Dracunculiasis (Guinea-worm disease)

Guinea worm is, in fact, a real worm. It is a large nematode, Dracunculus medinensis, which is ingested through drinking contaminated water.  This worm is the largest of the tissue parasite affecting humans. The adult female, which carries about 3 million embryos, can measure 600 to 800 mm in length and 2 mm in diameter. The parasite migrates through the victim's subcutaneous tissues causing severe pain especially when it occurs in the joints. The worm eventually emerges (from the feet in most of the cases), causing an intensely painful oedema, a blister and an ulcer accompanied by fever, nausea and vomiting.

Infected persons try to relieve the burning sensation by immersing the infected part of their body in local water sources, usually ponds. This also induces a contraction of the female worm at the base of the ulcer causing the sudden expulsion of hundreds of thousands of first stage larvae into the water. They move actively in the water, where they can live for a few days.

For further development, these larvae need to be ingested by suitable species of voracious predatory crustacean, Cyclops or water fleas which measure 1–2 mm and are abundant worldwide. In the cyclops, larvae develop to the infective third-stage in 14 days at 26°C.

When a person drinks contaminated water from ponds or shallow open wells, the cyclops is dissolved by the gastric acid of the stomach and the larvae are released and migrate through the intestinal wall. After 100 days, the male and female meet and mate. The male becomes encapsulated and dies in the tissues while the female moves down the muscle planes. After about one year of the infection, the female worm emerges, usually from the feet, releasing thousands of larvae and thus repeating the life cycle.

Several measures should be followed to curtail transmission of the disease:

• Effective surveillance to detect all cases within 24 hours of worm emergence and containment of all cases;
• Ensuring access to safe drinking water and converting unsafe sources to safe ones;
• The construction of copings around well heads or the installation of boreholes with hand pumps. This would prevent not only dracunculiasis but also diarrhoeal diseases.
• Regular and systematic filtering of drinking water derived from ponds and shallow unprotected wells or from surface water. Finely-meshed cloth or, better still, a filter made from a 0.15 mm nylon mesh, is all that is needed to filter out the cyclops from the drinking water;
• Treatment of unsafe water sources with temephos to kill the cyclops;
• Health education and social mobilization to encourage affected communities to adopt healthy drinking water behaviour.

The epidemiology of the disease is determined largely by the use of open stagnant water sources such as ponds and sometimes shallow or step wells. Artificial ponds are the main source of transmission.

Guinea-worm disease is seasonal, occurring with two broad patterns found in endemic areas of Africa, depending on climatic factors.

In the Sahelian zone, transmission generally occurs in the rainy season (May to August).

In the humid savanna and forest zone, the peak occurs in the dry season (September to January).

However, there are local variations in these patterns. Other risk factors are mobility and infection having occurred the previous year.

Guinea-worm disease is rarely fatal. Frequently, however, the patient remains sick for several months, mainly because:

• The emergence of the worm, sometimes several, is accompanied by painful oedema, intense generalised pruritus, blistering and an ulceration of the area from which the worm emerges.
• The migration and emergence of the worms occur in sensitive parts of the body, sometimes the articular spaces can lead to permanent disability.
• Ulcers caused by the emergence of the worm invariably develop secondary bacterial infections which exacerbate inflammation and pain resulting in temporary disability ranging from a few weeks to a few months.
• Accidental rupture of the worm in the tissue spaces can result in serious allergic reactions.