R. equi Foal Pneumonia: Support for Research Sought

Infectious respiratory diseases constitute one of the major causes of death in the horse industry. In addition to the sorrow caused, they also are major economic threats. One of the most common diseases in foals six months and younger is pneumonia. Although many different organisms can cause foal pneumonia, Rhodococcus equi (R. equi) is considered the most common culprit in a severe case. A nationwide survey indicated that respiratory disease is the third-leading cause of disease in foals and ranks second as a cause of death, following injury or wounds.

Because foals' active immune systems are still developing, they are susceptible to a number of infectious diseases. A Texas A&M study found that in foals, respiratory disease was the leading cause of disease and death. During a 2004-2005 study at a Kentucky breeding farm, 30% of foals developed R. equi pneumonia.

No horse breed or geographical region in the U.S. is exempt from foal pneumonia, which can be caused by a bacterium that is often present in horse farm soil and grows in the manure of grazing animals. The R. equi bacterium is similar to the one that causes tuberculosis (TB). Like TB, foal pneumonia caused by R. equi develops slowly and by the time clinical symptoms are detectable, the disease is in a relatively advanced stage. Indeed, some foals don't show signs of respiratory distress until the disease is irreversibly severe. Although effective treatments exist, such as the oral administration of azithromycin and rifampin, waiting until signs develop can result in a therapeutic course that is prolonged with lower chances for success. Thus, there is a critical need to discover methods for preventing foal pneumonia.

Investigators at several institutions have been working, often collaboratively, to further our understanding of the bacterium and the disease. They have had important breakthroughs, such as the demonstration that transfusion of hyperimmune plasma can reduce the frequency and the severity of pneumonia caused by R. equi, the identification and characterization of disease-causing factors of the bacterium, and the dissection of some aspects of the immune response of horses and foals to R. equi. Hyperimmune plasma provides passive immunity, but it is time consuming to administer and expensive to produce or buy. A vaccine to provide active immunity would be more convenient, but development of an effective one has proven elusive.

Those studying the disease are committed to improving foal health. Collaboration greatly increases the resources and opportunities for continued major breakthroughs that could reduce the burden of the disease. Foals that survive R. equi are less likely to race than foals that never contracted the disease, and breeding farms reputed to have an endemic problem with R. equi may lose clients out of concern for the welfare of the foals (despite the fact that this disease in general appears to occur at farms that use the management practices deemed superior!).

Much work remains to be done to build on these findings, including understanding the environmental conditions that might make infection more likely among foals. If a successful vaccine is to be developed, much more needs to be learned about the immune system of foals and how it will respond to R. equi. In addition, novel methods of vaccination may be needed to stimulate immunity very early in a foal's life.

Additionally, their findings are likely to have application to other infectious foal diseases, such as diarrhea and sepsis, a major killer of newborn foals. Studies funded by the Grayson-Jockey Club Research Foundation (www.grayson-jockeyclub.org) and the Morris Animal Foundation (www.morrisanimalfoundation.org) are currently in progress. Successful conclusion of these projects will help guide the research community toward the next steps necessary in combating the disease.

The equine veterinary community is issuing a collective call for support in this endeavor. Donations to the organizations named above as well as the American Quarter Horse Foundation (www.aqha.com/foundation), the American Association of Equine Practitioners Foundation (www.aaepfoundation.org), or your favorite veterinary school will help support foal pneumonia research and hopefully enable the discovery of a vaccine that will prevent the disease or ameliorate these early infections and provide an effective disease control.

Please contact the AAEP Foundation (www.aaepfoundation.org) for information about how to make donations for equine research, or call 800/443-0177 (within the U.S.) or 859/233-0147. This is just one of the many efforts that the AAEP is coordinating on behalf of the industry through the Equine Research Coordination Group (ERCG), which is comprised of researchers and organizations that support equine research. Organized last year with a mission of advancing the health and welfare of horses, the ERCG promoted the discovery and sharing of new knowledge, enhancing awareness of the need for targeted research, educating the public, expanding fundraising opportunities, and facilitating cooperation among funding agencies.--Noah D. Cohen, VMD, MPH, PhD, Dipl. ACVIM, and Stephen Hines, DVM, PhD, Dipl. ACVP

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