close encounters with the environment What’s Eating You? Dermacentor andersoni COL Dirk M. Elston, MC, USA, San Antonio, Texas CPT Chad Hivnor, MC, USAF, San Antonio, Texas Dermacentor andersoni (the Rocky noted for widely spaced eyes and pos- Mountain wood tick) is a large tick terior festoons. D andersoni has brown with small anterior mouthparts that are legs, and its coxa 1 (the attachment attached at a rectangular basis capituli. base for the first pair of legs) is bifid. Its scutum (hard dorsal plate) is ornate Male D andersoni have no ventral plates with large, deep punctations, and it is and their coxa 4 is greatly enlarged (Figure 1). The female tick has a Drs. Elston and Hivnor are from the Department of smaller scutum than the male, which Dermatology (MCHE-DD), Brooke Army Medical leaves a portion of the abdomen ex- Center, San Antonio, Texas. Dr. Elston is also from posed (Figure 2). The ticks are com- the Department of Dermatology at Wilford Hall Air monly found in open areas of low, bushy Force Medical Center, San Antonio. vegetation and are rarely found in The opinions expressed are those of the authors 1 and are not to be construed as official or as rep- heavily wooded areas. They are most resenting those of the Army Medical Department abundant throughout April and May, or the Department of Defense. The authors were and their numbers decline by July. full-time federal employees at the time this work An adult tick prefers to attach to the was completed. It is in the public domain. head, neck, and shoulders of its host, Reprints: Dirk M. Elston, MC, USA, Department of Dermatology (MCHE-DD), Brooke Army and clinical lesions present as pruritic, Medical Center, 3851 Roger Brook Dr, Fort Sam erythematous papules. Pruritus can be Houston, TX 78234-6200. intense and unrelenting, even with FIGURE 1. Male Dermacentor andersoni. VOLUME 67, FEBRUARY 2001 113 DERMACENTOR ANDERSONI FIGURE 2. Female Dermacentor andersoni. potent topical corticosteroid therapy. note that tick paralysis carries a mortal- Intralesional injections of triamcin- ity rate of greater than 10%. The tick is olone are often effective; however, some often hidden by scalp hair and is found lesions require excision. During the at an autopsy or by a mortician. course of engorgement, the saliva of Treatment of Rocky Mountain spot- D andersoni down-regulates cell-mediated ted fever must be started promptly and immunity,2,3 which may explain the de- is often based on a presumptive diagno- layed onset of many tick nodules. sis because delays in therapy can prove D andersoni is the major vector of fatal. Although there is no question that Rocky Mountain spotted fever in the therapy must be started as soon as pos- United States; Colorado tick fever; sible after symptoms occur and that Q fever; tularemia; and Rickettsia tetracyclines and chloramphenicol are peacockii, a new species of Rickettsia.4 Be- found to be active against the organism, cause the symptoms of Colorado tick the role of antibiotic prophylaxis after fever are nonspecific and overlap with tick bites remains controversial. A study those of Rocky Mountain spotted fever, by Kenyon et al6 suggests that a single specific diagnostic tests are needed. dose of tetracycline given more than Polymerase chain reaction amplifica- 48 hours before expected onset of symp- tion shows promise as a diagnostic tool.5 toms may prevent the disease. Optimal D andersoni is also closely associated timing of this single dose is difficult, with tick paralysis, which can be dra- however, because the disease incubation matic with rapid, progressive ascension period ranges from 4 to 10 days and may occurring 5 to 7 days after the attach- be related to the size of the inoculum.7 ment of a female tick. Removal of the A single dose given at the wrong time tick characteristically leads to immedi- can delay onset of symptoms but not ate improvement. Individuals with rap- prevent disease. There is no evidence to idly progressive ascending paralysis suggest that full courses of antibiotic should always be examined for therapy are less effective if started be- Dermacentor ticks. It is important to fore the onset of clinical symptoms; 114 CUTIS® DERMACENTOR ANDERSONI however, the cost-effectiveness of prophylactic reg- 3. Bergman DK, Ramachandra RN, Wikel SK. Dermacentor imens remains questionable. These regimens are andersoni: salivary gland proteins suppressing T-lymphocyte most likely to be cost-effective for patients who find responses to concanavalin A in vitro. Exp Parasitol. heavily engorged ticks in highly endemic areas— 1995;81:262-271. heavily engorged ticks have been attached to their 4. Niebylski ML, Schrumpf ME, Burgdorfer W, et al. Rickettsia hosts longer and are more likely to transmit disease peacockii sp. nov., a new species infecting wood ticks, than are ticks that have been briefly attached. Dermacentor andersoni, in western Montana. Int J Syst Bac- Although Rocky Mountain spotted fever is ver- teriol. 1997;47:446-452. tically transmitted from a tick to its offspring, this 5. Johnson AJ, Karabatsos N, Lanciotti RS. Detection of type of transmission decreases the viability of the Colorado tick fever virus by using reverse transcriptase offspring,8 which aids in containing the disease. PCR and application of the technique in laboratory di- agnosis. J Clin Microbiol. 1997;35:1203-1208. 6. Kenyon RH, Williams RG, Oster CN, et al. Prophylactic REFERENCES treatment of Rocky Mountain spotted fever. J Clin Micro- 1. Tick information sheet: the Rocky Mountain wood tick: biol. 1978;8:102-104. Dermacentor andersoni. Vet Clin North Am Small Anim Pract. 7. DuPont HL, Hornick RB, Dawkins AT, et al. Rocky Moun- 1991;21:49-50. tain spotted fever: a comparative study of the active im- 2. Ramachandra RN, Wikel SK. Effects of Dermacentor munity induced by inactivated and viable pathogenic andersoni (Acari: Ixodidae) salivary gland extracts on Bos Rickettsia rickettsii. J Infect Dis. 1973;128:340-344. indicus and B. taurus lymphocytes and macrophages: in vitro 8. Niebylski ML, Peacock MG, Schwan TG. Lethal effect of cytokine elaboration and lymphocyte blastogenesis. J Med Rickettsia rickettsii on its tick vector (Dermacentor andersoni). Entomol. 1995;32:338-345. Appl Environ Microbiol. 1999;65:773-778. VOLUME 67, FEBRUARY 2001 115.