Deer Worm Infection in Goats and Sheep

White-tail deer are a common sight on our farm. But seeing one grazing in our goat pasture gives me the willies. Why? Because white-tails can shed a hair-like nematode that causes deer worm infection in goats. In the days when little was known about this deadly parasite, I lost two of my Nubian goats. After I educated myself, I successfully treated two others.

Both medical terms for this disease are tongue-twisters: cerebrospinal nematodiasis and parelaphostrongylosis. No wonder the condition is more commonly called meningeal deer worm infection, deer worm infection, or simply m-worm.

Deer Worm in Deer

The deer worm (Parelaphostrongylus tenuis) parasitizes white-tail deer, but rarely causes illness in them. Mature worms live in the membranes that enclose a deer’s brain and spinal cord. Collectively these membranes are called meninges, hence the term meningeal deer worm.

The worms lay eggs in the deer’s blood vessels. Through the blood stream the eggs migrate to the lungs, where they hatch into larvae. The infected deer coughs up larvae, swallows them, and passes them in the mucus that coats its droppings.

Gastropods (slugs and snails) crawling over the droppings take in larvae. Within 3 to 4 months living inside the gastropod, the larvae become infective. They may remain inside the gastropod, or may be excreted in its slime trail.

While grazing, the same (or another) white-tail deer may ingest the infected slug or snail. Or it may eat vegetation coated with infected slime. In the deer’s abomasum, or fourth stomach compartment, the gastropod releases infective larvae. They then migrate to the deer’s spinal cord and brain, where they develop into mature egg-laying worms. At some point the infected deer develops immunity against invasion by additional larvae, limiting the number of worms in carries.

Deer Worm in Goats and Sheep

The reason meningeal deer worms don’t sicken white-tail deer is because the worms need healthy deer in order to complete their life cycle. A problem occurs, however, when a grazing animal such as a goat or sheep accidentally eats an infected slug or snail. The infective larvae release into the digestive system, the same as in white-tail deer, but now they are in unfamiliar and confusing territory.

The larvae don’t develop in the normal way, don’t follow their usual path through the central nervous system, and don’t mature into egg-laying worms. Instead they wander around within the spinal cord, destroying tissue and causing inflammation. They can damage different areas within the central nervous system, or even damage more than one area. So the resulting signs of illness vary from one infected animal to the next.

Animals that are susceptible to m-worm infection include deer other than white-tails — black-tail deer, fallow deer, mule deer, and red deer — as well as caribou, elk, moose, alpacas, llamas, goats, and sheep. Compared to infected goats and sheep, alpacas and llamas have benefited from more research, because of their greater susceptibility to deer worm and their higher monetary value.

In future blogs we’ll review how to recognize deer worm infection in goats, a method for successful treatment, and preventive measures you can take to protect your goats and sheep.