Mice Just As Important As Roaches In Allergy Studies

In the June 1997 issue of PCT, an article titled “Cockroaches Implicated in Childhood Asthma” discussed a paper presented in the New England Journal of Medicine. The article reviewed some of the results of the National Collaborative Inner-City Asthma Study (NCICAS) as to the sig-nificance of cockroach infestations and children allergies in inner-city areas. Well, now enter yet another important pest of inner-city dwellings: the house mouse.

At the American Academy of Allergy, Asthma and Immunology annual meeting in March 1999, researchers presented the results of a study that shows mouse allergen to be a major cause of asthma and allergic rhinitis in susceptible individuals in inner-city homes. This research is also being conducted by scientists from the Johns Hopkins Hospital in Baltimore working together with the National Collaborative Inner-City Asthma Study Group (NCICAS). An abstract of the study was released along with several other papers (including an update on cockroach allergens) on the Internet recently. The meeting abstract stated that these researchers discovered high levels of mouse allergens in several inner-city homes across the country.

THE STUDY. The scientists collected 1,969 dust samples from the homes of 663 asthmatic children from eight major cities. Samples were collected in the bedroom, kitchen and TV/living room. Samples were analyzed for the major mouse allergen, MUP (major urinary protein). Puncture skin tests of the asthmatic children showed that 18% of the children had sensitivity to mice and 20% of the children had sensitivity to rats. Within all homes, 95% of the children had detectable mouse allergen in at least one room with the highest levels found in the kitchens.

Baltimore homes showed the highest levels, with mouse allergens detected in 100% of sampled homes with a kitchen median of 7,865 samples. Other cities studied included Detroit (94%, 4,140); Bronx, N.Y. (99%, 4,068); St. Louis (100%, 1,960); Harlem, N.Y. (93%, 1,260); Washington, D.C. (96%, 734); Chicago (95%, 371); and Cleveland (86%, 325). Incidentally, these are the same cities that were part of the NCICAS study on inner-city cockroach allergens.

Although there will be many questions generated by these findings, the initial significance of this research cannot be understated. In inner-city areas, the house mouse is a major pest — particularly within multi-family housing complexes. In fact, since the advent of highly effective cockroach baits, the mouse in many cities has replaced the German cockroach as the number one pest in inner-city buildings. The mouse invades our homes, workplaces, schools, restaurants, warehouses and health care facilities. Indeed, few urban buildings are immune to having a mouse (or many mice) invade the structure sometime during the course of the building’s lifetime.

CONDUCIVE CONDITIONS. But what factors render inner-city areas so vulnerable to chronic, perpetual mouse infestations? First, mice in these areas have existed in all probability since the earliest days of the city itself. Thus, the mice populations are widespread throughout the city. Many of the mice we are attempting to control today are descendants of mouse populations stretching far back in history. Second, inner-city areas are structurally and enormously complex environments. Consider the three dimen-sional resource availability of the small mouse relative to nesting zones, protection from predators, finding food and hidden travelways. When cities are built and undergo literally thousands of structural (new buildings, remodeling, add-ons, etc.) and infrastructure (sewers, utility systems, roadways, etc.) improvements year after year, we in fact also create thousands of harborage spaces for mice. Many of these spaces remain, for the most part, inaccessible to us.

What’s more, when mice move into our dwellings, they often exist with us in an intimate proximity. The mouse invades our kitchens, bedrooms, closets and even the furniture upon which we relax and sleep.

In the kitchen, the room most reported in the NCICAS study to contain mouse allergens, the mouse typically nests within the bases of cabinets, stoves and refrigerators. The mouse makes daily forays within our cabinets, across counter tops, as well as commonly trampling upon and contaminating cooking implements and utensils. Mice living within bedrooms may deposit urine all along the baseboards underneath beds, as well as on the bed and bedding itself. Similarly, within the living rooms, the areas behind and beneath the sofa are often well-traveled (and “marked”) by mice.

Consider that mice typically urinate in micro-droplets in many, many spots as they forage and travel over their territories. Within a typical mouse infestation, literally thousands of micro-areas of surfaces can be covered with mouse urine. Thus, a chronic infestation of mice within an inner-city dwelling over many years clearly indicates a potential for an accumulation of mouse urine. In heavily infested ac-counts, most pest management pro-fessionals can attest to the readily noticeable “mousey odor” which is basically a result of accumulating mouse urine.

ALLERGY DISEASE CONSIDERATIONS. The ramifications of a study implicating the house mouse in allergy disease — or any other disease — is a matter which must be given serious consideration by city governments and associated health departments. In fact, compared to mouse control, cockroach control these days is actually easier in many ways than controlling mice. Typically the cockroaches are a contained population within a home or an apartment and can now be eliminated via a thorough application of baits and an ongoing monitoring program. With mice, because of the relatively large distances they can move, as well as the many secretive harborages and travel pathways available to them, the immigration potential of the mouse into inner-city buildings is much greater than that of the cockroach. Long-term control of mouse populations in city environments requires a truly proactive program. In addition to baiting or trapping efforts, such programs must include rodent-proofing programs of not only doors, but also utility systems leading into buildings. Unfortunately, many typical mouse control programs in our city apartments, office complexes and restaurants involves a reactive approach of installing a trap or bait when a mouse is spotted. This response is more a harvesting of mice than a control pro-gram. In homes containing allergen- sensitive individuals, harvesting programs will not suffice.

Dr. Robert Corrigan be reached at 765/939-2829.