Monitoring and Preventing EPE on Endemic Farms (AAEP 2011)

Equine proliferative enteropathy (EPE) is an emerging disease of young horses that veterinarians have been diagnosing more frequently over the past few years. This gastrointestinal disease is caused by bacterial organisms known as Lawsonia intracellularis. More and more cases are diagnosed each year, and the disease--which is known to cause significant financial loss for farms and horse owners--has become endemic on certain farms. Fortunately, researchers have learned enough in their studies to help endemic farms and farms with sporadic occurrences control EPE and detect cases.

During presentations at the 2011 American Association of Equine Practitioners Convention, held Nov. 18-22 in San Antonio, Texas, Nicola Pusterla, DVM, PhD, Dipl. ACVIM, an associate professor in the Department of Medicine and Epidemiology at the University of California, Davis, gave some suggestions on identifying and controlling EPE.

Identify Disease Early

Observable clinical signs of EPE--which typically affects weanling foals aged 3 to 13 months--include fever, lethargy, anorexia, peripheral edema (fluid swelling), diarrhea, colic, and weight loss. The disease also causes a thickening of the intestinal walls, which leads to malabsorption of protein and a low daily weight gain.

Pusterla explained that one of the keys to minimizing EPE impact on a farm is to identify sick foals early and separate them from the rest of the herd for seven to 10 days to avoid exposing healthy foals to L. intracellularis shedding.

Although they're sometimes subtle, early clinical signs--such as mild anorexia, a slight fever, and peripheral edema--should prompt owners to seek veterinary attention and diagnostic testing, Pusterla said.

Pusterla advises that veterinarians examine symptomatic foals using ultrasound, which often provides a visualization of potentially thickened intestinal walls. In addition he recommends pursuing a combination of molecular (polymerase chain reaction [PCR] test evaluation of feces or a rectal swab) and serologic diagnostic testing for L. intracellularis antibody titers.

"It's essential to combine both the molecular and serologic diagnostic testing because these modalities have high analytical specificity but variable sensitivity," Pusterla explained. Specificity refers to the probability that test results will be negative among patients who do not have the disease, and sensitivity indicates the probability that test results will be positive when run on a group of patients with the condition.

After diagnosing EPE in a foal, Pusterla recommends treating the animal with antimicrobials, often for two to three weeks. Supportive care; intravenous fluids, colloids, plasma transfusion, and additional nutrients; and anti-ulcer medications are often used in conjunction with the antimicrobial treatment, he noted.

Pusterla also noted that cases are diagnosed most commonly in the winter months after the foal is weaned.

When Disease Strikes, Monitor Others Closely

Once an index case has been confirmed on a farm, Pusterla said it's critical to isolate the affected animal and keep a close eye on any remaining healthy foals, as affected foals start shedding virulent organisms before clinical signs become apparent.

"This is best achieved through daily physical examination including temperature and the regular assessment of weight," he said, adding that routine blood work can be done to check the foal's protein levels as well, "since hypoproteinemia is a consistent hallmark of EPE."

He noted that the aforementioned blood tests can indicate prior exposure or early subclinical disease in an otherwise healthy foal. Veterinarians should closely monitor animals that test positive for exposure to the bacteria on these assays and check their total protein concentration regularly.

Additionally, practitioners should monitor foals with low protein concentrations due to low blood albumin levels (as identified via blood tests) closely via diagnostic tests and ultrasound, he added.

Pusterla also noted that endemic farms should keep records of when index cases are confirmed each year and begin monitoring foals--for clinical signs and L. intracellularis antibody titers--at least "four weeks prior to the historical first detection of clinical cases."

L. Intracellularis Vaccine

Pusterla also discussed a pilot study in which he and his colleagues examined a swine L. intracellularis vaccine for efficacy in protecting foals from EPE. The research team tested the rectally administered avirulent live vaccine on four foals.

Twelve foals were randomly assigned to a "vaccinated" group, a "nonvaccinated" group, and a control group. The first group was vaccinated 60 and 30 days before being experimentally infected with L. intracellularis. They also challenged the nonvaccinated group and didn't challenge the controls.

All of the vaccinated foals were protected from L. intracellularis infection, while three of the four nonvaccinated foals developed moderate to severe clinical signs of disease. None of the control foals developed EPE. No adverse effects were noted in any of the vaccinated foals.

While the vaccine was safe and effective, Pusterla cautions that it could be expensive for use in large herds of foals. One milliliter of the vaccine costs $1.20 to $1.50, and the research team used 30 mL per vaccination.

The vaccine should be considered on farms with known occurrence of EPE in an attempt to prevent EPE and reduce environmental contamination.

Take-Home Message

Pusterla noted that understanding EPE clinical signs and keeping a watchful eye on weanlings are critical for controlling the disease, especially on endemic farms.

"Until new information regarding the epidemiology of this disease is determined, preventative strategies are restricted to the use of an avirulent L. intracellularis vaccine," he suggested.

The good news is that foals diagnosed with EPE generally have good prognoses (with recovery rates as high as 93%), and EPE does not appear to have any impact on future performance. As with many conditions, early treatment can mean an increased likelihood the horse will fully recover. Careful monitoring can allow sick foals' treatment to begin more quickly, protect healthy foals from contracting disease, and get the animals on the road to recovery sooner.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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