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Intestinal Myiasis -- Washington

In June and August 1984, the mother of a 12-month-old Washington girl periodically observed "moving worms" in the child's stool. The child was asymptomatic. She was treated by her physician for a presumptive diagnosis of pinworm infection, first with pyrvinium pamoate and then with piperazine. However, the mother continued to see "worms" in the child's stool. In early September, fly larvae (maggots) were seen in each of two stool specimens collected on different days. These larvae were identified as living third-instars of Muscina stabulans, the false stable fly. Examinations of stool specimens from other family members showed no larvae. Careful questioning about the child's dietary history revealed that she was fed over-ripened bananas, which were kept in a hanging wire basket in the kitchen. Flies were frequently observed on and around the fruit. No treatment was prescribed, but the parents were instructed to cover all fruit kept in the house and to wash it before consumption. By the end of September, the mother ceased to find larvae in the child's stool. Reported by KL Matteson, DE North, S Helgerson, MD, Seattle-King County Dept of Public Health, EP Catts, PhD, Washington State University, Pullman, L Baum, Dept of Social and Health Svcs, J Kobayashi, MD, State Epidemiologist, Washington State Dept of Health; Div of Parasitic Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Myiasis is the infestation of live human and vertebrate animals with fly (dipterous) larvae, which, at least for a certain period, feed on dead or living tissue or ingested food of the host (1). Intestinal myiasis occurs when fly eggs or larvae previously deposited in food are ingested and survive in the gastrointestinal tract. Some infested patients have been asymptomatic; others have had abdominal pain, vomiting, and diarrhea (2,3).

Many fly species are capable of producing intestinal myiasis. Of 28 cases reported in 1963, M. stabulans was responsible for 4 (14%) (4). M. stabulans are common houseflies, and the females frequently oviposit from 140-200 eggs on food or decaying matter. These develop through three larval stages before pupation. The larval development is temperature-dependent and requires 10-20 days (2).

The finding of fly larvae in stool specimens does not necessarily denote intestinal myiasis. Many species of fly larvae that might be accidentally ingested with food cannot survive in the gastrointestinal environment. In such cases, although the dead larvae may be recognized on subsequent stool examinations, true host infestation is never established, and the condition is properly termed pseudomyiasis (5). Pseudomyiasis can also occur when female flies oviposit on uncovered fecal specimens before laboratory processing (6).

In addition to the intestine, myiasis can occur in other anatomic sites, including skin, eye, ear, nasopharynx, and the genitourinary tract; infestation may also occur in wounds (7,8). Over 50 fly species have been reported to cause human myiasis (2). Treatment of all forms of myiasis includes occlusive salves and dressings for cutaneous myiasis (7,8); manual removal of larvae in aural, genitourinary, and nasopharyngeal myiasis (7,9); application of a 15% chloroform in light vegetable oil solution (followed by manual removal) in wound myiasis (8); and administration of a mild cathartic agent in intestinal myiasis (10). Steroids, photocoagulation, and surgery have been tried with variable success to treat the various ocular manifestations of the disease (11). No effective chemotherapeutic agents are available for the treatment of any form of myiasis (7,8,10). Prevention of myiasis involves controlling the source of the larvae, the ovipositing female fly.

Although human myiasis is not reportable, CDC's Division of Parasitic Diseases was notified of 24 cases from 15 states in 1984. In nine (38%) of these, the larvae were found on stool examination. Four cases (17%) were cutaneous: three (13%), aural; one (4%), urinary; one (4%), nasopharyngeal; and six (25%), from unspecified sites. In a summary of 102 myiasis cases reported during the 11-year period 1952-1962 from 29 states, Canada, and Puerto Rico, 38 cases were cutaneous; 28 were enteric; and 46 involved other anatomic sites (nasopharyngeal, ocular, aural, and wound). Sixty-five percent of cases occurred during the warmer months (April through September), when fly populations are at their greatest (4). Myiasis has occasionally been reported as a hospital-acquired infection; case reports of these infections in obtunded intensive-care unit and convalescent home patients have recently been published (9,12).


  1. Zumpt F. The problem of intestinal myiasis in humans. S Afr Med J 1963;37:305-7.

  2. James MT. Flies that cause myiasis in man. Washington, D.C.: U.S. Department of Agriculture, 1947. (Misc. publication no. 631:134-7).

  3. Palmer ED. Entomology of the gastrointestinal tract: a brief review. Milit Med 1970;135:165-76.

  4. Scott HG. Human myiasis in North America (1952-1962 inclusive). Florida Entomol 1964;47:255-61.

  5. Laarman JJ, Van Thiel PH. A peculiar case of intestinal (pseudo)myiasis and a case of wound myiasis in the Netherlands. Trop Geogr Med 1967;19:187-91.

  6. Kenny M, Eveland LK, Yermakov V, Kassouny DY. Two cases of enteric myiasis in man. Pseudomyiasis and true intestinal myiasis. Am J Clin Pathol 1976;66:786-91.

  7. Bosworth AB, Marsden PD. Injurious arthropods. In: Strickland GT, ed. Hunter's tropical medicine. 6th ed. Philadelphia: WB Saunders, 1984:815-6.

  8. Herms WB, James MT. Medical entomology. 5th ed. New York: MacMillan, 1961:368-95.

  9. Barkin JS, MacLeod C, Hamelik P. Intestinal myiasis. Am J Gastroenterol 1983;78:560-1.

  10. Jacobson JA, Kolts RL, Conti M, Burke JP. Hospital-acquired myiasis. Infect Control 1980;1:319-20.

  11. Edwards KM, Meredith TA, Hagler WS, Healy GR. Ophthalmomyiasis interna causing visual loss. Am J Ophthalmol 1984;97:605-10.

  12. Greenberg B. Two cases of human myiasis caused by Phaenicia sericata (Diptera: Calliphoridae) in Chicago area hospitals. J Med Entomol 1984;21:615.

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