Capture Myopathy

Other names: Exertional myopathy, Overstraining disease, Exertional rhabdomyolusis

Cause

Capture myopathy (CM) is a non-infectious disease of wild and domestic animals in which muscle damage results from extreme exertion, struggle, or stress. CM often occurs as a result of chemical immobilization, capture, or transport, but can also be the result of other natural causes of stress.

Significance

Capture myopathy is an important cause of death in wild animals that are caught and handled by humans. People working with wildlife must take great care to prevent it. 

Species Affected

Capture myopathy can likely occur in any animal under extreme stress. Some species may be more susceptible than others because of their natural behavioral and physical characteristics. CM is best known in ungulates (hooved mammals) and birds, though it likely affects all captured wildlife. It has also been observed in coyotes, badgers, primates, and many other species. Some North American ungulates reported with this disease include white-tailed deer, mountain goats, bighorn sheep, pronghorn antelope, bison, moose, and elk. Birds reported with CM include flamingoes, sandhill cranes, snow geese, Canada geese, mallards, wild turkeys, gulls, bald eagles, and golden eagles. CM may even occur in fish and amphibians.

Distribution

Capture myopathy can occur anywhere in the world.

Transmission

CM can occur naturally when prey animals are attempting to avoid predation, but it is usually caused by humans. This is because animals are adapted to escape from predators, but are not adapted to struggle for long periods of time in man-made restraints. Capture myopathy occurs when animals overexert themselves (struggling in a trap for example) so much that physiological imbalances develop and result in severe muscle damage. Hotter temperatures and repeated chemical immobilization increase the risk of animals suffering from CM. 

Clinical Signs

Clinical signs vary depending on the species and the cause of exertion; the method of capture and restraint plays a major role in the occurrence of CM. Capture myopathy may result in sudden death, or clinical signs may develop hours, days, or up to two months following capture. Early clinical signs include elevated respiratory rate, heart rate, and body temperature. Body temperature increases during exertion and higher temperatures are often associated with death due to CM. Other clinical signs include depression, lack of response to stimuli, loss of coordination, weakness, muscle stiffness, tremors, muscle paralysis, recumbency, shock, and death. 

Diagnosis

Light-colored skeletal and occasionally cardiac muscle observed at necropsy is indicative of capture myopathy. Similar gross lesions may be found in animals with certain nutritional deficiencies, meaning specialized tests may be necessary to reach a diagnosis. Gross changes in muscle appearance may not be observable in animals that died acutely of CM.

Treatment

Treatment of wildlife suffering from CM is rarely successful, and animals often die from this condition.

Management

Anyone who captures and restrains wildlife should be aware of the risks of capture myopathy and should make every effort to prevent its occurrence. Wild animals should only be captured when necessary, and the negative affects that capture can have on an animal’s health should always be considered before beginning a management or scientific project. People should utilize capture methods that minimize animal stress, struggling, and handling time. For example, sound should be kept to a minimum, a blindfold should be placed over the animal’s eyes, and workers should use efficient capture methods that release the animal as soon as possible. Appropriate methods vary for each species, so research should be conducted in order to select the ideal capture method for the intended animal. 

Suggested Reading

  • Friend, M., and N. J. Thomas. Miscellaneous Diseases. Pages 361-368 in M. Friend, and J. C. Franson, technical editors. Field Manual of Wildlife Diseases: Birds. United States Geological Survey.
  • Williams, E. S., and E. T. Thorne. 1996. Exertional Myopathy (Capture Myopathy). Pages 181-193 in A. Fairbrother, L. N. Locke, and G. L. Hoff, editors. Noninfectious Diseases of Wildlife, Second Edition. Iowa State University Press, Ames, Iowa, USA.

Images

Pale muscles from capture mypopathyMuscles light in color due to capture myopathy, photo courtesy of A. Hattel