Ahmed Tayeh

The public and domestic domains in the transmission of disease.

This paper discusses the distinction between the transmission of infectious diseases within the domestic domain (the area normally occupied by and under the control of a household) and that in the public domain, which includes public places of work, schooling, commerce and recreation as well as the streets and fields. Whereas transmission in the public domain can allow a single case to cause a large epidemic, transmission in the domestic domain is less dramatic and often ignored, although it may account for a substantial number of cases. Statistical methods are available to estimate the relative importance of the two. To control transmission in the public domain, intervention by public authorities is likely to be required. Two examples show how environmental interventions for disease control tend to address transmission in one or the other domain; interventions are needed in both domains in order to interrupt transmission.

The impact of health education to promote cloth filters on dracunculiasis prevalence in the Northern Region, Ghana

This paper describes a health education intervention which was conducted during the 1990 dry season in 3 study villages in the Northern Region of Ghana, to reduce dracunculiasis prevalence in that area by promoting the use of cloth filters for drinking water and avoidance of water contact by sufferers. The impact of the intervention in reducing dracunculiasis prevalence was examined by comparing the period prevalence of infection in 1990 and 1991. The findings demonstrate that the intervention had a measurable but limited impact on dracunculiasis prevalence. Face-to-face health education was successful in persuading 56% of households to buy filters. Ownership of at least one filter for every 10 people in the household was associated with a reduction of at least 20% in the risk of dracunculiasis.

Water sources and other determinants of dracunculiasis in the Northern Region of Ghana

This paper describes a study carried out in a rural area of Ghana on the drinking water sources and other determinants of dracunculiasis (guinea worm disease). The results confirm the association between water source choice and the prevalence of the disease. A logistic regression model was used to show the combined effect of several behavioural, biological, and environmental risk factors. The important behavioural factors were related to the head of household, fetching of water, travelling, and farming. Age was found to be an important biological risk factor for dracunculiasis, but the greatest relative risk applied to those who had suffered from guinea worm disease in the previous year. Although males were significantly more infected than females when analysing the raw data, sex did not prove to be a significant risk factor in this model. Village of residence was an important environmental risk factor for dracunculiasis. Factors related to socio-economic status were not associated with the risk of infection. The paper concludes by presenting the policy implications of the study findings.

Why is dracunculiasis eradication taking so long

The long time needed for global eradication of dracunculiasis (Guinea worm disease) was not anticipated at the outset. The successful eradication of smallpox in 10 years compares with the target date set in 1985 for dracunculiasis eradication - 1995. Seventeen years after that date, transmission continues. Why? Various factors are responsible, mainly lack of resources, or resources ineffectively used. The example of Ghana, where the programme stagnated for a decade, sheds light on this delay. When more resources were put into Ghanas programme in 2007, transmission of the disease was interrupted in 3 years. The variable success of dracunculiasis eradication in different countries provides lessons for future disease eradication programmes.

Editorial: Dracunculiasis eradication by 2009: will endemic countries meet the target?

As the global campaign for eradication of poliomyelitis encounters delays and difficulties (Fine & Griffiths 2007), some eyes are turning to the eradication of dracunculiasis (Guinea worm disease) as the ‘other’ prospect offering a potential high-profile success for public health in the next few years (Al-Awadi et al. 2007). Certainly, dracunculiasis eradication has come a long way in two decades, eliminating the disease from Asia, more than halving the number of endemic countries, and reducing the annual incidence from an estimated 3.5 million in 1986 to only 25 000 today (Hopkins et al. 2005; Barry 2006). The impact of Guinea worm disease on agricultural productivity in some parts of Nigeria was once so powerful and widespread that it could be seen from space (Ahearn & de Rooy 1996); now there are whole countries in Africa where the disease is no more than a fading memory, and a small scar on the legs of the middle-aged. And this has been achieved in some of the most remote and undeveloped communities in some of the poorest countries on the planet. The remarkable success of the initiative over the last two decades can be judged from Figure 1, showing the trend in reported cases of the disease over the years, for eight of the countries which have interrupted transmission. Note the logarithmic scale. The dotted line to the right of the figure shows that most countries have achieved a reduction in incidence by 50% or better in a typical year, and sustained that rate of decline over a protracted period of time. The good progress made so far, and the need to maintain optimism among field staff and funders, has inspired the setting of target dates for eradication, which have suffered from wishful thinking over the years. Already in the early 1980s, the Indian national eradication programme was announcing a postponement of its national target by two years from 1984 to 1986 (CDC 1983). In the event, India did not achieve zero cases until 1997. A global target date was set when the World Health Assembly declared in 1991 its commitment to the goal of eradicating the dracunculiasis by the end of 1995. Even then, there were doubts whether this was achievable (Tayeh & Cairncross 1993). Other target dates were to follow, until a World Health Assembly resolution in 2004 put the target for eradication back to 2009. Such a target date can help to boost the advocacy effort at the international level and in the endemic countries (Cairncross et al. 2002), but setting a target which is not achievable devalues the currency, and diminishes its impact on stakeholders.

Certification of disease eradication: lessons from dracunculiasis.

Of the 20 countries where Guinea worm disease (dracunculiasis) had been endemic at the beginning of the eradication campaign in the mid-1980s, only 6 were still endemic in 2008, with the disease now focussed mainly in three countries: Ghana, Mali and Sudan (WHO 2009). Certification that the other 14 countries had interrupted transmission (six countries certified and eight countries to be certified in 2009 and 2011) is taking 5 years on average. Although sufficient funds are available and there were optimistic plans to interrupt disease transmission in the six endemic countries in 2009 (Rinaldi 2009), it will certainly take several years for this to materialize (Tayeh & Cairncross 2007). Certification of the eradication procedures will require at least three extra years of surveillance after interruption of dracunculiasis transmission in the last endemic country, and this will extend the time before the certification of eradication can be declared. Certification of dracunculiasis elimination (eradication from individual countries) is becoming important during this last phase of global eradication, as nearly two-thirds of the formerly endemic countries (14 of 20) still need certification and it is important to ensure that countries that are certified have interrupted disease transmission and that their surveillance systems are able to detect Guinea worm cases if any occur. At the same time there is a risk of overloading those remaining countries with challenging certification criteria, formulated 15 years ago when there was no experience of certifying the eradication of any parasitic disease. There is enough time to review and finetune the current certification procedures and practice in order to simplify them, while keeping the risk of re-occurrence, somewhere in the world, to the minimum. The review of these procedures (Box 1) can help in planning the certification of other diseases targeted for elimination or eradication. In 1995 WHO established the International Commission for the Certification of Dracunculiasis Eradication (ICCDE), the third such commission established by WHO after the commissions for smallpox and polio eradication. It is an independent group of experts at the global level with a mandate to set criteria and conduct the certification

Guinea worm: from Robert Leiper to eradication.

Guinea worm disease, dracunculiasis or dracontiasis, is an ancient disease with records going back over 4500 years, but until the beginning of the 20th century, little was known about its life cycle, particularly how humans became infected. In 1905, Robert Thomas Leiper was sent by the British colonial authorities to West Africa to investigate the spread of Guinea worm disease and to recommend measures to prevent it. While carrying out his investigations, he made important contributions to the aetiology, epidemiology and public health aspects of Guinea worm disease and provided definitive answers to many outstanding questions. First, he tested the validity of previous theories; second, he confirmed the role of water fleas, which he identified as Cyclops, as the intermediate hosts in the life cycle; third, he investigated the development of the parasite in its intermediate host; and fourth, he recommended measures to prevent the disease. [The crustacean Order Cyclopoida in the Family Cyclopidae contains 25 genera, including Cyclops which itself contains over 400 species and may not even be a valid taxon. It is not known how many of these species (or indeed species belonging to related genera) can act as intermediate hosts of Dracunculus medinensis nor do we know which species Fedchenko, Leiper and other workers used in their experiments. It is, therefore, best to use the terms copepod, or copopoid crustacean rather than Cyclops in scientific texts. In this paper, these crustaceans are referred to as copepods except when referring to an original text.] Leiper described the remarkable changes that took place when an infected copepod was placed in a dilute solution of hydrochloric acid; the copepod was immediately killed, but the Dracunculus larvae survived and were released into the surrounding water. From this, he concluded that if a person swallowed an infected copepod, their gastric juice would produce similar results. He next infected monkeys by feeding them copepods infected with Guinea worm larvae, and thus conclusively demonstrated that humans became infected by accidentally ingesting infected crustaceans. Based on these conclusions, he advocated a number of control policies, including avoidance of contaminated drinking water or filtering it, and these preventive measures paved the way for further research. The challenge to eradicate Guinea worm disease was not taken up until about seven decades later since when, with the support of a number of governmental and non-governmental organizations, the number of cases has been reduced from an estimated 3·5 million in 1986 to 25 in 2016 with the expectation that this will eventually lead to the eradication of the disease.