DOGS INFECTED WITH A HUMAN GRANULOCYTOTROPIC EHRLICHIA SPP. (RICKETTSIALES, EHRLICHIEAE)

Dogs were found to be susceptible to human granulocytotropic Ehrlichia spp. Infection was produced through the bite of Ixodes scapularis Say (= dammini Spielman, Clifford, Piesman & Corwin) nymphs and adults th at acquired infection while feeding as larvae on experimentally infect ed mice. Dogs were also infected by intravenous injection of mouse blo od or dog blood from parasitemic donors. Parasites were demonstrable i n neutrophils within 8 or 9 d after nymphs began feeding; prepatent pe riods were longer when infection was induced by adult tick feeding (18 d) or by transfusion of mouse blood (12 d). The shortest prepatent pe riod observed was 5 d in a dog infected by transfusion of blood from a parasitemic dog. Infections in dogs were mild and apparently transien t. Mild thrombocytopenia was the most commonly observed abnormality. P arasites could be detected by light microscopy during the acute phase of infection (4 or 5 d) and parasite DNA by polymerase chain reaction as early as 5 d after exposure but not at 6-9 d after morulae were fir st observed in neutrophils. Likewise, dog blood was infectious for mic e at 2 d but not at 25 d, and for dogs at 3 d but not at 13 d after mo rulae were first observed in neutrophils. Seroconversion occurred as e arly as 11 d after onset of tick feeding and persisted until dogs were euthanatized. Gross and histopathologic lesions were similar to those observed in dogs with E. canis (Donatien & Lestoquard), E. chaffeensi s Anderson, Dawson & Wilson, and E. ewingii Anderson, Greene, Jones & Dawson infections but were generally milder than any of these. The mod erate enlargement of lymphoid organs observed grossly was reaected his tologically as mild to moderate reactive hyperplasia, which was largel y follicular (B cell).