Meningeal Worm (P. tenuis) in Alpacas: Signs & Treatment

Urgent — contact your vet today

Early treatment makes a big difference. Don't wait more than a day.

A deer parasite that wanders into the spinal cord and brain of alpacas, causing weakness, incoordination and paralysis. It is one of the most important diseases of camelids in eastern North America.

Category: Parasites
Urgency: Urgent
Also called: Deer worm, Parelaphostrongylus tenuis, Brain worm

Signs & symptoms

Hind-leg weakness, stiffness or knuckling (often on one side first)
Wobbly gait, swaying, falling
Head tilt, circling or abnormal neck posture
Difficulty getting up; sitting like a dog
Lameness with no obvious leg injury
Complete paralysis in advanced cases

What causes it?

Parelaphostrongylus tenuis normally lives harmlessly in white-tailed deer. Deer pass larvae in their feces; snails and slugs pick them up, and alpacas accidentally swallow infected snails while grazing. In camelids the larvae migrate aimlessly through nervous tissue instead of completing their life cycle.

Risk factors

Pastures shared with or bordering white-tailed deer habitat
Wet, wooded or shady areas with many snails and slugs
Late summer through autumn after wet weather
Eastern and central U.S. and Canada

How vets diagnose it

There is no reliable live-animal test. Diagnosis is based on typical neurological signs, region and season, and a spinal fluid (CSF) tap showing high eosinophils. Definitive confirmation is usually at necropsy.

Treatment

Your veterinarian will typically use an extended course of a dewormer able to reach the nervous system together with anti-inflammatory drugs, plus nursing care: soft bedding, help standing, physical therapy and slings. Early treatment greatly improves the outlook; some animals recover fully, others keep a permanent gait abnormality.

Do not wait to see if it improves. Camelids hide illness, and by the time signs are obvious the problem is often advanced. Call your veterinarian.

Prevention

Ask your vet about a preventive deworming program during the snail season in endemic areas, balanced against the risk of creating resistant stomach worms
Fence deer out of pastures where possible (high fencing or double fencing)
Mow pasture edges, drain wet spots and remove brush piles and boards where snails hide
Create a gravel or wood-chip strip between woods and pasture
Keep alpacas away from wooded pasture edges in the evening and after rain

Background

Parelaphostrongylus tenuis is a neurotropic nematode parasite common to white-tailed deer, Odocoileus virginianus, which causes damage to the central nervous system. Moose, elk, caribou, mule deer, and others are also susceptible to the parasite, but are aberrant hosts and are infected in neurological instead of meningeal tissue. The frequency of infection in these species increases dramatically when their ranges overlap high densities of white-tailed deer.From Wikipedia — “Parelaphostrongylus tenuis”, licensed under CC BY-SA 4.0.

Research & references

PubMed lists 12 peer-reviewed papers on this topic in camelids. The most relevant include:

Assessment of cerebrospinal fluid analysis and short-term survival outcomes in South American camelids: A retrospective study of 54 cases (2005-2021). Bennett SJ, Adkins PRF, Schultz LG et al. Journal of veterinary internal medicine, 2022. PubMed 36151907 · DOI · Free full textOpen access · cited 2×
Doxycycline as an inhibitor of p-glycoprotein in the alpaca for the purpose of maintaining avermectins in the CNS during treatment for parelaphostrongylosis. Agbedanu PN, Anderson KL, Brewer MT et al. Veterinary parasitology, 2015. PubMed 26371853 · DOI · cited 7×
Epidemiological Investigation of Meningeal Worm-Induced Mortalities in Small Ruminants and Camelids Over a 19 Year Period. Keane C, Marchetto KM, Oliveira-Santos LGR et al. Frontiers in veterinary science, 2022. PubMed 35464381 · DOI · Free full textOpen access · cited 4×
Cerebrospinal parelaphostronglylosis in llamas. Brown TT, Jordan HE, Demorest CN Journal of wildlife diseases, 1978. PubMed 739583 · DOI · cited 15×
Gastrointestinal ulceration and pulmonary aspergillosis in a llama treated for parelaphostrongylosis. Quist CF, Dutton DM, Schneider DA et al. Journal of the American Veterinary Medical Association, 1998. PubMed 9589133 · cited 6×
Analysis of heavy-chain antibody responses and resistance to Parelaphostrongylus tenuis in experimentally infected alpacas. Purdy SR, Gagliardo LF, Lefman S et al. Clinical and vaccine immunology : CVI, 2012. PubMed 22593238 · DOI · cited 3×

Frequently asked questions

What is meningeal Worm (P. tenuis) in alpacas?

A deer parasite that wanders into the spinal cord and brain of alpacas, causing weakness, incoordination and paralysis. It is one of the most important diseases of camelids in eastern North America.

What are the signs of meningeal Worm (P. tenuis)?

Hind-leg weakness, stiffness or knuckling (often on one side first), wobbly gait, swaying, falling, head tilt, circling or abnormal neck posture, difficulty getting up; sitting like a dog and lameness with no obvious leg injury.

How do you prevent meningeal Worm (P. tenuis)?

Ask your vet about a preventive deworming program during the snail season in endemic areas, balanced against the risk of creating resistant stomach worms. Fence deer out of pastures where possible (high fencing or double fencing). Mow pasture edges, drain wet spots and remove brush piles and boards where snails hide.

Is meningeal Worm (P. tenuis) an emergency?

Urgent — contact your vet today. Early treatment makes a big difference. Don't wait more than a day.

This page is educational and does not replace advice from a veterinarian who has examined your animals. Camelid medicine uses many drugs “extra-label”, so dosing must come from your vet. In an emergency, call your vet first. Read our disclaimer · How we write and review content.