Lyme Disease and Anaplasmosis Common Among Pennsylvania Horses

Scientists looked at disease prevalence in horses suspected to have tick-borne infections and compared test performance.

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tick on horse
Researchers recently confirmed that both anaplasmosis and Lyme disease are important prevalent tick-borne infections commonly found in Pennsylvania horses. | Courtesy Dr. Marianne Sloet

Researchers recently confirmed Lyme disease and other tick-borne infections are common among Pennsylvania horses, with the bacteria Anaplasma phagocytophilum and Borrelia burgdorferi often responsible for these infections.

A. phagocytophilum causes anaplasmosis, while B. burgdorferi is associated with Lyme disease, and both are spread to horses through bites from infected ticks. Anaplasmosis often mimics Lyme disease, with both infections capable of causing fever, laminitis, or other clinical signs that might resemble those of other diseases.

Researchers from the Pennsylvania Department of Agriculture recently conducted a survey using polymerase chain reaction (PCR) testing and serology to evaluate 271 Pennsylvania horses suspected to have tick-borne infection. “This study assesses tick-borne infections for two important diseases in Pennsylvania horses within the context of concerns from horse owners and veterinarians about presence of these infections,” said Deepanker Tewari, BVSc, PhD, Dipl. ACVM, director of the Pennsylvania Veterinary Lab, in Harrisburg, and a co-author on the study.

Tewari and his colleagues found that 25.5% of the horses were positive for A. phagocytophilum antibodies—indicating Anaplasma exposure—on both the IDEXX SNAP 4Dx Plus Lateral flow immunosorbent assay (SNAP) and indirect fluorescent antibody (IFA). As far as Lyme is concerned, 77.1% of horses tested positive for the presence of B. burgdorferi bacteria on at least one test, indicating exposure.

“The study showed Lyme disease exposure in a good number of horses suspected of tick-borne infections, which is not surprising, as the Lyme-disease-carrying deer ticks are widely prevalent in our region,” said Tewari.

Researchers also found that IFA testing was most effective for detecting antibodies related to anaplasmosis, while the SNAP test was highly successful in identifying the bacteria associated with Lyme disease (compared to IFA).

Tewari said the study confirmed that both anaplasmosis and Lyme disease are important prevalent tick-borne infections commonly found in Pennsylvania horses.

“We recommend that horse owners seek veterinary care when clinical signs and disease conditions that can be suspected for tick-borne infections are present in their animals,” he said. “A combination of screening using lab available tests, along with clinical signs and history, can help veterinarians arrive at a correct diagnosis and preventative measures and treatments.”

The study, “Prevalence of Anaplasma phagocytophilum and Borrelia burgdorferi infection in horses from Pennsylvania (2017-2019) using antibody and organism-based detection,” appeared in the Journal of the American Veterinary Medical Association in September 2022.


Written by:

Haylie Kerstetter, Digital Editor, holds a degree in equine studies with a concentration in communications and a minor in social media marketing. She is a Pennsylvania native and, as a horse owner herself, has a passion for helping owners provide the best care for their horses. When she is not writing or in the barn, she is spending time with her dog, Clementine.

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