Pests of Medical Interest
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- Delusory Parasitosis
Delusional parasitosis is a psychiatric condition where people have the mistaken belief that they are parasitized by bugs, worms, or other creatures.
The following article was originally published in the September/October 2005 Disease Control Newsletter: Volume 33, Number 5.
Many physicians have encountered patients who claim to be parasitized by mites, fleas, lice, worms, or other unidentified organisms. While some patients may have parasitic infestations, many are suffering from a psychiatric condition known as delusional parasitosis (DP), also called delusions of parasitosis. This condition is the mistaken belief that one is infested by ectoparasites or infected with internal parasites. Often, because of the delusion, it is impossible to convince the patient that the infestation is not real. This article summarizes approaches to diagnosis and treatment of this clinically challenging disorder.
Typically, DP patients are older women, but younger people (including men) can be affected. Other than their delusion, patients usually appear to be normal. Most patients describe the infestation as being on or just under the skin, in or around body openings, or internal (particularly in the stomach or intestines). They often believe that the parasites are also widespread in the environment, especially in their homes. The typical DP patient has suffered from the infestation for some time and has seen numerous physicians and other professionals (eg, parasitologists, entomologists, and exterminators). Many patients describe previously seen medical professionals as uncaring and incompetent. The Minnesota Department of Health (MDH) receives many calls from DP patients with such stories. The calls increase in the winter months coinciding with drier conditions in homes. The patients often submit abundant samples of human tissue, lint, scabs, dust, and other objects for identification as parasites and strongly reject negative findings by those who examine these samples. Self-mutilation can occur in severe cases. The wounds appear in areas accessible to the patient, where they have attempted to excavate the parasites. Many DP patients have tried a long list of remedies, including potentially dangerous levels of pesticides. Patients often have detailed records of their findings, complete with diagrams of the suspected parasite. In some cases, the patient’s medical history is convincing enough that family members secondarily share the delusion. It is also not uncommon to hear accounts of excessive cleaning/ disinfecting of the home environment.
The diagnosis of DP is a lengthy process involving the following steps:
- Take a careful case history.
- Perform a complete physical examination and laboratory evaluation, including skin scrapings and/or biopsies, blood counts, chemistry profile, thyroid function tests, and vitamin B12 levels.
- Rule out other medical conditions (eg, diabetes, atopic dermatitis, and lymphoblastomas) with skin manifestations that can appear to be caused by arthropods.
- Work with entomologists or parasitologists to rule out true infestations (eg, scabies mites, animal mites, lice, fleas, and bed bugs).
- Rule out other organic causes (eg, allergies and contact dermatitis).
- Rule out history of drug abuse (especially in younger or male patients).
The most effective management of DP cases is a team approach among health care providers, dermatologists, psychiatrists, and entomologists or parasitologists. The primary health care provider should take the lead in incorporating all of the above disciplines into the patient’s care. The provider should take special care in suggesting to the patient that he or she may be suffering from a mental disorder. While there is often resistance by patients to seek psychiatric help, many will do so if they are told that psychiatrists may help them to live better with their parasite problem. Psychiatrists are needed to confirm the diagnosis and to provide long-term treatment, including therapy with antipsychotic drugs such as pimozide. Healthcare providers should avoid empiric treatment with lice or scabies medications without evidence of an infestation, as this may exacerbate the condition. MDH is available to help identify unknown arthropods that are submitted through a physician.
Significant portions of this article were adapted from two references that provide more detailed discussion and additional references:
- Murray, WJ. Delusional parasitosis. Clin Microbiol Newsl. 2004;26:73-77.
- University of California, Davis, Bohart Museum of Entomology. Delusional parasitosis.
Accessed September 2005.