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SALMONELLOSIS

Note for Pet Owners:

This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Salmonella can be transmitted to humans, and so this disease is a zoonosis. Proper hygienic precautions should be taken after contact with animals which could be carrying the disease, especially children and people with impaired immune function. For practical purposes this means all pets and domestic livestock as well as wild animals.

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Description
Salmonella poisoning (or salmonellosis) is one of the commonest forms of zoonosis with infection being transmitted directly or indirectly from animals to humans, or from infected food products (meat, eggs, dairy products) to humans. Salmonellosis  occurs in most countries and affects all animal species.

Cause
The cause of Salmonellosis are gram-negative, motile bacteria called Salmonella which are part of the family Enterobacteriaceae, and are usually found in the intestinal tract. These bacteria infect many species of animal including amphibians, birds, mammals (including humans), insects and reptiles. In addition, the organism can survive in the environment so in-contact objects, bedding etc can carry them. However, the commercial heat-processing of foods kills the organism.

There are many different strains of  Salmonella and not all of them cause disease. Species which are harmful  to domestic animals and humans include the following :

  • Salmonella arizonae
  • Salmonella choleraesuis
  • Salmonella enteritidis
  • Salmonella typhi and paratyphi (the cause of typhoid in humans - does not affect animals)
  • Salmonella typhimurium - the type most commonly isolated from humans and animals

As a general rule strains of Salmonella that can attach to and invade the intestine lining (mucosa) and multiply in the hosts cells, and which are encapsulated or mucoid tend to be more harmful (pathogenic) than other strains. The ability of these "pathogenic" strains to invade the mucosa depends on the presence of  pili or flagella. Some forms of Salmonella produce toxins as well as causing direct injury to the intestine wall. If the organisms get into the blood stream (called septicaemia) they can travel to other organs including the heart, kidneys, liver, spleen, lymph nodes or brain and cause serious disease and death. Similarly, the toxins can get into the blood (called toxaemia) and cause damage in other organs.

Infection is usually through direct or indirect ingestion of the organism from contact with animal faeces on animals or in the environment, or contact with contaminated food, water or objects (eg feeding bowls). Occasionally the infection can be transmitted by airborne spread.

A large number of Salmonella organisms need to be eaten because many are killed by acid in the stomach. Infected animals can shed the organisms in faeces or orally even if they do not show any signs of illness.

Salmonella dublin is transmitted from cattle to humans via contact with vaginal secretions

Breed Occurrence
There is no breed predisposition to infection, but animals kept in faecally contaminated environments (eg farm livestock) or that eat faeces (coprophagia), groom companions or share feeding and drinking bowls are at high risk to contract the infection.

Predatory animals (eg cats) that kill and eat infected species (eg birds) are also at risk.

Young animals, animals with poor immune responses (natural or drug-induced), animals subjected to stress and animals suffering from malnutrition or obesity are at greater risk from exposure to Salmonella. Animals given oral antibiotics (eg ampicillin)  may have lower resistance to Salmonellosis because the antibiotic alters the numbers of  normal, protective bacteria in the gut.

In cats and dogs it has been estimated from tests that up to 36% of healthy dogs and 18% of healthy cats have Salmonella in their faeces, and the number of animals carrying the disease is thought to be higher than these findings.

Species commonly infected with Salmonella which may be of importance and risk to humans include :

Human workers most at risk to contract salmonellosis include :

  • Animal handlers
  • Butchers
  • Food handlers
  • Kitchen workers
  • Veterinarians

Signs

Many animals can be infected with Salmonella but show no signs at all.. These present a real risk to humans especially young children who may handle infected pets eg terrapins and other reptiles. So basic hygiene is important when handling pets, cleaning out their environments or handling food and water bowls. Hands should always be washed thoroughly after handling pets and related objects. 

When disease occurs the main signs are associated with gastrointestinal damage :

  • Diarrhoea - often watery and containing mucus or blood
  • Vomiting
  • Inappetance
  • Increased salivation (cats)
  • Increased thirst
  • Abdominal pain - all species but especially horses (colic)

But other signs include

  • High body temperatures
  • Depression
  • Dehydration
  • Weight loss
  • Weakness
  • Shock
  • Death

If the bacteria or toxins get into the bloodstream other signs may be seen according to the organs affected, for example :

  • Brain
    • Blindness
    • Excitability
    • Fits (seizures or convulsions)
    • Flicking of the eye (nystagmus) - calves
    • Staggering
    • Paralysis of the hind legs
  • Eye
    • Conjunctivitis with enlarged lymph nodes (in cats)
  • Joints
    • Arthritis in multiple joints - especially in young animals that survive the acute stage of the disease
  • Liver
    • Jaundice
  • Lungs
    • Cough
    • Difficulty breathing (called dyspnoea)
    • Nose bleeds
    • Pneumonia - all species but especially pigs
  • Lymphatics
    • Enlarged lymph nodes (with conjunctivitis in cats)
  • Skin
    • Dark red to purple discolouration on abdomen or ears (pigs) due to haemorrhages

Localised infections can occur in many tissues causing local abscesses or infection eg in bone Salmonella can cause osteomyelitis.

In young animals or animals infected in the uterus the signs may be :

Severe disease due to septicaemia or toxaemia is most likely to occur in very young animals, whereas gastrointestinal signs are more likely in adults. Animals that survive the acute stage of the disease and any septicaemia or toxaemia, may develop chronic disease with persistent diarrhoea , fever and weight loss.

In HUMANS the signs are similar and include :

  • Abdominal pain
  • Vomiting
  • Diarrhoea
  • Dehydration
  • Fever
  • Headaches, and eye pain
  • Nausea

Salmonella dublin is transmitted from cattle to humans and causes a cutaneous form of disease (dermatitis)  with the formation of nodules and pustules

Complications
Animals recovering from Salmonellosis shed organisms in their faeces for at least 4-6 weeks, and this can start again if the animal is stressed - for example if horses are transported.

A real concern is the development of strains of Salmonella that are resistant to many antibiotics - eg Salmonella typhimurium DT104 which is present in people, cats and dogs and other species in the USA and UK.

Diagnosis
Diagnosis of Salmonellosis is usually made by the identification of Salmonella organisms in :

  • Faeces
  • Vomitus
  • Swabs taken from the oral cavity
  • Blood
  • Synovial fluid from the joints 

Unfortunately, many animals will be positive for organisms but the Salmonella present may not be causing any clinical signs that the animal has. In addition, negative cultures may not mean that the animal does not have Salmonellosis - especially if there are large numbers of other organisms present as well. For this reason suspect cases should have samples tested every 2-3 weeks.

It is important that fresh samples are transported to the diagnostic laboratory correctly in Amies transport medium with charcoal.

Treatment
For acute, severe cases of Salmonellosis prompt treatment is needed to save the animal, and a variety of therapeutic agents have been used including:

  • Intravenous fluids - sometimes plasma
  • Antibiotics* - for example chloramphenicol, trimethoprim-sulphonamide combination drugs and amoxicillin.
  • Lactulose
  • Prostaglandin-inhibitors - may be effective when toxins are causing increased fluid losses in the intestine
  • A Salmonella antiserum containing antibodies  is available against some forms of Salmonella

*However - antibiotic use (especially chloramphenicol) should be reserved for animals with severe disease, and  is not recommended for animals with  gastrointestinal signs only - because of the risk of bacterial resistance developing.

The environment and objects should be disinfected with one of the following  :

  • Bleach 
  • Formalin (20%) - 1 hour
  • Gluteraldehyde (2%) - 1 hour
  • Ethylene oxide gas (equipment in veterinary facilities)
  • Phenol-based disinfectants

or

  • Autoclaved (equipment in veterinary facilities)

Prognosis
Poor for young animals with acute, severe infections and septicaemia or toxaemia. Better for adult animals.

 

Updated October 2013