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Meningeal Worm Infections in Llamas

Llamas and alpacas are still gaining popularity in the United States due to the versatility of these animals. Besides being raised for their fiber, they are also raised for their hides, meat and ability to cany heavy loads in rugged country. Because of this increasing  popularity,   it  is   important   for veterinarians to have a basic grasp of llama medicine and diseases.

Llamas are susceptible to many parasites, from nematodes and cestodes to sarcocysts and coccidia. One parasite which is of great importance to llama producers    is    the    meningeal    worm, Parelaphostrongylustenuis. The llama, as well as other animals, such as wild cervids and domestic small ruminants, is an aberrant host of this parasite, while the white-tailed deer is the normal host. This parasite does not cause clinical disease in white-tailed deer, but in the llama it causes high morbidity and mortality. The P. tenuis larvae migrate through the spinal cord of aberrant hosts, causing neurological deficits. Clinical signs observed in affected llamas include lameness, incoordination, difficulty rising, paraplegia, paralysis, circling and blindness. Clinical signs appear around 45-53 days post-infection. This disease is a serious threat to llama producers for numerous reasons: 1) it has been shown that as few as five larvae can cause 100% morbidity and 67% mortality in llamas, 2) once in the spinal cord,anthelmintic treatment is ineffective, and 3) white-tailed deer, as well as the intermediate host of meningeal worms, snails and slugs, are commonly found in many areas of the United States where llama farms are located.

A definitive diagnosis can only be made post­mortem, by demonstrating larvae or adult meningeal worms in the brain or spinal cord. Recently, researchers have observed a CSF abnormality of eosinophilic  pleocytosis  associated  with  the infection.     Eosinophilic  pleocytosis  of the cerebrospinal  fluid  may  indicate  verminous encephalitis, but is not a definitive finding, since other conditions can cause eosinophilicpleocytosis. Also, P. tenuis can occur without this finding in the CSF. Studies are being performed, using an ELISA test to identify meningeal worm infections in goats. Hopefully in the near future, this test can be modified and used successfully in the llama industry.

This condition is very difficult to treat because of the severity of the neurologic signs, the difficulty in definitively diagnosing the presence of the parasite, and because many anthelmintics cannot cross the blood-brain barrier. Ivermectin has been suggested as part of the management of this disease because it can cross the blood-brain barrier, but it is ineffective once the larvae are in the spinal cord.

Prevention of the disease, to date, remains the best management tool. Llama producers should use deer-proof fencing around their pastures and clear out thick ground cover to discourage the establishment of the intermediate hosts, slugs and snails. In regards to prophylactic anthelmintic use, there is considerable controversy. Some suggest Ivermectin use at three week intervals, but there is concern over the development of resistance of gastrointestinalnematode populations, as well as the actual effectiveness of the drug in llamas. Pyrantelpamoate, fed on a daily basis, has also been suggested for prevention of meningeal worm infestations, but this has not yet been clinically proven.

- byAlenaK.Duncan, Class of 1997

- Edited by M. Randy White, DVM,PhD



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