Muscle Worms

Muscle Worms

Causative Agent

Muscle worms are nematodes that parasitize muscle and lung tissue of some cervids.
Two species are known to cause disease in BC:
- Parelaphostrongylus andersoni
  - muscle worm of caribou and occasionally white-tailed deer.
- P. odocoilei
  - muscle worm of mule deer and black-tailed deer; occasionally mountain goat, mountain sheep and caribou.

	Click on the photo to enlarge.

	Adult muscle worm, P. odocoilei in muscle of mule deer from Alberta .

Distribution

Geographic:

P. andersoni
- documented in Northern BC as well as in southeastern and south-central area of the province.

P. odocoilei
- documented on Vancouver Island, the Okanagan Valley, and in coastal mountain goats and some populations of mountain sheep.

Seasonality:

New infections begin during periods when vegetation is greening up.
Larvae are passed in the feces at varying intensities throughout the year.

Hosts, Transmission and Life Cycle

P. andersoni

Adult worms are delicate and thread-like and are found in association with blood vessels and connective tissue of the loin and thigh muscles.

Adult worms are often found in the meat of “backstraps”, back muscles close to the vertebrae.

Adult worms are 19 - 35 mm in length and approximately 0.1 mm in width.

The dark, threadlike intestine of adult worms is noticeable against muscle tissue.

Hosts, Transmission, and Life Cycle:

Adult male and female worms are often found paired.

Females deposit eggs into veins of hosts which are then carried to the lungs where they hatch in small blood vessels.

Larvae move up the through the lungs and into the trachea where they are coughed up, swallowed, and passed in the feces.

Larvae must then penetrate the body of a land snail to develop into the infective stage.

The snail and infective larvae are then inadvertently ingested by caribou and white-tailed deer while feeding.

P. odocoilei

Adult worms are delicate and thread-like, whitish with a central thin, black intestine. Like P. andersoni, they are found in association with blood vessels and connective tissue of the loin and other muscles, primarily in mule and black-tailed deer.

Adult worms are about 56 mm in length and approximately 0.2 mm in width.

Hosts, Transmission, and Life Cycle:

Similar to that of P. andersoni.

Signs and Symptoms

P. andersoni

Natural infections in caribou and white-tailed deer are generally well tolerated.
In general, the signs listed below are observed in heavy infected animals; young are more susceptible than older animals.
Notable signs in caribou include:
- reluctance to stand
- weakness
- panting
- short steps
- arched back
Signs in white-tailed deer are more severe and include:
- hemorrhage on surface of back and thigh muscles
- green abscesses may be observed near eggs in lungs or worms in muscle
- small (up to 1mm in diameter) nodules may be observed in the lung

P. odocoilei

Outward signs of disease are rarely seen with P. odocoilei.
Laboured breathing may be observed in infected animals.
Other signs are similar to those described above for white-tailed deer infected with P. andersoni.
Recent research has identified this parasite in mountain sheep and mountain goats. There is some evidence that heavy infections of larvae can damage lungs of Stone’s sheep, but further studies are required to understand any role the parasite plays in the health of these sheep.

Meat Edible?

Carcasses containing P. odocoilei and P. andersoni are safe for human and animal consumption since they do not affect the quality of meat.

Samples for Diagnosis

Submission of adult worms from loin or thigh muscles is necessary to confirm infection.
Submitting fecal samples may also aid in diagnosis.