Investigating the prevalence of Panola Mountain Ehrlichia in calves and ticks from a cow-calf herd in northwest Arkansas

Panola Mountain Ehrlichia (PME) is an emerging disease in the United States, transmitted by Amblyomma americanum. PME was first discovered in Georgia following a goat infection in 2005. Since 2005, two cases of natural PME infections have been reported (in a human and a dog), but the pathogen has been shown experimentally to also infect white tailed deer. PME is widely distributed across the eastern United States due to the range of the vector.

Concerningly, PME is most closely related to Ehrlichia ruminantium, the causative agent of heartwater in ruminants. However, its pathogenicity in cattle is currently unknown. Previous tick-borne disease surveillance efforts in Arkansas detected PME positive ticks from a herd with a history of an undiagnosed disease resembling anaplasmosis. Therefore, a longitudinal study is being conducted to investigate if this herd is exposed to, and infected by, PME. During fall calving in 2022, blood samples were taken at birth to confirm calves had not been exposed to Ehrlichia. Blood collections and tick checks were performed at approximately 100 days old, 200 days old, and 1 year. Collected ticks were identified to species and tested for bacteria in the family Anaplasmataceae using qPCR. Blood samples were tested using the same qPCR. Positive samples were amplified using a groEL PCR and amplicons were Sanger sequenced for identification.