Dealing with Delusional Infestation
During the winter months, the number of samples submitted to the Utah Plant Pest Diagnostic Lab dramatically decline. This time of year, though, there is an increase in one particular type of pest problem-those that don’t actually exist. I am referring to a medical condition known as Delusory Parasitosis, or Delusional Infestation (DI). A delusional state is a psychological disorder defined as a false belief based on incorrect inference about external reality that persists despite evidence to the contrary. People with delusional infestation believe that they, their belongings, house, family, etc., are infested with arthropods. Only medical doctors are able to diagnose DI and prescribe medications or therapies that may help control the delusion, but diagnosticians and Extension personnel need to know how to recognize the signs of this condition and how to deal with people suspected to suffer from DI. Straightforward communication with suspected sufferers may encourage them to seek appropriate treatment.
First, it is critical for diagnosticians to recognize DI symptoms (see Table 1 for a list of common symptoms). People with DI often fail to provide samples containing pests (Fig. 1 & Table 2), but can provide vivid and detailed descriptions of their morphology, life cycle, and habits. If the pest description sounds odd, continue to ask questions. Usually, they will describe pests that defy science or that fall outside of what is possible for arthropod life cycles and habits; sometimes they will describe excessive pest control measures applied to their living space or body. The role of a diagnostician is only to examine samples for the presence or absence of arthropods. If human or animal parasites (e.g., fleas, lice, etc.) are detected, recommend that they consult a physician or veterinarian (if the source is a pet) for treatment.
In the case of DI, actual arthropods are rarely found. When a client with suspected DI has submitted a sample I give a simple diagnosis: “there were no arthropods present in the submitted sample.” Usually, more samples will be submitted in which the client insists contain the pest. Again, I inspect the sample and give a simple response. After the 3rd or 4th submission, I provide the client with the USU fact sheet on human parasites, which discusses DI in detail. Most of the time, the client does not agree with the diagnosis.
Most importantly, never agree with the client that an arthropod is present if it is not; this will only perpetuate their delusion. Try and persuade the client to accept non-arthropod possibilities for their problems, such as environmental irritants, medical diseases/conditions, medication side effects or interactions, depression, emotional stress, etc. (see our fact sheet “Human Parasites” for a complete list). Ultimately, these clients should be diagnosed and treated by a psychiatrist.
For a more detailed discussion of DI, visit the link to our fact sheet provided above. If you have access to online journals, a 2009 publication in Clinical Microbiology Reviews by Freudenmann and Lepping summarizes over 500 articles on DI.
-Ryan Davis, Arthropod Diagnostician