(Epizootic Cellulitis, Pinkeye, Stable Pneumonia, Shipping Fever)
Equine Influenza should not be a problem if horses are routinely vaccinated, AND if new arrivals are isolated from the herd for 2-3 weeks and vaccinated. However, NO vaccine provides 100% protection, and infection IS POSSIBLE in vaccinated horses. These horses may remain SUBCLINICAL SHEDDERS of the virus. This one isn’t really high on the rule out list due to severity of clinical signs in client’s horses, prior vaccination, and the fact that according to the client, there have been no new additions or visitors for several months.
Infectious agent: Orthomyxovirus (an enveloped segmented ssRNA virus). Equine influenzas are Type A.
History: Occurs in OUTBREAKS. It’s most common in young horses, especially at racetracks, horse shows, and during transport (planes, etc.), and it is seasonally more prevalent in the summer and fall. Influenza spreads rapidly in susceptible horses, and is usually introduced by a subclinical shedder of virus.
Clinical Signs: Poor performance may be first indication. HACKING, dry, nonproductive COUGH, depression, anorexia, fever, serous nasal discharge, enlarged and tender submandibular and retropharyngeal lymph nodes, secondary bacterial infections may occur and include guttural pouch empyema and sinusitis.
THE PROBLEM IS IT CAN BECOME SYSTEMIC IF NOT TREATED PROPERLY. What you'll see is edema of trunk and limbs, inflammation of tendon sheaths, heart, GI tract, kidney, and severe ocular and pulmonary lesions.
Transmission: aerosol
Incubation Period: 1-3 days
Shedding Period: up to 8 days after clinical signs begin
What's the pathogenesis?
| HA glycoprotein (hemagglutinin) attaches its spikes to respiratory epithelial cell receptors, and enters the cell via endocytosis. Viral replication occurs and new viral particles are released into the airway to infect other cells or become aerosolized. In 1-3 days this invasion causes necrosis and desquamation of respiratory epithelial cells, exudation of protein-rich fluid into airways, and clumping of cilia, impairing the mucociliary apparatus for up to 4 weeks. Exudate accumulates and predisposes to secondary bacterial infections. | |
Diagnosis: Use clinical signs! Confirm with virus isolation or serology. For virus isolation, best samples are nasal, nasopharyngeal swabs or a tracheal aspirate, all collected early in the course of the disease. For serology collect 2 samples, 2-3 weeks apart, to find rising titer - a four times or greater rise in HA titer is needed to make a diagnosis (except in subclinical or vaccinated horses who may not show a rise in titer!). Bloodwork may show mild to moderate normocytic, normochromic anemia, leukopenia, and lymphopenia early in the disease. Recovering horses may show monocytosis, neutrophilia if secondary infection present. CK, AST, and LDH may be elevated if myositis occurs.
Treatment and Prevention: Symptomatic, as the disease usually resolves in 7-14 days on its own. Complete rest for 3-4 weeks (guideline 1 week of rest for every day of fever) and good ventilation are very important to prevent systemic disease. Antibiotics only if secondary bacterial disease present. A booster vaccination during an outbreak may help. Severe cases may take 3-4 months to resolve. Quarantine any affected barn for at least 4 weeks. Clean and disinfect stalls, equipment, transport vehicles after recovery.
To prevent, always isolate affected horses and new arrivals. Vaccinate adults and foals starting at about 9 months of age. Use 3 or more doses during initial series. Vaccinate mares 4-6 weeks before foaling. A single dose MLV vaccine can be given at 11 months of age. There is no set vaccination protocol for all horses. Contact AAEP (American Association of Equine Practitioners) for current vaccination protocol.
AAEP
4075 Iron Works Parkway
Lexington, KY 40511
