Diseases of Unknown Etiology

Veterinarians are often faced with outbreaks of disease of unknown etiology because of limited client resources or diagnostic tools. If multiple horses are exhibiting clinical signs, which should signal the high probability of infectious disease, a response level equal to that for an outbreak of the worst possible scenario (e.g., salmonellosis for fecal-oral or strangles for respiratory outbreak) is appropriate. A response of this level immediately imposes strict limitations on the traffic of animals and human caregivers to limit spread of disease.

If a foreign animal disease (FAD) is suspected, the farm should immediately (1) restrict all animal movement and (2) contact the state’s U.S. Department of Agriculture (USDA) veterinary office. A USDA veterinary medical officer (VMO) or a specialist trained in FAD detection will inspect the farm, collect data, and obtain appropriate diagnostic samples. At the time of VMO involvement, the USDA recommends and enforces quarantine measures and makes further recommendations for disease control, usually in coordination with the respective state department of health (see Chapter 68.)

Stalls

Equine farms that experience frequent infectious disease outbreaks are often overcrowded and have poor sanitation. A limit of one acre per horse is appropriate for farms with well-tended pastures, and horses supplemented with hay when necessary. Organic debris is a major contributory factor to environmental contamination by pathogens. Management practices that may predispose to this debris include inadequate cleaning and sanitation of buckets and waterers, feces in hay mangers or feed buckets, manure buildup in stalls and run-in sheds, and on-site long-term storage of animal waste. The veterinarian should emphasize in client education that these conditions predispose to disease outbreaks and to increased expense in the form of labor, medications, veterinary visits, loss of use of animals (especially pertinent to performance horses and breeding stock), and potential mortality.

Where possible, stalls should ideally be constructed of nonporous materials such as painted concrete block (Fig. 67-1) or varnished or polyurethane-treated wood. Raw wood stalls cannot be thoroughly disinfected. Type of flooring is also critical for pathogen control; there is no reliable methodology for decontamination of dirt floors. Removable rubber mats can harbor infectious organisms beneath them and are difficult to remove, disinfect, and replace routinely because of their weight and size. Regardless of materials present at the time of an outbreak, a routine cleaning and disinfection plan should be prepared (Box 67-1). Raw wood stalls can be thoroughly swept, removing as much organic matter as possible. Dirt, clay, sand, and porous stall floors should be completely mucked out and wet areas sprinkled with barn lime and allowed to dry. Fans may be necessary to facilitate drying. Aisleways and tack rooms should not be neglected in yearly cleaning.

Fig. 67-1 Nonporous concrete-block stalls with concrete floors provide surfaces that can be completely cleaned, the most labor-intensive part of cleaning and disinfecting stalls.

Pest Control Plan

Farms should implement plans for year-round rodent control to prevent transmission and buildup of potential pathogens in the environment. Mice can ingest very small amounts of Salmonella that exponentially grow in their gut and are excreted in fecal pellets, seeding the equine environment with high concentrations of bacteria. Vermin may also act as mechanical fomites and physically carry pathogens around the barn and farm. Proper storage of feed and use of approved baits and humane traps may help in control, although a professional exterminator may need to be consulted in many cases. The use of rodenticides must be carefully monitored because horses are susceptible to most of these poisons.

Birds may also harbor pathogenic organisms and participate in the mechanical spread of infectious materials after an outbreak begins. Unfortunately, the movements of birds can be extremely difficult to control. Netting to prevent birds from nesting in rafters may be effective but is not foolproof and comes at significant cost in materials and labor. An alternative is to close off barn rafters and remove nesting sites that routinely appear in equine housing.

Bat nests should always be removed by a professional because of the risk of inhalation of rabies virus from dried saliva in these areas. Bat houses should never be built around barns to reduce insect populations because of the risk of rabies to humans, horses, and other mammals.

Insects may serve as biologic or mechanical vectors for the transmission of pathogens from one horse to another or from one area of the farm to another. Information regarding barn insect sprays, fans, and management techniques for removing standing water has been widely disseminated since the emergence of West Nile virus into North America.¹

Traffic Control

Horses should be housed in groups that are matched according to age and use. Whenever possible, groups should not be commingled. Figure 67-2

Stay updated, free articles. Join our Telegram channel

Join