A groundbreaking study shows some rats in the Downtown Eastside are carrying a bacterial disease that can infect humans and, in severe cases, lead to kidney failure, bleeding in the lungs and meningitis.

The first results from the study, published Thursday in the journal PLoS ONE, found rats trapped over the course of one year tested positive for leptospirosis, a disease that mostly causes flu-like symptoms in humans and is commonly found in developing countries.

The results are the first definitive findings to come out of the Vancouver Rat Project, a three-year study helmed by Abbotsford-based researcher Dr. Chelsea Himsworth that aims to fill a knowledge gap about the characteristics of local rats, the pathogens they carry and the potential crossover to humans.

“There’s never been a comprehensive study of rats on any subject in Canada. Ever,” explains Himsworth, a veterinarian completing her PhD through the University of B.C.’s school of population and public health.

With a specialty in neglected zoonotic risks — diseases that spread from animals to humans — in urban centres, Himsworth embarked on the Vancouver Rat Project in 2011 to fill what she sees as a blind spot in the scientific research community.

“It really fascinates me that when you actually look into the scientific literature, we know a lot more about elephants and whales and grizzly bears than we do about rats,” she says.

Himsworth attributes that fact to the failure of the parasitic rodents to capture our collective imagination, in spite, or perhaps because of, their proximity to us.

Indeed, in the hierarchy of wildlife nobility, rats often rank near the bottom. While we celebrate in science and art animals that remind us of our more becoming attributes — loyal horses, strong elephants, mysterious, intelligent whales — rats are more a lurking presence, half-hidden in the shadows.

As Himsworth puts it, they are our closest, strangest bedfellows, yet, from a scientific standpoint, we really don’t know who we’ve been sleeping with.

That dearth of knowledge could leave us vulnerable to new health challenges posed by rats in a rapidly changing, globalized world.

With half the world’s population now living in cities and a corresponding increase in zoonotic diseases, Himsworth became consumed by what she calls “the rat question.” She wondered whether the same critters that spread pandemics such as the bubonic plague in the Middle Ages could potentially become the source for other zoonotic diseases in an era that has seen SARS, bird flu and swine flu outbreaks in the last decade.

The leptospirosis findings are particularly timely, Himsworth says, given the disease is beginning to present in humans living in cities in the developed world. Rat-borne instances of leptospirosis have been discovered in people living in Baltimore and cities in France. The U.S. Centre for Disease Control also states the disease, which has historically been found in rural communities and the developing world, is increasingly showing up in inner-city children in the U.S.

Himsworth’s next phase of study will determine whether there’s been any crossover to humans in the Downtown Eastside, where the disease could spread to humans through exposure to rat urine or contaminated water. Her team is spending this year collecting blood samples of 200 residents in the neighbourhood.