Dracunculus medinensis: A Human Parasitic Nematode

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Introduction to Family Dracunculidae

Species belonging to nematode worm family Dracunculidae thrive in the tissues of birds, reptiles, and mammals. Several genera and species of the family are remarkably similar with respect to morphological characteristics. For example, species found in reptile hosts have few differences from those found in mammals.

The most studied species of Family Dracunculidae are those belonging to the genera Dracunculus, Micropleura, and Avioserpens. Many species of Dracunculus are typical parasites of snakes found in the United States. Micropleura species are found in turtles and crocodiles in India and South America, while Avioserpens has species in marine birds.

Dracunculus species are common parasites of mammals. Dracunculus insignis parasitizes raccoons, opposums, muskrats, and other carnivorous animals, especially those living in semiaquatic habitats. D. medinensis is widespread in confined regions of India, Africa, and the Middle East. The parasite has been observed from humans in the United States many times, but these cases may have been caused by D. insignis. Actually, D. insignis may well be a strain of D. medinensis perhaps not normally infective to human beings. This may explain the scarcity of reports of it (D. insignis) in American people. It is, however, infective to rhesus monkeys. D. medinensis has been a prevalent parasitic dracunculid nematode in humans for centuries; by virtue of its medical importance, it deserves a thorough discussion in this series of articles. (Mehlorn and Armstrong 2001; Matthews 1998)

Dracunculiasis through the Ages

Since antiquity, D. medinensis (a.k.a. guinea worm) infection has been known for the most part of Africa and the Middle East, where it causes painful suffering even today. Hopkins (1992) has estimated that there are approximately 3 million infected people worldwide.

Due to its noticeable big size and the striking effects of infection, it is not surprising that the worm was mentioned many times by classical writers. For example, the Greek author and tutor of Ptolemy VII sons gave a clear description of the disease. He described the worms as serpent-like creatures chewing or biting the arms and legs of the people living along the Red Sea. He added that that the worms quickly withdrew themselves whenever they are touched and they cause horrible pain whenever they move between the muscles. Roman and Greek authors like Actuarus, Aetius, Aegineta, Soranus, Paulus, Galen, and Pliny all described the illness, but probably most of them never saw an actual case. Arabian and Spanish scholars also mentioned the disease in their writings, but unlike most of the Greek and Roman scholars, they had firsthand observations of the disease. (Grove 1990)

Treatment by winding the worm out of the body was described by Velschius in 1674. Parasitologists in Europe remained ignorant of D. medinensis until about the start of the 19th century when medical officers of the British army began their services in India. Information regarding the worm slowly accumulated, but this information was gathered and analyzed by a young Russian scientist and traveler Aleksej Fedchenko. He gave the first detailed description of the worm’s morphology and life cycle. He discovered that humans become infected by ingesting infected copepods and this discovery paved the way in finding ways for dracunculiasis prevention. (Grove 1990)

References

  • Hopkins DR. 1992. Homing on helminthes. Am. J. Trop. Med. Hyg. 46:626-634.
  • Grove DI. 1990. A history of human helminthology. Wallingford, Oxon. UK: CAB International.
  • Matthews B. 1998. An Introduction to Parasitology. Cambridge University Press.
  • Mehlorn H and PM Armstrong. 2001. Encyclopedic Reference of Parasitology. Published by Springer.