Life Cycle of Dracunculus Medinensis

Dracunculus medinensis, more commonly known as the guinea worm, is a parasite found in a variety of animals, as well as humans. Occurring predominantly in Africa and India, dracunculus medinensis most often infests horses, cows, dogs, wolves, baboons, and monkeys. In 2007, nearly 97% of all cases occurred in the African countries of Ghana and Sudan.The parasite is transmitted to humans that drink water containing water fleas (Cyclops) infected with the worms' larvae. The dracunculus medinensis life cycle takes at least a year to complete.

Stage One

In its larval stage, dracunculus medinensis spreads when a mature female emerges through the skin of her host into water, where she releases larvae.

Microscopic water fleas eat the larvae. Hosts then ingest the water fleas by drinking the contaminated water, completing the first stage of the worms' life cycle.

Stage Two

The ingested larvae, which are resistant to digestive juices, burrow through the host's intestinal wall, abdominal cavity and lymphatic system to subcutaneous (beneath the skin) tissue, and begin the next stage of their development. This stage takes about six weeks.

Stage Three

Over the next year, the larvae develop into adults. When they're roughly one year old, the tiny males (1/3 inch to 1 inch) mate with the much larger (2 feet) females. The males then die, and become engulfed in the females' tissues.

When their larvae are mature, the pregnant females begin traveling through the host's subcutaneous tissues to the surface of the skin. They usually migrate to the lower legs or feet.

Stage Four

The female guinea worm creates an ulcer by burrowing through the host's skin. When the host seeks relief by immersing the ulcer in water, the worm expels larvae into the water through her mouth. This process can continue for days, whenever the ulcer is in the water. The female worm then dies, leaving an abscess at the site where she emerged, potentially leading to infection.

Stage Five

The newly released larvae can survive up to three weeks in the water. Muddy water extends their survival period. Water fleas eat the larvae, which go through a two-week period of growth and molting before they are ready to infect a new host. The cycle begins anew when new hosts drink the water containing the fleas.

Considerations

Dracunculus medinensis feeds on its host's blood while growing. Even so, its host usually shows no symptoms of infestation until just before the worm is ready to emerge. The host may then develop swelling and inflammation at the site where the worm will surface, and possibly a fever.

There is neither a vaccine nor a drug for dracunculus medinensis infestation. The emerging worm can be wrapped around a stick and pulled out by centimeters each day. In locations with hospital facilities, surgical removal is possible as long as the worm hasn't formed an ulcer.

References

• CDC Guinea Worm Disease Fact Sheet
• UC Davis Nemaplex

Resources

• More about Guinea Worm Disease