MENINGEAL WORM UPDATE

Dr. Stephen Angelos, DVM, DACVIM

If you have small ruminants like sheep, goats, llamas, or alpacas you have probably heard us discuss deworming to prevent a disease called meningeal worm infection. This winter we have seen more cases of meningeal worm than in the previous three winters combined. Meningeal worm, or brain worm, is an infection of the nervous system caused by Parelaphostrongylus Tenuis, a parasite that is host adapted to white tailed deer. In deer, it rarely causes problems. Unfortunately, when non-deer ruminants like sheep, goats, LARGE ANIMAL MEDICAL ASSOCIATES llamas, alpacas, and other non-domestic ruminants inadvertently eat the parasite while they are grazing, the parasite will migrate through nerve tissues in the spinal cord or brain and cause many different serious clinical signs. Staggering, paralysis, and hind limb weakness are just some of the signs we commonly see. Fortunately, by deworming every 4 to 6 weeks the parasite can be killed before it enters the spinal cord or brain. Once the parasite is inside the protected environment of the nervous system, it is much harder to kill, and even if it is killed it usually has caused damage that may be permanent.

There are currently some studies at Cornell University looking at different treatment regimens to find the method that results in the best outcome for infected animals. While there is no vaccine to prevent meningeal worm infection, there is evidence that a vaccine could protect against the parasite. Other research is looking at ways to improve the effectiveness of ivermectin at crossing into the nervous system. Currently, high doses of fenbendazole and anti-inflammatory medications, are how we treat these cases. The best way to prevent infection is to deworm susceptible livestock every 4 to 6 weeks. We generally recommend that this be done from about March 1 through January 1 but depending on the severity of freezing in the spring or fall, these dates are not fixed. Because the parasite needs an intermediate host (land snail or slug) to complete its life cycle, try to avoid pasturing livestock in areas that border woodlands, or that have low wet areas. In the fall, fallen leaves can provide additional protection to slugs and snails, so avoid these grazing areas, if possible. Other things that deter deer like guardian dogs, human activity, or deer fencing can also help. Barriers to slugs and snails are another method used by some livestock owners (stone or sand perimeters around small paddocks can help) but make sure you do not use poison to try to control these critters. The risks of toxicity from accidental exposure to small animals or livestock/wildlife is greater than the benefit. If you have any questions about meningeal worm or its prevention, please call us!