Abstract. Following intravenous inoculation with horse blood-infected with the agent of human granulocytic ehrlichiosis (HGE) from a human fatality, two rhesus macaques (Macaca mulatta) exhibited pyrexia and lethargy on days 4-12 postinfection (PI). Hematology revealed neutropenia, thrombocytopenia, and anemia, with ehrlichial morulae in monocytes and neutrophils on days 4-12. Blood was polymerase chain reaction (PCR)-positive on days 4-12 and bone marrow was PCR-positive on day 11. There was a minor increase in gamma-glutamyl transpeptidase on day 12 and serum interferon-␥ levels increased by day 18. Seroconversion occurred on day 20 PI to a titer of 100 by day 22. Western blot bands characteristic of HGE included 25-, 44-, 80-, 94-, 105-, and 125-kD 10 The development of clinical signs appears to be largely host-species dependent. An early attempt to infect non-human primates with Ehrlichia equi was successful based on visualization of ehrlichial inclusions within the cytoplasm of neutrophils.3 However, that study was hampered by the lack of some diagnostic procedures such as the polymerase chain reaction (PCR) and DNA sequencing, cytokine assays, and other immunologic assays. Moreover, the investigators did not know at that time that E. equi or its close relative, the agent of human granulocytic ehrlichiosis (HGE), was capable of producing life-threatening disease in humans. 1 In the present study, we report successful experimental infection of rhesus macaques with the HGE agent from a severely ill human case. This animal model of human disease is important for further studies of HGE diagnosis, management, and pathogenesis.
MATERIALS AND METHODS
Animals and inoculation.Three rhesus macaques were pre-screened for ehrlichiosis by serology and E. equi-specific PCR. Monkey 312 was a 16-year-old reproductively intact female who had been used previously for breeding and a teratogenesis study (zinc deprivation). Monkey 121 was a 17-year-old intact female with a history of use for breeding and anti-progestin drug studies. Monkey 324 was a 14-yearold intact female from the breeding colony. Monkeys 121 and 312 were inoculated intravenously with fresh horse blood containing 2 ϫ 10 6 neutrophils of which 15% contained HGE agent strain BDS inclusions (morulae); monkey 324 was control-inoculated with 2 ϫ 10 6 uninfected horse neutrophils. All monkeys were monitored twice a day for clinical signs of disease, including lethargy, inappetance, and depression. Rectal temperature was assessed at the time of each blood sample collection. Blood samples were collected every two days into tubes containing EDTA for Wright-Giemsa staining and PCR and without anticoagulant for serology and serum chemistry. Bone marrow aspirates were performed on days 3, 11, and 14 postinfection (PI) and submitted for cytology and PCR. On day 21 PI, monkeys 121 and 324 were killed with an intravenous overdose of barbiturate and necropsied. Samples from tissues were either snap-frozen in liquid nitrogen for PCR or fixed overnight in 10% buffered forma...