Dilon, a young male feral cat at the Humane Rescue Alliance and Medical Center in the District on March 22. (Astrid Riecken/ For The Washington Post)

A new program from the District of Columbia’s animal control services, the Humane Rescue Alliance, proposes to tackle the city’s rat population by throwing cats at the problem. The Blue Collar Cats program plans to adopt cats out to businesses, apartments and homeowners and to allow these cats to wander freely to hunt.

Superficially, this strategy makes sense. Cats are instinctive predators, and many of us grew up watching cats chase rodents in cartoons. It’s natural, right? Not quite.

Not only does this program violate D.C. code, it also fails to account for the fact that cats are ineffective rat controllers that cause plenty of damage in their own right.

According to D.C. code, “no owner of an animal shall allow the animal to go at large.” An owner is defined as anyone “who purchases or keeps an animal in temporary or permanent custody.” The Blue Collar Cats program encourages (even relies on) a violation of law. It also conflicts with many veterinarians’ advice that cats remain indoors for their own safety.

Even if it were legal, the program would be a bad idea. Contrary to popular opinion, cats do not effectively control urban rat populations. A 2009 study led by Johns Hopkins School of Public Health scientists evaluated cat-rat interactions in Baltimore. The researchers concluded that cat predation on rats was “sporadic” and had “relatively little impact on size of the rat population.” The study also found that when cats did chase rats, they largely ignored the frequently aggressive adult rats.

And even though cats kill rats, cats also kill beneficial native animals. Cats are opportunistic predators and kill a wide variety of native species, some of which may be threatened or endangered and all of which are already struggling to survive in a human-modified environment.

The costs to wildlife are enormous. Outdoor cats kill 1.3 billion to 4 billion birds and 6.3 billion to 22.3 billion mammals in the United States annually and have contributed to the extinction of 63 species worldwide.

Introducing cats as “green” rodent control undermines the work of conservation agencies fighting feverishly to protect ecosystems for current and future generations. For example, many of the District Department of Energy and the Environment’s species of greatest concern, such as the wood thrush and Eastern cottontail, are threatened by cats.

Free-roaming cats also increase rather than diminish public-health risks. Like rats, cats can carry and transmit a variety of parasites and diseases to humans and wildlife, including rabies, hookworms, cat-scratch disease, typhus and plague. One-off rabies immunization, a frequent hallmark of programs that intentionally release cats, is insufficient. The National Association of State Public Health Veterinarians has declared that a cat must be vaccinated initially, given a booster at one year and then given boosters at recommended intervals, usually one to three years, to be safely immunized. Anything less puts the cat and the public at risk.

And then there is toxoplasmosis, a disease caused by infection with the parasite Toxoplasma gondii, which requires felines to complete its life cycle. The parasite’s infectious eggs, called oocysts, are excreted via cat feces; a single cat can excrete hundreds of millions of oocysts, which remain infectious and persist in the environment long after the feces have disappeared. Accidental ingestion or inhalation of an oocyst causes infection, and a growing body of evidence consistently points to widespread environmental contamination with T. gondii from free-roaming cats.

T. gondii not only harms and kills wildlife, but it also is dangerous for people . Infections can cause miscarriage, blindness, memory loss, organ failure and death. Pregnant women and people with compromised immune systems are especially susceptible, which is why doctors advise against cleaning litter boxes when pregnant. In stark contrast to the Humane Rescue Alliance’s suggestion, flower beds and sandboxes, two locations where people frequently dig in the earth, are entirely inappropriate places for cat defecation.

Rat control is an important component of city life, but the Blue Collar Cat program relies on a flawed strategy that will do more harm than good. The program violates D.C. code, endangers wildlife and sacrifices public health. It is time to put this idea back on the shelf.

The writer is director of Invasive Species Programs of the American Bird Conservancy.