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Early diagnosis crucial for foal pneumonia
Rhodococcus equi remains particularly insidious threat to foals


DVM360 MAGAZINE


Steeve Gigučre, DVM, PhD, Dipl. ACVIM, Department of Large Animal Clinical Sciences at the University of Florida, currently is working on a study to look at why foals are more susceptible than adult horses; it will be presented at the ACVIM meeting in June.

"We will probably have some insight as far as what is different in the immune system of foals, or why foals are more susceptible."

An ounce of prevention Limiting the number of foals infected is important to reduce its prevalence and reduce the rate of further contamination and incidence.

A cost-effective and clinically-effective way to screen for early cases of R. equi was determined to be CBC and fibrinogen. It was found that it is useful to monitor foals every two weeks by taking a CBC and fibrinogen, beginning at about 4 weeks of age. If you have a high CBC and fibrinogen, it does not necessarily mean the foal has R. equi, but further testing is warranted. You might pull that foal out and do more intensive diagnostics to figure out if in fact it was R. equi or some other cause of infection.

"One thing that some people are suggesting is treating all foals early to reduce their shedding and reduce their exposure," Hines suggests. "One thing they are studying at Texas (A&M) is treating all foals with antibiotics to see if you can reduce the number of cases and the amount they shed. But there are problems with doing that, the bacteria may build-up resistance. But it uses the foals to reduce the environmental load."

Chaffin and colleagues began the study January 2005. The study is being done at numerous farms around the country, endemic farms that have greater than 20 percent of their foals infected with R. equi annually. The study is aimed at determining the prophylactic effects of azithromycin on the prevalence of R.equi pneumonia. Based on two findings, the hypothesis is that the administration of azithromycin every other day for the first two weeks of life will decrease the prevalence of R. equi pneumonia. First, foals become infected with R.equi during the first few days of life, and second, there is a window of opportunity for R.equi to establish infection in those foals at that time. Also based on some work in neonatal foals with azithromycin, showing that it does have good absorption, and does achieve high intracellular concentration.

"We hope to generate enough data with 2005 to answer our hypothesis," Chaffin says. "I really don't know if it will work or not. I think we have enough foals enrolled in the study. Assuming enough foals complete the study, we should be able to shed some light or doubt on this hypothesis, by the end of 2005."

Another promising tool for prevention of R. equi pneumonia is hyperimmune plasma. "The bottom line is that hyperimmune plasma probably helps reduce the incidence of R. equi pneumonia, however it doesn't totally prevent the disease," Gigučre states. "What's important to remember is that if you are going to give hyperimmune plasma, which is fairly time consuming and expensive, you shouldn't be lulled into a false sense of security. You should still be vigilant and try to use other methods to diagnose cases early. Basically it's not like if you give it, you can be sure that the foal will not develop R. equi pneumonia, but it does seem to help."

According to Gigučre, it is important to use other methods to help prevent onset of or catch the disease early. Maybe to do some blood work at regular intervals on all the foals on those farms with a high prevalence of the disease, perhaps do routine ultrasound of the chest, every couple of weeks. On some farms, they do chest ultrasounds of all the foals to detect lesions before the foals start having clinical signs.

"The earlier you make a diagnosis, the more successful you're likely to be with your therapy," Gigučre recommends. "We found that the CBC, especially the WBC count, was more effective as far predicting those foals that would subsequently develop R. equi pneumonia."


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Source: DVM360 MAGAZINE,
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