Thursday, August 23, 2012

A very unpleasant souvenir

DNA Barcoding in Medicine

Imagine you are back from a wonderful vacation in the Tibetan mountains and aside from all the great memories you bring back a nasty and painful surprise. 

This happened to a German tourist who seem to have a mysterious disease. The Tibet traveler complained about severe pain and swellings across the upper part of the body. After several months of suffering a physician was able to extract a small white maggot from one of the swellings. As the physician suspected an infection with fly larvae she submitted the sample to the State Collection in Munich.

The resident fly specialist Dieter Doczkal was able to identify the maggot as larva of the yak warble fly (Hypoderma sinense) using DNA Barcoding.

Hypoderma sinense (source ZSM Press Release)
Larvae belonging to the genus Hypoderma (Diptera, Oestridae) cause myiasis in wild and domestic ruminants that is characterized by migrations within deep tissues. Especially in Asia this is a significant problem for livestock breeding. The adult fly will lay eggs on the foreleg of an animal, these will then be ingested by licking.  Once swallowed the eggs will pass on through the esophagus muscles and the spinal cord before re-emerging just beneath the skin.  When they re-emerge, the larvae cause swellings or warbles under the skin, causing quite some pain to the infected animal. 
Warble fly larvae under the skin of a caribou

These parasites can also infest humans with similar consequences: The infestation in hosts often causes serious tissue destruction by the larval migrations in the body. Fortunately humans are incidental hosts meaning that such infestations are rare and accidental.Actually this case is only the second ever reported for this particular fly species. The first was also a tourist traveling in India.

Identifying adult flies is a difficult business already but even for experts it is often impossible when it comes to larvae. This is what makes this case so exciting as Doczkal was able to match a COI sequence retrieved from the maggot to some Hypoderma sinense records on BOLD ( a database that hosts the majority of DNA Barcode data .

This is a good example how a library of DNA Barcodes for pathogens, parasites and creatures that transmit disease-causing organisms can help to distinguish them, as well as allowing eggs and juveniles to be identified accurately, something that is currently extremely difficult. The library is still far from complete and requires a lot of efforts from researchers and public health experts but already the method has been proven very useful.

By the way - the patient felt much better after the larva was removed.

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