Anaplasma phagocytophilum infection in American robins and gray catbirds: an assessment of reservoir competence and disease in captive wildlife

Abstract

Anaplasma phagocytophilum (Dumler et al.) is the bacterial agent of human granulocytic anaplasmosis, an emerging infectious disease. The main vector of A. phagocytophilum in the United States is the blacklegged tick (Ixodes scapularis (Say)) and various small and medium-sized mammals are reservoirs. Previous studies indicate that birds are exposed to A. phagocytophilum; however, because no studies have directly investigated avian susceptibility, reservoir competence, and morbidity for A. phagocytophilum, uncertainty remains as to what role birds could play in its transmission ecology. In a controlled laboratory study, we tested whether two species, the American robin (Turdus migratorius (L.)) and the gray catbird (Dumetella carolinensis (L.)), can become infected with and then transmit A. phagocytophilum to feeding ticks, and whether exposed birds develop disease. Wild caught, seronegative birds (n = 10 per species) were exposed to A. phagocytophilum-infected I. scapularis nymphs (day 0). Transmission was assessed by xenodiagnosis on days 7, 14, 42, and 77; blood was assayed for bacteremia and serology. A. phagocytophilum was detected using quantitative polymerase chain reaction targeting the 16s rRNA gene. One robin infected 2 of 13 larval ticks (15%) on day 7; no other birds were found to infect feeding ticks at any time. Birds did not develop bacteremia, specific antibodies or significant illness because of exposure. Mouse controls became bacteremic, infected feeding ticks, and seroconverted. Our results suggest that these two avian species are unlikely to play a significant role in the maintenance of the agent of human granulocytic anaplasmosis and that avian serosurveys may not be a reliable indicator of A. phagocytophilum exposure.