Preventing Salmonella Spread in Horses

In the equine industry horses are constantly in transit to and commingling at venues such as veterinary hospitals, racetracks, horse shows, breeding farms, and training stables. Therefore, they are continually at risk of acquiring infectious diseases caused by opportunistic organisms, including Salmonella.

This bacterium is a common cause of gastrointestinal (GI) disease outbreaks at equine hospitals and farms. Salmonellosis is important to prevent because ill horses are difficult to treat and could die, remediating an outbreak is costly, and humans could also become sick. Because a vaccine to protect horses against Salmonella does not exist, environmental and equipment disinfection, isolation of sick or new horses, good hand hygiene, and education are crucial parts of an infection prevention program.

What Is Salmonellosis?

Salmonella enterica is transmitted via the fecal-oral route. The range of clinical signs, plus clinically normal horses’ ability to shed the bacteria intermittently, make managing salmonellosis difficult. There are three types of infected horses: silent carriers (those infected but without clinical signs and not shedding), subclinical carriers (no clinical signs) with fecal shedding, and shedders with clinical signs.

Key ways to prevent infection and protect susceptible horses and people include identifying subclinical shedders, managing contact between sick and healthy horses, employing personal hygiene techniques (hand-washing, clean clothing, etc.), and cleaning and disinfecting the environment.

Salmonella-positive horses that have recovered but remain shedders and must be discharged from the hospital pose a management challenge. The risk exists for Salmonella to spread to other horses back at the farm.

Focus on the Environment

It’s important that veterinarians inform owners about a horse’s positive Salmonella status and educate them on infection prevention measures, such as isolation, disinfection, and proper manure and bedding handling.

Here’s why: Salmonella can survive on surfaces for months to years, depending on moisture, temperature, and bacterial type. It can persist on porous surfaces (untreated wood, unsealed concrete, etc.) that are difficult to clean and disinfect. It can also form biofilms, or resistant bacterial communities, which serve as reservoirs and potential infection sources.

Fomites—objects, such as twitches, tack, and endoscopes, that can harbor infectious microbes—also play important transmission roles. A sick or subclinical shedder could contaminate these objects and the environment. People using poor hand or footwear hygiene, for example, might then disseminate environmental pathogens to different areas of a property.

In human health care hand or glove contamination correlates with environmental contamination: The more soiled the environment, the higher likelihood that hands will become contaminated and spread pathogens to patients and other surfaces. This is likely true for equine hospitals, as well. Researchers in one study collected positive Salmonella samples from high-touch areas such as stall door bolts, light switches, telephones, keyboards, etc. (Traverse et al. 2015).

Thus, cleaning and disinfection are paramount for horse and human safety at hospitals and farms. If a stall that housed an affected horse was not cleaned and disinfected properly, it could put the next horse at risk of becoming sick from the microorganisms left on its surfaces. In fact, researchers have repeatedly identified suboptimal environmental hygiene as a contributing factor in Salmonella outbreaks at large animal hospitals.

Veterinarians implement rigorous infection control measures when horses with Salmonella are at the clinic. But the farm environment is not the same as that of an equine hospital; continuing with these precautions on the farm can be more challenging (for example, clinic walls and floors are less porous and designed to be disinfected). Horses at home are less likely to be exposed to a variety of pathogens than hospitalized horses, and they are generally healthier and might be more resistant to Salmonella infection.

Take-Home Message

Measures geared toward minimizing contagious infectious GI disease spread and educating owners must be part of the care veterinarians provide. Not meeting these standards of care represents a failure to uphold ethical responsibilities to patients and clients. Work as a team with your veterinarian to improve infection prevention practices and help advance the equine industry in this area as a whole.