How to Recognize Deer Worm Infection in Goats

Knowing how to recognize deer worm infection in goats can be tricky, because not all goats are affected in exactly the same way. Further, signs of deer worm infection can resemble a number of other diseases of goats. But being able to recognize the signs of this deadly disease is essential for a successful outcome.

Signs of Deer Worm Infection

Deer worms (Parelaphostrongylus tenuis) affect a goat’s brain or spinal cord, resulting in neurologic signs. The most obvious sign is lack of coordination. The first indication can appear between 11 days and 9 weeks after a goat ingests an infective deer worm larva.

Initial signs often appear at the animal’s back end. The rear leg muscles seem to weaken or become stiff, causing the animal to walk unsteadily. While moving around, the goat may appear not to know where to place its hind hooves.

Other signs may include head tilting, arched or twisted neck, circling, rapid eye movements, blindness, gradual weight loss, lethargy, and seizures. Some infected animals prefer to be alone, and may stand motionless in the middle of the pasture or in the barn doorway.

Itchiness can result from worms migrating along nerve roots. As a result, the goat will scratch vertical raw sores along its shoulders and neck.

Because of the variable nature of this illness, signs may appear in any order or combination. And they may or may not get progressively worse.

Deer worms typically do not affect an animal’s alertness or its interest in food and water. This infection therefore differs from similar appearing diseases that cause an affected goat to become lethargic and lose interest in eating and drinking.

A chronic case of deer worm infection can result in incoordination and unsteadiness. It can go on for months or even years.

An acute infection can cause rapid death. One day the goat appears to be fine, the next day it’s gone.

Diagnosing Deer Worm Infection

Deer worms do not complete their life cycle in an aberrant host (defined as any infected animal other than a white-tail deer). So, unlike with stomach or intestinal parasites, you won’t find deer worm eggs or larvae in a goat’s droppings. This factor rules out using fecal testing as a diagnostic tool.

A spinal tap can provide a possible, but not definite, clue if the cerebrospinal fluid has higher than usual levels of white blood cells and protein. White blood cells are primarily eosinophils — disease-fighting cells that attack parasites and can result from inflammation caused by parasites. Excessive protein indicates leakage from damaged blood vessels. Both conditions may be caused by deer worm, but also by other ailments.

So far no known method will definitively diagnose deer worm in a living animal. The only way to identify the infection for certain is to find worms or larvae on the animal’s brain or spinal cord. Doing so, of course, requires a necropsy, meaning the animal must either die from the infection or be euthanized.

A presumptive diagnosis — an educated guess as to the most probable cause of illness — involves answering five pertinent questions. The answer to each individual question does not result in a definite diagnosis. However, considered together they offer a pretty good indication as to whether or not deer worm is the likely offender.

Presumptive Diagnosis

• Did the infected animal graze in or near white-tail habitat? This question is easy to answer, because white-tail deer are easy to see. Traditionally they have concentrated in the eastern states. But they are now just about everywhere in the United States and Canada. In some areas they are so numerous and destructive, they are considered pests (“rats with antlers”).

• Does the grazing area harbor terrestrial slugs or snails? Slugs and snails are typically abundant in low-lying, damp, and poorly drained fields. But they occur in other areas when the weather is persistently damp over long periods and in fields where vegetation is overgrown. Long bouts of rainy weather that prevent timely mowing of pastures create moist cover for slugs and snails, instead of exposing them to debilitating sunlight and heat.

• Are the signs of illness consistent with deer worm infection? The signs of deer worm infection are not the same for all goats. Therefore, determining if signs are consistent with deer worm may not be so easy. In my case, all four of my infected goats initially developed stiff back legs. They also sought to separate themselves from the rest of the herd. And they maintained appetite. These signs are just three possible indications of deer worm infection.

• Could the same signs be the result of some other disease? Three other neurologic illnesses in goats are polioenceophalomalcia (polio), listeriosis (listeria), and caprine arthritis encephalitis. Knowing your herd history, and consulting a reliable book, such as Holistic Goat Care, can help you eliminate these possibilities.

• How well does the infected animal respond to treatment? After losing two Nubians to what, to me at the time, was an unknown cause, I took a crash course in how to recognize deer worm infection in goats. Subsequently I successfully treated two other Nubians. I can’t prove that all four goats were infected with deer worm. But given the facts, two veterinarians I consulted agreed that deer worm was the most likely cause.