ESSENTIALS OF DIAGNOSIS
Tick bites are typically painless, and <50% of patients with tickborne disease present with a known bite.
Consider tickborne diseases (TBDs) in the summer months for patients who present with fever, myalgias, and headaches but without GI or upper respiratory symptoms who live in tick-endemic regions of the United States.
Diagnosis can be difficult because of nonspecific symptoms and difficulty in timely confirmatory testing.
Treatment with doxycycline should be initiated when Rocky Mountain Spotted Fever, human granulocytic anaplasmosis, and/or ehrlichiosis is included in the differential diagnosis.
Tickborne diseases are on the rise in the United States. Several factors contribute to this surge, including suburban development, climate change, a rise in human outdoor activities, and an increase in vector hosts such as White-Tailed deer. Lyme disease is the most widely known tickborne illness to the public, as well as the most common. During 2000–2010 there were 250,000 reported cases of Lyme disease in the United States, although there has not been an incremental increase in the number of cases reported each year. However, the incidence of reported cases of anaplasmosis, babesiosis, ehrlichiosis, and Rocky Mountain Spotted Fever have all increased over that period of time and are the next most common TBDs after Lyme. The tickborne illnesses mentioned above will be discussed in detail in this chapter. Numerous other diseases are associated with ticks as vectors, many of which are emerging. (For more information regarding these illnesses, visit the following CDC webpage: http://www.cdc.gov/ticks/).
One factor that is essential to the diagnosis and treatment of TBD is the geographic distribution of the particular disease (Figure 53-1). Lyme disease, Rocky Mountain Spotted Fever (RMSF), ehrlichiosis, human granulocytic anaplasmosis (HGA), and babesiosis are all associated with particular species of ticks. Table 53-1 lists the six tick species of significance for this chapter, including their distribution and primary hosts. However, the patient rarely presents with the actual tick attached, and therefore visual identification of species is typically unnecessary.
Table 53-1. |Favorite Table|Download (.pdf) Table 53-1.
|Tick (Common Name/Species Name) ||Primary Range ||Transmits ||Additional Facts |
|Black-legged tick/deer tick (Ixodes scapularis) ||Northeastern USA, Great Lakes region ||Lyme, HGA, babesiosis ||Can remain active in warmer winters |
|Western black-legged tick (Ixodes pacificus) ||Pacific Coast, particularly northern CA ||Lyme, HGA ||Rates of infection are low |
|American dog tick (Dermacentor variabilis) ||East of Rockies ||RMSF ||Also known as wood tick |
|Rocky Mountain wood tick (Dermacentor andersoni) ||Rocky Mountain states ||RMSF ||Live in elevations 4000–10,500 feet |
|Lone Star tick (Amblyomma americanum) ||Southeast USA, but can be Texas to Maine ||Ehrlichiosis ||Bites can be particularly irritating |
|Brown dog tick (Rhipicephalus sanguineus) ||Throughout USA ||RMSF ||Primary host–dogs |
Distribution of key tickborne diseases 2010 (babesiosis not included). (Data from Centers for Disease Control and Prevention, ...