Pruritic rash in a recent traveler to central America: Chikungunya virus fever in a recent traveler

Differential diagnosis. Given the patient's travel history and extensive exposure to mosquitoes-and the general wisdom of Occam's razor-infection with dengue virus or chikungunya virus (CHIKV) seemed most likely to explain the fever, rash, polyarthralgia, lymphopenia, and mild thrombocytopenia. Both viruses are prevalent in El Salvador. However, infection with either typhus or spotted fever group rickettsia (prevalent in Central America) also could have explained the headache, fever, and generalized rash. Other diagnostic possibilities consistent with some, but not all, of the clinical picture included measles, rubella, leptospirosis, infection with Epstein-Barr virus, enterovirus, or parvovirus B19, and syphilis. Empiric therapy. The patient was admitted to the hospital and given doxycycline for empiric treatment of rickettsial infections; leptospirosis might also have benefited from this treatment. Diagnostic testing. Blood cultures were negative. Serologic studies (IgG and IgM) for dengue virus, Rickettsia rickettsii, Rickettsia typhi, Rickettsia prowazekii, and Leptospira (total antibody), were obtained and returned negative. Heterophile antibodies and the rapid plasma reagin test were negative, as was a serum polymerase chain reaction (PCR) assay for parvovirus B19 DNA. A serum PCR test for CHIKV was negative, as was an assay for serum IgG antibodies against CHIKV. However, a serum CHIKV IgM antibody assay was positive at a titer of 1:160 (reference range >1:10, performed at Focus Diagnostics, San Capistrano, CA).