Listeriosis is widespread in the environment. People, other mammals, birds, fish, crustaceans and insects can be infected.


Listeria monocytogenes

Other names

  • Listeria


Listeria is found worldwide with clinical disease in animals occurring more commonly in temperate climates than tropical or subtropical climates.


Ruminants, sheep, humans, birds, fish, crustaceans, insects

Affected animals

  • cattle
  • pigs
  • sheep
  • dogs
  • horses
  • farm animals

Clinical signs

In animals

Listeriosis is primarily a disease of ruminants, particularly sheep. The major clinical signs are:

  • encephalitis
  • abortion
  • septicaemic disease  (in pigs and horses).

In the farm environment, listeria has been isolated from water troughs, manure, soil and animal feeds. It is commonly present in silage.

In humans

Listeriosis has a wide range of effects in people, including:

  • inflammation of the brain
  • headache
  • chills
  • fever,
  • myalgia
  • nausea and vomiting
  • neck stiffness
  • convulsions, and
  • possibly stupor and death.

It is particularly serious in pregnant women and their infants, older people and immuno-compromised individuals. Premature, stillborn or acutely ill infants may be born to infected mothers.

How it is spread

The disease is quite rare in people, with about 2 human cases per million occurring annually.

The disease can be contracted from other people who are carrying the disease, domestic and wild animals, poultry, soil, fish, crustaceans, vegetables, water, contaminated foodstuffs, sewage and mud. Most healthy people eat foods that contain small amounts of listeria with no apparent illness.

Risk period

Risk factors such as poor nutritional status, sudden changes in climate and transport can predispose animals to infection.



Pregnant women and other susceptible people should avoid contact with potentially infected animals. Susceptible people are also advised to avoid high-risk foods such as chilled ready-to-eat foods, raw seafood and unpasteurised dairy products.

People handling aborted animal foetuses, particularly from sheep and cattle, should use protective equipment.

Control is difficult because of the ubiquitous occurrence of the organism. Vaccines are available but their efficacy needs further evaluation. Antibiotic treatment may be successful if begun early in the course of the disease.


Antibiotic treatment can be successful, although newborn infants have a high mortality rate despite treatment.