Norway rats are your consummate “where you go, we go also” species, being as well adapted to urban living as we are. Meaning that the diseases we’ve blamed on them are most likely grounded in reality.
Yet widespread instances of the most spectacular of those diseases — the Black Plague that devastated much of the Old World long ago — have virtually disappeared. Is it because this dread disease’s vector, the Oriental rat flea, also disappeared? No. Rats aren’t the only animals that harbor these fleas. In North America the plague lives on in the unlikeliest of places — in the American Southwest among ground squirrels, prairie dogs, and the rat fleas they harbor, infecting roughly 10 people each year.
A Norway rat drops down a grate in New York City, looking for food or shelter. A flea that finds food and shelter on such a rat is capable of transmitting the plague pathogen.
But what about our cities? If New York City could serve as a model organism, so to speak, then new research published this week from a Cornell and Columbia University collaboration means we’d best keep tabs on city rats and the tiny critters that call them home. NYS IPM’s urban entomologist Matthew Frye and his colleagues in New York live-trapped 133 Norway rats. Using a fine-tooth rat comb, Frye found about 6,000 parasites, including lice, mites — and more than 500 rat fleas.
The good news first: none of the fleas carried the plague. But they did carry other nasty diseases.
It’s unlikely the plague has gotten a toehold in New York. Even so, Frye is alarmed. “If these rats carry fleas that could transmit the plague to people,” says Frye, “then the pathogen itself is the only piece missing from the transmission cycle.”
What to do to help keep it that way? Since avoiding fleas is just as tricky as avoiding rats, core IPM practices are key. They include prevention (caulking and installing snug-fitting door sweeps, for instance) and careful sanitation (cleaning or removing every possible food and water source — indoors and out — be it spilled dog chow and soda pop, or leaky pipes and discarded deli containers).
Once you’ve gotten the rats out — then what? After all, those fleas and the diseases they vector are a troupe of “where you go, we go also” species on the micro level. “It’s not that the parasites that get left behind can infest our bodies,” Frye says. “But they can feed on us while seeking other rats to infest.”
Frye’s research was part of an earlier project looking at the pathogens that rats themselves — not just their fleas — could carry. That study noted a disturbing number of viral and bacterial diseases rats fall prey to — including a handful that could spell grave consequences for us.