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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