Perspectives: Delusional Parasitosis

CDC Yellow Book 2024

Posttravel Evaluation

Author(s): Susan McLellan

Delusional parasitosis (DP) is the term most often applied to a condition in which a patient presents to a health care provider with an established conviction that they are infected with an arthropod or parasite. Although not unique to travelers, many of those who present with DP have a history of travel, and travel and tropical medicine specialists often assist in evaluating these patients at the request of colleagues.

Clinical Presentation

Primary DP is diagnosed when no underlying medical conditions typically associated with disordered thinking are present. Affected people frequently were previously successful in their professions, relationships, and other activities. In the absence of a prior history of a mental health disorder, DP is considered only after multiple visits for care. Symptoms (e.g., itching, skin sensations) are most common and lead to a preponderance of literature from the dermatologic field. Clinical manifestations also can be neurologic (e.g., “brain fog,” fatigue, pain, weakness); gastrointestinal (e.g., constipation, diarrhea, sensation of movement in the gut); and auditory or visual. Morgellons syndrome is a specific variant in which sufferers see fibers emerging from the skin.

Secondary DP occurs in association with identifiable health conditions (e.g., alcoholism, bipolar disease, severe depression, drug abuse, schizophrenia, syphilis, thyroid disorders, vitamin deficiencies). In such cases, treatment of the underlying condition might resolve the fixation on parasite infestation.

Unique to DP is the conviction that the illness is due to a parasite, and the frequent auditory or visual identification of it; patients often can describe or draw the organism (“a blue and black body with 8 legs”) or define activity and intent (“they buzz when they get angry”). Submitting multiple specimens collected from clothing, orifices, skin, stool, toilets, and around the house is common (the “specimen sign”). With the advent of mobile phones, we now also have the “digital specimen sign,” photographs of skin lesions and purported parasites. In many cases, family members or friends are drawn into the delusion in a “folie a deux”; in a more disturbing scenario, a parent might project the delusion onto a child, resulting in potentially harmful attempts to cure the illness.

People suffering from DP can present without objective physical manifestations, or, in the classic dermatologic case, with few to extensive skin lesions attributed to the parasite. Patients might have tried multiple home therapies, including potentially toxic applications or injections (e.g., pouring permethrin in the ears to quell the buzzing of the insects, as reported by one of my patients). Patients often are prescribed empiric treatments for parasitic or arthropod infections by well-meaning practitioners. These treatments are rarely successful, but they are often reported to have provided temporary symptomatic relief—a placebo effect reinforcing the patient’s erroneous belief that they are infected with a parasite.

Often, the next step is referral to a specialist, with the hope on the part of the referring provider that “they will know something I don’t,” “the patient will believe Dr X,” or “Dr X will assume care of the patient.” Eventually, depending on their presentation, description of symptoms, and the number of practitioners seen, a patient with DP will have undergone multiple examinations of specimens, biopsies of skin or other body parts, colonoscopies, imaging, and laboratory evaluations, none of which reveals a reasonable parasitic cause for their symptoms, and which are usually all “normal.”

Suggestions to consider alternative diagnoses are rarely accepted; in particular, recommendations that the patient try psychiatric medications, even just for symptom relief, are frequently met with anger and rejected out of hand. Both patient and practitioner become frustrated; the patient feels they are being told “it’s all in your head,” and the practitioner is exhausted from the attempt to be compassionate and medically appropriate while faced with an often angry and occasionally insulting patient.

Approach & Management

Therapy for DP has relied on the use of antipsychotics. Pimozide, which selectively blocks dopamine type-2 receptors, was the drug first reported to be useful in the condition, and several series indicated a good response in most patients who accepted it. Currently, second-generation antipsychotics (SGAs) are preferred because of a lower side effect profile; no randomized clinical trials are available, however, and reported cases suggest similar efficacy.

Hence, our paradoxical “state of the art” is to treat a patient who is convinced that they do not have a mental health issue with a recognizable antipsychotic. Getting to a point where the patient will consider such medication takes nuanced communication, sympathy, and a great deal of time over multiple appointments. Referral for psychiatry consultation is notoriously unsuccessful. How best to approach the patient who presents with a fixed conviction that they have a parasite, then? Two concrete characteristics are necessary for a successful therapeutic relationship to develop: (1) the provider must be willing to take on a patient who will be complicated, emotionally challenging, needy, and time consuming; and (2) the patient must be willing and able to maintain a relationship and follow up with the provider, meaning the provider must be both geographically and financially accessible.

Ideally, the patient has a primary care provider (PCP) who can act as the long-term caregiver and assure that any other medical needs are being addressed in an integrated manner. Unfortunately, in many cases, the DP sufferer has rejected early providers and is at the stage of traveling long distances to seek out “experts” with whom they cannot feasibly establish an ongoing relationship. In such cases, one approach is for the “expert” to require that the patient identify a PCP, and to discuss the case with them with the goal of education and support, to assure a reasonable work-up for true parasites or any other underlying reversible causes, and to assist and guide them in working with the patient. Such long-distance consultation might enable rebuilding of the PCP–patient relationship with assurance that the “experts” are guiding the diagnostic and therapeutic approach.

Whichever provider accepts a patient with potential DP, a long-term relationship should be expected. Moriarty et al. have suggested a thoughtful, phased, multi-visit approach in which the health care provider takes the patient through the stages of considerate but strategic history-taking, managed expectations, appropriate diagnostic approach, and eventual introduction and maintenance of antipsychotic therapy. Low doses of medication are usually effective in improving or resolving symptoms, but maintenance should continue for months, and relapse is common. See Box 11-03 for a list of additional considerations.

Treating patients with DP can be exhausting and frustrating, and it is easy for practitioners to dismiss these patients as out of their scope of expertise and disruptive to their usual practice. If a relationship of trust can be maintained, however, pharmacologic therapy combined with ongoing behavioral support can be successful in reversing a debilitating condition. Primary care providers should be encouraged and enabled to provide these interventions; specialists with experience in DP can be invaluable as mentors, even from a distance.

Box 11-03 Delusional parasitosis: management suggestions for health care providers


Allow the patient to tell their story but set limits on expectations for each visit.
Assure patients they are not alone in having these kinds of problems (e.g., “We have seen this before and have been able to help.”).
Neither agree nor argue with patients about the delusion itself, but affirm the severity and significance of the symptoms they describe.


Do not be distracted by the patient’s interpretation of cause; pay attention to the history and consider alternative conditions that can cause similar symptoms.
Review records, including all medications, both prescribed and over the counter; obtain basic laboratory studies and thyroid function and sedimentation rate; consider hepatitis and HIV testing, syphilis serology, toxicology, vitamin deficiencies.
Send specimens brought in for formal analysis; allow the patient to choose the best examples.


Reassure patients about the results of basic laboratory tests (e.g., “The labs we have done indicate that your bone marrow, kidneys, liver, thyroid, etc., are all healthy and working properly.”).
As clinical reports return indicating no parasites found in specimens and no other underlying pathologies, introduce the idea of symptom control as a strategy (e.g., “We know it is safe to focus on symptoms even if we haven’t found the cause.”).
Don’t make a distinction between mental and physical health; instead, discuss the growing understanding of the mind–body connection and how we are just learning about how neurologic signaling affects our bodily well-being.
Explain the use of an antipsychotic drug in terms of addressing the mind–body connection (e.g., “You don’t have schizophrenia, but this medication has helped people who have the same kind of problem; we don’t yet fully understand how or why it works.”).
As much as possible, recruit the patient’s family and friends to help the patient normalize what might have been a severely disrupted life.

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Moriarty N, Alam M, Kalus A, O’Connor K. Current understanding and approach to delusional infestation. Am J Med. 2019;132(12):1401–9.

Munro A. Monosymptomatic hypochondriacal psychosis manifesting as delusions of parasitosis. Arch Dermatol. 1978;114(6):940–3.

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Söderfeldt Y, Groß D. Information, consent and treatment of patients with Morgellons disease: an ethical perspective. Am J Clin Dermatol. 2014;15(2):71–6.

Suh KN, Keystone JS. Delusional infestation (delusional parasitosis). In: Ryan ET, Hill DR, Solomon T, Aronson NE, Endy TP, editors. Hunter’s tropical medicine and emerging infectious diseases, 10th edition. Philadelphia: Elsevier; 2020. pp. 1132–6.

. . . perspectives chapters supplement the clinical guidance in this book with additional content, context, and expert opinion. The views expressed do not necessarily represent the official position of the Centers for Disease Control and Prevention (CDC).