An Unusual Cause of Rectal Bleeding: Intestinal Myiasis

Abstract

Rectal bleeding is a common problem in pediatric gastroenterology practice. The most common causes in school-age children include anal fissure, infectious colitis, polyps, Henoch-Schönlein purpura, and inflammatory bowel diseases (1). Except for these conditions, some elusive etiologies may also lead to rectal bleeding. In this case report, we present an 8-year-old girl with rectal bleeding due to intestinal myiasis, which persisted despite treatment with purgatives, albendazole, and levamizole. CASE REPORT A previously healthy 8-year-old girl was admitted with intermittent painful and bloody defecations lasting for 1 month. According to her mother's observation blood was either mixed within the stool or dripped after the stool was passed. Rectoscopy was performed in another hospital 2 weeks prior and it was reported to be normal. The patient was then transferred to our department for further evaluation. Her mother periodically observed 8 to 10 moving worms in the child's stool. The girl's vital signs, anthropometric measurements, and physical examination were normal. Complete blood count, peripheral blood smear, erythrocyte sedimentation rate, coagulation tests, biochemical investigations, and urinalysis were within normal limits. Her plain abdominal x-ray and ultrasonography were normal. Microscopic examination of the stool showed abundant erythrocytes and 8 to 10 leukocytes per field, and the stool culture was nonspecific. During the follow-up period 2 active parasite larvae were seen. Fecal samples sent to the Biology Department revealed larvae of Fannia canicularis (Figs. 1 and 2) (stereomicroscope, Leica MZ 7.5 with DFC 280 camera attachment, Leica Applications Suite software, version 2.4.0R1). F canicularis was in the third instar larval stage. It was minute, brown, and flattened dorsoventrally in shape (Fig. 1). The remnant head sclerite was developed; mouthhooks were paired and symmetrical (Fig. 1). Although the ventral was without bristles, a pair of well-developed echinulate spinous processes were present in dorsocentral and laterals of each of the abdominal segments (Fig. 2). The larva had 2 expansions called spiracles that had 3 branches in their apical parts and were on the front of the dorsoanal segment (Fig. 2). The dorsal view of adult F canicularis is shown in Figure 3(2).FIGURE 1: (A) General morphological view of Fannia canicularis. The larva was brown and flattened dorsoventrally (original magnification ×15). (B) Head sclerite is developed; mouth hooks are paired and symmetrical (original magnification ×50).FIGURE 2: (A) A pair of well-developed echinulate spinous processes are in dorsocentral and laterals of each of the abdominal segments (original magnification ×50). (B) The larva has 2 expansions called spiracles that have 3 branches in their apical parts and are on the front of the dorsoanal segment (original magnification ×50).FIGURE 3: Adult Fannia canicularis, dorsal view. (Illustration courtesy of http://www.padil.gov.au use with permission.)Finally, F canicularis was thought to be the cause of the bleeding. The patient was diagnosed as having intestinal myiasis. Even though no specific treatment is valid for the treatment of intestinal myiasis, purgatives, albendazole, and levamizole were reported to cure the disease in some patients (3,4). Therefore, we applied purgatives at first, but because the patient's complaints continued, albendazole 400 mg/day for 7 days was used. Because the treatment with albendazole was not effective, colonoscopy was performed and a fragile mucosa and live larvae were seen on descending colon mucosa. A few could be removed and biopsy samples were taken through the colon. Levamizole 2.5 mg · kg−1 · day−1 was given as a single dose and mesalazine was added to the therapy because of mucosal inflammation detected histopathologically. The patient's complaints decreased after mesalazine therapy. She still used the drug for 1 month, but the mother occasionally observed slight rectal bleeding without larvae in it. DISCUSSION Myiasis is a term used for the invasion of living human or vertebrate animal tissues by the larvae of various dipterous flies that, at least for a certain period, feed on the host's dead or living tissue, liquid body substances, or ingested food (3–5). More than 50 fly species have been reported to cause myiasis in humans. Myiasis infestation can occur in some anatomical sites, including skin, eye, ear, nasopharynx, genitourinary tract, intestine, and in wounds (3,5). The severity of myiasis depends on the location of the infestation. Fannia and its relatives, which differ from other muscid myiasis flies, are placed in a separate family, Diptera: Fanniidae. Fannia is the largest genus in the family of Fanniidae, distributed in all zoogeographic regions of the world, and comprises more than 285 species, the majority of which are from the Holarctic region. F canicularis is widespread around the world, occurring on all of the continents (6). The little housefly breeds in animal excrement or decaying vegetable material. Appendages on the eggs enable them to float on top of semiliquid material. The larvae develop through 3 instars and change from translucent white to brown as they mature. Larval F canicularis is adapted to tolerate a wide moisture range at its developmental site, making it particularly difficult to control. To distinguish among the species it is necessary to examine closely the lateral processes and other characteristics, especially in the posterior region (6). Intestinal myiasis in humans is probably related to ingestion of undercooked food or water containing fly larvae. The presence of numerous larvae in 1 or more consecutive stool specimens is diagnostic (4,7). Some flies may lay eggs in open wounds, larvae may invade unbroken skin or enter the body through the nose or ears, and still others may be swallowed if the eggs are deposed on the lips or on food. Reports about intestinal myiasis in children from all over the world are scarce (8). There are a few reports of intestinal infestation, especially from developing countries such as India (4). Clinical presentation is variable, including asymptomatic cases, abdominal pain, nausea and vomiting, or anal pruritus. Intestinal and urinary myiasis are especially difficult to diagnose (4,9). To the best of our knowledge, there is no report of intestinal myiasis presented with rectal bleeding in the scientific literature. Although intestinal myiasis can be benign or even asymptomatic, it can manifest with severe clinical symptoms, as in the present case report, depending on the number and species of fly larvae and their location within the digestive tract (9). Although intestinal myiasis does not have a specific treatment, no persistent case has been reported so far. Because rectal bleeding without maggots continued after defined treatments, we speculated that histopathologic inflammatory process triggered by the maggots was the cause of ongoing rectal bleeding. Therefore, we decided to use an anti-inflammatory agent that can be effective in colonic disease, mesalazine. In conclusion, we emphasize that myiasis must be kept in mind in differential diagnosis of rectal bleeding, especially in children living in unhygienic conditions.