Delusional infestation by proxy--what should veterinarians do?

Delusional Infestation (DI), also termed Ekbom’s Syndrome or delusional parasitosis, is a psychiatric disorder that manifests as an unshakable false belief of being infested with living or inanimate pathogens. The chief complaint of patients with DI is a rigid belief against all medical evidence that they are infested. Approximately 40% of reported cases are due to a primary psychosis, while the remaining 60% are secondary to neurologic or other psychiatric disorders, side effects of medications, substance abuse, or other metabolic diseases (1). Most commonly, DI manifests as a mono-delusional disorder, where only the patient experiences the delusion on their body. However, variants of this disorder exist, including a shared delusion (also known as folie a deux), in which more than one person believe themselves to be infested, and DI by proxy (DIP), in which the patient projects the delusion onto a third party who usually cannot share the delusion (e.g., a pet, a young child, or a mentally disabled person) (1). Recently, we proposed a third variant, termed a double delusional infestation (DDI) (2), in which the patient believes that both they, and a third party who cannot share the delusion, are infested. There are sporadic case reports of DIP, in which the delusion was projected onto a pet or a child (3–6). Authors have suggested that this is a “rare” manifestation of DI (7). However, recently, we examined this phenomenon via a survey of veterinarians, and identified over 700 cases in which the veterinarian was reasonably convinced that the client was suffering DIP or DDI (2). Thus, from this study, it appears that the disorder, while relatively uncommon in everyday veterinary practice, occurs frequently enough to be of concern to the clinician. Furthermore, because the projection is onto a pet, the client is unlikely to present to a physician or be referred for psychiatric evaluation, explaining the apparent “rarity” of the condition in the medical psychiatric literature. In our study, we examined the courses of action taken by the clinician, both in the initial diagnosis, and in any recommendations that they made by means of a survey amongst 724 veterinarians from several countries (mainly the US and Canada) recruited via the Veterinary Information Network (VIN, www.vin.com) (2). Furthermore, we identified frustration in many of the respondents in not knowing what should or should not be done with clients presenting with suspected DIP. Therefore, based on this study, we have now attempted to provide veterinarians with some guidelines that might assist them in dealing with clients in whom they suspect DIP or DDI.

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