What is listeriosis?
Listeriosis is an important infectious disease of goats most commonly causing encephalitis, but also capable of causing blood poisoning and abortion. The organism can be shed in the milk of normal carrier goats as well as sick goats and the zoonotic potential (transmission to humans) of listeriosis is a concern.
What are the symptoms of listeriosis?
The abortion form usually shows no other symptoms. It can only be diagnosed by growing the organism from the aborted fetus in a laboratory.
The nervous or encephalitic form has a rapid course and causes death in 24 to 48 hours after symptoms appear. Symptoms include circling in one direction, high fever, lack of appetite, red tissues around the eyes (maybe with blindness), and depression. Affected animals may have a paralysis of one side of the face, represented by a droopy ear, drooping eyelid, and saliva running from limp lips. Up to 20% of the goats in a herd may be involved. When near death, the animal will lie down and may have fits. Confirming diagnosis can only be made in a diagnostic laboratory but isolation of the organism from goat tissues and organic materials such as animal feeds can be problematic.
What are the causes of listeriosis? How is it transmitted?
Listeriosis is caused by the bacterium Listeria monocytogenes and is commonly seen in cooler climates. Listeriosis is spread when goats swallow, inhale, or get the bacteria in their eyes.
The bacteria are very hardy and are common in soil, silage not fermented (not acidified) properly, put up too dry or not compacted tight enough to protect it from the air. The bacteria are also common in round bales of hay that have started to rot, feed bunks that are not cleaned regularly and in which some feces and wet feed leftover accumulate and ferment, rotting woody debris, manure, and milk, urine, and drainage of the eyes and nose of infected animals. Environmental and fecal contamination are more common sources than silage in goats overall because most goats are never fed silage.
Though easily killed by common disinfectants, the listeriosis organism can survive in feces, soil, spoiled round bales of hay and silage, dirty feed bunks, rotting woody debris, etc., and animal tissue for five or more years. Listeriosis is a common clinical problem in intensively managed dairy goats in North America and Europe. The source of infection in herds is not always clear. Wild mammal and bird excreta may be the original sources of the bacteria, which then persist in soils, on plants, and in feed bunks and feed.
Factors predisposing to clinical listeriosis in goats are similar to those reported for other farm animals and include increased stress from poor nutrition, parasitism or other disease occurring at the same time, advanced pregnancy, and sudden changes in weather, feeds or general management procedures. A history of silage feeding is not a prerequisite in outbreaks of caprine listeriosis. An increase occurrence of listeriosis in fall and winter has also been observed in goats, though cases occur year around. The disease is most common in adult goats.
How can listeriosis be treated or prevented?
There are no effective treatments for small ruminants, and they usually die after infection. Large doses of penicillin may help in some cases. When an outbreak occurs, infected animals should be isolated. If silage or round bales of hay are used, their use should be discontinued. Recently introduced animals should be considered suspect as carriers. Floors, pens, sheds, feed bunks, mineral feeders, etc. should be thoroughly cleaned and disinfected.
Can listeriosis be a human health concern?
Listeriosis can cause serious diseases in humans. Be extremely careful when handling sick or dead animals. Do not eat any part of the sick or dead animal. Wash hands and disinfect clothes and shoes. Use all sanitary measures possible. If a herd is infected and milking animals have aborted, milk should be boiled or pasteurized before use. Pregnant animals should avoid infected animals. Symptoms may range from a mild irritation on the hands and arms from assisting in the delivery of a kid to a severe blood poisoning disease. Encephalitis and abortion of pregnant women may also be produced by listeriosis.
Publication date: Oct. 9, 2015
Revised: Sept. 17, 2020
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