Disease: Salmonellosis

This page provides general information about this condition; reveal the text by clicking on the green headers. Press releases, results from DWHC investigations as well as other useful documents and relevant literature can be found at the bottom of the page.

Pathogen

Salmonellosis is the disease caused by infection with bacteria belonging to the Salmonella genus of bacteria. Two species of Salmonella are recognised, S. enterica and S. bongori, and salmonellosis in warm-blooded animals is typically caused by different serotypes of the enterica sub-species of S. enterica. This gram negative, non-spore-forming bacteria is readily killed in the environment by high temperatures and standard disinfectants.

Susceptible species

Salmonella can infect a wide range of birds, mammals, reptiles and amphibians.

Infection has been reported in a many European wild mammal species including wild boar, European hares, badgers, foxes, hedgehogs, rodents and to a lesser extent, deer. A wide range of serovars of the subspecies S. enterica enterica have been isolated in these cases and this tends to reflect the types of Salmonella circulating in the environment.

Salmonellosis in wild birds is also known as avian paratyphoid and, when associated with mortality, is typically caused by the typhimurium serotype of S.enterica enterica. Outbreaks have been reported in many European countries, with infection and mortality rates being particularly high in songbirds such as finches and sparrows, whilst other species such as gulls may carry the bacteria in the intestines without becoming ill.

Signs in animals

Infection with Salmonella spp. can cause a variety of signs ranging from non-clinical carrier status to peracute septicemia (blood-poisoning) and death. The type of disease that develops depends on a range of factors including the amount of infectious bacteria ingested and the age and health status of the animal as well as the seroptype of the bacteria.

Infection in songbirds often causes severe lesions in the upper gatrointestinal tract (crop and oesophagus) where the bacteria is thought to enter the body; the bacteria is spread via the blood to other organs and lesions commonly occur in the liver and spleen and death following from septicemia. Often birds are not seen before they die but when signs are noticed they tend to be vague and can include lethargy, ruffled and puffed up feathers and closed eyes.

In mammals, depending on the severity of the infection and the serotype of the bacteria, clinical signs can include diarrhoea and weight loss (associated with damage to the intestines where the bacteria enters the body), or in the septicemic form, lethargy, loss of appetite, abortion, diarrhoea and death.

Infection of animals

As Salmonella bacteria are typically found in the gastrointestinal tract and shed into the environment via the feces, the most common means of infection is via ingestion of food or water contaminated with feces. In gulls this may occur through feeding at waste tips or sewage outflows; birds of prey may be infected by eating carcasses of infected animals; garden birds that frequent feeders, particularly those species that tend to feed on seeds or crumbs on the ground, may become infected from fecal contamination of these feeding sites – and for this reason outbreaks amongst songbirds are typically seen over the winter months. Carnivores such as cats and foxes can become infected after ingesting infected prey such as wild birds.

Albeit less common, infection via the mucous membranes of the eyes, nose and mouth has also been reported.

Symptoms in people

As in other animals species, salmonella infection in people can range from a sub-clinical carrier state to self-limiting gastroenteritis (diarrhoea and sickness) and in severe cases, septicemia.

Infection of people

Salmonellosis is a serious zoonotic disease; people are most often infected with Salmonella via ingestion of food or water contaminated with this bacteria. Wild birds are thought to be an important source of infection in humans, either via direct contact or indirectly via hands that have been contaminated with bird feces or pets that have had contact with birds.

Geographical distribution

Salmonella is found throughout the world in animals and humans and can survive in some environments contaminated by human activities e.g. raw sewage, intensive farming practices and some forms of waste disposal.

Whilst it is known that the bacteria is ubiquitous, monitoring of infection levels in wildlife is performed to provide information about particularly high levels of Salmonella in a certain areas or populations.

Preventative measures

On an international level, European member states must perform surveillance of the prevalence of Salmonella on pig and poultry farms which are seen as a major source of infection in wildlife. In addition, strict rodent control methods are required to stop the spread of infection from farmed animals to local wildlife. Nationally, farming practices and waste and sewage disposal methods should be closely regulated to prevent environmental contamination.

Individual risk can be minimized by observing good hygiene; for example, washing hands thoroughly after contact with animals and birds, especially before eating; and, ensuring that birds and pets are kept away from food preparation areas.

Several tips for those wishing to feed garden birds:

  • Clean feeders and bird tables daily and disinfect them regularly with a product such as dilute household bleach (5% Sodium hypochlorite); rinse them thoroughly and allow to dry before putting out new food.
  • Re-position feeders regularly to avoid dropped food and feces accumulating in one spot.
  • Rinse out bird baths daily and allow to dry before re-filling.
  • During an outbreak feeding should be reduced stopped during 2-4 weeks.
  • Disposable gloves should be worn when handling dead birds and when cleaning; wash your hands thoroughly afterwards, especially before eating or drinking.

 

Infectious Diseases of Wild Mammals and Birds in Europe (1). Somerset, GB: Wiley-Blackwell, 2012. ProQuest ebrary. Web. 29 September 2016.

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