis, particularly in prenatal diagnosis of toxoplasmosis and in immunocompromised patients with disseminated toxoplasmosis. PCR detection of the parasite in fluid specimens (blood, amniotic fluid, CSF, urine, vitreous, and aqueous fluid) as well as fetal and brain tissues is indicative of active infection.300–303

Treatment

Treatment should be initiated in all patients with acute or active disease or congenital infection, and in immunosuppressed individuals.3 Sulfadiazine and pyrimethamine act synergistically and together provide effective therapy.123 Clindamycin can be used in sulfonamide-allergic patients. Co-trimoxazole was recently reported to be effective in the treatment of toxoplasmic lymphadenitis.304