For spotted fever–group rickettsioses, immunostaining of skin rash or eschar biopsy specimens, or a PCR assay using DNA extracted from these specimens, can help provide a pathogen-specific diagnosis.
The reference standard for diagnosis of tickborne rickettsial diseases is the indirect IFA assay using paired serum samples obtained soon after illness onset and 2-4 weeks later. Demonstration of at least a fourfold rise in antibody titer is considered confirmatory evidence of acute infection. Patients usually do not have diagnostic serum antibody titers during the first week of illness, and a negative IFA assay or enzyme-linked immunosorbent assay (ELISA) result during this period does not exclude the diagnosis of tickborne rickettsial diseases.
Powassan virus has two subforms: lineage 1 and lineage 2. Lineage 1 is transmitted by Ixodes cookei or Ixodes marxi, and lineage 2 is transmitted by Ixodes scapularis. Both have been shown to cause human disease, with similar clinical manifestations.
For ehrlichiosis and anaplasmosis, diagnosis during the acute stage can be made using PCR amplification of DNA extracted from whole blood. PCR assay of whole blood is less sensitive for diagnosis of RMSF than it is for ehrlichiosis or anaplasmosis; however, sensitivity increases in patients with severe disease.
For more on the workup of tickborne diseases, read here.
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Cite this: Richard H. Sinert. Fast Five Quiz: Test Yourself on Clinical Information About Insect Bites - Medscape - Jun 16, 2017.