Articles of Interest
BY ROBERTA M. DWYER, DVM, MS, DIPL. ACVPM
Salmonella, Rhodococcus equi, strangles, rotavirus, and multiple other contagious disease outbreaks... these are the bane of horse owners, farm managers, and trainers. One strangles outbreak can wreck a show season, cause cancellations of breedings, sales, and racing dates, and tarnish the reputation of a farm. The horror stories are numerous, and we have to keep an important fact in mind--no vaccine for any disease of humans or animals is 100% effective. For some pathogens, such as R. equi (which causes pneumonia in foals) and Salmonella, no commercial vaccines are available, period. Preventive medicine rests not only on properly timed vaccinations, detailed farm management, deworming, and adequate nutrition, but also on disinfection. Disinfecting stalls, aisleways, horse trailers, and equipment isn't fun, but it is a necessary part of reducing the risk of disease entering your farm and causing outbreaks. If nothing else, the outbreak of foot and mouth disease (FMD) in Great Britain and other countries has emphasized the necessity for thorough disinfection in controlling disease. (The virus that causes FMD is a tough, very contagious bug, but does not affect horses.)
Several factors need to be taken into consideration prior to disinfection. What types of surfaces do you need to disinfect, what pathogens are of primary significance, and what chemical is going to have a reasonable expectation of efficacy under these circumstances? No disinfectants that can kill all of the equine pathogens are safe for use in horse facilities. It is critical to understand that the more porous the surface, and the more organic matter that is present, the less likely that any disinfectant will work! Here's an outline for disinfecting a stall with non-porous surfaces such as varnished wood, painted concrete block, etc. WARNING: Allow 45-60 minutes for completion of the task, and expect major sweat production!
It is impossible to adequately disinfect porous floors such as packed clay, sand, dirt, or other materials. Bedding should be completely removed, and wet areas should be limed and allowed to dry. In humid areas, fans may be needed for drying. This will eliminate some organisms that are highly susceptible to drying, such as Leptospira, but not many other major equine pathogens. Thickly bedding the stalls will place some distance between any pathogens in the soil and the horse.
The interaction of surface, pathogen, and disinfectant was studied by Susan Ewart, DVM, PhD, Dipl. ACVIM, and others from Michigan State University, and reported in the April 1, 2001, issue of the Journal of the American Veterinary Medical Association. Different surfaces (wood, stainless steel, galvanized steel, plastic, and others) were cleaned, contaminated with a culture of Salmonella in broth, then disinfected with different chemicals to determine their germicidal effects. The study pointed out the complex interactions between surfaces, Salmonella, and disinfectant, and concluded that bleach was effective on most surfaces. However, bleach is readily inactivated in the presence of any organic matter--such as feces or pus--which is where Salmonella would likely reside in the farm environment.
This study points out the multiplicity of factors that go into killing only one pathogen. Imagine the complexity of adding in other bacteria and viruses that infect horses! There are few easy answers, and research is ongoing on many fronts. From personal experience with farm outbreaks of disease, as well as communication with several university clinicians who have dealt with outbreaks in clinics, the cleaning step is the most important when disinfecting any surface. If the organic matter isn't removed, or as with porous surfaces can't be sufficiently removed, disinfection might not kill the viruses and bacteria. The hardest step thus is also the most critical. Some bacteria can produce an outer film that protects them and helps them adhere to a surface. One example of a "biofilm" is plaque on your teeth. Just rinsing with an antiseptic (a "disinfectant" for skin and mucous membranes) won't sufficiently remove and kill oral bacteria. This is why brushing and flossing (scrubbing the surfaces with a cleanser) are so important. Biofilms are receiving much more attention by researchers, as antibiotic resistance (resistance of pathogens to commonly used antibiotics) is knocking at the doors of both human and veterinary medicine.
Phenolic disinfectants are used in Kentucky international quarantine stalls, and are commonly used on farms and equine hospitals. Phenols are not as readily inactivated in the presence of organic matter as is bleach, and they will kill rotavirus, a pathogen of significant importance on breeding farms. Further in-depth discussions about disinfectants and farm management techniques to contain infectious disease outbreaks can be found in "Disinfecting Stables" in the November 1999 issue of The Horse, online. Staying alert for poor hygiene and regularly disinfecting your farm properly will help you avoid costly disease outbreaks.
Do Not Mix Chemicals
While on one farm, I asked the farm manager what was in the spray bottle next to the tack room sink labeled "Hand Rinse." He replied that it was a mixture of three different commercial disinfectants. "I figured if one didn't work on people's hands, one of the others would," he said. The three chemicals were labeled for use on surfaces, not human skin.
Mixing different chemicals is like playing with fire. Toxic gases can be produced causing respiratory failure, severe and/or permanent skin damage, and the list goes on. (Plus, attorneys would have a field day with civil liability for causing physical harm to your employees.)
A thorough scrub with liquid soap and warm water (if available), followed by drying with disposable paper towels, is adequate for skin cleansing. Besides, if you are working with highly contaminated bedding or materials, you should be using disposable gloves.
As far as disinfectants for stalls, foot baths, etc., never mix chemicals unless specifically told to do so by a professional who knows disinfectants. You might be instructed to clean a surface with one disinfectant, rinse, then apply another disinfectant, which is different than pouring two chemicals in your sprayer and spraying the walls with a potentially deadly mixture! Always read and follow label instructions. This is for your safety as well as that of the employees for whom you are responsible. --Submitted by Steve Smith