Big Brown Bat

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Big Brown Bat

Eptesicus fuscus

IDAPA Classification: Protected Nongame
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Health Issues Which May Affect This Animal

What Causes This Disease?

Rabies is caused by a Lyssavirus of the Rhabdoviridae family.

Where Is The Disease Found?

Rabies is found in all parts of North America and the rest of the world in many species of carnivores including domestic dogs, domestic cats, red foxes, arctic foxes, skunks, and raccoons. In Idaho, the only rabies virus strain present is the bat-associated strain. Because these bat strains can be transferred from bats to other mammals, all mammals with signs of neurological disease should be considered a potential source of rabies. Rabid animals, primarily bats, have been detected in almost every county in Idaho with between 10-20 cases per year.

Signs of Disease

Rabid animals typically behave abnormally and may show daytime activity in a nocturnal species such as a bat, loss of fear of humans, or unprovoked aggression. They may have a dropped jaw and appear to be foaming at the mouth. Rabid animals may also appear weak or paralyzed (dumb rabies) or may appear agitated and excited or paralyzed and frightened (furious rabies). Sometimes, rabid animals do not show any signs of illness before death from rabies. Most bats affected by rabies are found on the ground, unable to fly, during daylight. But rabies should be considered if bats are encountered in newly opened cabins, or in rooms where people that are sleeping may not have been aware of the bat.

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What Causes This Disease?

White-nose syndrome is fungal disease caused by Pseudogymnoascus destructans. The fungus appears as white fuzzy growth on the wings, ears, face, and tail membranes of afflicted bats. The Pd fungus shows optimal growth at 54.5-60.4 F (12.5-15.8 C) which is similar to temperatures found in bat hibernacula. The fungus is capable of invading the skin of bats during hibernation when bat body temperature is significantly lowered and the immune response is suppressed.

Where Is The Disease Found?

The fungus that causes WNS is endemic in Europe and Asia but illness and death in bats there is minimal compared to North America. In the US, the presence of WNS in bats was initially detected in a cave in New York in winter 2006-2007. Since then, millions of bats have died as the disease has spread over most of eastern North America. WNS has reported from 31 states and 5 Canadian provinces and the fungus has been confirmed in bat hibernacula in two additional states. In March 2016 WNS was found in a Little Brown Myotis in Washington and subsequently WNS or Pd have been found in Yuma Myotis and Silver-haired bats.

Signs of Disease

The fungus that causes WNS affects the ability of bats to hibernate. It appears to alter behavior of bats resulting in delayed arousal from torpor following disturbance, aberrant behavior including increased activity during normal hibernation periods or roosting in abnormal sites. Susceptible bat species may exhibit high levels of winter mortality in and around hibernacula. Bats affected by WNS usually have white or gray powdery fungus growing on the muzzle, ears, wings and tail membranes and may be in thin body condition and dehydrated. Wing damage (thin membranes, depigmented areas, holes, tears, flakey skin) may be seen on affected bats.

Read More About White-nose Syndrome in bats