Doctor, there's a tadpole in my feces!

Case 2

A 36-year-old male resident of a coastal Nova Scotia community presented to his family physician after he noted moving objects in his feces (Figure 1). Although concerned and revolted, he was asymptomatic. He was worried that the organisms were an intestinal parasite he had passed in his stool. The organisms were approximately 2.5 cm long and resembled tadpoles. The fecal sample was sent to the Parasitology Section at the Queen Elizabeth II Health Sciences Centre in Halifax, Nova Scotia, for identification.

Figure 1.

Rat-tailed Eristalis larvae

What was the diagnosis?

Diagnosis

The objects were tentatively identified as the ‘rat-tailed’ maggots of a syrphid, or drone fly, of the genus Eristalis. Our patient was advised to collect several subsequent stool specimens on different days. No drone fly larvae were found in the patient’s subsequent stool samples.

On further questioning regarding the circumstances under which the original larvae were found, we learned that the stool in question had not been flushed into a closed septic system, but had remained in an ‘open cistern’ for a brief period before being discovered by another individual. In all likelihood, the organisms were already present in the cistern and migrated to the fecal ‘food supply’ prior to their discovery.

No further treatment or follow-up was recommended.

Discussion

Also known as a hover fly or flower fly, the drone fly is quite large and resembles a honeybee. The adult fly visits flowers and collects nectar; however, the larval stage of this insect is far less fanciful – the female fly lays hundreds of eggs on decaying organic matter, including feces (1).

The developing larvae feed on decomposing organic material. The tail-like structure is actually a breathing tube, allowing the larvae to flourish in very wet environments and to feed on submerged material with their breathing tubes extended to the surface (2). These larvae may invade farm out-buildings in large numbers in search of a dry location when they are ready to pupate (1).

It has been suggested that humans acquire Eristalis tenax intestinal myiasis by ingesting the fly eggs, or early-stage maggots, in contaminated food or water (2,3). The larvae then develop in the intestine, feeding on luminal contents. However, there is some question as to whether they can survive the anaerobic environment of the intestine. Alternatively, it has been suggested that the female fly may deposit eggs in the perianal area and the newly hatched maggots crawl into the rectum and develop there, extending their breathing tubes through the anus like a diver’s snorkel (4).

Since the beginning of the twentieth century, there have been sporadic reports of individuals passing the larvae of Eristalis tenax in stool (2,3,5,6). One of the most recently reported cases (2) involved a 42-year-old woman in south Australia, who recovered small numbers of the larvae from her stool repeatedly over a period of approximately 14 days. She had no physical symptoms. Most commonly, patients report anal discomfort and anal pruritis (4,6). Dizziness and nonspecific abdominal pain have also been described (3,6).

Dorland’s Illustrated Medical Dictionary defines ‘myiasis’ as “a condition caused by infestation of the body by fly maggots” (7). The definition implies that the larvae are continuing their development on, or in, the host. No species of fly, however, requires passage through the human intestine for completion of its life cycle, and most fly larvae passed in the stool are incidental.

The term ‘intestinal pseudomyiasis’ has been used to describe the accidental entrapment of a swallowed larva passing, alive or dead, through the digestive tract (4,8,9). Dorland’s defines ‘pseudomyiasis’ as “the presence of fly maggots in the digestive tract due to ingestion; if present in large numbers, they may cause diarrhea and other symptoms” (7).

Our case, in which the larvae are presumed to have migrated to stool after it was passed, might more correctly be called intestinal pseudo-pseudomyiasis; however, we propose the less perplexing ‘failure to flush syndrome’.