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Oh, Rats!

New study of rat ecology and disease in B.C. may offer control insights.

Everyone knows rats are bad news, but experts only could guess at the real threat posed by rat-human contact until now.

himsworthThe Vancouver Rat Project, led by Dr. Chelsea Himsworth of the University of British Columbia, is the first in-depth study of rat ecology, their diseases, and the risks they may pose to human health in Canada.

The focus of the three-year study is Vancouver’s Downtown Eastside neighborhood, also known as ‘Canada’s poorest postal code.’ Himsworth will discuss preliminary results at Pest Management Canada 2012 on March 10 in Vancouver. She offered these insights:

Q. What kind of infectious diseases do rats carry and how widespread is the problem?

A. In the past three years, at least nine outbreaks of rat-associated plague were reported in six countries. Twelve outbreaks of leptospirosis were counted in nine countries, with one outbreak in Manila, Philippines, having as many as 2,158 cases. Other diseases are hemorrhagic fever with renal syndrome, murine typhus, and Haverhill and rat-bite fevers.

The number of actual cases is likely higher. Excepting the plague, doctors aren’t required to report cases of rat-associated disease. Many of these diseases have non-specific symptoms and go undiagnosed.

Q. How are diseases transmitted from rats to humans?

A. Numerous ways. Leptospira spp. and Seoul hantavirus are found in the urine of infected rats. This urine can contaminate drinking or recreational water supplies, or dry and be inhaled as dust.

Bacteria like the plague-causing Yersina pestis and Rickettsia typhi, the source of murine typhus, are spread when fleas bite infected rats and then bite humans.

Less common are diseases spread by rat bites, such as the transmission of the bacteria Streptobacillus monilliformis, which causes rat-bite fever. Rats even may spread Salmonella spp. in their feces.

These organisms usually don’t cause visible illness in rats, so healthy looking rats could be carrying dangerous bacteria and viruses.

Q. What’s the likelihood of humans contracting rat-associated diseases?

A. These diseases occur most commonly in impoverished, densely populated areas with poor sanitation and substandard housing. Also, homeless people and intravenous drug users, particularly those with decreased health or immune function, have an increased risk of exposure and infection. A New York study found 46 percent of intravenous drug users tested had antibody against the rat-associated bacteria Bartonella elizabethae, indicating they’d been exposed to and/or infected with this bacteria.

Given the right circumstances, anyone could be exposed to rat-associated disease regardless of socioeconomic status.

Q. What have you learned so far?

A. The distribution of rat populations in the Downtown Eastside neighborhood is irregular. One block will have hundreds of rats while an adjacent block has almost none. We’re in the process of teasing out what it is about each block that encourages or discourages rat infestations.

We’ve also learned rats in different blocks have different levels of health. Surprisingly, rats from less ‘crowded’ blocks (blocks with fewer rats) are in poorer condition and have more fighting wounds compared to rats from more crowded blocks.

The characteristics of these populations determine how diseases are transmitted between rats and the risk of transmission to people.

This summer the project will shift from studying rat ecology to the disease analysis phase.

Q. How will this research affect pest management and other professionals?

A. It will help us understand whether rats pose a health threat to people in Canada. Right now we have no scientific data to support the claim that the risk is minimal or serious.

Pest control professionals and municipal officials can use the data to develop targeted control strategies. It will help health care professionals increase surveillance of rat-associated diseases and develop prevention strategies.

Q. How can the pest control industry support this research?

A. Pest control professionals have a wealth of knowledge about rats and rat infestations. Some B.C. professionals participated in an Internet survey and we hope to reach more with a shorter version of the survey at Pest Management Canada 2012.

The Vancouver Rat Project is supported by UBC School of Population and Public Health, Canadian Institutes of Health Research, BC Centre for Disease Control, Urban Health Research Initiative, City of Vancouver, Vancouver Area Network of Drug Users, Structural Pest Management Association of BC and affiliated pest control professionals.


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