Listeriosis in Alpaca: Circling Disease and Brainstem Infection

Listeriosis is a bacterial infection caused by Listeria monocytogenes. In alpacas, the most concerning form is neurologic listeriosis, where the bacteria travel along nerves and cause inflammation in the brainstem. This is why people often call it circling disease. Affected alpacas may lean, walk in circles, develop a head tilt, or show one-sided facial nerve problems.

Although alpacas are not classic ruminants, they are still susceptible to many of the same feed-related infections seen in sheep and goats. The organism is widespread in the environment and can survive in soil, feces, water, and feed. Poor-quality silage is a well-known source, especially in colder months when stored feed is used more often.

This condition is an emergency because neurologic signs can worsen quickly. Some animals decline over 24 to 48 hours, while others show a more gradual progression. Early veterinary care matters because treatment is most effective before severe brainstem damage, recumbency, or swallowing problems develop.

Listeriosis can also have public health importance. Listeria monocytogenes is zoonotic, so anyone handling a sick alpaca, aborted tissues, contaminated feed, or manure should use gloves, wash hands well, and follow your vet's biosecurity advice.

Listeria monocytogenes is the cause of listeriosis. This bacterium is hardy and common in the environment. It can live in soil, decaying vegetation, water, feces, and feed. Alpacas are usually exposed by eating contaminated feed or drinking contaminated water, then the organism enters through the mouth. In neurologic cases, it is thought to move along cranial nerves to the brainstem.

A major risk factor is poorly fermented or spoiled silage, especially silage with a higher pH that allows the organism to multiply. Outbreaks are classically associated with winter and spring feeding of stored forage. Even if only part of a bale or pile looks spoiled, that can still be enough to create risk.

Other factors may increase susceptibility, including oral injuries from coarse feed, dental disease, stress, overcrowding, sudden ration changes, and heavy environmental contamination. Because alpacas with neurologic disease can look similar regardless of cause, your vet will also consider other differentials such as polioencephalomalacia, otitis media/interna, brain abscess, trauma, parasitic disease, and other infectious encephalitides.

Animal-to-animal spread is less important than environmental and feed exposure, but fecal-oral contamination can contribute within a group. If one alpaca becomes ill, it is wise to review feed storage, remove suspect forage, and monitor herd mates closely with your vet.

Diagnosis usually starts with the pattern of signs and a careful neurologic exam. In ruminants and camelids, circling, unilateral cranial nerve deficits, depression, and head tilt strongly raise concern for listeriosis. Your vet will ask about feed history, especially silage use, recent ration changes, and whether other animals have shown neurologic or reproductive problems.

There is no single perfect stall-side test for the brainstem form. Your vet may recommend bloodwork to assess hydration, inflammation, and metabolic problems, but normal or nonspecific results do not rule listeriosis in or out. In some cases, cerebrospinal fluid testing, culture, PCR, or advanced imaging may be discussed, especially if the signs are atypical or the alpaca is not responding as expected.

Because several diseases can mimic circling disease, diagnosis often includes ruling out other causes. Polioencephalomalacia, ear infection, brain abscess, trauma, toxicities, and other encephalitides can all look similar. Definitive confirmation may require postmortem testing of brain tissue if an animal dies or is euthanized.

In practice, your vet may begin treatment based on a strong clinical suspicion rather than waiting for perfect confirmation. That approach is common with listeriosis because early antimicrobial therapy can improve the chance of survival.

Prevention centers on feed quality and hygiene. Do not feed spoiled, moldy, or poorly fermented silage. If you use stored forage, inspect every batch closely and discard material with obvious spoilage, foul odor, heating, slime, or visible contamination. Clean feeders and water sources regularly so manure and decaying plant material do not build up.

Store feed to reduce moisture damage and wildlife contamination. Because Listeria monocytogenes survives well in the environment, good manure management and reduced crowding also help lower exposure. If one alpaca develops suspected listeriosis, remove the suspect feed source immediately and ask your vet whether herd mates need monitoring.

Pay attention to oral health and feed texture. Coarse stems, sharp plant material, and dental problems may increase the chance of small mouth injuries that let bacteria enter. Routine herd health checks, prompt attention to animals that go off feed, and careful observation during winter and spring can help catch problems earlier.

There is no routine vaccine used for prevention in alpacas. The most practical plan is thoughtful forage selection, clean feeding practices, and fast veterinary evaluation of any alpaca with depression, circling, head tilt, or facial nerve changes.