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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).
References
Zumpt F. The problem of intestinal myiasis in humans. S Afr
Med
J 1963;37:305-7.
James MT. Flies that cause myiasis in man. Washington, D.C.:
U.S. Department of Agriculture, 1947. (Misc. publication no.
631:134-7).
Palmer ED. Entomology of the gastrointestinal tract: a brief
review. Milit Med 1970;135:165-76.
Scott HG. Human myiasis in North America (1952-1962
inclusive).
Florida Entomol 1964;47:255-61.
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.
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.
Bosworth AB, Marsden PD. Injurious arthropods. In:
Strickland
GT, ed. Hunter's tropical medicine. 6th ed. Philadelphia:
WB
Saunders, 1984:815-6.
Herms WB, James MT. Medical entomology. 5th ed. New York:
MacMillan, 1961:368-95.
Barkin JS, MacLeod C, Hamelik P. Intestinal myiasis. Am J
Gastroenterol 1983;78:560-1.
Jacobson JA, Kolts RL, Conti M, Burke JP. Hospital-acquired
myiasis. Infect Control 1980;1:319-20.
Edwards KM, Meredith TA, Hagler WS, Healy GR. Ophthalmomyiasis
interna causing visual loss. Am J Ophthalmol 1984;97:605-10.
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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