Spot diagnosis. The patient was otherwise asymptomatic, but was somewhat appalled when the object in the first image passed out per rectum.

Measured 2.8 metres in length (image courtesy of SGH Department of Microbiology)

Magnified view, showing segments more clearly

An egg obtained from one of the segments (image courtesyof SGH Department of Microbiology)

Questions:

1. What is the diagnosis?
2. How did the patient acquire this?

[Updated 2nd July 2016]

This is clearly a tapeworm – there are no other human parasites that grow to such length. The question is what tapeworm, which will also help answer how the patient had acquired the worm. We can acquire tapeworm primarily by consuming undercooked pork (Taenia solium), beef (Taenia saginata) or fish (Diphyllobotrium spp. or in rare cases, Diplogonoporus grandis). Beef and pork tapeworm eggs look alike, although their heads (scolices) are quite different. In this particular case, the scolex of the worm probably remained within the patient, but the egg in the photo does not have the thick shell characteristic of Taenia eggs (see CDC’s gallery here). Instead, the egg most closely resembles those of fish tapeworms. There is an excellent review on tapeworm human infections that was published in 2009 in Clinical Microbiology Reviews, and which still remains relevant today.

Most fish tapeworms are acquired by consumption of raw or undercooked freshwater fish, as well as fish that spend a considerable amount of their lifespan in freshwater, such as salmon. However, rarely, human infection can also occur from consumption of raw marine fish, including redlip mullet (Korea) and Japanese sardines. It is important to note that infections in humans are almost always asymptomatic, and hence is likely to be more common that reported. Medical textbooks commonly list fish tapeworm infections (diphyllobothriasis) as a cause of vitamin B12 deficiency, a factoid that is dutifully regurgitated by medical students and residents on questioning, but this is extremely rare.