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To the Editor: A 42-year-old woman living in rural South Australia
presented with a history of passing actively swimming "fish-like
creatures" with her stool. There were no other symptoms (apart from a
sense of revulsion). Specimens brought in by the patient were
cylindrical larvae about 2.5 cm long with a "tail". Based on the
characteristic morphology, they were identified by our local
pathologist as "rat-tailed maggots", or larvae of the introduced
drone fly (Eristalis tenax). The patient saw one to three of
the larvae on about five occasions over a 2-week period, whereupon
they spontaneously ceased to occur. She remained asymptomatic.
There was nothing to suggest that the patient had a low standard of
hygiene.
 | The specimen, apparently passed with stool, was identified as a "rat-tailed maggot", or larva of the introduced drone fly (Eristalis tenax).
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Infestation of live humans or vertebrate animals with larvae of
Diptera (fly) species is known as myiasis -- for part of their life
cycle, the larvae feed on dead or living tissue or the ingested food of
the host.1 Pseudomyiasis is the term
used for deposition of maggots on faeces immediately after they are
passed. Recognition of dead larvae in stool also comes into this
category, as host infestation has not been established.
A few patients with intestinal myiasis with drone fly larvae have been
described previously, with the mode of infestation presumed to be
consumption of water or food contaminated with fly larvae or
eggs.2,3,5
 | Life stages of Eristalis tenax: (a) larva; (b) pupa; and (c) adult fly.
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The rat-tailed maggot usually breeds in drains, sewage pools, and
other stagnant water. Although the larvae live on decaying organic
matter, they must breathe air. For this, the breathing tube (the tail)
is extended or contracted depending on the depth of the liquid in which
they are feeding.
Our patient had a septic toilet system. It is possible that the maggots
could have bred in the tank and travelled upstream to the toilet bowl.
The tank, however, was 10 metres away and appeared normal when opened
and inspected, and no other family members noted the maggots in their
stool.
Doubts have been expressed about the theory that accidentally
ingested fly larvae could survive in the environment of the
gastrointestinal tract. Zumpt proposed an alternative kind of
intestinal myiasis due to Eristalis tenax called "rectal
myiasis".1 Flies, attracted to faeces,
may deposit their eggs or larvae near or into the anus, and the larvae
then penetrate further into the rectum. The larvae may then feed on
faeces at this site, as long as the breathing tube reaches towards the
anus. Although our patient had no symptoms, anal pruritus or
discomfort has been described in other reports.4,5
Phillip B Whish-Wilson
General practitioner
PO Box 1118
Mount Barker, SA 5251
- Zumpt F. The problem of intestinal myiasis in humans. S Afr Med
J 1963; 37: 305-307.
-
Lakshminarayana CS, Kanchana MV, Janakavalli R, Mallika M.
Intestinal myiasis due to Eristalis tenax. J Indian Med Assoc
1975; 65: 234-235.
-
Aguilera A, Cid A, Regueiro JM, et al. Intestinal myiasis caused by
Eristalis tenax (letter). J Clin Microbiol 1999; 37:
3082.
-
Hall MC. A note regarding myiasis, especially that due to syrphid
larvae. Arch Intern Med 1918; 21: 309-312.
-
Cookson HA, Oldroyd H. Intestinal infestation by larvae of a drone
fly. Lancet 1937; 2: 804.
©MJA 2000
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