Salmonella in Horses - Hoofbeats

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SALMONELLA SALMONELLA

There are more than 2200 distinct variations within the species of bacteria (serovars) of salmonellae and all are considered possible pathogens that can cause disease for horses.

In Australia, Salmonella typhimurium is the most common cause of salmonellosis. It produces intestinal disease (such as diarrhoea) in horses, and other animals including dogs, cats, birds, humans and many other species. Cases are usually sporadic with an affected horse here or there, but may become an epidemic/outbreak depending on the severity or harmfulness of the organism, the level of exposure (i.e., how many bacteria gain entry to the body) and individual horse factors. Recently there have been outbreaks of Salmonella in horses in Australia.

Adult horses: Signs of illness in adult horses include fever; colic; shock; severe watery, foul-smelling diarrhoea that might contain blood; weakness and loss of appetite. Although it is one of the most common infectious causes of diarrhoea in adult

Dr Jen Stewart is currently the only practicing equine veterinarian and clinical nutritionist in Australia with more than 40 years experience. Jen has been developing premium formulas for studs, trainers and feed companies - such as Mitavite - in Australia and around the world. Consulting to leading international studs and trainers in various countries

Dr Jennifer Stewart CEO BVSc BSc PhD Dip BEP Equine Veterinarian and Consultant Nutritionist.

Dr Jennifer Stewart www.jenquine.com Equine Veterinarians Australia

working on research projects and being involved in nutritional management of a variety of equine clinical conditions, including colic, tying-up, laminitis, performance problems, developmental orthopaedic diseases and post-surgery. Jen’s vision is to provide a world best-practice in equine veterinary nutrition and to BRING SCIENCE TO YOUR FEED BIN.

There are many equine infections, and these can have varying effects on your individual horse or herd. Salmonella is one that is extremely contagious and requires good biosecurity to protect both horses and humans.

horses, importantly, Salmonella can develop without diarrhoea. Complications of salmonellosis include laminitis, bacteremia (viable bacteria within the bloodstream) and septicemia (blood poisoning), renal (kidney) failure, clots, hepatitis (inflammation of the liver) and pneumonia (infection of lungs).

FoA ls: In foals especially, Salmonella can get into the blood stream and travel to many organs, including the liver, lungs and joints. Affected animals show dullness, depression, fever, lameness and joint swelling. Clinical signs include hemorrhagic diarrhoea (blood mixed in with manure), pneumonia, meningitis (inflammation of the membranes around the spinal cord and brain) and septic arthritis.

d i Agnosis A nd tre Atment is based on clinical signs, very low white blood cell counts (neutropaenia) and faecal culture to grow the organism. A minimum of three, and usually five, cultures is necessary because Salmonella is only intermittently shed in the manure and in small numbers.

Treatment is principally supportive and needs to be aggressive – i.e., prompt and ongoing intensive replacement of fluid and electrolyte losses and intestinal protectants. Fluid replacement may require 80 litres per day and the diarrhoea and metabolic derangements can take 7 – 10 days to resolve.

Antibiotic treatment is often of little use and your veterinarian will determine on a case-by-case basis if they are indicated. The choice of antibiotic is difficult and antibiotic sensitivity and resistance patterns can change during the disease process. Hence your veterinarian may request culture and antibiotic sensitivity testing of multiple manure samples.

The prognosis for your horse varies with the case. Many horses may have Salmonella and never show clinical signs. Others can become sick and require intensive therapy – and some die suddenly despite intensive therapy.

They may also become infected by direct contact with infected horses or surfaces that have been contaminated with manure from an infected individual. Mice, chickens, pigeons, and wildlife can be sources of Salmonella.

C A rriers: Some horses are carriers – i.e., they don’t show any signs of infection or illness, but can actively spread the bacteria. Because they generally shed the bacteria intermittently in their manure and often without any signs of illness, Salmonella carriers are particularly difficult to identify.

If stressed, carriers may develop clinical signs.

Stress leads to a rapid multiplication of the bacteria and can be caused by transportation, intestinal microflora upset, other illnesses, overcrowding, abrupt change in diet, intensive physical

t r A nsmission: The most common sources of infection are contaminated feed and water and carrier birds, rodents, horses and other farm animal species that excrete the bacteria. Salmonella is usually transmitted by the ‘faecal-oral’ route (i.e., from manure contamination of the mouth) although infection may also occur through the mucous membranes of the eyes and the nose via aerosol droplets. Continued

WHAT IS SALMONELLOSIS and how does it affect your horse?

Salmonellosis is a bacterial disease that can affect both foals and adult horses. The bacteria spread easily from horse-to-horse contact and by shared tools, water buckets, hands, etc., on which bacteria can ‘hitch a ride’ to the next horse.

This disease can upset the gut in horses and foals. It can cause debilitating–and even deadly–diarrhoea. Symptoms in adult horses include diarrhoea, fever and lethargy in mature horses, however the signs in foals are more serious. Some horses do not show clinical signs, so seemingly well horses can harbour the bacteria, and when stressed, they can shed it or become ill themselves.

Horses may pick up Salmonella from the pasture, feed or water sources if these have been contaminated by the faeces of infected animals (including birds and other horses).

one of the most commonly diagnosed infectious causes of diarrhoea in adult horses

M ANAGING OUTBREA kS

The following measures are critical if an outbreak occurs:

• Isolate all sick animals. This may mean isolating an entire stable, paddock or property.

• Horses that have been exposed to sick animals should not have any contact with non-exposed animals.

• Involve your veterinarian and diagnose the cause of the disease as soon as possible.

• Limit movement of people and equipment.

• Restrict access to isolation areas.

• Use disposable overalls, gloves and foot guards.

• At every entrance and exit place foot baths with the appropriate disinfectant – water won’t do the job and not all disinfectants are effective against Salmonella. Your veterinarian will know which ones to use and for how long you need to stand in the footbath – a quick dip is not enough.

• Spray all vehicles and tyres with disinfectants.

• Wash and sanitise hands regularly through the day.

• Dispose of bedding and manure so other horses aren’t exposed to it.

• Control access of wildlife, birds and rodents to feed, water and bedding.

• Check whether you need to report the disease to the government – this varies between states.

Proper cleaning and disinfecting requires knowledge of the bacteria. Even the correct disinfectants will not be effective in destroying Salmonella unless the surfaces are cleaned first. The most important part of the disinfection process is the hard work of first cleaning all surfaces with a detergent, then rinsing before applying the disinfectant (Table 1). All organic material, dirt and debris must be removed by pressure washing or steam cleaning before disinfecting – taking care that the wash doesn’t spread and contaminate other areas or the environment.

activity, antimicrobial treatment, surgery and gastrointestinal tract disorders. Shedding may persist for days to weeks and although some horses are consistently positive on manure culture, a negative culture does not rule out intermittent or low-level shedding of Salmonella.

In most cases, the amount of bacteria shed in the manure of convalescing horses is relatively small and doesn’t present a risk. Among horses that have recovered from salmonellosis, approximately 2/3 will have ceased shedding after one month and around 90% after four months. However, if the variant is especially virulent or is able to survive and proliferate in the environment, persistent faecal shedding of the bacteria could pose a risk to other animals or humans.

Shedding decreases over time and many horses will stop shedding altogether.

mA n Agement o F F oA ls –special attention is needed:

Except for normal foal heat diarrhoea, any foal with diarrhoea should be considered infectious and contagious. No in-contact foals should be moved to other locations because there is a high chance they could be incubating the disease and be a source of infection for other parts of the property if they are moved. Although this may seem extreme, the expense of an all-out diarrhoea outbreak due to Salmonella far outweighs the inconvenience of separating sick foals. Isolation should be intensive, with protective clothing (gloves, gowns, and shoe coverings – or better, dedicated footwear that does not leave the isolation area) worn before entering the isolation area. Dedicated grooming and mucking out tools and thermometers must

Table 1. STANDARD DISINFECTION PROCEDURE FOR NON-POROUS SURFACES IN STABLES, AISLES AND FLOATS, EQUIPMENT AND CLOTHING

1 Remove all buckets, feed tubs and bedding.

2 Sweep the walls and floor of the stall to remove all organic matter.

3

Use a hose with spray nozzle to wash all surfaces with detergent - for stubborn stains, keep the surface wet for 10–20 minutes, then scrub by hand.

4 Starting at the top, rinse with water. Corners and drains may require a second cleaning.

5 Remove as much water as possible so the disinfectant doesn’t become diluted.

6 Don protective clothing and starting at the top, apply the disinfectant as per the product instructions.

7 Do NOT rinse but allow to dry.

8 During an outbreak repeat the cleaning and disinfection.

9 Scrub all buckets, feedbins and equipment with detergent, rinse, dry and apply disinfectant and leave for 10 minutes.

10 Rinse thoroughly with water and allow to dry.

11

Rinse dirt, manure etc. from towels, clothing etc. then soak in disinfectant for 10 minutes before washing with laundry detergent.

be used – and all cleaned and disinfected after use. Manure should not be allowed to contaminate groundwater or be accessed by other horses and should never be spread onto paddocks.

Prevention = biose C urity:

Prevention of salmonellosis is difficult because the organism is present in the environment as well as in the manure of some healthy animals. The environment is at greatest risk for Salmonella contamination from a diarrhoeic horse because bacteria will spread over a relatively large areacracks in walls and stalls, on the surface of water buckets or automatic watering devices, and in bedding materials that may be spread by wind or careless foot traffic.

Horses testing positive for Salmonella should remain isolated until they stop shedding based on multiple negative cultures. It is important to note that these horses may shed again if they are sufficiently stressed.

Salmonellae can persist in the environment and soil can remain contaminated for over 300 days, and water for nine months. Although it can be killed by desiccation (removal of water) and exposure to sunlight, Salmonella can survive in dried manure for up to 30 months. Freezing doesn’t kill the bacteria and it can survive over two years in infected ice cream!

bioseCurity PlAn:

To prevent the introduction of Salmonella, it is important to have a biosecurity plan. Some method of isolating new arrivals and sick horses is important. New horses should be isolated for approximately two-to-three weeks and monitored for diarrhoea or signs of respiratory disease. Salmonella is very infective, and control measures require strict attention to sanitation. Foot baths, protective clothing, isolation, and proper disposal of faeces are basic when caring for infected or shedding horses. Personal hygiene is important because human infections can occur from exposure to this organism.

Zoonoses are diseases that can be transmitted to humans from animals. Salmonella can move between animals and humans. Thus, people can and do become infected with Salmonella from horses. Ingesting contaminated faeces causes Salmonella in people. Signs of Salmonella in humans vary from none to severe gastrointestinal disease and medical advice is essential. Practice good hygiene. Always wash your hands before eating and don’t touch objects with manure-contaminated hands.

Understanding disease transmission and effective management practices are both essential in preventing equine diseases. Your veterinarian is the best source of advice because successful disease prevention includes an effective vaccine and a rigid management

protocol that carefully evaluates and isolates new arrivals, prevents stress and overcrowding, recognises clinical symptoms, and deals with disease quickly. Preventive hygiene and the use of effective disinfectants are essential to the management program.

A balanced diet is one of the best defences a horse has against disease and for recovery and convalescence. Every nutrient is important and deficiencies or imbalances in essential amino acids, fatty acids, vitamins, minerals and fibre can compromise immune function.

Fortunately, the steps involved in control and prevention of Salmonella also are applicable to most other equine infectious diseases. The cost and work involved with isolation, disinfection and good management can more than pay for themselves in the long run of not having to deal with salmonellosis, rotavirus, and other diseases.

All content provided in this editorial is for general use and information only and does not constitute advice or veterinary opinion. The content does not consider individual circumstances, is not intended as a substitute for advice, and should not be relied upon as advice or in place of consultation with your equine veterinarian. For full disclaimer, please refer to our website: www.jenquine.com.au

Spray wash all surfaces with detergent, then scrub by hand.