CONTACT US   027 6936 007        PAY ONLINE

Rats and their alarming bugs


If the past few years have taught us anything, it’s that our well-being is intimately linked to the health of animals.

The current Ebola epidemic probably got its start when someone came into contact with an infected animal, perhaps a monkey or a fruit bat. The virus causing Middle East respiratory syndrome appears to spread from camels to humans.

Yet animal pathogens remain a scientific terra incognita. Researchers have begun studying  animals in far-flung parts of the world to learn more about what infects them.

Recently, a team of pathogen hunters at Columbia University went on an expedition closer to home. They conducted a survey of the viruses and bacteria in Manhattan’s rats, the first attempt to use DNA to catalog pathogens in any animal species in New York City.

“Everybody’s looking all over the world, in all sorts of exotic places, including us,” said Ian Lipkin, a professor of neurology and pathology at Columbia. “But nobody’s looking right under our noses.”

On Tuesday, Dr. Lipkin and his colleagues published their initial results in the journal mBio. Although the scientists examined just 133 rats, they found plenty of pathogens. Some caused food-borne illnesses. Others, like Seoul hantavirus, had never before been found in New York. Others were altogether new to science.

The researchers could not say how ill New Yorkers were getting from these rat-borne agents, but already the results were raising alarms among experts.

Peter Daszak, the president of EcoHealth Alliance, a scientific organization that researches the links between human health and wildlife, called the study “shocking and surprising,” particularly given the close quarters shared by rats and New Yorkers.

“This is a recipe for a public health nightmare,” he said.

It has been hard for scientists to measure the medical threat that rats pose. Identifying pathogens has traditionally been a slow, painstaking business, requiring researchers to rear microbes in labs.

In 2012, Cadhla Firth, then a postdoctoral research scientist in Dr. Lipkin’s lab, and her colleagues picked four buildings and a park in Manhattan where they set traps. Luring the rats into them proved harder than Dr. Firth expected.

“New York rats are a lot wilier than rats in other cities,” she said. “We had to bait traps and just leave them open for a week.”

Once the scientists caught the rats, they took samples of blood, urine, feces and tissues from a number of organs. After extracting DNA from the samples, they sifted through the gene fragments.

First, the scientists looked for disease agents previously found in rats. They discovered bacteria that caused food poisoning, such as Salmonella and a strain of E. coli known to cause terrible diarrhea. They also found pathogens that caused fevers, such as Seoul hantavirus and Leptospira.

Then the scientists searched the rats for new species of viruses. So far, they have identified 18 unknown species related to viruses already shown to cause diseases in humans. Two of the new species, were similar to the virus that causes hepatitis C.

David Patrick, the director of the School of Population and Public Health at the University of British Columbia, called the identification of new viruses “groundbreaking.”

“These viruses may or may not have any links to human illness, but it is good to be able to describe them in detail,” he said.

The viruses resembling hepatitis C could prove to be the most important discovery in the survey, not because rats might give us hepatitis C. (They will not.) But scientists may be able to glean clues from the rat viruses to fight the disease, which affects about 150 million people worldwide.

Hepatitis remains a mysterious disease, because lab animals do not suffer the same symptoms as humans when they are infected with the human virus. Infecting lab rats with the new rat viruses could change all that.

“It’s still a few steps to go before you can call it an animal model, but I think overall it’s a really exciting finding,” said Alexander Ploss, a molecular virologist at Princeton University.

Some experts cautioned that we have yet to understand how much harm the rat pathogens are doing to residents. “I don’t see it as a call to wage war on rats just yet,” said Angela Luis, a biologist at the University of Montana.

Dr. Lipkin and his colleagues are now collaborating with the New York City Department of Health and Mental Hygiene and the Centers for Disease Control and Prevention to look for signs of infection from some of the rat pathogens in the blood samples of New Yorkers.

Jay Varma, the deputy commissioner for disease control at the New York City Department of Health, said the study would not lead to any immediate changes in how the city deals with rats, but the data would help health officials better understand how diseases spread.

“We live in a world where humans are in the minority,” he said. "We as a society probably haven’t done enough to understand the true ecology of bacteria and viruses.”

The study should alert New York to monitor rats and control them better, Dr. Lipkin said.

“I think people are going to have to start paying attention to this,” he said. “But that’s Bill de Blasio’s problem. I’m just doing the science.”

-by Carl Zimmer