Acute Clinical, Hematologic, Serologic, and Polymerase Chain Reaction Findings in Horses Experimentally Infected with a European Strain of Anaplasma phagocytophilum

Abstract

Six horses were experimentally infected by administration of horse blood containing a Swedish strain of Anaplasma phagocytophilum. The polymerase chain reaction (PCR) signal was consistently detected 2-3 days before appearance of clinical signs and persisted 4-9 days beyond abatement of clinical signs, whereas diagnostic inclusion bodies were 1st noted on average 2.6 +/- 1.5 (SD) days after onset of fever. Clinical signs and hematologic changes were largely indistinguishable from those previously reported for diseases caused by A phagocytophilum (formerly Ehrlichia equi--"Californian agent") and the human-derived human granulocytic ehrlichiosis agent. Horses 1st demonstrated antibody response 12-16 days after inoculation, 2 cases of which were still febrile, and serotiters rapidly peaked within 3-7 days of clinical illness. One horse died during the acute stage of disease, but initial clinical signs and hematologic changes were similar to those of other infected horses. This report shows that, despite minor genetic differences, a European equine-derived strain of A. phagocytophilum may be similar in pathogenicity to the Californian agent. The PCR used holds promise to widen the diagnostic window and would also be diagnostic during the initial days of clinical disease when inclusions in neutrophils in blood smears are not yet apparent.

Equine granulocytic anaplasmosis in the Czech Republic

“…Pyrexia was reported to be the most constant clinical sign both in natural (Büscher and others 1984, Bermann and others 2002, Butler and others 2008) and experimental infections, and is the first sign to become apparent (Franzén and others 2005). The only afebrile horse in the present study was a five-year-old mare.…”

Serological and molecular detection of Anaplasma phagocytophilum in horses reared in Korea

“…This may be attributed to the fact that antibodies against A. phagocytophilum persist in the blood longer than the antigen. Horses inoculated intravenously with A. phagocytophilum showed seroconversion at 12-16 days post-inoculation (Franzen et al 2005), and serum antibodies persisted for 300 days after inoculation (Nyindo et al 1978). Therefore, the fact that 16 samples were positive by serological assay but negative by nPCR indicates that the horses were previously exposed and were not currently infected.…”

Comparison of Sampling Sites and Laboratory Diagnostic Tests for S. equi subsp. equi in Horses from Confirmed Strangles Outbreaks

“…Thus, similar to recent findings in other horse bacterial infections, PCR is of value early in disease when more traditional diagnostic methods can be falsely negative. 17 Regarding the 3 horses completely negative to S. equi, two were sampled on day 2 of their clinical signs occurring, and being presumably early in the disease may have had minimal detectable shedding. The remaining S. equi negative horse was sampled after 9 days of the initial outbreak, which is beyond the early stages when shedding is reportedly low.…”