PARELAPHOSTRONGYLURTENUIS INFECTION IN LLAMAS

Within the past few years, thre has been an explosive increase in the number of llama owners in Indiana.  This dynamic situation has created a demand for local practitioners for services and advice per­taining to llamas.  Therefore, in order to meet the growing needs of llama owners, Indiana veterinarians are taking the time to learn more about llamas through conferences, phone con­sultations, and recently pub­lished literature.  A reported problem in llamas that has been seen with increased frequency here at Purdue University Ani­mal Disease Diagnostic Labora­tory (ADDL) is Parelaphos-trongylustenuis (P. tenuis) infection in llamas.  This ar­ticle will discuss the clinical signs, diagnosis, and treatment associated with P. tenuis in­fection as well as bring to light means of prevention and control of this disease.

Infected llamas may display incoordination, head tilt, hypermetria,ataxia, paresis, and tetraplegia.  A common manifestation is gradual onset of posterior ataxia and weak­ness that progresses to the forelimbs.  Because the para­site has a predilection for the spinal cord, the presenting clinical signs are dependent upon the location of the para­site within the spinal cord. Therefore, P. tenuis infection can manifest itself in a varie­ty of other ways and should always be considered as a dif­ferential for CNS disease of llamas.

The frustration of local practitioners and llama owners lies in the diagnosis of cerebrospinalparelaphostrongy-losis.  Unfortunately, a definitive antemortem diagnosis for this disease does not exist.  Hints for diagnosing CNS disease associated with P. tenuis are clinical signs, ex­posure to white tailed deer or terrestrial snails, eosinophil-ia with possibly elevated pro­tein in the CSF, and response to treatment.  Other parasites have been reported to cause eosinophilicpleocytosis in the CSF, but in light of pastures shared by white-tailed deer, cerebrospinalparelaphos-troangylosis is the primary differential diagnosis.  Be­cause the parasite doesn't reach maturation in llamas, routine parasitological tech­niques are not effective for diagnosis P. tenuis infection. Postmortem identification of larvae in the spinal cord can be a difficult task, but is the best diagnostic technique cur­rently available.

Treatment of cerebrospinal parelaphostrongylosis cases in llamas can be equally as frus­trating.  The treatment protocol involved the use of supportive care, anti-inflammatory drugs, and anthel-minthics.  Phenylbutazone has been reported to be a safe anti-inflammatory drug for Hamas, and has been used to treat the inflammation associ­ated with CNS larval migration of P. tenuis.  The dewormersivermectin (at the cattle dose) or oral fenbendazole (at 30 mg/kg daily for 5 days) have been reported to be beneficial in treating cerebrospinal pare­laphostrongylosis of llamas. May be frustrating because the effectiveness of treatment de­pends on multiple factors in­cluding the duration and sever­ity of clinical signs.  Treat­ment is not consistently effec­tive.

In order to effectively pre­vent P. tenuis outbreaks, veterinarians and llama owners must be aware of the life cycle of the parasite and how it involves llamas.  The defini­tive host of P. tenuis is the white-tailed deer, and the adult lives within the meningesof white-tailed deer, rarely causing clinical signs.  Eggs are laid by the adults and de­velop into LI larvae.  LI lar­vae migrate to the lungs, are coughed up, swallowed, and passed in the feces of infected deer.  LI larvae require snails and slugs to serve as interme­diate hosts before they can develop into infective L3 lar­vae.  Ingestion of L3 larvae by deer and migration to CNS me­ninges complete the life cycle of P. tenuis.  However, when an aberrant host, like llamas, ingests the L3 infective lar­vae, the parasite doesn't limit itself to the meninges, but invades the deeper nerve tis­sues and, results in cerebro­spinal parelaphostronghylosis.

The first step in effective prevention of cerebrospinal parelaphostrongylosis is reduc­ing pasture co-habitation of llama and white-tailed deer. The use of adequate fencing can help reduce the incidence of disease on a farm.  The use of mulloscicides like metaldehydeto control the snail population are not recommended because of their questionable efficacy and the added risk of inducing in­toxication in the llamas.  A better means of control is to restrict llama access to moist wet areas on fields where snails and slugs reside.  Fence off or drain any unnecessary pasture ponds in order to re­duce the exposure of llamas and deer to snails and slugs.  Pro­tocols involving the use of various dewormers such aiver­mectin and fenbendazole every four to six weeks are apparently effective in killing the P. tenuis larvae before they reach the CNS.  By disrupting the life cycle through multiple route, veterinarians and llama owners can effectively reduce the risks of P. tenuis out­breaks and in the long run pro­duce healthy llamas and happy owners.

Jim Raymond-Class of 1995 Edited by W.G.VanAlstine