Llamas and alpacas can become infected with Parelaphostrongylus tenuis or meningeal worm as it is more commonly known. White-tailed deer are the natural host for the parasite and do not usually have the life threatening form found in other ruminant species. P. tenuis is found everywhere that white-tailed deer are found. This includes the Southern, Eastern and Northern United States.
White-tailed deer are the natural host for the parasite P. tenuis. The life cycle of the parasite in the deer is fairly complex. Adult worms reside in the veins and sinuses of the dura mater (the tough covering between the brain and the skull) where they lay their eggs. The eggs travel through the bloodstream and reach the lungs. Once in the lungs, the eggs hatch into larvae in the alveoli (the tiny air sacs in the lungs where oxygen is exchanged). The larvae are then coughed up and swallowed by the deer and the larvae are passed in the feces. The larvae then enter small ground dwelling slugs and snails and mature for 3 to 4 weeks. The snails are then ingested by the deer. Once in the stomach, the larvae penetrate the stomach wall and enter spinal nerves. The larvae travel up the nerves to the spinal cord where they mature for 20 to 30 days. The adult worms move into the subdural space (where cerebrospinal fluid is found) and travel up to the brain. Once in the brain, the adult worms go through the dura mater and into the veins and sinuses where they normally reside. This entire life cycle takes 82 to 91 days to complete in the white-tailed deer.
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In many other ruminant species, the parasite larvae migrate into places where they don't normally in the white-tailed deer. The snails are ingested and the larvae migrate up the spinal nerves to the spinal cord but then seem to get lost. The larvae begin to migrate throughout the spinal cord and the brain instead of the subdural space where the cerebrospinal fluid is found (this is actually around the spinal cord and brain, not in it). This causes damage to the central nervous system which may be severe enough to result in death. Other species which have been affected by meningeal worm are sheep, goats, llamas, alpacas, camels, moose, caribou, reindeer, wapiti, fallow deer and mule deer.
Animals can become infected in the spring, summer or fall. Disease is usually seen in the fall and winter about 3 to 4 months after infection. Often only one animal is infected at a time on a single farm. There may be more than one animal infected at once or more than one animal infected on a single farm over the years. Infected animals will show a wide variety of symptoms which include, but are not limited to:
Generally, animals with more severe symptoms have a worse prognosis. There is no way to definitively diagnose meningeal worm in a live animal. Finding clinical signs (symptoms) and laboratory values consistent with meningeal worm are used to make a diagnosis of meningeal worm. In a dead animal, the spinal cord can be cut into slices and examined microscopically for P. tenuis. This is currently the only way to definitively diagnose meningeal worm. The worms are difficult to find and even though no worms are found, the animal may still have had a meningeal worm infection.
There are ways to prevent infection in areas where white-tailed deer populations are located. Ivermectin can be given at the regular deworming dose once a month during the spring, summer and fall. It will kill all the larval stages of P. tenuis which have not yet entered the spinal cord. This will protect against migrating larvae for 7 to 14 days. Strongid C may be administered daily to animals during the spring, summer and fall. A deer proof fence may be put up around all pastures to prevent white-tailed deer from travelling through and depositing feces containing the meningeal worm larvae. A paved or gravel area can also be placed along the fence to prevent the migration of snails and slugs which may be carrying meningeal worm larvae from outside the pastures. A molluscicide may also be used to kill the infective snails and slugs. Deer proof fencing and paved/gravel areas are much too expensive for most farms. Monthly ivermectin or daily Strongid C during times of infection are much more economical and practical solutions for most farms. A molluscicide may be dangerous to the llamas and many owners do not want to put pesticides on their pastures.
There are many options for treating a case of meningeal worm. None have been proven to be effective in a controlled study. All treatments include some type of dewormer along with steroids and anti-inflammatory agents. The dewormers kill the parasite while steroids and anti-inflammatory agents prevent damaging inflammation and swelling of the spinal cord from the dying parasites. The dewormers which have been used are TBZ, levamisole, diethylcarbamazine, ivermectin and fenbendazole. The dosages and durations of treatment all vary.
Good supportive care is very important for the best recovery possible of any patient with meningeal worm. It is just like physical therapy for llamas. This is essential to maintain blood flow to the muscles to keep them healthy. Damage can occur from laying on the muscles and restricting blood flow too long. Using a sling which will support the llama and allow it to walk around without having to support it's entire weight increases movement and blood flow. Safely using a swimming pool or a pond to allow a llama to swim will do an even better job of improving blood flow through passive movement. Regular muscle massages are another way of accomplishing the same task. All animals with good supportive care will recover better than without good supportive care.
Last updated on April 13, 1997
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