Fever in horses can develop for many different reasons, but there is always a concern about an infectious disease that could spread to others on the property. Lutz Goehring, DVM, MS, PhD, DACVIM, DECEIM of the University of Kentucky presented a podcast sponsored by Idexx about strategies when dealing with a febrile horse.
Besides taking steps to mitigate the horse’s fever with appropriate pharmaceutical drugs, Goehring explained a process that all should consider. First, the horse should be isolated with no chance of contact with others. Veterinarians (and staff) handling the sick horse should wear PPE, particularly a gown and gloves. It is important to stay out of the line of projectile sneezing or coughs from the sick horse, he said. All other horses on the property should have rectal temperatures checked twice daily to identify illness as soon as possible. Any other horse on the premises with a rectal temperature >100.80 F should be reported to the attending veterinarian.
Physical Exam for Horse with Fever
The physical exam is all important. Goehring recommends checking submandibular lymph nodes and palpating to see if the horse is tender there. He also recommends examining the retropharyngeal lymph nodes. Does the horse have nasal discharge? What about limb edema, which when present is a red flag for EHV-1? If there is a concern about EHV-1, also check the horse’s tail tone and observe for urine dribbling, difficulty urinating or ataxia. These signs could indicate that the horse has the neurologic form (EHM) of EHV-1.
He recommends checking the entire horse from all sides to align body systems with the presenting complaint. What is the horse’s stance? Is the abdomen tense? Is breathing normal? Auscultate the lungs including with a rebreathing bag to listen for additional or absent lung sounds. Normal breathing should return within 3-4 breaths following use of the rebreathing bag.
Laboratory samples are important to ascertain a definitive diagnosis. If strangles is a concern, then he advises that a nasopharyngeal wash is the best sampling method rather than using a swab. If EHV-1 is a concern, then in addition to a nasal swab (taken with protective gloves covered with a rectal sleeve), he recommends also pulling blood in an EDTA heparinized purple top tube. Often at the initial febrile period of viremia, it is possible to miss an EHV-1 diagnosis with just a nasal swab, so blood evaluation is important. EHV-1 doesn’t usually show any specific changes in a chemistry panel or a CBC. Also, SAA, especially when taken at a single time point, does not tend to elevate with subclinical EHV-1. However, an infected horse might have a significantly higher SAA value compared to non-infected, healthy horses [Pusterla, N.; Miller, J.; Varnell, S.; et al. Investigation of the Usefulness of Serum Amyloid A in Characterizing Selected Disease Forms of Equine Herpesvirus-1 Infection. Journal of Equine Veterinary Science Sept 2021, vol 104].
Isolation for Sick Horse
Another important step in managing a febrile horse relies on client education about the importance of isolation. The sick horse should have no contact with other horses; no visitors should go in and out of the isolation area; designated personnel should be assigned to treat and care for the sick horse; and all barrier precautions should be taken with appropriate biosecurity measures.
Importance of Taking Precautions
Fever might result from other non-specific causes that pose no harm to other horses on the property. However, performing diagnostic tests and taking biosecurity precautions until reaching a definitive diagnosis can save a lot of heartache, and it can potentially mitigate the spread of serious health issues to the rest of the herd.