Humans Could Be Contributing to Rabies Outbreaks

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A better understanding of skunk behavior could slow the spread of wildlife rabies in Flagstaff, Arizona, and other urban areas.

People in urban areas are creating conditions for skunks to live in close proximity to one another, leading to more interaction not only with themselves and other wildlife but also with humans and pets. New research at Northern Arizona University shows that one unfortunate result could be increased outbreaks of the rabies virus.

A better understanding of skunk behavior could slow the spread of wildlife rabies in Flagstaff, Arizona, and other urban areas. In the last decade, Flagstaff has seen three major wildlife rabies outbreaks among its urban and suburban areas, with more than 30 cases reported between 2004-2005 and 2008-2009. The record number of cases has catalyzed research into the causes of these outbreaks.

Tracking skunk behavior

According to Dr. Tad Theimer, vertebrate biologist and an associate professor at Northern Arizona University, the rabies virus had apparently jumped from bats to a new host in Flagstaff.  “Initially, these skunks appeared to have somehow found a way to keep the virus going independent of the bats,” says Dr. Theimer, “but now it appears that bats have infected either skunks or foxes in each of the three rabies outbreaks in Flagstaff.  Now we need to understand not only how the disease is transmitted among skunks once they are infected, but how they are infected by bats in the first place.” Bats can infect skunks and other mammals, such as grey foxes, and then the disease can be spread among those mammals and potentially into domestic cats, dogs, or even humans. This poses a significant risk to human and pet health.  

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A variety of devices were used to track skunk behavior, including live trapping.

A variety of devices were used to track skunk behavior. These devices included a combination of live trapping, radio telemetry, and video-camera monitoring. For example, monitors showed skunks scavenging dead bats. One video captured a mother skunk carrying a bat into her den where her young likely ate it, displaying one way that rabies could transfer from one host species to the next. “Not only can the mother skunk now get the disease, but also her young,” Dr. Theimer explained.

Food and shelter major contributors

During a second test, which analyzed the transfer of the disease from skunk to skunk, cameras were placed near cat food dishes and bird feeders in the backyards of resident volunteers. Yet again, Dr. Theimer and his team witnessed surprising behaviors: “The number of times we saw skunks biting one another went way up once we put out cat food. We never saw that kind of interaction with bird feeders.” 

The key to controlling rabies outbreaks in skunks is to stop the problem at its source. 

But food is not the only draw. The abundance of shelter in urban areas has also been a major contributor to higher skunk numbers as they find safety and warmth beneath homes. The ability for skunks to access shelter, as well as food, is allowing skunks to reach much higher numbers in suburban areas compared to the surrounding pine forests, thereby increasing the likelihood that they will contract and transmit rabies.

“We feel these results provided us with some good evidence that showed how behaviors of skunks can change, depending on what kind of food and shelter is being offered and where,” said Dr. Theimer. For example, the research team noticed more aggressive behaviors as skunks fought for the easily accessible food and shelter provided by people. And these human influences are what Dr. Theimer believes could be the primary contributing factor for the rise of rabies outbreaks of skunks in Flagstaff— especially in the winter and spring months.

Encouraging skunk population to self-regulate

“My goal is to try to get residents to remove or reduce all human sources of food and shelter [around their homes] so that the skunk population can self-regulate,” says Dr. Theimer. “Often it is easier for people to call pest control, rather than fence in their deck or remove all of their food dishes. What they often forget to realize is that two to three days later another skunk will move in.” The key to controlling rabies outbreaks in skunks is to stop the problem at its source.

--Candice Giffin