[Rodent Control] The House Mouse: Hidden Threats, Your Benefits

The house mouse, Mus domesticus, is a ubiquitous urban mammal pest in many cities around the world. It has proven itself adept at infesting multiple unit buildings of all sizes, complexity and operation. Such buildings often contain hundreds and sometimes thousands of structural and equipment voids of varying shapes, sizes and micro-environments. These urban spaces are ideal for the small, highly adaptable house mouse to exist and to thrive. Examples of such buildings include high-rise apartment buildings and condos, hotels, schools, hospitals, office buildings, shopping malls and a host of others. The fact of the matter is (whether we like it or not), the mouse is more the “companion animal” to the human species than is the cat or the dog.

In New York City for example, the mouse is so entrenched that it would be relatively difficult — and I suspect even rare — to locate a multiple unit building that does not have at least a few mice. Actually, it is more probable that many New York City multiple unit buildings contain established mouse infestations that have been present since the opening of the building itself.

But what is the overall significance of this human/mouse co-existence in buildings? In general, we know that the mouse is an economic and health pest inside buildings. We know from the thousands of case histories that mice inside our buildings attack and contaminate our foods as well as travel across food dishes, utensils and the surfaces we use to prepare food. They also scurry over our work desks, tables, chairs, beds and clothes. In only one week, a single mouse can deposit thousands (literally) of micro-droplets of urine and hundreds of fecal pellets in our living spaces and/or onto the furniture and equipment in which we constantly touch with our hands and fingers (the primary human appendages in which we collect and then ingest or absorb microbes that give us colds, the flu and worse). Even though this is a disconcerting image to most of us, it is somewhat a relief to know that most epidemiologists do not classify the mouse as a major health threat because it does not transmit diseases associated with high mortality rates (at least not yet).

Certainly, this does not mean the mouse is a harmless pest. We know, as we will see later in this article, that mice have the potential to transmit illness to us. And to the point of this article, there is something unique about house mice and diseases in urban areas. Namely, there are several mouse-borne diseases that are overlooked and ignored by people, or misdiagnosed by physicians. Why? Because these illnesses closely resemble common everyday ailments. Or, they are ailments that are not severe in their symptoms or duration, so people fail to seek the further medical diagnosis necessary to correctly identify the specific illness.

Additionally, mice, similar to rats and squirrels, gnaw on wires and cables of all types inside buildings, planes, trains, automobiles, computer systems and a myriad of mechanical devices causing directly, or indirectly, electrical shorts, fires and/or serious mishaps. But in the scope of trying to pinpoint the cause of these malfunctions, what inspector is able to discern the typical tiny mouse incisor marks on wiring? Undoubtedly, most times such damage remains hidden.

All in all, society in general under-recognizes and under-emphasizes the health significance of the urban mouse. So, let’s examine this issue a bit deeper. Which mouse-borne diseases may be going unnoticed because we assume they are something else — something more ordinary?

HAY FEVER OR MOUSE ALLERGENS? Inside multiple unit buildings, pest professionals servicing for established mouse infestations frequently note the classic “mousey odor.” This odor is mostly due to the accumulated mouse urine from the infestations. Up until the late 1990s this odor was dismissed as an unpleasant, but overall mild nuisance. Then, research from Johns Hopkins said that the house mouse’s urine contains a protein that can trigger asthma in sensitive individuals. The protein is appropriately named mouse urinary protein (MUP). In most cases of MUP sensitivity, the classic symptoms of asthma occur (i.e., watery eyes, shortness of breath, wheezing and coughing). But in severe cases, MUP can cause life-threatening and even fatal reactions.

The Johns Hopkins research estimates that about 18 percent of asthmatic children nationally test positive for mouse allergen sensitivity. In New York City alone, this equates to about 54,000 asthmatic children being MUP sensitive. But for so many years (and still currently depending on an examining physician), people on a global scale with asthma symptoms are misdiagnosed as allergic to pollen, dander or “something in the air.”

Considering the prevalence of the mouse in our multi-unit buildings and the fact that mice deposit thousands of micro-droplets of urine as discussed earlier, building occupants are exposed to the urinary proteins via inhalation, by skin contact or by both. And as if the asthma symptoms are not bad enough, skin contact with mouse urine for some people can cause rashes and itching (causing them to imagine they have developed a skin problem, or they are being attacked by fleas, bedbugs or some mysterious “mite”).

The significance of mouse infestations and their role in MUP asthma and other
MUP-related ailments cannot be under-appreciated.

THE 'FLU' OR LCM? Lymphocytic choriomeningitis (LCM) is an illness caused by a virus (LCMV). This virus becomes established within the feces and body fluids of the house mouse. Similar to mice being overlooked in cases of asthma, recent research has found that LCM is another overlooked and under-diagnosed disease in urban areas where mice are prevalent.

Within multiple unit buildings where LCM-infected mice are established, building occupants become infected by inhaling infectious aerosolized particles of rodent urine, feces or saliva, or by ingesting food contaminated in one form or another by infected mice.

Onset of LCM occurs from one week to two months after exposure to the virus, although about 50 percent of the people that contract LCM are asymptomatic (no outward signs or symptoms). With other cases, LCM infections include fever, headache and muscle pains, which as most of us know, is how you feel when you have come down with a case of the flu. Most people tend to wait it out by resting in bed, drinking fluids and so forth.

About 20 percent of the cases produce mild meningitis (i.e., an inflammation of the membranes [meninges] that envelop the brain and spinal cord). In the most severe cases, the fatality rate ranges from 2 to 5 percent. Still, with the exception of the worst cases, most people make a full recovery from LCM within three weeks.

The notable point is that the experts hypothesize LCM is established world-wide and that tens of thousands of people are infected by this virus each year but many of the cases are dismissed as ordinary flu. Considering the ubiquitous distribution of the house mouse in structural environments and the suggestion by researchers that LCMV is an overlooked pathogen, LCM may be among the most significant mouse-borne illnesses to the general public.

CHICKEN POX OR RICKETTSIALPOX? Rickettsialpox is a disease caused by a special group of bacteria, the rickettsia, which are parasitic on cells. Several rickettsial diseases are transmitted to people from fleas, lice, mites and ticks, and some involve rodents as the reservoirs of these diseases. Notable rickettsial diseases include murine typhus, scrub typhus and Rickettsialpox. Rickettsialpox is caused by the bacteria Rickettsia akari and is associated with house mouse infestations that have become established within multiple unit buildings of several large cities.

The Rickettsialpox bacteria are carried only by the house mouse mite Liponyssoides sanguineus. This mite lives almost exclusively on house mice (although it has also been found on Norway rats in Arizona and Utah). This mite also causes dermatitis in people.

Victims that are bitten by infected house mouse mites in mouse-infested buildings suffer headaches, rashes and fever. But Rickettsialpox often goes undetected or unreported because: (a) it is commonly misdiagnosed as chicken pox (which is not caused by bacteria, but rather a virus) because of the similarities of the skin rash and the other symptoms; (b) the symptoms of Rickettsialpox generally are not severe and most people fully recover after a week or so. This causes people to not become alarmed, nor seek any further medical attention or testing; and, (c) it is considered an uncommon disease, with only about 1,000 cases having been reported in the United States.

Consequently, many physicians are not alert to the possibility of skin pox cases being Rickettsialpox. In turn, maybe this adds to the disease remaining “uncommon.” Similar to “asthma” and the “flu” cases discussed previously, no one knows how many cases of “chicken pox,” are in fact mouse-borne Rickettsialpox. But in the cities of New York, Cleveland, Philadelphia, Boston and West Hartford, Conn., where the Rickettsialpox bacteria is established, cases of “chicken pox,” especially those originating in mouse-infested multiple unit buildings, should be further tested for Rickettsialpox because this has important ramifications for all the other occupants of the building.

THE HIDDEN SERVICE BENEFITS. So, in urban zones, how many mice do you control on one route every month? Dozens? And probably several hundred throughout the course of a year — right? Moreover, among the 15,000 pest management companies and the thousands of municipal pest professionals in the United States, how many mice as a whole do pest management professionals control every year?

The next time you perform a service for mice in one of the multi-unit structures discussed here, remember this: as you finish up and leave the account, no one is following behind you dissecting the mouse carcasses to profile them for pathogenic proteins, viruses or bacteria. Nor is there a medical entomologist combing the pelages searching for mite, tick or flea vectors.

But my guess is that if we could somehow pass a “pathogen Geiger counter” over any of mice you control, we might all be a bit surprised with what would be present yet remains hidden — hidden to us, to physicians, to emergency room doctors and to your clients.

And so too hidden are the benefits that probably are provided to residents and office workers of multiple unit buildings. You are very likely, without knowing it and depending on the thoroughness of your work, alleviating or even eliminating the discomfort of the asthmatic children in the entire apartment building. Or you may be preventing a family, or maybe several families within an apartment complex from contracting LCM or Rickettsialpox.

As a species, humans are very tangible-oriented; we best understand that “what you see is what you get.” This is how we make purchasing decisions for cars, houses, clothing and so forth. Well, what you don’t see is also what you can get. It is the job of the pest professional everywhere to actually help prevent humans from “getting things” whether they are seen or unseen.

If the world of mice and their microbes were more readily visible to us, then for sure those of us working in pest management would be viewed in a different light of community importance by the persons answering the door, or those inside schools, office buildings, hospitals and day care centers that bicker to “get the price down” on those sales contracts associated with top-quality mouse control work.

The author is a leading rodent control specialist and president of RMC Consulting, Richmond, Ind.

Cryptobiotic Mammals

Many of the rodents — especially the commensal rodents — are cryptobiotic animals. This means they possess a biology and behaviors that are “secretive.” Rats and mice are active at night, utilize secluded, hidden or inaccessible areas as harborages, and are attracted to darkened or shadowy areas during activity periods. Additionally, the cryptobiotic nature of these pests is accentuated by their quick movements in response to possible danger and their habit of remaining close to their harborage.

Rodents quickly scurry for nearby cover when they detect vibrations and/or movements, which often enables them to escape capture or detection. It is common for clients to state that they thought they saw something scurry out of the corner of their eye, but when they looked it was gone. Thus, rodents often remain undiscovered by people until their numbers increase. In part, it is this cryptobiotic behavior that is responsible for the public to often perceive that these pests seemingly appeared “from outta nowhere.” Examples of other crytobiotic pests in urban areas include bats, cockroaches, carpenter ants, silverfish and termites.

Editor’s Note: This is an excerpt from Bobby Corrigan’s book “Rodent Control: A Practical Guide for Pest Management Professionals.” To order, call 800/456-0707 or visit www.pctonline.com/store.