Dracunculus is a genus of spirurid nematode parasites in the family Dracunculidae.
The worms can reach a metre in length. If one simply pulls off the protruding head of the worm, the worm will break and leak high levels of foreign antigen which can lead to anaphylactic shock and fast death of the host. Hence it is important to remove the worm slowly (over a period of weeks). This is typically undertaken by winding the worm onto a stick (say, a matchstick), by a few centimetres each day.
Life cycle
All members of Dracunculus are obligate parasites of mammals or reptiles. Adult females reside just under the skin, and eventually form a blister in the host's skin through which they access the environment. When the blister comes into contact with water, the female releases several hundred thousand first-stage ("L1") larvae. L1 larvae must be ingested by a cyclopoid copepod, which serves as an intermediate host. Inside the copepod, the larvae develop to the third-stage ("L3"). Definitive hosts acquire Dracunculus by incidentally ingesting infected copepods while drinking water, or by consuming a paratenic host (e.g. a frog or fish) that has itself consumed a copepod. Inside the definitive host, the L3 larvae leave the digestive tract and migrate to deeper tissues, where within 60–70 days they undergo their final two molts to form sexually mature adults. Male and female adult worms then mate, and pregnant females migrate back to the host's skin – typically to an extremity – and form a blister to repeat the cycle.
Distribution
Dracunculus worms are distributed globally, though each species has a narrower range. The majority of Dracunculus species described infect reptiles – predominantly snakes. D. medinensis was historically widespread in sub-saharan Africa and South Asia,
Species
Reptile-infecting species
There are 14 accepted Dracunculus species, 10 of which infect reptiles. Eurasia hosts several reptile-infecting Dracunculus species. D. oesophageus was originally described from the esophagus of the viperine water snake, and has been described several times since. The remaining three Eurasian reptile-infecting species have been described a single time each: D. coluberensis from an Indian trinket snake, and D. alii and D. houdemeri from Checkered keelback snakes in India and Vietnam respectively. D. medinensis is now most common in dogs, particularly in Chad, where it may spread via fish or frogs as paratenic hosts.
D. insignis infects dogs and wild carnivores, causing cutaneous lesions, ulcers, and sometimes heart and vertebral column lesions. Like D. medinensis, it is also known as Guinea worm, as well as Dragon or Fiery Dragon. The range of D. insignis is limited to North America.
D. fuelliborni parasitizes opossum, D. lutrae parasitizes otters, and D. ophidensis parasitizes reptiles.