Meningeal Worms and Goats

by Sherri Talbot Meningeal worms — scientifically called Parelaphostrongylus tenuis and more commonly known as the “deer worm” or “brain worm” — are a parasite that primarily lives in the digestive systems of white-tailed deer. A type of roundworm, these parasites are usually harmless in their natural host, living out their natural lifespans without harming the deer. White-tailed deer have a high tolerance for infestations, and the meningeal worm can often live for several years in the deer without causing harm. However, in recent decades, the white-tailed deer’s territory has begun to overlap more with that of moose, caribou, and domestic livestock. This has caused brain worms to transmit to other, less-resistant hosts, often resulting in behavioral changes, weakness, and death in infected animals. 

Meningeal worms begin their life cycle in the body of an inconsequential-looking slug — or, more commonly, a snail. These hosts and the meningeal worms all prefer wet conditions and do not enjoy the heat, so infestations can be found primarily in the eastern United States and are least common in the dry Southwest. White-tailed deer ingest brain worms by accidentally swallowing infected snails hiding in the vegetation. The parasite finds its way to the lungs, where it cycles through the next phase of its life cycle. Eventually, the deer coughs up and re-ingests it into their stomachs, where it travels through the entire digestive system, finally defecated out onto the ground. Uninfected snails eat the mucus off the outside of the deer’s feces, infecting themselves with the brain worm, and the cycle begins anew.  

When moose or livestock eat these infected snails, however, the results are much different. Rather than traveling to the lungs to continue their metamorphosis, “brain worms” get their name because they instead end up in the animal’s central nervous system. Infection in the spinal cord and brain results in animals becoming disoriented, weak, going blind, and eventually dying. Reports from hunters about moose walking in circles or showing fearlessness around humans are becoming increasingly common in areas with a heavy brain worm infestation.  

Similar symptoms can be observed in goats with meningeal worms. It is important to look for behavioral changes, such as goats that begin to tilt their heads for no apparent reason, appear weak, walk in circles, or show partial paralysis signs. These signs may appear gradually or suddenly and may be intermittent as the brain worm moves through different parts of the spine or brain. Animals often continue to eat well, even as they lose coordination. In other cases, animals may look thinner as they lose the ability to eat. Treatment, especially in advanced cases, is often expensive and unsuccessful.  

Prevention of meningeal worms is often the best route for avoiding the loss of animals. Medications are available for prevention, but while some sources highly suggest using drugs like Ivomec and/or Panacur, other sources claim this does little but develop medication-resistant worms in the goats. Vets consulted for this article stated that they will often use medications for prevention in llama or alpaca — where the likelihood of infestation is much greater — but that in goats, this rarely is useful. Instead, they suggest that goat owners use natural prevention methods and observe for signs of possible infestation. If detected early, veterinarians can use very large doses of specific dewormers to treat meningeal effectively. The choice of dewormer often depends on the region and should only be given by a vet, both due to the amounts needed and because vets are most likely to know which dewormers the goats will respond to in your area. 

Naturally preventing situations that can lead to transmission is the best route to keep goats healthy. As the snails that carry meningeal enjoy wet conditions, prevent goats from accessing swampy areas, ponds, or other wet terrains. Alternately, fence these areas off from the deer that spread the parasite. Mow frequently, since slugs and snails both enjoy long grass. Snails may also hide under mounds of dead leaves or other damp refuse, so keeping areas cleaned of leaf piles, mounds of cut grass, and other attractions cuts down the risk of ingestion.  

When wet ground is unavoidable, whether due to landscape or weather, consider adding insect-eating predators such as ducks, which enjoy the same wet weather that snails and slugs also relish. Frogs and toads will also eat insects but can be harder to move into the needed areas. It is important to remember that, if you decide to try out ducks as an insect removal option, they will also eat any frogs or toads that might pre-exist in the area.  

Many other parasites and diseases can be mistaken for meningeal worms. The vet we spoke with stated that we could often find contradictory information on treatment and symptoms because it is hard to discern whether the animal suffers from brain worms or other issues. Did the treatment work because the dewormer kills meningeal worms, or because the goat was suffering from another parasite? Absolute confirmation is challenging without an autopsy, so getting a vet diagnosis is always the best practice.  

Originally published in the 2021 special issue of Goat Journal — Goat Health from Head to Hoof Vol. 2 — and regularly vetted for accuracy.