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What is the prognosis of horses infected with WNV and demonstrating clinical signs?

The prognosis for recovery from WN encephalitis varies and depends on many factors. Factors such as the horses age, health status prior to infection, level of clinical signs demonstrated, as well as the level of care the animal requires and recieves all factor into the chances the horse has of surviving and leading a productive and healthy life. Animals which do not become recumbent and are able to stand unassisted have a better prognosis than horses that become recumbent. In horses which are recumbent, intermittent or focal neuropathies have a better prognosis than animals with complete flaccid paralysis.

The case fatality of West Nile encephalitis in horses is approximately 30-40%. In horses that progress to complete paralysis of one or more limbs, mortality rates are significantly higher at 60-80%.

Many horses are euthanized due to humane reasons or the cost of treatment, however, spontaneous death has been seen to occur. It also often occurs that many horses are euthanized due to sequelae of the disease. Sequelae often involves trauma due to the thrashing of horses in the neurologic phase of the disease. Trauma seen in these patients can range from lacerations to rupture of the diaphragm, skull fractures, and broken limbs and vertabrae. Trauma can also lead to sepsis and associated complications. Prolonged recumbency can lead to pulmonary infections as well as skin and muscle necrosis. Dysphagia leads to a decrease in water intake, which can predispose the animal to renal failure with the administration of NSAIDs.

In horses which recover from the infection, 80-90% of owners report that the horse returned to normal function 1-6 months after the disease. Approximately 10% of owners report long term deficits ranging from weakness or ataxia in one or more limbs, fatigue with exercise, focal or generalized muscle atrophy, and changes in personality or abnormal behavior.

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Reference

The Merck Veterinary Manual.
http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/102700.htm

Image References

The World's Online Animal Marketplace: http://www.animaroo.com/infocenter/images/horses/thoroughbred.jpg

Maryland Department of Health and Mental Hygiene: http://edcp.org/html/wn.html

 

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