Monday, March 2, 2009

Threat of the "Ninja Worm"

On any given day, this is the scene in the fields behind our pastures. The tiny dots everywhere are deer. Our farm is like a wildlife magnet. In addition to several turkeys, there is often a large herd of deer behind our house. We have counted as many as 40 turkey and 100 deer all hanging out together in the fields at one time. It is like a wildlife sanctuary!

At night, our dog runs from window to window growling. When I get up to see what is outside, I often find deer right outside our windows. I have watched them rear up onto their hind legs and have "boxing matches" right in our yard. They seem to like to play "reindeer" games when the sky is clear and the moon is full. Unfortunately our road is a deer highway as well. Several deer have been hit in front of our house this winter. While this deer situation may be a hunter's dream...it is an alpaca farmer's nightmare. Why you ask??? Because of the much feared and much dreaded "Ninja Worm."
Well, it is not actually called the "Ninja Worm"...it is called the Meningeal Worm or paralaphostonguylus tenius. Although, when you hear the word Meningeal...is sounds sort of like Ninja...at least it did when we first heard about this internal parasite. It is also dangerous and deadly...much like a ninja. Meningeal worm is a parasite of the white-tailed deer that completes its life cycle within the deer without significant effects. However, if this parasite infests an unnatural host, like an alpaca, it moves into the spinal cord and brain and causes neurological effects that are often fatal. (Schoenian, 2007)

"The life cycle of the meningeal worm requires terrestrial snails or slugs as intermediate hosts. White-tailed deer become infested with P. tenius by eating snails or slugs that contain the infective stage of the larvae. The larvae migrate through the deer's gut and eventually move into the central nervous system where they mature into adults, produce eggs, and the life cycle begins again. However, when P. tenius-infected snails and slugs are ingested by aberrant hosts, the larvae migrate into the brain and/or spinal cord. The larvae do not mature into adults, but rather wander through the central nervous system causing inflammation and swelling which damages sensitive nervous tissue producing a variety of neurologic symptoms. Experimental evidence suggests that it takes 10 to 14 days for the parasite to reach the brain and/or spinal cord after the animal eats the infected snail or slug" (Schoenian, 2007).

Meningeal worm is very difficult to diagnose in live animals because it cannot be detected with a fecal exam (because eggs are not produced that are passed on the the feces) or a blood test. Symptoms of meningeal worm infection include:
-light limp or weakness in one or more legs
-partially or completely paralysis
-blindness
-head tilt
-circling
-disinterest in or inability to eat
(Schoenian, 2007)

Treatment of meningeal worm can be costly and time consuming. In most cases, infected animals remain alert and continue to eat and drink normally until the infection has progressed too far to treat it successfully. Meningeal worm is often fatal and difficult to treat. If the alpacas do survive through treatment, they often remain partially or completely paralyzed.

Because this parasite is so dangerous and difficult to detect and there is a very high concentration of deer surrounding our farm, we try to prevent our alpacas from picking up meningeal worm. Our pastures are on high and dry ground in order to avoid wet environments where slugs and snails like to hang out. All of our alpacas also get monthly injections of Ivomec as a dewormer. Although other parasites, will build up a resistance to Ivomec, meningeal worms will not because they cannot complete their life cycle within an alpaca. We also plan to get some chickens and ducks for our farm this year, in hopes that they will not only produce eggs and meat for us, but they will eat the sneaky intermediate hosts...slugs and snails...before they can ever reach the alpacas.


Meningeal Worm: Brain Worm-Dear Worm,
paralaphostonguylus tenius, University of Maryland Cooperative Extension (2007) by Susan Schoenian.

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