147 Serological and molecular detection of Anaplasma in East Texas horses

Abstract

Anaplasma phagocytophilum (AP) is a tick-borne bacteria that cycles between the tick, Ixodes scapularis and the hematopoietic cells of vertebrate hosts. AP is responsible for the disease equine granulocytic anaplasmosis, a generally transient infection characterized by fever, depression, inappetence, ventral edema petechiae, icterus, ataxia, recumbency, muscle stiffness, and, in severe cases, death. Current infection with AP is detected through PCR analysis of an animal's immune cell DNA, while serum antibody titers determine if a horse has previously been infected with AP. Other regions and countries have reported wide ranging prevalence of serum reactive horses, with 17 to 67% of apparently healthy horses being serum reactive and 8% of these being PCR positive. There were 130 clinically healthy horses aged from 1 to 29 years old included in this survey, 70 from Texas, and 11 from New Jersey, and 49 from New York. Horses from Texas were chosen based on location in the state and high potential for tick exposure, the latter 2 states were included as populations with known tick exposure. From each horse, blood was collected for serum and DNA. DNA was screened by nested PCR for the 23s rRNA gene of the Anaplasmataceae family. Samples positive for 23s were analyzed by conventional PCR for the msp2 gene of AP. Lastly, serum was analyzed by immunofluorescence antibody test to detect antibodies against AP. Seventeen horses were positive for 23s, with 4, 3, and 10 from Texas, New Jersey, and New York, respectively. Of these, 2 Texas horses were positive for msp2. Further, 107 horses tested positive for antibodies against AP, with 47, 11, and 49 from Texas, New Jersey, and New York, respectively. The observed 80% seroprevalence is similar to that reported from other countries and indicates high exposure to tick populations.