Discovery of mouse droppings may hold answers to NYC’s high asthma rates

Oh, hell!

As if you needed another reason to avoid rats in NYC, researchers at Weill Cornell Medicine have identified a fungus in the city’s rats that exacerbates food allergies.

The study authors note that there is a high prevalence of human asthma in NYC neighborhoods with an abundance of rat sightings, suggesting that all that rat droppings may be to blame.

The fungus, Kazachstania pintolopesii, is found in the stomachs of these mice and is shed in their feces. While more research is needed to determine what happens when people are exposed to it, the study draws a link between it and asthma in nearby people.

“You can see this in the Bronx, you can see it in certain areas of Brooklyn,” senior study author Iliyan Iliev, an associate professor of immunology, told The Post.

It is unclear whether the fungus is present in the intestines of humans, mice or other animals – and whether it has the ability to “jump” hosts.

In mice, mushrooms can induce a type 2 immune response, which protects the creatures against worms and other parasites, but also worsens food allergies.

“There is a lining of the gastrointestinal tract, which is a layer of mucus, so it protects us from pathogens,” Iliev explained.

“If the diet changes or if antibiotics are taken, the mucus layer is essentially shrinking,” he continued. “This causes the fungi to come into very close contact with the underlying epithelium and immune cells, and that produces this type 2 immune response.”

Iliev pointed out that this response is good for mice because they are often exposed to parasites, but this benefit may not help humans much.

Iliev’s team identified the fungus in mice caught on farms in NYC, Los Angeles and Maryland, as well as in laboratory mice. They plan to widen their net to see if this fungus is present in mice elsewhere.

“Rats in big cities, they are close to the human population,” said Iliev. “They’re breaking into their homes, gardens, parks and everywhere.”

NYC rats tend to make their home inside buildings, while rats thrive in the streets and alleys here.

Mice can contaminate food with their droppings and can leave behind urine, saliva and hair that contain proteins that act as allergens, exacerbating asthma symptoms in humans.

Iliev said further research is needed to determine whether the increased incidence of asthma is related to rat urine or dander, fungi shed in feces, or other factors altogether.

The Weill Cornell Medicine findings were published Wednesday in the journal Nature.

Iliev hopes these preliminary results will enlighten researchers about this fungus, especially if they are developing drugs to be tested in mice or using mice to study allergies or parasite infections.

The team plans to learn more about how the fungus triggers the type 2 immune response and whether it is present in the gut microbiome of other animals, such as mice.

“That’s what we’re very interested in learning,” Iliev said of the mice. “They share similar habitats. The internal temperature in the stomach and the gastrointestinal tract are very similar, so I don’t understand why [the fungus] it wouldn’t even survive in other animals.”