Bye Bye Bad Bugs

Disinfection is not a dirty word!

The following scenarios are based on fact; the names of the farms and diseases have been omitted purposely to worry you even more.

Scenario 1 After a scenic weekend trail riding in the Ozarks with 50 other trail riding enthusiasts, you and your horse return home for some rest. Your horses are rough and ready animals that are used to spending the majority of their time in a pasture, and all six horses reside in one pasture.

Three days later your trail horse has a runny nose and looks a bit lethargic, but, after all, it is August, and he might have allergies. The next day he has a dry cough, so you call your veterinarian. By week's end, all of the horses have a fever and a cough. Some have very high fevers (104ºF+), which with the high ambient temperatures causes you significant concern.

You already have canceled your plans to attend next weekend's horse show, where you'd hoped to win the trail class, because none of your horses is well enough to ride.

Scenario 2 The owner of the farm you manage purchased a new broodmare from several hundred miles away. The transport company informs you of her delivery date and time.

After unloading her, you put her in a stall to get some rest and make sure her temperature is normal and she has no repercussions from the van ride. The next day she is ready to get outside and stretch her legs, so you turn her out with other broodmares, and with the exception of one troublemaker, the mares accept her into the herd.

Three days later one mare develops acute diarrhea and must be hospitalized because of severe dehydration. The disease spreads to other broodmares, and two abort their fetuses. Multiple fecal cultures identify the causative bacteria, and, while the new mare has a positive culture, she remains healthy. A pathogen carrier lurks.

Situations like those described occur frequently. Not all animals returning to a farm or entering a herd cause disease outbreaks, but the ones that do cause significant costs in veterinary bills, potential loss of performance or life, and increases in labor. It is hard to put a price tag on concern about sick animals and possible loss of a farm's reputation.

Aren't Vaccines Enough?

For vaccine-preventable disease, owners must remember that no vaccine has been produced that is 100% efficacious in all animals. Even the maximum response to a vaccine is contingent upon the health of the horse, stress levels, age, organ function, medications, and a host of other factors.

Some diseases that have a major impact on horses do not have a commercially available vaccine to help reduce the risk of disease. Rhodococcus equi infections and salmonellosis are notable examples.

So, how do you reduce the risk of your horses getting ill?

Vaccination, deworming, proper nutrition, adequate housing, and plenty of space are key elements to preventive medicine. Overcrowding horses causes stress, which diminishes the immune response and increases the pathogen load for the environment.

Bio-what?

This is where the concepts of biosecurity and biocontainment are important. While the word biosecurity has just recently been used in medical literature, it commonly means to take measures to prevent the introduction of an infectious agent onto a premises. Most infectious disease control veterinarians consider biosecurity to involve housing, movement of people and animals (requirement of a health certificate, examination of animals on arrival, pre-entry testing for infectious diseases), manure management, disinfection, and other elements of the horse's physical environment rather than vaccination and deworming.

Others consider everything done to prevent pathogens (including vaccination) part of biosecurity. One source of ambiguity is that the term biosecurity is not uniformly defined in English dictionaries.

Biocontainment is a word that is gaining usage to describe control efforts to contain and eliminate (if possible) the pathogen on a premises. This means disease control measures, which, in some instances, might include vaccination.

Both biosecurity and biocontainment can be used to refer to an area as small as a stall; using a hospitalized patient example makes this clear. For the hospitalized patient with colic, biosecurity measures help prevent pathogens of another horse in the facility from entering the patient's stall. Biocontainment means trying to prevent any enteric (intestinal) pathogens of this high-risk colic patient from being spread from its stall to other horses.

While biosecurity practices appear to be common sense, not every owner abides by standard preventive health measures. According to the National Animal Health Monitoring System, Equine '05, only 32% of operations quarantined new equids prior to adding them to the resident herd. For horses that stayed on the premises for less than 30 days during the previous 12 months (visitors), only 17% of operations quarantined those horses prior to contact with the resident animals. As you can see from the first two case scenarios at the beginning of this article, not separating animals brought to the farm can be a critical mistake in farm management.

On a farm level, ideally, measures are taken to continually reduce the risk of horses becoming sick from infectious agents (biosecurity) and to lessen the chance of sick horses spreading illness to other horses on the farm (biocontainment). The simple explanation is that disinfection and farm management disease prevention methods are effective in both!

Disinfection Factors: Environment

Horses live in stalls, pastures, and paddocks, all of which contain dirt and manure. The best nonporous surfaces, such as poured rubber floors and painted concrete block walls, even after scrubbing, will likely have some organic matter (dirt, manure, secretions, etc.) hiding in corners, behind waterers, and in crevices. Compare that to a human health care facility's stainless steel, disposable plastics, and solid surfaces (not wood-sided stalls!). The presence of organic matter can reduce the effectiveness of all commonly used disinfectants. The question is, how much?

Bleach and quaternary ammonium compounds (recognized by "-ammonium chloride" in their active ingredients) are readily inactivated by organic matter; in other words, they don't work if a surface cannot be thoroughly cleaned prior to their use.

Phenolics are better suited for use when facilities cannot be completely cleaned (the majority of horse facilities). Peroxygenase disinfectants (Virkon S) are also gaining acceptance for use in equine facilities based on experimental studies.

Disinfection Factors: The Germs

Common equine pathogens of concern are listed in the table to the right. The spores of clostridial organisms, which cause tetanus, botulism, and some diarrheal diseases, are by far the most difficult to kill via chemical disinfection. These bacteria form spores while they exist in soil and manure, which makes them virtually impossible to completely destroy on a farm. However, thorough cleaning can reduce the number of spores present.

Rotavirus is difficult to kill since it is a virus that is not coated with a lipid (fatty) envelope, like influenza virus and other common equine disease-causing viruses.

The virus' lipid envelope presents an easy way to disrupt the virus and make it inoperable. Detergents degrade and emulsify fats, just like those in viral envelopes, so a cleaning with detergent prior to disinfection is a primary way to eliminate many pathogens.

Disinfection Factors: The Surfaces

The more porous a surface, the more difficult it is to adequately clean and disinfect. Raw or untreated wood surfaces are highly porous, but can be made more manageable with thorough cleaning and application of a marine-quality varnish or polyurethane. This results in a smooth surface that can be cleaned and will not absorb fluids.

Unpainted concrete block is also highly porous and difficult to adequately clean and disinfect. A concrete sealant or several coats of an enamel paint can not only seal the concrete, but also smooth out the surface's many small divots that can trap organic matter and pathogens.

Rubber mats that are sealed around the edges to stall walls to prevent seepage of fluids and materials beneath them are useful. While rubber is porous, if the mats are properly sealed, they can be adequately cleaned and disinfected.

Asphalt and concrete can be easily cleaned and disinfected, but they can be hard on horses' legs unless stalls are heavily bedded. These surface materials are often used in areas where contagious animals will be housed, and where disinfection will be routinely performed.

Disinfection Factors: The Chemicals

There are so many disinfectants to choose from, and the choices are so confusing. Details of different disinfectant types appear in the table below. It's obvious that no one disinfectant does it all. Only by heating items to high temperatures can all bacteria, viruses, spores, parasites, fungi, and other microorganisms be completely killed. That procedure is known as sterilization, which surgical instruments and other medical materials and biomedical waste undergo. That cannot be done on all of the surfaces throughout a farm.

The best choice is a disinfectant that can work in organic matter (compounds that work in 10% organic matter are best; 5% next best) and against the pathogens of most concern, which should be noted on the label. It should also be relatively easy to dilute or reconstitute (if a powder), and it should be safe to use with regular personal protective equipment (gloves, eye protection, and coveralls).

Do not forget to routinely clean and disinfect barn aisleways, tack stalls, grooming tie stalls, and other areas where animals and humans routinely trek. Horse trailers should be cleaned and disinfected prior to and after the high-use season, but also after any sick horse has been transported.

The Happy Ending

A large breeding operation with four broodmare barns began having 2- to 10-day-old foals develop diarrhea. Each day the farm manager was faced with up to four more sick foals, some requiring hospitalization. At that time, no vaccine existed for the culprit--rotavirus.

The barns were constructed of raw untreated wood and had packed clay floors; the surfaces in these barns were not going to be changed anytime soon. The plan became that on the first sunny, warm day, all 30 mares (some with young foals, some due to foal) in the most heavily infected barn would be turned out in their large pasture and the entire barn would be cleaned and disinfected from top to bottom. Even the sick foals were turned out so the cleaning could be accomplished, since virtually every mare and foal in that barn had been exposed to the virus.

Stalls were dried with fans after the last disinfectant was applied, bedding was replaced, and cleaned buckets were filled with water. Mares and those with foals were brought back into the barn. The sick foals recovered, and no new cases developed. The outbreak was stopped.

Take-Home Message

Disinfection is a critical part of every horse farm's biosecurity and biocontainment plan. Routine cleaning and disinfecting can reduce the pathogen load in a facility and help reduce the risk of disease. During an outbreak situation, disinfection of stalls and equipment might be the action that stops the outbreak cold.

Pathogens of Horses and Disinfection Challenges
Pathogens Disease Comments
Klebsiella spp Foal septicemia Routinely found in the environment; easily killed
Enterobacter spp Foal septicemia ""
Pseudomonas spp Foal septicemia ""
Escherichia coli Foal septicemia ""
Actinobacillus spp Foal septicemia ""
Rhodococcus equi* Pneumonia, diarrhea, other localized infections in young foals Routinely found in soil and manure; difficult to kill
Rotavirus Diarrhea in foals less than 6 months of age Nonenveloped virus; killed with phenols
Clostridium spp Tetanus, botulism, diarrhea, sudden death (all ages) Spore-forming bacteria that are difficult to kill; found in soil and manure
Salmonella spp* Septicemia, diarrhea, localized infections (all ages) Can be very difficult to manage in an outbreak situation
Streptococcus equi* Strangles Easily killed
Influenza virus* Respiratory disease Enveloped virus; easily killed
Herpesvirus* Respiratory disease, abortion, and neurologic disease Enveloped virus; easily killed
Equine viral arteritis* Abortion, systemic disease Enveloped virus; easily killed

* Pathogens can cause disease outbreaks.
Note: Vector-borne diseases are not included in this table.

About the Author

Roberta Dwyer, DVM, MS, Dipl. ACVPM

Roberta Dwyer, DVM, MS, Dipl. ACVPM, is a professor within the University of Kentucky's Maxwell H. Gluck Equine Research Center and editor of Equine Disease Quarterly.

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