Ehrlichia equi Infection of Horses from Minnesota and Wisconsin: Detection of Seroconversion and Acute Disease Investigation

Abstract

Equine granulocytic ehrlichiosis (EGE) is caused by infection with Ehrlichia equi. EGE has been reported primarily in northern California, where E equi is transmitted by the tick Ixodes pacificus. Reports of EGE and the emergence of human granulocytic ehrlichia in Minnesota prompted a seroprevalence study of E equi in horses of Minnesota and Wisconsin. Tick (Ixodes scapularis) endemic areas of Minnesota and Wisconsin were compared to nonendemic regions of Minnesota. Indirect fluorescent antibody was used to detect the presence of serum antibodies to E equi. Serum samples from healthy horses, 375 samples from I scapularis endemic counties, and 366 samples from nonendemic counties were screened at a 1:40 dilution. Results demonstrated a seroprevalence of 17.6% in endemic areas versus 3.8% in nonendemic areas. Ehrlichial DNA from 2 samples was successfully amplified by polymerase chain reaction and 919 base pairs were sequenced. The DNA sequence of 1 Minnesota/Wisconsin strain differed from the GenBank strain (M73223) of E equi at positions 84 and 886 and from the MRK strain of E equi at position 84, and was identical to the human granulocytic ehrlichiosis (HGE) agent. The 2nd Minnesota/Wisconsin strain was identical to the 1st with the exception of a substitution of "A" at position 453 that is not present in E phagocytophila, E equi, or HGE agent strain sequences. Based on the results of this study, we concluded that E equi is present and causes infection in horses in Minnesota and Wisconsin. The occurrence of infection is higher in tick endemic regions.

SEROLOGICAL EVIDENCE OF EXPOSURE TO <italic>Anaplasma phagocytophilum</italic> IN HORSES FROM THE RIO DE JANEIRO STATE MOUNTED POLICE BRED IN THE URBAN ZONE

“…phagocytophilum antibodies, what means sex is not a risk factor for A.phagocytophilum infection. This corroborates with the findings of Bullock et al (34) in 733 equids studied in the region of Minnesota and Wisconsin. There was no significant variation (p=0.0596) in the seropositivity for anti-A.…”

“…Engvall & Egenvall (33) concluded, differently from the results for the Rio de Janeiro Mounted Police, the prevalence increases with the age what turns it a risk factor due to the higher rate of exposition to the tick during life. This age is also the most commonly used for work and sport; therefore, these animals are more often exposed to potential risk factors including journeys, exposure to animals from other regions, and stress (33,34) . In this study we did not verify significant difference for males and females in the seropositivity for anti-A.…”

Equine Granulocytic Anaplasmosis, A Neglected Disease: Risk Factors Associated with Prevalence of Antibodies in Equines

“…Out of the 612 Equidae investigated from the state of Rio, there was no significant difference in seroreactivity for A. phagocytophilum between sexes (P=0.0984), corroborating the findings of authors of a study [33], who also did not observe differences in infection according to the sex of the animal in 733 horses studied in the region of Minnesota and Wisconsin (USA).…”

Whole genome transcription profiling of Anaplasma phagocytophilum in human and tick host cells by tiling array analysis

“…Clinically, membrane bound Ap colonies, called morulae, are seen in peripheral blood neutrophils. The white-footed mouse ( Peromyscus leucopus ) is considered to be the primary reservoir for the Ap variant responsible for HGA, but other mammals are also susceptible [ 1 - 4 ]. Ticks do not pass Ap to their offspring, but to mammals they feed upon, which transmit it back to ticks, and so the organism cycles between tick and mammalian hosts.…”