---
title: "Understanding Parasitic Identification in Delusional Parasitosis"
id: "plos-one-21-bridging-perception-and-reality-parasitic-identification-in-delusional"
canonical_url: "https://medichelpline.com/clinical-feed/plos-one-21-bridging-perception-and-reality-parasitic-identification-in-delusional"
content_type: "clinical_feed_article"
specialty: "Infectious Disease"
source_name: "PLOS ONE (Medicine)"
source_url: "https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0358452"
published_at: "2026-09-18T14:00:00.000Z"
evidence_level: "Journal Feed"
license: "CC-BY-NC-4.0 / Informational Use"
---
# Understanding Parasitic Identification in Delusional Parasitosis
## Provenance & Clinical Metadata
- **Canonical URL:** https://medichelpline.com/clinical-feed/plos-one-21-bridging-perception-and-reality-parasitic-identification-in-delusional
- **Specialty:** [Infectious Disease](https://medichelpline.com/clinical-feed/infectious-disease.md)
- **Primary Source:** PLOS ONE (Medicine)
- **Source URL:** [Original Journal Publication](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0358452)
- **Published At:** 2026-09-18T14:00:00.000Z
- **Evidence Rating:** Journal Feed
## Executive GIST (TL;DR)
- **Delusional parasitosis (DP)** is a psychiatric condition where individuals believe they are infected with **parasites**. - Patients often submit samples containing nonparasitic materials for examination, complicating diagnosis. - In a study of **382 clinical specimens**, only **28.3%** were found to contain actual parasites, including species like _Trichuris trichiura_ and _Enterobius vermicularis_. - The remaining samples mostly included artifacts such as food residues and synthetic fibers. - Notably, **84 patients** were diagnosed with DP, highlighting the need for improved **diagnostic protocols** and interdisciplinary communication. - Effective laboratory identification of true parasitic infections is vital to prevent misdiagnosis and subsequent unnecessary treatments.
## Clinical Analysis & Structured Key Points
Bridging perception and reality: Parasitic identification in delusional parasitosis | PLOS One Browse Subject Areas ? Click through the PLOS taxonomy to find articles in your field. For more information about PLOS Subject Areas, click here . Article Authors Metrics Comments Media Coverage Reader Comments Figures Figures Abstract Background Delusional parasitosis (DP) is a psychiatric condition in which individuals hold a fixed, false belief that they are infected with parasites. These patients frequently consult parasite clinics and submit household or biological debris, often nonparasitic in origin, for parasitological examination. Although parasitologists are not directly responsible for treating this psychiatric disorder, they play a key role in identifying or excluding parasitic infections and guiding appropriate care. Misidentification of artifacts as parasites may result in unnecessary treatment, prolonged distress, and, in some cases, delayed diagnosis of DP. Thus, this study examined specimens submitted for parasitological diagnosis with the aim of assessing diagnostic accuracy and evaluating the role of laboratory confirmation in managing suspected parasitic infections. Methods This retrospective study analyzed 382 clinical specimens submitted for parasitological examination to the Department of Helminthology, Faculty of Tropical Medicine, Mahidol University (June 2014–June 2022). All specimens were examined macroscopically and microscopically using standard parasitological techniques. Results Parasitic infections were present in 108 (28.3%) specimens, including nematodes, cestodes, and trematodes, such as Trichuris trichiura , Enterobius vermicularis , hookworm, and Taenia spp. The remaining 274 (71.7%) specimens included negative fecal specimens and specimens comprising various artifacts, such as food residues, plant materials, synthetic fibers, skin flakes, and other debris. This study was concurrently performed using outpatient data obtained from the Parasite Excellence Clinic, Hospital for Tropical Diseases, Faculty of Tropical Medicine, Mahidol University. Notably, 84 patients were ultimately diagnosed with DP. Conclusions Accurate parasite identification is crucial to ensure proper treatment in true parasitic infections and prevent DP misdiagnosis. This study highlights the importance of an integrated parasitology–psychiatry approach, particularly when patients present with persistent symptoms despite negative laboratory test results. These findings support the establishment of diagnostic protocols and improved interdisciplinary communication to enhance care for patients with suspected parasitic infections. Citation: Yoonuan T, Piyaphanee W, Srinukham S, Wonguten U, Charunwatthana P, Watthanakulpanich D (2026) Bridging perception and reality: Parasitic identification in delusional parasitosis. PLoS One 21(9): e0358452. https://doi.org/10.1371/journal.pone.0358452 Editor: Marcello Otake Sato, Niigata University of Pharmacy and Medical and Life Sciences, JAPAN Received: April 14, 2026; Accepted: September 1, 2026; Published: September 18, 2026 Copyright: © 2026 Yoonuan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The datasets generated and/or analyzed during the current study contain potentially sensitive patient information, and are therefore not publicly available due to ethical and legal restrictions. Researchers who meet the criteria for access to confidential data may submit a request to the Office of the Ethics Committee for Human Research, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand. For any request for data relevant to this paper, please contact this email: tmectropmed@mahidol.ac.th . All Images relevant to this study are available as Supplementary Material accompanying this article. Funding: The author(s) received no specific funding for this work. Competing interests: The authors have declared that no competing interests exist. Introduction The increasing accessibility of health information online has led many patients to self-diagnose based on symptoms. Although the availability of information empowers patients, it also creates diagnostic challenges when expectations are unmet by laboratory test results. Patients often attribute unexplained symptoms to parasitic infections and seek laboratory test confirmation at specialized centers. However, despite repeated negative test results, some patients persist in their beliefs, raising suspicion of DP (DP; also known as Ekbom syndrome) [ 1 ]. DP is defined as a fixed false belief of infection in the absence of objective evidence, such as parasites, insects, vermin, or maggots, that persists for at least 1 month [ 2 – 5 ]. It is also referred to as dermatophobia, parasitophobic neurodermatitis, parasitophobia, or entomophobia [ 6 , 7 ]. DP is frequently associated with tactile and olfactory hallucinations, anxiety, and self-inflicted lesions [ 8 ]. However, clinical functioning is not markedly impaired, and behavior and personality show no apparent deterioration [ 9 ]. Furthermore, DP does not result from the direct physiological effects of a substance (e.g., a drug of abuse or a medication) or a general medical condition. There are two types of DP: primary DP, which is idiopathic, and secondary DP, which is either functional (associated with schizophrenia, paranoia, depression, and anxiety disorders) or organic (due to drug abuse, hypothyroidism, cancer, cerebrovascular disease, tuberculosis, neurologic disorders, vitamin B12 deficiency, or diabetes mellitus) [ 10 – 12 ]. Thus, accurate laboratory diagnosis is critical, not only for confirming true parasitic infections but also for ruling them out, which is essential for appropriately managing suspected DP [ 10 , 13 ]. Although psychiatric in origin, DP frequently presents in parasite clinics in Thailand, likely due to public perception, accessible parasitological services, and prevailing cultural beliefs. This study investigates the types of specimens submitted for parasitological analysis, the outcomes of those examinations, and how laboratory test results influence clinical management. Special attention is given to persistently negative cases, where DP should be considered as a diagnosis. The present study aimed to evaluate the role of parasitological examination and morphological identification in distinguishing true parasitic infections from pseudoparasitic or non-parasitic materials among patients with suspected parasitosis, particularly those later diagnosed with DP. In addition, this study sought to characterize the types of submitted specimens, patterns of specimen referral, and demographic characteristics of patients presenting with suspected parasitic infections at the Hospital for Tropical Diseases, Faculty of Tropical Medicine, Mahidol University, during an 8-year retrospective period. Materials and methods Sample collection and analysis From June 2014 to June 2022, 382 clinical specimens were analyzed by the Department of Helminthology at Mahidol University, including 122 specimens from internal sources (Parasite Excellence Clinic and Inpatient Department, Hospital for Tropical Diseases, Faculty of Tropical Medicine, Mahidol University) and 260 specimens from external sources (private laboratories and other hospitals). Fecal samples were examined for helminth eggs using the Kato–Katz method and simple smear technique. Strongyloides stercoralis was detected using either agar plate or polyethylene tube culture techniques [ 14 , 15 ]. Nonfecal samples and foreign objects were examined using stereomicroscopy. Body fluid samples were centrifuged, followed by microscopy examination of the sediment. Microscopy and identification Specimens submitted by patients were examined by experienced parasitologists from the Department of Helminthology, Faculty of Tropical Medicine, Mahidol University. Personnel involved in specimen identification had formal training in medical parasitology and extensive experience in the morphological identification of helminths and pseudo-parasitic materials encountered in clinical practice. Identification procedures were performed using standard parasitological techniques, including stereomicroscopy, light microscopy, together with established taxonomic keys and diagnostic references. All specimens were systematically accessed for characteristic parasitic morphology, including egg morphology (3S: size, shape, shell, 2C: color, content), as well as the presence of specific characteristics such as esophagus configuration, proglottids, larvae, suckers, spines, cephalic alae, cervical alae, and bursae. Accurately morphological identification requires both technical expertise and rigorous quality control procedures. Ambiguous, unusual, or fragmented specimens were reviewed and cross-checked among experienced senior personnel to minimize diagnostic uncertainty. Representative specimens were photographically documented and archived as reference materials when appropriate, and routine comparison with established morphological criteria was performed. Continuous training in helminth morphology and diagnostic parasitology was also emphasized to maintain diagnostic competency. Particular attention was paid to differentiating true parasitic organisms from non-biological materials and environmental contaminants, including synthetic fibers, plant materials, arthropod larvae, and other pseudoparasitic objects that may resemble helminths macroscopically or under low magnification. These quality control measures were especially important in DP-related submissions, where misidentification could reinforce false beliefs, delay psychiatric intervention, or lead to unnecessary antiparasitic treatment. Patient data collection and sample inclusion Patients’ demographic data (age and sex) and clinical characteristics were obtained from the Medical Record Department at the Hospital for Tropical Diseases, Faculty of Tropical Medicine, Mahidol University. Due to ethical considerations, these data are not publicly available. Data were accessed for research purposes between 13/06/2024 and 15/09/2024. A formal prospective sample size calculation was not initially performed because this retrospective observational study employed a consecutive inclusion (total sampling) approach, whereby all eligible specimens submitted between June 2014 and June 2022 were included. However, to assess the adequacy of the analyzed sample, a post hoc estimation for prevalence studies was performed using the formula n = Z2P(1−P)/d2n = Z^2P(1-P)/d^2n = Z2P(1−P)/d2. Due to limited epidemiological data regarding delusional parasitosis-related specimen submissions, a conservative expected proportion of 50% was applied with a 95% confidence level and 5% precision. The estimated minimum sample size was 384 specimens, which was comparable to the final analyzed dataset of 382 specimens. Ethical considerations This retrospective study used data from medical records. The study was approved by the Faculty of Tropical Medicine Ethics Committee, Mahidol University (MUTM 2024-047-01), approved on 12 June 2024). All data were fully anonymized before being accessed for research purposes. Results Outcomes of parasitological examination Of the 382 analyzed specimens, 108 (28.3%) tested positive for parasites, cestodes and nematodes were the most frequently identified helminths including Trichuris trichiura , Enterobius vermicularis , Hymenolepis nana , and Taenia spp. which hookworms and Taenia spp. represented the largest proportion of submitted intact or partially worm specimens. Most positive identification were achieved through preserved characteristic morphology despite fragmentation or partial degradation of the submitted specimens. The remaining 274 (71.7%) specimens included negative fecal and body fluid specimens or specimens of nonparasitic materials, such as plant debris, undigested mushrooms, synthetic fibers, and nonparasitic organisms ( Table 1 ). Download: PNG larger image TIFF original image Table 1. Type and number of specimens submitted to the Department of Helminthology, Mahidol University, for parasitological examination. https://doi.org/10.1371/journal.pone.0358452.t001 Among the positive cases, all specimens containing worms, some of which only consisted of fragments, were carefully examined and identified based on specific morphological characteristics. Among the 35 partial worm specimens, certain morphological characteristics remained preserved, facilitating identification. One specimen contained creamy-colored fragments that were long, thin, and thread-like, with a width < 0.5 mm. Microscopic examination revealed a stichosomal esophagus. Although the posterior end of the worm was absent, these features were sufficient to identify the specimen as Trichuris spp. ( Fig 1A ). Another specimen was identified as E. vermicularis . Although it was incomplete, approximately one-third of the body was present, and microscopic examination revealed a portion of the uterus containing numerous D-shaped eggs, characteristic of E. vermicularis ( Fig 1B and 1C ). Both male and female specimens of the zoonotic hookworm Ancylostoma ceylanicum were identified ( Fig 1D – 1F ). Other specimens identified based on preserved distinct morphological features included Gnathostoma larvae ( Fig 1G ), Dirofilaria spp. ( Fig 1H ), Diphyllobothrium latum ( Fig 1I ), and Taenia spp. ( Fig 1J , 1K ). One specimen consisted of a tiny strobila, ~1 cm long, composed of gravid proglottids, each <1 mm wide. The segments contained colorless eggs measuring 30–40 µm in diameter, with an oncosphere and characteristic polar filaments. These features were consistent with H. nana . Although Anisakis spp. is an uncommon parasite in Thailand, four larval specimens from a Japanese patient were submitted by an external laboratory ( Fig 1L and 1M ). Among the 161 fecal samples submitted, 10 (6.21%) contained helminthic eggs. Download: PNG larger image TIFF original image Fig 1. Specimens submitted to the laboratory. (A) partial worm specimen of Trichuris spp.; (B) partial worm specimens of E. vermicularis ; (C) magnified detail of (B) showing a D-shaped egg of E. vermicularis ; (D) buccal capsule of Ancylostoma ceylanicum showing teeth; (E) posterior end of female hookworm; (F) posterior end of male hookworm; (G) Gnathostoma larva; (H) Dirofilaria spp.; (I) short strobila fragment of Diphyllobothrium latum ; and (J) segment of Taenia spp.; (K) gravid proglottid of Taenia saginata showing uterine branches; (L) Anisakis spp.; (M) showing the mucron of Anisakis spp.; (N–P) plant fragments (N-O, Enokitake mushroom ( Flammulina velutipes )); (Q–U) non-helminthic organisms, and (V) a common blind snake ( Indotyphlops braminus ). https://doi.org/10.1371/journal.pone.0358452.g001 The most commonly submitted specimens were nonhelminthic foreign objects. Several specimens contained undigested plant fibers ( Fig 1N – 1P ), such as the Enokitake mushroom ( Flammulina velutipes , also known as the golden needle mushroom). When consumed, Enokitake mushrooms are not always fully digested, resulting in the excretion of visible, long, slender stalks and small caps in the feces. Other nonhelminthic specimens included larvae collected from toilet water. These larvae typically exhibited segmented bodies, sometimes with pairs of prolegs or legs, as well as anal setae and antennae. Vermiform larvae, such as midge larvae from the order Diptera, were also observed. Other samples resembling worms were identified in specimens collected in bathrooms or flush toilets ( Fig 1Q – 1U ). There were a few cases of juvenile earthworms. One live, worm-like specimen, dark brown in color and showing active movement, was received with a note requesting identification to determine whether it was an Ascaris worm. Mouthpart examination revealed the absence of three lips. The specimen had two tiny black eye-like dots and scaled skin, identifying it as a common blind snake ( Indotyphlops braminus ) ( Fig 1V ). Other nonhelminthic submissions included synthetic fibers ( Fig 2A ), crusted discharge ( Fig 2B – 2D ), unidentified objects ( Fig 2E – 2G ), plant fiber ( Fig 2H ), loofah fragments ( Fig 2I ) and small rolls of wet tissue paper ( Fig 2J ). These items were often submitted wrapped in tissue paper ( Fig 2K ) and placed in household containers, including cosmetic jars, drinking water bottles, and ziplock plastic bags ( Fig 2L – 2O ). Download: PNG larger image TIFF original image Fig 2. Other nonhelminthic submissions from patients diagnosed with delusional parasitosis. (A) fiber; (B-D) crusted discharge; (E-G) unidentified objects, (F, magnified detail of E); (H-I) plant fiber (I, loofah); (J) pieces of roll wet tissue; and (K-O) containers. https://doi.org/10.1371/journal.pone.0358452.g002 Temporal trends and referral patterns Although 108 specimens (28.3%) were confirmed to contain parasites, most submissions (274/382, 71.7%) consisted of non-parasitic materials, degraded specimens, environmental contaminants, or specimens in which no parasites were detected. These findings indicate that most submitted materials represented pseudoparasitic or nonhelminthic objects rather than true parasitic infections. The pattern of specimen submissions also reflected increasing referrals of patients with persistent concerns regarding parasitic infections, particularly among individuals later diagnosed with DP. Many patients repeatedly sought parasitological confirmation despite previous negative investigations and submitted a wide variety of materials collected from feces, skin, bathrooms, household environments, and personal belongings. Some patients attended the clinic on several occasions or submitted recurrent specimens through external hospitals and laboratories before a final diagnosis of DP was established. These repeated consultations and persistent parasitic concerns illustrated the prolonged diagnostic trajectory commonly encountered in DP patients and highlighted the challenges in distinguishing true parasitic infection from delusional infestation in routine clinical practice. Distinct differences were observed between specimens submitted by DP patients and those from patients with confirmed parasitic infections or transient non-DP concerns. Confirmed parasitic infections most commonly involved intact worms, partial worm fragments, fecal specimens containing eggs, or other clinically relevant biological samples. In contrast, DP patients more frequently submitted non-biological or environmental materials, including synthetic fibers, plant debris, tissue fragments, crusted discharge, wet tissue paper, insect larvae, and household contaminants. Synthetic fibers and textile-like materials were particularly common and were often perceived by patients as motile or invasive organisms. Plant fibers and undigested food residues, especially mushroom fragments, also represented recurrent source of misidentification. The relatively low proportion of positive findings among fecal specimens (10/161, 6.21%) contrasted markedly with the high proportion of positive identification among submitted partial worms or worm fragments (94/96, 97.9%), highlighting the importance of morphological expertise in the identification of fragmented helminthic specimens. In contrast, all worm-like materials and insect larvae submitted by patients (74/74) were ultimately determined to be non-parasitic or unrelated to human helminthic infection. Demographic data and parasitic prevalence According to data from the Medical Record Department, Hospital for Tropical Diseases, Faculty of Tropical Medicine, Mahidol University (2014–2022), among the 4,055 patient records, 868 patients with susp
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