Listeria monocytogenes is a serious zoonotic bacterium that causes severe illness in both animals and humans. Zoonotic means the organism can naturally transmit from animals to people. Humans can contract the disease, called listeriosis, from goats through direct contact and consumption of contaminated products.
Listeria Infection in Goats
The bacterium L. monocytogenes is ubiquitous, found commonly in soil, water, and decaying plant matter. Goats typically contract listeriosis by ingesting contaminated feed, most frequently spoiled silage or improperly fermented hay. Environmental sources, such as soil or bedding contaminated by feces, also serve as reservoirs for infection. The organism can survive and multiply in cold temperatures, making its presence in stored feed a persistent risk.
In goats, the disease presents in two primary forms: neurological and reproductive. The neurological form, often called “circling disease,” results from the bacteria infecting the brainstem. Clinical signs include fever, facial paralysis, and a tendency to move in circles or stumble.
The reproductive form of the disease causes significant losses, manifesting as late-term abortions, stillbirths, or the birth of weak kids. Goats with this form often show no other signs of illness, making the infection difficult to detect before the abortion event. Animals that appear healthy can also be asymptomatic carriers, shedding the bacteria in their feces and milk.
Transmission Pathways to Humans
Transmission of L. monocytogenes from goats to humans occurs through several distinct pathways, mainly involving the ingestion of contaminated food products. The most common route is consuming raw, unpasteurized goat milk or dairy products made from that milk, such as soft cheeses. The bacteria can be shed directly into the milk from an infected udder, even if the goat shows no signs of mastitis. Since L. monocytogenes can grow at refrigeration temperatures, storing contaminated raw milk does not prevent the risk of infection.
Direct contact with infected animals or their birthing products also represents a significant transmission risk. The bacteria are shed in high concentrations in the placenta, aborted fetuses, and vaginal discharge of goats experiencing a reproductive infection. People who assist with kidding or handle these materials without strict hygiene can become infected through breaks in the skin or mucous membranes.
Indirect transmission can occur through contact with the contaminated farm environment. The organism is shed in the feces of infected and carrier animals, polluting barn floors, bedding, and water sources. Humans can pick up the bacteria from these surfaces and accidentally ingest it, such as by touching their mouth with unwashed hands. Meat from infected goats can also carry the bacteria, especially if the carcass is contaminated during processing.
Human Health Implications and Prevention
Listeriosis in humans typically presents with mild, flu-like symptoms such as fever, muscle aches, and fatigue. For high-risk individuals, however, the infection can become invasive and life-threatening. The bacterium can spread beyond the gut to the nervous system, potentially leading to severe complications like meningitis or meningoencephalitis.
High-risk populations include pregnant women, newborns, the elderly, and people with compromised immune systems. For pregnant women, listeriosis can cause miscarriage, stillbirth, premature delivery, or serious infection in the newborn. In elderly or immunocompromised patients, the invasive form of the disease results in a high mortality rate.
To prevent listeriosis from goats, avoiding the consumption of unpasteurized goat milk and dairy products is a primary recommendation. Pasteurization involves heating milk to a specific temperature for a set time, which effectively kills the L. monocytogenes bacteria. Even if the milk comes from seemingly healthy animals, it should be pasteurized as a safety measure.
Strict hygiene practices are necessary, especially for individuals who work closely with goats. Thorough handwashing with soap and running water is necessary immediately after handling goats, particularly after assisting with births or cleaning stalls. Gloves should always be worn when handling aborted materials or treating sick animals, and these contaminated materials must be safely discarded. Avoiding the feeding of spoiled or moldy hay to goats also helps minimize the initial source of infection on the farm.