Reptile infection with anaplasma phagocytophilum, the causative agent of granulocytic anaplasmosis

Granulocytic anaplasmosis (GA) is a potentially fatal tick-borne rickettsial disease that occurs sporadically in the far western United States. We evaluated the prevalence of Anaplasma phagocytophilum in multiple species of lizards and snakes from enzootic sites in northern California, described the infestation prevalence of its tick vector Ixodes pacificus on reptiles, and conducted an experimental challenge of western fence lizards (Sceloporus occidentalis) and Pacific gopher snakes (Pituophis catenifer) with A. phagocytophilum delivered via needle inoculation or tick bite. Both serologically and polymerase-chain reaction (PCR)positive lizards (seroprevalence = 10.8%, PCR prevalence = 10.2%) and snakes (seroprevalence = 5.8%, PCR prevalence = 11.7%) were detected among wild-caught animals. A DNA sequence of the A. phagocytophilum groESL gene from a PCR-positive snake was 100% homologous to that of the human-derived A. hagocytophilum. Experimental attempts to infect nave animals were unsuccessful for snakes (n = 2), but 1 of 12 lizards became infected for 1 wk only by tick bite. Xenodiagnostic I. pacificus larvae that fed on a PCR-positive lizard did not acquire or transmit rickettsiae. Our findings suggest that lizards and snakes are exposed to A. phagocytophilum by infected ticks, but that they do not serve as primary reservoir hosts of this rickettsia.