Back to Stories & News

December 15, 2022 — For more than four decades, Morris Animal Foundation has funded research into bacteria-causing diseases in horses. For many bacterial pathogens, the horse’s immune system successfully eliminates the invading bacteria and resulting infections often resolve themselves. However, some horse patients may require specialized veterinary care and intervention to help them get back on their hooves.

Here’s a snapshot of some of the ways the Foundation is helping horses impacted by harmful bacteria.

Foal Pneumonia
Rhodococcus equi, a naturally occurring bacterium in soil, is the most devastating cause of pneumonia in foals aged 3 weeks to 5 months. Antibiotic-resistant R. equi is an emerging treatment challenge. A practical, long-term solution to this health concern is to decrease widespread use of commonly used antibiotics in foals with pneumonia.

Foundation-funded researchers recently showed that gallium maltolate, a semi-metal compound with antimicrobial and anti-inflammatory properties, is highly active against R. equi. In a clinical trial of client-owned foals with subclinical pneumonia (meaning ultrasound scans found lesions on their lungs but the foals had no clinical signs), researchers showed gallium maltolate minimized the development of antibiotic-resistant bacteria in the gut as measured in stool and soil samples. While further study in foals with severe, symptomatic pneumonia is warranted, researchers hope gallium maltolate will be a promising new tool to help mitigate the emergence of antibiotic-resistant strains of R. equi – especially important to farms endemic for this difficult-to-treat bacteria.

Potomac Horse Fever
Potomac horse fever (PHF), first recognized in 1979 in horses on farms adjacent to the Potomac River, is caused by the Neorickettsia risticii bacteria (formerly known as Ehrlichia risticii). PHF is an important cause of diarrhea and gastrointestinal upsets in horses, as well as reported abortions in pregnant mares.

PHF can be fatal in some horses. Intermediate hosts of the bacteria include freshwater snail larvae and aquatic fly species, including mayflies. Horses are exposed to the bacteria when drinking from creeks, rivers or ponds in the summer months. As this is a noncontagious infection (the bacterial host needs to be ingested), preventive measures to minimize risk of exposure include providing clean drinking water, eliminating standing water sources where insects may breed and turning off stable lighting at night that may attract insects.

Foundation-funded researchers helped identify the causative bacteria for PHF in the 1980s following several disease outbreaks. Findings led to early diagnostics and the development of a vaccine. Today’s vaccine continues to offer some protection against infection, but it’s primary use is to help reduce severity of the disease in areas where PHF is endemic.


Salmonella
Salmonella is one of the most common bacterial diseases of adult horses. Infection can occur via contamination of the environment, feed or water, or by contact with animals actively shedding the bacteria, Salmonella enterica. Infected animals also can transmit the disease to humans.

Disease outbreaks occasionally occur at veterinary hospitals and other settings where horses congregate, such as boarding facilities, fairs and shows. Once an area is infected, it is difficult to control the spread of the infectious agent without extreme measures, including extensive disinfection. To add to the challenge, infected horses can be asymptomatic and continue to shed the bacteria intermittently, posing a threat to other animals and owners.

While salmonella is common in horses, little is known about the health-related determinants of the disease, making it difficult to develop effective control and management plans. Foundation-funded researchers looked at how long horses can shed the salmonella bacteria in their feces. Early data suggests an infected horse can intermittently shed bacteria for more than 40 days, necessitating long-term management of affected animals. Findings from this study are providing much-needed guidance for owners and veterinarians trying to minimize outbreaks and infections of stable-mate horses and other animals.

Bacterial Joint Infections & Biofilms
Many different types of bacteria can lead to persistent joint infections in horses. Bacterial infections in other locations in the horse usually can be eliminated with a course of antibiotics. However, when bacteria enter a joint, they interact with joint fluid and clump together in a free-floating biofilm that creates a barrier to evade antibiotics. This results in persistent infections that cause painful inflammation and arthritis in the horse.

Foundation-funded researchers developed a new strategy to improve treatment of persistent joint infections in horses. The team successfully created a novel platelet-rich plasma lysate from platelets, immune cells and synovial (joint) fluid from healthy horses and tested its immune system targeting properties in equine cells. Data showed the novel platelet-derived biologic can help breakup biofilms and kill antibiotic-resistant infections within the joint. The biologic also helps the immune system fight off the infection and protects vulnerable cartilage from damage. Researchers hope platelet-rich plasma will be a valuable tool in fighting persistent bacterial joint infections in horses and potentially save lives. Clinical trials in horses are ongoing and generating some promising results.

How You Can Help

Support life-saving veterinary research for horses – as well as dogs, cats and wildlife. Your gift will help researchers develop better diagnostics, treatments and preventive to help animals around the world, including research into bacterial diseases for multiple species. Your gift today offers a healthier tomorrow for all animals that share our homes and the wild places we love