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Chapter 160: Zoonotic Infections

Bryan B. Kitch; John T. Meredith

INTRODUCTION

The World Health Organization defines zoonotic infections as those diseases and infections that are naturally transmitted from vertebrate animals to or from humans. Zoonotic infections are often encountered in emergency care. Ticks are one of the most important vectors of human infectious diseases in the world.

A zoonotic infection has presenting symptoms similar to many acute infections: fever, headache, myalgias, malaise, and weakness. Given this, a specific diagnosis is often difficult. Particular exposures or occupations that involve animal contact carry an increased risk of disease (Table 160–1). Recent travel, particularly in spring, summer, and early fall, or history of habitation in an underdeveloped country, are also risk factors. Zoonoses can occur at any time of the year, but in temperate climates, most zoonoses happen in the spring and summer.

Table 160–1

Risk Factors for Zoonotic Infection

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Table 160–1

Risk Factors for Zoonotic Infection
Risk Category Examples
Agricultural workers Farmers, cattle ranchers, sheep ranchers, and migrant workers
Animal processing workers Slaughterhouse workers, animal hide processors, and workers in manufacturing who deal with animal products
Outdoor enthusiasts Forestry workers, lumbermen, surveyors, park rangers, hunters, spelunkers, and fishermen
Pet owners Those living alongside a dog, cat, bird, rodent, rabbit, reptile, or fish
Professionals Veterinarians, animal researchers, and animal handlers
Immunocompromised patients Those with congenital immunodeficiencies, diabetes mellitus, alcoholism, renal failure, liver failure, cancer, splenectomy, or human immunodeficiency virus

Zoonoses that can present as an undifferentiated febrile illness are listed in Table 160–2.

Table 160–2

Common Systemic Zoonotic Infections

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Table 160–2

Common Systemic Zoonotic Infections
Agent Animal Reservoir Physical Findings Diagnostic Tests Treatment
Aeromonas species Fish, reptiles Nonspecific fever, severe crepitant cellulitis with systemic toxicity, gastroenteritis — See chapter 159, "Food and Waterborne Illnesses"
Brucella canis Dogs Nonspecific fever Serologic testing, blood culture Doxycycline plus gentamicin or rifampin. TMP-SMX plus gentamicin in children
Capnocytophaga Dogs and cats Fever, septic shock, and meningitis from infected bite Culture of bite wound Amoxicillin-clavulanate or clindamycin. Pip-Tazo or a carbapenem plus clindamycin/vancomycin for shock
Chlamydophila psittaci Birds Fever, flulike illness, pneumonia, endocarditis, sepsis Serologic testing and sputum culture Doxycycline. Azithromycin and levofloxacin are alternatives
Coxiella burnetii Cattle, sheep, goats. Occasionally cats Fever, pneumonia, hepatitis, meningitis, endocarditis Serologic testing, PCR Doxycycline, with the possible alternative of a fluoroquinolone or macrolide
Ehrlichia species Ticks Nonspecific fever, sepsis, meningitis, hepatitis Clinical diagnosis, serologic testing, peripheral blood smear, immunocytologic testing, PCR Doxycycline recommended for all patients (even children and pregnancy). Rifampin is alternative.
Leptospira species Birds, dogs, rodents Fever, pneumonia, conjunctivitis, lymphadenopathy Darkfield microscopic examination of body fluids, serologic testing Penicillin G IV. Ceftriaxone IV alternative. Mild disease: oral doxycycline or amoxicillin or azithromycin
Francisella tularensis Rabbits, cats, wild animals, biting insects Fever, sepsis, meningitis, pneumonia, hepatitis, rash Serologic testing (poses hazards to laboratory staff) IV aminoglycosides. Alternative: Doxycycline ...

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