Parelaphostrongylus tenuis (the “meningeal worm”) resides in white-tailed deer without causing clinical disease but is the catalyst for devastating neurologic disease in camelids, and sometimes in sheep and goats as aberrant hosts. If you practice where deer and camelids co-exist, monitor closely for signs like hindlimb weakness and ataxia.
Who Gets Sick (and Who Doesn’t)
Deer are asymptomatic carriers, whereas llamas, alpacas, and small ruminants develop progressive neurologic signs after infection. Seasonality follows intermediate host (gastropod) activity, but cases can appear whenever an animal encounters infective larvae.
Clinical Signs to Know
Expect a number of neurological deficits, including:
- Ataxia
- Pelvic limb weakness
- Circling
- Stiffness or lameness
- Scoliosis (occasionally)
Animals may appear to improve temporarily after anti-inflammatory therapy, misleading owners, but clinical deterioration often resumes.
Diagnosis by Clinical Sign Recognition
No simple ante-mortem test or gold-standard treatment exists for P. tenuis. Clinicians diagnose the disease by recognizing characteristics and clinical signs and confirming findings with CSF when feasible. During necropsy, collect biopsies to confirm infection.
The absence of fever can help distinguish P. tenuis from listeriosis, but clinical overlap occurs. Rely on pattern recognition and pragmatic testing to guide your diagnosis.
Treatment Realities
There’s no definitive, universally effective treatment regimen. Clinicians typically use anthelmintics such as fenbendazole or ivermectin but must stay alert for resistance issues. Combine anthelmintics with anti-inflammatories, attentive nursing care, and physical support. Prepare owners for a guarded prognosis, especially if animals become recumbent.
In-Field Prevention
- Exclude deer: build sturdy fencing at least 9-10 feet high to prevent deer access
- Strategic deworming: use targeted anthelmintic protocols during at-risk seasons (every 30-45 days from spring to fall, tailored to avoid resistance) while following local guidance
- Pasture management: drain standing water, control vegetation, and rotate grazing areas to reduce gastropod vectors
Prevention is Key
With Parelaphostrongylus tenuis, clinicians cannot rely on a definitive test or standardized treatment protocol. That reality makes prevention the most powerful intervention. Focus on reducing exposure through effective deer exclusion, thoughtful pasture and gastropod control, and strategic, resistance-conscious deworming plans. Clear owner education about environmental risk and early neurologic changes helps set realistic expectations and supports earlier intervention when cases arise.
More from Zuku Learning
- Master more NAVLE® concepts
- Subscribe to the Question of the Day to receive a NAVLE® question delivered to your inbox daily
- Review the No Zebras: How to Triage your NAVLE® Study for Maximum Points blog
- Review the How to Triage your NAVLE® Study for Maximum Points blog
