Investigating Respiratory Disease

Debra Sellon, DVM, PhD, of Washington State University’s College of Veterinary Medicine, presented guidelines for systematically investigating and treating foal respiratory disease outbreaks. "While many outbreaks of respiratory disease in foals are infectious in nature, this is not always the case," she began. "Environmental factors can have a profound effect."

Sellon suggested six steps for investigating/controlling outbreaks:

1. Evaluate farm and individual history. Look into prior infections on the farm, deworming status, parasite surveillance, vaccination status, exposure to transient horses, and ages of affected foals.
2. Inspection of premises. Check barn ventilation, hay and straw storage, bedding, hygiene practices, sanitation, pasture access, pasture condition (vegetation, soil, population density), and population characteristics (ages, group sizes, transient vs. permanent horses, etc.).
3. Examination of individuals. Do a complete physical examination, rebreathing exam, and laboratory exam, and examine other foals (which might have subclinical disease that you can stop early).
4. Figure out which organism is responsible for infectious disease. The veterinarian should now be able to develop a list of differential diagnoses ranked in order of likelihood for that farm. Ancillary diagnostic tests such as transtracheal wash or nasopharyngeal swabbing might help identify the responsible pathogen(s).
5. Separate sick foals from exposed but not sick foals, and separate unexposed, healthy horses from both groups. Control of human and animal traffic through the quarantine area is essential.
6. Treat affected foals. Use appropriate antimicrobials for the diagnosed cause and suggest any environmental changes that might help (cleaning stalls  when horses are outside so they are not exposed to all that dust, improving ventilation, etc.).

Sellon added that corticosteroids might help stop the cycle of inflammation in selected difficult, chronic cases (if active bacterial infection is no longer thought to be the cause)