Guinea worm disease nears eradication

Wednesday, 3rd of February 2016

The Lancet Infectious Diseases, Volume 16, No. 2, p131, February 2016

Editorial

Guinea worm disease nears eradication

DOI: http://dx.doi.org/10.1016/S1473-3099(16)00020-7

Only two infectious diseases have ever been eradicated: smallpox, of which the last naturally transmitted case occurred in 1977, and rinderpest, a disease of cattle and related ungulates, officially declared eradicated in 2011. This year might see a remarkable doubling in the list of eradicated diseases, with both polio (about which we wrote in the August, 2015, issue) and guinea worm no longer being naturally transmitted.

Guinea worm disease, or dracunculiasis, is a parasitic disease caused by the nematode wormDracunculus medinensis. People become infected when they drink water contaminated with copepods (water fleas), which are the vector of the disease. When ingested copepods are dissolved by gastric juice, larvae of dracunculus are released, which then penetrate the stomach or intestine. Mating between male and female worms occurs in connective tissue about 3 months after infection, after which male worms die. Female worms migrate, usually to lower limbs, about 8–10 months after infection. Emergence of the worm through the skin to shed larvae causes an intense burning and itching sensation. Patients may try to relieve symptoms by immersing the lesion in water sources that are also used for drinking, which in turn allows larvae to infect copepods and continue the life-cycle. The disease is seldom fatal, but the only form of patient management is the slow extraction of the emerging female worm by winding it around a stick, which can take weeks during which time the patient may be too incapacitated to carry on activities of daily living.

Tropical and semi-tropical Africa and Asia were once plagued with guinea worm disease, but it began to disappear as water treatment improved from the 19th century. By 1986, when the World Health Assembly adopted a resolution calling for the eradication of the disease, there were an estimated 3·5 million cases annually in 21 countries, with 120 million people at risk. The past 30 years have seen a stunning decline in cases to just 126 in 2014 and 22 in 2015. Only four countries are now affected: Chad (nine cases in 2015), Ethiopia (three), Mali (five), and South Sudan (five).

A notable feature of the campaign to eradicate guinea worm disease is that it has involved neither drug treatment nor vaccination—there are none. Instead, simple measures that prevent people from becoming infected have been effective. These include stopping people from drinking water contaminated with copepods by providing safe sources such as wells or bore holes, filtering water through a fine mesh (a folded cotton cloth is effective), boiling, or treating water sources with a larvicide to kill copepods. Furthermore, people with emerging guinea worms must be prevented from entering water sources by community level case detection and using volunteers to guard water supplies. Community buy-in is clearly essential for these preventive measures to be effective, alongside promotion of health education and behaviour change.

This successful campaign to eradicate guinea worm might never have happened without the efforts of former US President Jimmy Carter, whose foundation, the Carter Center, has been leading eradication efforts since 1986. The Carter Center has coordinated funding, persuaded companies to donate larvicides and materials for water filters, liaised with governments, and even organised a 6 month “guinea worm cease fire” during Sudans civil war. The estimated cost of the eradication campaign since 1986 is a remarkably thrifty US$350 million. By comparison, the polio eradication programme has cost about $9·5 billion.

There have been some bumps along the road to success. In Chad, after more than a decade of no indigenous cases of guinea worm disease, ten cases were reported in July, 2010. Surveillance in the country has been enhanced by training more than 2500 volunteers in more than 880 villages, and monetary rewards are offered for information leading to confirmation of cases. Eradication in Chad faces a further challenge because D medinensis, which was considered as a purely human parasite, has been found to infect village dogs. The dogs might become infected by eating entrails of fish harbouring infective larvae. Additional control measures to interrupt this potential source of human infection have already been instituted in Chad.

The Chad experience shows that the final phase of disease eradication can present unique difficulties. Nevertheless, although certification of disease-free status takes at least 3 years from the final case being reported, there is reason to hope that the last case of guinea worm disease in human history will occur in 2016.

For Carter Center Guinea Worm Eradication Program seehttp://www.cartercenter.org/health/guinea_worm/index.html

For more on dogs infected with guinea worm see http://www.nature.com/news/dogs-thwart-effort-to-eradicate-guinea-worm-1.19109