SALMONELLA INFECTION AND VACCINATIONS

SALMONELLA

Salmonella is a common bacterial infection which strikes foals in particular soon after birth. In its commonest form it causes scours.

THE SALMONELLA BACTERIA

The salmonella organism is usually carried by normal mares that shed the bacteria when giving birth. Up to 10% of normal mares may be carriers of the bacteria and shed it into the environment.

Salmonella organisms are common contaminants of the environment but thrive in organic material (eg faeces) and foods containing animal products. Adults eating infected feeds or faeces may get no symptoms but will pass the bacteria to their foals at birth through faecal contamination of the foal.

There are over 2500 serotypes of Salmonella but Salmonella typhimurium is the commonest.

The higher the horse density, particularly in foaling areas, the bigger the number of bacteria which will be in the environment, so it is particularly common on larger studs and areas where horses are placed under stress (eg Veterinary Hospitals).

Approximately 30% of infected horses will shed the bacteria for at least one (1) month and a small percent may continue to shed for up to four (4) months.

THE SALMONELLA DISEASE

Adults generally do not show signs except for the occasional individual which could develop colitis. These animals die rapidly. In foals, signs develop within 12 to 72 hours of ingestion of bacteria and range from mild transient scours similar to foal heat scours to projectile watery foul smelling diarrhoea with fever, depression and colic. Occasionally in foals which have not received enough colostrum, it may cause pneumonia, navel ill, joint ill and encephalitis. Some horses may die without scouring.

DIAGNOSIS OF SALMONELLA

The bacteria is very difficult to isolate even from known carriers and shedders. Faecal cultures and rectal mucosal biopsies must be preformed on a daily basis for 5 to 7 days to have any chance of isolating the organism.

TREATMENT OF SALMONELLA

Treat adults with intravenous sulphonamides or enrofloxacin according to sensitivity tests, and supportive therapy (scour powder, peptosil and intravenous fluids).

Foals generally require more intensive supportive therapy and antibiotics.

Treatment will generally not reduce the duration or course of the infection or stop bacterial shedding but it will prevent secondary infections. Antibiotic resistance is common.

CONTROL OF SALMONELLA

Wash mares down after foaling and after passage of the placenta with disinfectant (eg betadine). Move mares and foals from the foaling paddocks as soon as possible. Remove faeces and organic debris from foaling paddocks, stables and drains etc and disinfect with phenolic compounds, iodophors, 1 in 30 chlorine bleach, or 2% formaldehyde. Allow access to direct sunshine if possible.

Ensure all veterinary equipment eg. Stomach tubes, are thoroughly disinfected. Attend affected animals last on the stud and ensure infection is not spread on boots or clothing.

As with many disease processes, stresses such as prolonged cold and/or wet weather, overcrowding, internal parasites and under-nutrition are predisposing factors so they should be avoided if possible.

SALMONELLA VACCINATIONS

Vaccination against Salmonella typhimurium is available. All animals require two doses 4 to 6 weeks apart and an annual booster.

Broodmares should receive their second dose or annual booster approximately six weeks before foaling to a minimum of 10 days before foaling.

Foal vaccination should begin at 4 months.

The vaccine will cause some pain and swelling at the injection site and should not be given into the neck.