Plague, Bat Rabies and Raccoon Roundworm: Avoiding Diseases from Wildlife

By Carol U. Meteyer and Gail Moede Rogall

A black-tailed prairie dog (Cynomys ludovicianus) runs back to its burrow in Wind Cave National Park, South Dakota, after release from a trap. It is part of a field test of an oral plague vaccine developed by USGS scientists. Marisa Lubeck, USGS.

Zoonoses are diseases that pass from animals to people, such as rabies and plague. People can protect themselves by avoiding direct contact with wildlife and with wildlife feces and urine, so controlling these diseases is largely a matter of education, avoidance and prevention.

The U.S. Geological Survey studies wildlife diseases where wildlife, domestic animals, people and the environment meet. Its National Wildlife Health Center (NWHC), working with the U.S. Fish and Wildlife Service and other disease specialists, has published circulars on seven zoonotic diseases, each with steps to protect yourself and others. This fact sheet highlights three of them.

This is not medical advice. If you are worried that you have been exposed to a disease, contact your health care provider.

Plague

• Cause: the bacterium Yersinia pestis. Its natural hosts are rodents and fleas, but people and pets can be infected by touching infected rodents or by the bite of an infected flea.
• Where: in prairie dogs, mostly in grasslands and the arid Southwest; often in ground squirrels too. It occurs in most of the Western States, and has turned up in squirrels inside Denver's city limits.
• How it spreads: mainly by fleas, in summer. It can kill every prairie dog in an affected colony.
• How little it takes: as few as 10 bacteria can cause infection, and one milliliter of blood can hold 100 million (Abbott and Rocke, 2012).

Counties where animal or flea samples tested positive for plague, 1970 to 2009 (green) — most of them west of the 100° west meridian, where the infection is common in wildlife. Each red dot is one human case, 1970 to 2007, placed at random in its county; they are most common in the Southwest and Pacific States. Map based on K. Gage, Centers for Disease Control and Prevention.

Staying safe

• Know where plague occurs, and watch for plague warnings from public health departments.
• Keep away from rodents and their burrows, which may hold fleas.
• Don't handle sick or dead rodents.
• Watch your pets. Cats that catch wild rodents can carry infected fleas into the house, or pass plague straight to the people who look after them.

The NWHC and the University of Wisconsin-Madison have developed an oral plague vaccine for wildlife, now in field trials as a way to manage plague in wild prairie dogs (Rocke and others, 2017). More on plague and human health: CDC.

Bat rabies

Rabies is a virus that attacks the nervous system of mammals. Its natural hosts are bats and many carnivores — dogs, cats, foxes, raccoons and skunks.

The United States sees only one to two human cases a year, yet preventing rabies costs an estimated $245 to $510 million a year: vaccinating domestic animals, testing wildlife and domestic animals nationwide, and treating about 40,000–50,000 people bitten by a possibly rabid animal each year.

Among insect-eating bats, surveys found rabies in about 0.1 percent of apparently healthy bats and up to 10 percent of bats found sick or dead (Constantine, 2009).

Rabid animals submitted to the CDC in 2015 — 5,508 in all, 5,089 (92.4 percent) of them wild:

By tracking the strains of the virus in these animals, public health specialists have shown that bats are the most common source of rabies exposure in people.

Why bats catch people out

• Few people know bats can carry rabies to pets and people.
• Bat bites are small and easy to miss. People are more likely to seek treatment after a bite from a fox, stray cat or raccoon than from a bat.
• Exposure comes from a bite, from handling sick or dead bats, or from bat saliva.
• Young naturalists who brought sick or dead bats to school have exposed dozens of people, all of whom then needed treatment.
• If a bat is found in a bedroom where someone was sleeping, their health care provider can talk through whether they may have been exposed.

Human rabies can be greatly reduced by spreading awareness that bats are a source of infection, and by limiting people's and pets' contact with bats and wild carnivores.

Bats also matter: they eat insect pests of crops and forests, and without them, farm losses in North America alone would exceed an estimated $3 billion a year (Boyles and others, 2011). When bats roost in a home, professionals can remove them safely, without harming them.

Raccoon roundworm

Baylisascaris procyonis is a roundworm that lives in raccoon intestines; its eggs pass in raccoon feces. Researchers estimate that over 50 percent of raccoons in the United States carry it (Kazacos, 2016).

• In another animal, swallowed eggs hatch into larvae that migrate through the body's tissues — a condition called larva migrans.
• The best-known form is a potentially fatal encephalitis, when larvae reach the brain or spinal cord of people or other animals.
• Human cases: fewer than 25 documented in the United States, but usually severe. A 2017 study found evidence that people can be exposed without becoming ill (Weinstein and others, 2017).
• Other victims: wild animals, zoo animals and domestic animals.

A raccoon (Procyon lotor). David Menke, U.S. Fish and Wildlife Service.

Latrines are the risk. Raccoons return to the same spots to defecate, building piles that can concentrate the worm's eggs, and soil contaminated by them is one route to people. Children are most at risk, since they are more likely to put dirty fingers or soil in their mouths. The parasite's prevalence in urban raccoons is what puts people at risk.

Discourage raccoons from living around your home

• Don't keep, feed or adopt wild animals.
• Keep food out of reach, and trash containers tightly closed.
• Close off attics and basements.
• Cover sandboxes when not in use — raccoons may use them as latrines.
• Remove fish ponds (raccoons eat the fish and drink the water) and other water sources.
• Remove bird feeders.
• Clear brush, so raccoons don't make a den on your property.

The CDC explains how to find and remove raccoon latrines.

The seven circulars

The NWHC's zoonoses circulars, as of January 2018, prepared with the U.S. Fish and Wildlife Service:

Contact: National Wildlife Health Center, U.S. Geological Survey, 6006 Schroeder Road, Madison, WI 53711.

Sources

Based on Information to Prevent Human Exposure to Disease Agents Associated with Wildlife—U.S. Geological Survey Circulars on Zoonotic Disease, by Carol U. Meteyer and Gail Moede Rogall, USGS Fact Sheet 2017–3077, U.S. Geological Survey; a work of the United States government in the public domain. Funded by USGS Contaminant Biology and the National Wildlife Health Center. The map, the photographs of the prairie dog and the raccoon, the list of ways to discourage raccoons and the list of circulars are taken from the fact sheet's PDF, which the import had left out; its photographs of a cat and a little brown bat, credited to outside photographers, are not reproduced.