Entomology (Study of Bugs)/Rat mites
QUESTION: I am hoping for your advice on how to handle a pest situation that has been ongoing in my apartment for over 6 months. In the fall, I started receiving bites from an unidentified source. (The dermatologist said the skin papules resembled arthopod bites rather than irritation from some environmental allergen, but we couldn't figure out which insect.) After several weeks, one morning I finally caught 4 insects the size of a period crawling on me and my phone. My dermatologist sent one specimen to the USDA which identified it as a tropical rat mite in early December. I told building management which had pest control treat my apartment by spraying a one-time application of Steri-Fab on the floors of my apartment and putting residual products in the baseboard. They also inspected surrounding units for rodents and placed snap traps for rodents and glue traps for additional mites.
Since that December treatment, I have continued to receive similar bites. Pest control has inspected my apartment several times and has not found any mites on glue traps nor evidence of rodent activity near my apartment. As a result, they seem to think that I am no longer suffering from a rat mite problem and that there is another cause for my skin irritation. Based on my layman's understanding of the literature on rat mites, I am not sure that the rat mite problem was completely addressed/eliminated in the first place since pest control never located and eradicated a potential primary host for the mites (rodents). I know from my neighbors that there has been rodent activity recently in other parts of my building.
How likely do you think it is that rat mites are still the source of the problem? Are there any alternate causes (besides rat mites) that we should be investigating?
I should note that we have ruled out fleas and bed bugs. I should also note that my cat is being treated prophylactically with selamectin on a monthly basis and was deemed pest-free by my vet.
Thank you in advance for your help,
Any rodent can serve as host to this group of mites so complete elimination of hosts may not be possible. Certainly host control is important, for a variety of reasons not all related to rat mites. The mites are best managed with normal cleaning since widespread application of insecticide won't be very effective and can in the end be potentially hazardous for occupants of the building. These mites do not generally infest buildings and tend to remain with the host's nest. One more thing to carefully consider - there are many causes of skin lesions that resemble insect/mite bites. Be sure to consider food and respiratory allergies. In my experience allergies are far more likely causes of these reactions than mites, especially since you are no longer finding mites.
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QUESTION: Dr. DeAngelis,
Thank you for your quick response. I have consulted a dermatologist several times since this ordeal began and even before catching specimen she believed that the appearance of the lesions resembled arthopod bites rather than a reaction from food or other respiratory allergies. The identification of the rat mite specimen further strengthened her belief in arthropods as the cause.
Is it possible that there is a host nest nearby that has not been located (e.g., in the walls, crawl spaces between apartments, etc) or even a neighbor's pet rodents? I agree that it is strange that we haven’t caught any more mites, but the continual appearance of new bites seems like evidence they’re still around. It seems possible that the mites' movement pattern would mean that they would not pass over a sticky trap unless it happened to lie directly in the path between where they're entering the apartment and where they are sensing myself and my cat (probably where we spend the most time resting--the bed, the kitchen table, etc).
Assuming mites are still present, do you have any advice for trying to catch a sample? (e.g., places where they tend to cluster, types of traps to use)
ANSWER: There are no traps per se for rat mites. The sticky traps are used but these can be "hit-or-miss". How about a pet rodent that might serve as a sort of "sentinel chicken" (chickens that are used to detect mosquito-borne diseases)? If mites are present they might be attracted preferentially to the rodent where they could more easily be detected.
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QUESTION: Thanks, Dr. DeAngelis. A sentinel rodent is an innovative idea for attracting the mites.
If we do detect more mites, what would the next steps for eliminating the mites be? I know you said earlier that general cleaning helps with mite control, which I assume means regularly steam cleaning/vacuuming carpets, etc. Would a heat treatment (as is sometimes used for bed bugs) work? I am wary of repeating the pesticide treatment because of the concerns you noted above. A heat treatment has the benefit of wider reach/increased effectiveness--reaching much more than what gets sprayed by pesticide in the moment.
It also seems like something needs to be done to locate and eradicate the primary host (rats) or else the mites will keep coming back. I am wondering if rats were trapped inside crawl spaces or walls after autumn rodent proofing, if rodents are somehow still entering the building, or if perhaps even someone's pet rodents are the source. Pest control has put traps into some of the more accessible crawl spaces, but there are some wall spaces that they haven't investigated yet.
I doubt that heat treatments would be very effective and can be very expensive. If mites are entering from the outside then a heat treatment of the living space would miss the source. Also, a regular rodent control programs seems like a good idea in any event.