Overview

Listeriosis is a disease that affects many animal species, but is most common in ruminants (such as cattle, sheep and goats).

It can cause neurological problems, abortion and other symptoms. People are also susceptible to listeriosis infection from consuming contaminated food and must take precautions to stay healthy.

Cause

Listeria monocytogenes is the bacterium that causes listeriosis.

It is found throughout the environment, especially in:

  • soil
  • manure
  • spoiled silage or hay

Outbreaks are usually associated with some kind of stress, such as poor-quality feed or sudden changes in weather. The bacteria can also be present in the feces of healthy, unaffected animals and people.

Clinical signs

Listeriosis usually affects ruminants such as cattle, sheep and goats, and causes a range of clinical signs in these animals.

Affected animals will typically:

  • have a fever
  • have a poor appetite
  • appear depressed

In some cases, animals may:

  • have paralyzed face muscles
  • be uncoordinated
  • walk in a circle with their neck twisted to one side
  • press their heads against a solid surface
  • have mastitis (rare)
  • have pinkeye (rare)

Animals in the late stages of pregnancy may abort or give birth to stillborns. Some animals die from the disease.

Birds

Birds, such as chickens, turkeys, geese, ducks, canaries and parrots can also be infected by listeriosis. Birds may show no signs of disease or may be depressed, paralyzed or may die suddenly. Some birds may also have diarrhea.

Rabbits, pigs, dogs and cats

Listeriosis can also affect rabbits, especially pregnant does, as well as pigs, dogs and cats. These animals will have a fever and a poor appetite, will appear depressed and may have diarrhea or respiratory problems.

Treatment

A veterinarian can diagnose listeriosis and prescribe antibiotics for infected animals. Treatment may not be successful in the later stages of the disease.

Remove suspicious feed from the diet to prevent further cases.

Prevention and management

Control of listeriosis is difficult, since the bacteria are present throughout the environment.

It is recommended to:

  • feed livestock off the ground
  • separate sick animals from the herd and examine them promptly

Avoid:

  • feeding spoiled silage to animals
  • allowing silage to become contaminated with soil during harvesting
  • close grazing practices that increase the risk of soil ingestion

Transmission to humans

Listeriosis is not directly transmissible from animals to humans. However, in rare situations, outbreaks of listeriosis occur in humans.

How humans become infected

People become infected by consuming:

  • contaminated vegetables
  • unpasteurized milk or milk products
  • improperly cooked meats
  • foods that pose a higher risk if contaminated after processing, such as hot dogs, deli meats and cheese

The bacteria survive at refrigerator temperature ranges.

Reduce your risk

To reduce the risk of exposure, you should:

  • discard foods that are past their "best before" date
  • prevent cross-contamination during food handling
  • wash, prepare and cook foods to recommended internal temperatures

Symptoms for humans

Symptoms may start suddenly and include:

  • vomiting
  • nausea
  • cramps
  • diarrhea
  • constipation
  • severe headache
  • fever

Some people experience only mild, flu-like symptoms.

Some infections may become severe and can:

  • develop into an infection of the brain, leading to neurological signs
  • result in a loss of pregnancy

Those that are pregnant, people with weakened immune symptoms, the young and the elderly are highly susceptible to listeriosis and should speak to their health provider about additional precautions.

Reporting

Veterinary laboratories in Ontario and veterinarians who use a laboratory outside of Ontario must report cases of listeriosis to the Ministry of Agriculture, Food and Agribusiness (OMAFA). OMAFA will monitor and ensure that the disease is kept under control.