Diagnosis of rickettsial diseases in dogs and cats

Rickettsial agents, including those in the genera Anaplasma, Ehrlichia, Neorickettsia, and Rickettsia, are important and common vector-borne pathogens of dogs and cats. Disease induced by these organisms ranges from clinically inapparent to severe and potentially fatal. However, laboratory confirmation of a rickettsial etiology can be complicated by a number of factors, including the wide spectrum of disease induced by these organisms, an often low and widely fluctuating level of organism present in infected animals, cross-reactions on serologic and molecular assays, and the presence of co-infections. Correct diagnosis is most likely to be reached when multiple diagnostic strategies, including careful microscopic examination of stained blood films or tissues, both specific and broad serologic tests, and a suite of molecular detection assays, are used in concert. Accurate interpretation of diagnostic tests requires awareness of the likelihood for multiple agents, including novel organisms, to be responsible for the results seen in a given patient. This review provides an overview of current strategies used to diagnose rickettsial infections in dogs and cats.