Listeriosis

Other Names: Circling disease

Cause

Listeriosis is a disease of domestic and wild animals, and occasionally humans, caused by bacteria in the Listeria group. Listeria monocytogenes is the species typically responsible for causing clinical illness. Listeriosis was first described in laboratory animals in 1926, and was first reported in wildlife in 1927 in South Africa.

Significance

People are occasionally infected with listeriosis following the consumption of contaminated food or raw milk. The elderly, neonates, pregnant women, and immune compromised people are more susceptible to this disease, and it can be fatal in these groups. Contact with animals is usually not a means of transmission of Listeria to humans. People are advised to cook meat and eggs thoroughly, rinse raw vegetables before eating, wash hands, surfaces, and utensils used for food preparation, and not to consume unpasteurized milk or cheeses.

Species Affected

L. monocytogenes has been isolated in many species of terrestrial and aquatic mammals, birds, reptiles, amphibians, and fish. Clinical illness has been observed in wild ruminants including white-tailed deer, moose, roe deer, fallow deer, giraffes, and llamas. The disease has also been reported in wild carnivores, hares, rabbits, waterfowl, and primates. Domestic animals are susceptible to Listeriosis, as are humans.

Distribution

L. monocytogenes occurs in soil and contaminated vegetation worldwide, but disease is more frequent in temperate and colder climates. Listeriosis occurs sporadically in wild populations, but outbreaks occasionally occur and are usually associated with contaminated feeds stored outside. Listeriosis is diagnosed sporadically in white-tailed deer in Pennsylvania.

Transmission

Animals acquire listeriosis following consumption of material from a contaminated environment. The bacteria can be found in soil, sewage, stream water, dust, vegetation, and silage. The bacteria may be introduced to the environment in the feces of an infected animal. New infections occur when animals ingest the bacteria in contaminated feed or water and it either enters cuts or abrasions in the oral cavity or directly crosses the intestinal lining. Insects may be able to transmit Listeria, but this is probably not a significant cause of disease transmission.

Humans can become infected by consuming food contaminated with the bacteria.

Clinical Signs

Clinical listeriosis can have three different presentations: uterine infection, encephalitis (inflammation of the brain), and septicemia (infection of multiple organ systems). Uterine infection usually results in abortion with no other obvious clinical signs. Animals with encephalitis may exhibit depression, loss of coordination, and paralysis. These animals may also have a one sided ear droop, walk in circles in one direction, and may have inflammation of the eye. Animals with the septicemic form of listeriosis rarely show clinical signs and are often found dead.

Diagnosis

Listeriosis is diagnosed by isolating L. monocytogenes in samples of aborted placenta or fetus, or brain tissue, and occasionally other tissues or bodily fluids of infected animals.

Treatment

Some antibiotics are successful in treating listeriosis, but treatment is usually not attempted in wildlife.

Management/Prevention

It would be unrealistic to attempt to control L. monocytogenes in the environment. However, feeding silage to captive and free-ranging ruminants always presents the risk of causing listeriosis, so spoiled silage should not be fed to domestic animals and should not be discarded for wildlife. It would be unrealistic to attempt to control L. monocytogenes in the environment. However, feeding silage to captive and free-ranging ruminants always presents the risk of causing listeriosis, so spoiled silage should not be fed to domestic animals and should not be discarded for wildlife.