Q. It is well known that mosquitoes, fleas, lice and ticks transmit human diseases, but what about cockroaches?

A. The proven health risks of cockroach infestation seem to be predominantly those of filth, food contamination and allergic asthma rather than direct transmission of disease, according to an extensive review of public health risks from all kinds of pests conducted by the World Health Organization.

Because many studies have found that cockroaches feed on human excrement and transfer or excrete pathogens, they have a strong secondary role in the spread of some diseases. But the W.H.O. review in 2008 concluded, “definitive evidence that cockroaches are vectors for human disease is still lacking.”

[Like the Science Times page on Facebook. | Sign up for the Science Times newsletter.]

There is a substantial list of bacteria, funguses, molds and a couple of viruses that cockroaches can carry from place to place, not to mention an amoeba that causes dysentery, another parasite that causes giardiasis and the virus that causes polio.

But asthma caused by allergy to cockroaches themselves is the big public health concern. For example, a 2005 study found that children living in poorer urban areas in the United States were at greater risk of asthmatic illness from cockroach allergy than from allergies to dog or cat dander or to dust mite excretions.