Listeriosis in Goats
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Winter weather often means feeding stored feed, as pasture is no longer sufficient or available. In the Northern Hemisphere, snow may bury the field. The increased risk of certain diseases comes with increased moisture and stored feedstuffs. One such of those is listeriosis.
The cause of listeriosis is the bacteria Listeria monocytogenes. This hardy little microbe seems particularly fond of dwelling in more temperate climates. It lives readily in soil and the gastrointestinal tracts of many mammals and other animals, and it particularly loves moist environments.
Animals can become infected with the bacteria through ingestion, inhalation, or contact with mucous membranes or wounds. While many animals in a herd can be exposed to the bacteria, only a few will develop clinical signs of disease.
How does listeriosis present in goats?
Goats affected by Listeria infection generally show two different types of disease. Pregnant goats infected with Listeria will have late-term abortions. They can also have stillbirths or early neonatal deaths. Animals with abortion generally show no other signs of the infection.
The second form of infection in goats is encephalitic, or nervous system infection. The bacteria infects the spinal cord, brain stem, and brain, causing goats to develop neurologic signs.
Goats with encephalitic Listeria have nerve paralysis on one side of their face, causing the lip, eyelid, and ear droop. They circle in one direction and can even exhibit signs of blindness. They’ll also have an elevated temperature, lethargy, and inappetence.
In goats, Listeria is commonly due to the feeding of large round bales that have molded and rotted. However, even small hay bales can be sources of infection.
Due to Listeria’s fondness for moist environments, ruminant infection is often associated with consuming contaminated silage feeds. As owners rarely feed silage to goats, the disease is more commonly due to the feeding of large round bales that have molded and rotted. However, even small hay bales can be sources of infection if they’re soggy or moldy.
How is listeriosis in goats spread?
The bacteria readily shed from infected animal’s feces, urine, milk, and other bodily fluids, resulting in easy transmission throughout a herd. Thankfully, not every animal in a herd will develop clinical disease, though, in goats, up to 20% of a herd can experience a severe outbreak.
Diagnosis of Listeria infection can be difficult as veterinarians must identify the bacteria. Blood serology testing is unreliable, as symptomatic and non-symptomatic animals can have signs of immune reaction to the bacteria.
In animals experiencing abortion, owners must submit the fetus and placenta to a lab for testing. In animals with neurologic symptoms, there are limited diagnostic options before death.
Despite the bacteria often being shed in bodily fluids, it isn’t always reliably isolated in sick animals. The bacteria can sometimes appear on spinal fluid assessment, but lack of evidence of the bacteria doesn’t always mean it isn’t there. After the death of an animal, the bacteria can be identified in nervous tissue samples. This is often the best way to confirm the diagnosis.
How do you treat Listeria in goats?
Treatment for Listeria involves aggressive antibiotic therapy with supportive care. Penicillin is the drug of choice, in either intravenous formation or intramuscular. It’s given at high doses twice daily. Other antibiotics, such as oxytetracycline and ceftiofur, can also be used.
Even though Listeria will often only affect a few animals in a herd, it’s a pathogen of great importance due to its zoonotic potential. Humans exposed to the bacteria can become ill, and pregnant women are at risk of abortion.
To be successful, owners must treat cases aggressively and early. Even with aggressive treatment, the recovery rate in small ruminants with encephalitic Listeria is only 30%. Animals that experience infection don’t develop long-term immunity and can, unfortunately, develop the disease again.
Listeria isn’t the only worry.
When concerned about Listeria infection, there are several other conditions to consider. In animals with abortion, there are many abortion-causing infections, such as Chlamydia and Campylobacter.
The only way to identify the cause of abortion is through testing of the fetus and placenta. If any animal experiences abortion, submit samples for testing. When concerned about a goat exhibiting signs of encephalitic Listeria, one should always be aware that animals with rabies can exhibit similar symptoms.
Take care in handling animals showing signs of neurologic disease, especially in areas with rabies endemic in wildlife. Other conditions, such as lead poisoning, vestibular disease, and brain abscesses, can appear similar to listeriosis.
Prevention of Listeria is preferable to treatment.
With such a poor recovery rate, Listeria prevention is preferable to treatment. Unfortunately, there isn’t a vaccine for Listeria available in the United States. Aim prevention at providing clean, well-stored feedstuffs. Monitor large round bales for increased moisture and mold.
If Listeria is a cause of illness, changing feed and thoroughly cleaning feed bunks is recommended. Sick animals should be separated to prevent the spread of disease. As animals can shed the bacteria without being affected, keep new additions to a herd separated for several weeks before introduction.
Listeriosis in goats can present a danger to their human handlers.
Even though Listeria will often only affect a few animals in a herd, it’s a pathogen of great importance due to its zoonotic potential. Humans exposed to the bacteria can become ill, and pregnant women are at risk of abortion. The risk of human infection is most significant with animals experiencing abortion due to Listeria, as the bacteria are shed in birthing fluids.
In contrast, encephalitic animals have the disease contained within the nervous system. The bacteria can also be shed in milk, providing another avenue of human infection. Appropriate pasteurization will kill the bacteria. Because the bacteria can be shed even by healthy animals, it’s one of the many pathogens that have resulted in the recommendation to pasteurize milk products.
Listeria may not affect many animals in a herd, but it has a lower chance of recovery with treatment than many illnesses. Timely intervention increases the likelihood of recovery. If any goat in a herd is experiencing abortion or signs of neurologic illness, it’s best to consult the herd veterinarian as soon as possible. Rapid identification of the issue can result in improved outcomes for the goats and reduced risk of human illness from possible zoonotic disease.
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DR. KATIE ESTILL DVM is a veterinarian consultant for Goat Journal, Countryside & Small Stock Journal, and Countryside online. She works with goats and other large livestock at Desert Trails Veterinary Services in Winnemucca, Nevada.
SOURCES: Pezz Constable, Peter D. Merck Veterinary Manual. “Listeriosis in Animals” Reviewed/Revised June 2021/Modified Oct 2022. https:// www.merckvetmanual.com/generalized-conditions/listeriosis/ listeriosis-in-animals
