Monday, October 7, 2013

Bats and disease

Wild bats, like this one hanging from a doorway,
should never be touched or handled without leather
gloves. There is a significant risk that any bat acting
unnaturally may be rabid.
Surely bats are one of the most interesting and important wildlife pests we encounter in pest control.  Bats become pests when they roost in or around human buildings.  They can create a major odor problem with their guano, but even more importantly, can carry and transmit human disease. Bat carried diseases are known as zoonoses.

A zoonosis is a disease that is normally harbored within an animal host, but given the right conditions can jump from animal to human. Rabies is a zoonosis, as is West Nile virus. Like all true zoonoses, both diseases normally infect and complete their development within a non-human, animal host.  Some zoonoses depend on a vector, a carrier species that transmits a disease between hosts.  This is the case with West Nile virus, which is normally transmitted by mosquitoes from bird to bird, but occasionally to humans.  It's estimated that about 60% of all known human pathogens are zoonoses.

Sometimes zoonoses are spread directly from the animal host to human without a vector. Rabies is an example of a zoonosis without a vector. Humans get rabies from certain animals, including bats, when the virus is transmitted via a bite or through direct contact with the infected animal's saliva or blood.

Last week six Albuquerque middle school boys learned about zoonoses the hard way.  The boys were on the playground when they found a sick bat and carried it to their biology teacher.  The teacher immediately put the bat in a box and reported it.  The New Mexico Department of Health tested the bat immediately and confirmed that it had rabies.

Even though none of the boys reported being bitten they will all have to undergo four rabies vaccinations over a two week period. Bat bites are not always evident as bat teeth are very fine and may not leave noticeable wounds.  Also should even small amounts of saliva from the bat contact the skin, virus particles may be taken into the body through a small cut or by rubbed into the eyes or mouth.

All this should serve as a reminder for anyone who encounters rabies susceptible wildlife (bats, skunks, coyotes and foxes are the most important carriers) to take precautions and avoid handling live or dead animals.  Rats and mice, by the way, are not known rabies carriers.

For National Geographic fans, I found an exceptionally interesting article on zoonotic diseases by David Quammen in the October 2007 issue. Also, Quammen has written a recent book (part basic infectious disease, part history, part travelogue) on the subject called Spillover, the term used for the phenomenon when a disease agent undergoes a change, or series of changes, that causes it to jump from a reservoir host into an other species for the first time.

For more information on bats in schools or any other site, see the Bats in Schools webpage hosted by Janet Hurley.  For information about rabies and its treatment see the Texas Department of State Health Services webpage on rabies.

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