Meningeal worms — a dangerous threat

One of the perks of buying sheep from us is the after-sale support that I provide for as long as the new shepherd needs it. I live by the concept that no question is a dumb question if sincerely asked, so people tend to feel comfortable asking me about anything that seems unusual or abnormal. As a result, I often get a phone call, email, or text as soon as things begin to go wrong — a definite plus that helps avoid sheep catastrophes and potential loss of life.

Such a situation arose the other day when I returned an early morning call just after finishing my chores. A new shepherdess was concerned because one of her new flock of eight Romeldale/CVMs purchased earlier this summer was “very sick.”

The first thing I asked when I returned the call was how she knew that the ewe lamb was actually sick. Had she taken her temperature (what I tell new flock owners is the first step in determining an illness)? Yes, she had taken the ewe’s temp and it was high-normal, not actually a reason for concern. Then I asked what made her think the girl was actually sick. What had she seen that shouted to her that there was serious illness in the flock and in this girl, specifically? Her answer set alarm bells ringing in my mind. She was right; this was critical!

The evening before, the ewe lamb had been a bit spooked and had run straight into a fence. She had later become separated from the flock, but when reunited, she had run into the group with little control, smashing into other sheep and eventually falling over onto the ground. The new shepherdess needed to say no more. With this information and a quick glance at the calendar, I knew exactly what we were dealing with — and we needed to act very quickly if there was any hope of saving the ewe.

The meningeal worm is an internal parasite that is usually found within white-tail deer. The problem is that deer often share grazing areas with livestock, and specifically, small ruminants like sheep, goats, llamas and alpacas.  Unfortunately, when meningeal worms (or Parelaphostrongylus tenuis) take up residence in these aberrant (atypical) hosts, it is a much more damaging adversary. Instead of remaining in the digestive system as do most internal parasites, it crosses into the circulatory system and makes its way through the body, eventually crossing the blood/brain barrier into the central nervous system where it wreaks havoc. Symptoms can be quite varied, depending on exactly where the worm makes its new home, but can include partial paralysis, confusion, blindness, loss of hearing, lack of balance, and inability to maintain correct body temperature (either very high or very low, depending on the environmental temperature), among other neurological symptoms. As the worm burrows through brain or spinal cord tissue, these symptoms continue to increase in number and worsen in degree until death ensues. The only hope for survival is to rapidly kill the worm and reduce brain swelling, in hope that the sheep has enough undamaged neurological tissue to make due throughout the remainder of its life. July through October is prime time for this particular parasite, since deer have been dropping larvae in their manure through the entire summer. It seems that if I get a call about meningeal worms in this geographic area, it generally comes in August or later.

The problem is that there is no easy test for the presence of meningeal worm in a host — and the symptoms can vary widely, depending on the location of the worm in the central nervous system. The only way to be sure that a sheep has or has had a meningeal worm is to dissect the brain and spinal column to find the worm or its path of damage. This is obviously of little use if you hope to save the sheep!

For those who are new to sheep or to this disease, the treatment for a meningeal worm can be heartrending. Since many drugs do not easily cross the blood-brain barrier, normal levels of deworming are ineffective in this battle. In 2013, the treatment for meningeal worm in aberrant hosts like sheep, llamas, etc., was changed. Ohio State University showed that using Ivermectin, a common and typically effective dewormer, was ineffective against meningeal worms once neurological symptoms became obvious. Once these symptoms appear, the current recommended treatment is to dose with extremely high levels of white dewormer (10x the usual dosage of a drug in the fenbenzadole family) for five consecutive days to kill the parasite, and a dose of corticosteroid for the first three days of treatment to reduce swelling in the areas where the worm has already caused damage. Some vets will also suggest injectable Ivermectin for a few days in addition to these other drugs. Just the thought of giving such a high level of dewormer to one’s sheep without a proven diagnosis can be terribly intimidating to any shepherd who cares for their flock.

Yet, time is of the essence in treatment. In my experience, unless treatment is begun in the hours after symptoms first appear, a slow and agonizing death becomes more and more likely as the worm creates ever greater brain damage. Yes, the dose of dewormer may seem extreme, and the shepherd may worry that it will kill the sheep, but the meningeal worm will certainly kill the sheep, sooner rather than later. Isn’t it worth the possibility that the sheep might live if dosed according to the current protocol? And if they happen to die from the treatment, it will spare them a slow and painful decline.

The new shepherd who called me decided to dose their ewe lamb and to do so quickly. Within 24 hours of their lamb exhibiting symptoms, they had given her the first large dose of dewormer, the additional injectable dewormer, and the corticosteroid. They had moved the ewe lamb into the barn with a friend, and by the next day, there was a bit of hope. Although the lamb was still very sick (seemingly blind, with poor balance and quite a bit of confusion), she was holding her own and perhaps even a bit improved.

There are additional facts to share about this parasite, and I’ll do so in my next blog post.

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3 Comments

  • Erika says:

    Thanks for another very timely posting. One of my new sheep started showing subtle signs of meningeal worm infection and had a rapid improvement with fenbenzadole. Fortunately I was on the look out for it because the seller had a lamb recently diagnosed just before we bought the sheep. You confirmed my choice to treat early and aggressively.

    • Dee says:

      I’m so happy you were able to treat quickly and aggressively, as that seems to be the key with this horrible parasite. Did your new sheep fully recover?

  • Erika says:

    Yes, it is so great to see her scampering around the paddock with her other buddies.

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