Setback for campaign to eradicate Guinea worm disease

Arabella Gray discusses new research investigating the role of domestic dogs in sustaining Guinea worm disease in Africa.

Identifying correlates of Guinea worm (Dracunculus medinensis) infection in domestic dog populations

Few human infectious diseases have been driven as close to eradication as dracunculiasis, caused by the Guinea worm parasite (Dracunculus medinensis). The number of human cases of Guinea worm decreased from an estimated 3.5 million in 1986 to mere hundreds by the 2010s. In Chad, domestic dogs were diagnosed with Guinea worm for the first time in 2012, and the numbers of infected dogs have increased annually. The presence of the parasite in a non-human host now challenges efforts to eradicate D. medinensis, making it critical to understand the factors that correlate with infection in dogs. In this study, we evaluated anthropogenic and environmental factors most predictive of detection of D. medinensis infection in domestic dog populations in Chad. Using boosted regression tree models to identify covariates of importance for predicting D. medinensis infection at the village and spatial hotspot levels, while controlling for surveillance intensity, we found that the presence of infection in a village was predicted by a combination of demographic (e.g. fishing village identity, dog population size), geographic (e.g. local variation in elevation), and climatic (e.g. precipitation and temperature) factors, which differed between northern and southern villages. In contrast, the presence of a village in a spatial infection hotspot, was primarily predicted by geography and climate. Our findings suggest that factors intrinsic to individual villages are highly predictive of the detection of Guinea worm parasite presence, whereas village membership in a spatial infection hotspot is largely determined by location and climate. This study provides new insight into the landscape-scale epidemiology of a debilitating parasite and can be used to more effectively target ongoing research and possibly eradication and control efforts.

Dogs and the classic route of Guinea Worm transmission: an evaluation of copepod ingestion

Dracunculus medinensis, the causative agent of Guinea worm disease in humans, is being reported with increasing frequency in dogs. However, the route(s) of transmission to dogs is still poorly understood. Classical transmission to humans occurs via drinking water that contains cyclopoid copepods infected with third stage larvae of D. medinensis, but due to the method of dog drinking (lapping) compared to humans (suction and/or retrieval of water into containers), it seems unlikely that dogs would ingest copepods readily through drinking. We exposed lab raised beagles to varying densities of uninfected copepods in 2 liters of water to evaluate the number of copepods ingested during a drinking event. We confirmed dogs can ingest copepod intermediate hosts while drinking; however, low numbers were ingested at the densities that are typically observed in Chad suggesting this transmission route may be unlikely. Overall, the relative importance of the classic transmission route and alternate transmission routes, such as paratenic and transport hosts, needs investigation in order to further clarify the epidemiology of guinea worm infections in dogs.

Population genetic analysis of Chadian Guinea worms reveals that human and non-human hosts share common parasite populations

Following almost 10 years of no reported cases, Guinea worm disease (GWD or dracunculiasis) reemerged in Chad in 2010 with peculiar epidemiological patterns and unprecedented prevalence of infection among non-human hosts, particularly domestic dogs. Since 2014, animal infections with Guinea worms have also been observed in the other three countries with endemic transmission (Ethiopia, Mali, and South Sudan), causing concern and generating interest in the parasites' true taxonomic identity and population genetics. We present the first extensive population genetic data for Guinea worm, investigating mitochondrial and microsatellite variation in adult female worms from both human and non-human hosts in the four endemic countries to elucidate the origins of Chad's current outbreak and possible host-specific differences between parasites. Genetic diversity of Chadian Guinea worms was considerably higher than that of the other three countries, even after controlling for sample size through rarefaction, and demographic analyses are consistent with a large, stable parasite population. Genealogical analyses eliminate the other three countries as possible sources of parasite reintroduction into Chad, and sequence divergence and distribution of genetic variation provide no evidence that parasites in human and non-human hosts are separate species or maintain isolated transmission cycles. Both among and within countries, geographic origin appears to have more influence on parasite population structure than host species. Guinea worm infection in non-human hosts has been occasionally reported throughout the history of the disease, particularly when elimination programs appear to be reaching their end goals. However, no previous reports have evaluated molecular support of the parasite species identity. Our data confirm that Guinea worms collected from non-human hosts in the remaining endemic countries of Africa are Dracunculus medinensis and that the same population of worms infects both humans and dogs in Chad. Our genetic data and the epidemiological evidence suggest that transmission in the Chadian context is currently being maintained by canine hosts.

Dracunculiasis Eradication: Are We There Yet?

This report summarizes the status of the global Dracunculiasis Eradication Program as of the end of 2017. Dracunculiasis (guinea worm disease) has been eliminated from 19 of 21 countries where it was endemic in 1986, when an estimated 3.5 million cases occurred worldwide. Only Chad and Ethiopia reported cases in humans, 15 each, in 2017. Infections of animals, mostly domestic dogs, with Dracunculus medinensis were reported in those two countries and also in Mali. Insecurity and infections in animals are the two main obstacles remaining to interrupting dracunculiasis transmission completely.

Possible Role of Fish as Transport Hosts for Dracunculus spp. Larvae

To inform Dracunculus medinensis (Guinea worm) eradication efforts, we evaluated the role of fish as transport hosts for Dracunculus worms. Ferrets fed fish that had ingested infected copepods became infected, highlighting the importance of recommendations to cook fish, bury entrails, and prevent dogs from consuming raw fish and entrails.

Recurrence of Guinea Worm Disease in Chad after a 10-Year Absence: Risk Factors for Human Cases Identified in 2010-2011

A decade after reporting its last case of Guinea worm disease (GWD), a waterborne parasitic disease targeted for eradication, Chad reported 20 confirmed human cases from 17 villages-10 cases in 2010 and 10 cases in 2011. In 2012, the first GWD dog infections were diagnosed. We conducted a case-control study during April-May 2012 to identify human transmission risk factors and epidemiologic links. We recruited 19 cases and 45 controls matched by age, sex, time, and location of exposure based on the case patients' periods of infection 10-14 months earlier. Data were analyzed with simple conditional logistic regression models using Firth penalized likelihood methods. Unusually, GWD did not appear to be associated with household primary water sources. Instead, secondary water sources, used outside the village or other nonprimary sources used at home, were risk factors (matched odds ratio = 38.1, 95% confidence interval = 1.6-728.2). This study highlights the changing epidemiology of GWD in Chad-household primary water sources were not identified as risk factors and few epidemiologic links were identified between the handfuls of sporadic cases per year, a trend that continues. Since this investigation, annual dog infections have increased, far surpassing human cases. An aquatic paratenic host is a postulated mode of transmission for both dogs and humans, although fish could not be assessed in this case-control study due to their near-universal consumption. GWD's evolving nature in Chad underscores the continued need for interventions to prevent both waterborne and potential foodborne transmission until the true mechanism is established.

Elimination of Guinea Worm Disease in Ethiopia; Current Status of the Disease's, Eradication Strategies and Challenges to the End Game

Dracunculiasis, also named Guinea Worm Disease (GWD), is one of the Neglected Tropical Diseases (NTDs) caused by a parasitic nematode known as Dracunculus medinensis and has been known since antiquity as 'fiery serpent' from Israelites. It is transmitted to humans via drinking contaminated water containing infective copepods. Given, its feasibility for eradication, the Guinea Worm Eradication Program (GWEP) was launched in 1980 with the aim of eradicating the disease. Since its inception, GWEP has made an extraordinary progress in interrupting transmission. Globally, the number of reported cases reduced from 3.5 million in 20 countries in 1986 to only 22 cases in 2015 from only four countries namely South Sudan, Mali, Chad and Ethiopia. Since Mali has interrupted transmission of GWD in 2016, currently, the disease remains endemic in only three sub-Saharan African countries namely, South Sudan, Chad and Ethiopia. Each endemic country has its own national Guinea Worm Eradication Program. In Ethiopia, the Ethiopian Dracunculiasis Eradication Program (EDEP) which was established in 1993 has made remarkable move towards interruption of disease transmission and now the endgame is fast approaching. The EDEP with support mainly from The Carter Center, WHO, and UNICEF has reduced GWD by more than 99% from 1994 to 2015. In 2015, only 3 indigenous cases in humans and 14 in animals (13 in dogs and 1 in baboon) were reported. In 2016, 3 human cases, 14 dogs and 2 baboon infections were reported.. Refugee influx from the Republic of South Sudan (RSS), increased animal infections with unknown role in transmission of Dracunculiasis, the presence of hard to reach communities and lack of safe water sources in remote non-village areas remain among important challenges at this final stage of GWD eradication in Ethiopia. This paper reviews progress made towards Guinea Worm Eradication with a focus on the experience of the Ethiopian Dracunculiasis Eradication Program (EDEP), and intervention strategies that need further intensification to realize the endgame. Eradication strategies encompassing community education for behavioral change including raising awareness towards cash reward for reporting Guniea Worm Disease (GWD) and animal infection, case containment, surveillance systems, provision of safe water supply, and ABATE chemical application are discussed. It also summarizes challenges the end game faces and recommendations to strengthen the eradication effort.

The peculiar epidemiology of dracunculiasis in Chad

Dracunculiasis was rediscovered in Chad in 2010 after an apparent absence of 10 years. In April 2012 active village-based surveillance was initiated to determine where, when, and how transmission of the disease was occurring, and to implement interventions to interrupt it. The current epidemiologic pattern of the disease in Chad is unlike that seen previously in Chad or other endemic countries, i.e., no clustering of cases by village or association with a common water source, the average number of worms per person was small, and a large number of dogs were found to be infected. Molecular sequencing suggests these infections were all caused by Dracunculus medinensis. It appears that the infection in dogs is serving as the major driving force sustaining transmission in Chad, that an aberrant life cycle involving a paratenic host common to people and dogs is occurring, and that the cases in humans are sporadic and incidental.

Centers for Disease Control and Prevention. Progress toward global eradication of dracunculiasis--January 2011-June 2012

Dracunculiasis (Guinea worm disease) is caused by Dracunculus medinensis, a parasitic worm. Approximately 1 year after initial infection from contaminated drinking water, the worm emerges through the skin of the infected person, usually on the lower limb. Pain and secondary bacterial wound infection can cause temporary or permanent disability that disrupts work and schooling for the entire family. In 1986, the World Health Assembly (WHA) called for dracunculiasis elimination and the Guinea Worm Eradication Program, supported by The Carter Center, World Health Organization (WHO), United Nations Children's Fund (UNICEF), CDC, and other partners, was coalesced to assist ministries of health of endemic countries in meeting this goal. At that time, an estimated 3.5 million cases occurred annually in 20 countries in Africa and Asia. This report updates published and previously unpublished surveillance data reported by ministries of health and describes progress toward global dracunculiasis eradication. In 2011, a total of 1,058 cases were reported. As of 2012, dracunculiasis remained endemic in only four countries. Through June 2012, worldwide reductions in reported cases continued, compared with the first 6 months of 2011. Failures in surveillance and containment, lack of clean drinking water, and insecurity in Mali and parts of South Sudan continue to challenge dracunculiasis eradication efforts.

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 Ghana's 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.

Centers for Disease Control and Prevention (CDC). Renewed transmission of dracunculiasis--Chad, 2010

Transmission of dracunculiasis (Guinea worm disease), a waterborne, parasitic disease targeted for eradication, was thought to have been interrupted in Chad since 2000, when the last case was reported. However, in 2010, 10 cases were confirmed by the Chad Ministry of Public Health (Ministère de la Santé Publique [MSP]) and the World Health Organization (WHO) during field investigations in which rumored cases were investigated and nearby villages were actively searched for additional cases. Because patients were not prevented from contaminating water sources, new cases were expected in 2011. During January-February 2011, MSP, WHO, and CDC conducted an investigation to gather additional information to guide prevention and response activities before the 2011 transmission season. Seven districts where cases had been confirmed or suspected in 2010 or where dracunculiasis was endemic during 1994-2000 were surveyed. The results of those surveys indicated that residents of 116 (55%) of 210 villages and 13 (87%) of 15 nomad camps consumed water from unsafe sources; 157 (75%) of 209 village key informants (KIs) and five (33%) of 15 nomad camp KIs knew about dracunculiasis. Thirty-one villages had confirmed or suspected cases during 2009-2011 and were classified as at-risk, requiring weekly active surveillance and urgent pre-positioning of materials for the 2011 transmission season. Nomadic populations are at risk for dracunculiasis because of unsafe water consumption and minimal knowledge of the disease. These populations also require targeted surveillance and prevention efforts (e.g., filter distribution, education, and case containment) to interrupt dracunculiasis transmission .

Centers for Disease Control and Prevention (CDC). Progress toward global eradication of dracunculiasis, January 2009-June 2010

In 1986, the World Health Assembly (WHA) called for the elimination of dracunculiasis (Guinea worm disease), a parasitic infection in humans caused by Dracunculus medinensis. At the time, an estimated 3.5 million cases were occurring annually in 20 countries in Africa and Asia, and 120 million persons were at risk for the disease. Because of slow mobilization in countries with endemic disease, the 1991 WHA goal to eradicate dracunculiasis globally by 1995 was not achieved. In 2004, WHA established a new target date of 2009 for global eradication; despite considerable progress, that target date also was not met. This report updates both published and previously unpublished data and updates progress toward global eradication of dracunculiasis since January 2009. At the end of December 2009, dracunculiasis remained endemic in four countries (Ethiopia, Ghana, Mali, and Sudan). The number of indigenous cases of dracunculiasis worldwide had decreased 31%, from 4,613 in 2008 to 3,185 in 2009. Of the 766 cases that occurred during January--June 2010, a total of 745 (97%) were reported from 380 villages in Sudan. Ghana, Ethiopia, and Mali each are close to interrupting transmission, as indicated by the small and declining number of cases. The current target is to complete eradication in all four countries as quickly as possible. Insecurity (e.g., sporadic violence or civil unrest) in areas of Sudan and Mali where dracunculiasis is endemic poses the greatest threat to the success of the global dracunculiasis eradication program.

Progress in dracunculiasis eradication in Oyo state, South-west Nigeria: a case study

BACKGROUND

Dracunculiasis currently occurs in only 5 countries, Nigeria inclusive.

OBJECTIVE

To study the prevalence and management of the guinea worm disease at the threshold of its eradication in Oyo state.

METHODS

KAP questionnaires were administered to head of households and cyclopoid copepods in domestic water sources were identified and checked for infection. Prevalence of infection in the study population was monitored and reasons for continued transmission in the area ascertained.

RESULTS

Fifty three cases were reported in study area in 2004 and 2005 but no cases in 2006. Five hundred head of households were interviewed in ten villages. 43.9% believe the disease is in the blood and further probing shows that 54.6% believe infection is due to inherited susceptibility. 1.8% used antibiotics for treatment while 37.1% used herbs. Boreholes, wells, treatment of ponds with Abate™, filter distribution and health education were interventions in place. Un-infected Halicyclops korodiensis and Africyclops curticornis were recovered from ponds.

CONCLUSION

Ignorance especially belief in inherited susceptibility, lack of sustained safe water sources and influx of infected immigrant farmers are major variables responsible for the continued presence of the disease in the state.

Centers for Disease Control and Prevention (CDC). Progress toward global eradication of dracunculiasis, January 2008-June 2009

Dracunculiasis is a parasitic infection caused by Dracunculus medinensis. Persons become infected by drinking water from stagnant sources (e.g., ponds) contaminated by copepods (water fleas) that contain immature forms of the parasite. In 1986, the World Health Assembly (WHA) called for the eradication of dracunculiasis (Guinea worm disease) at a time when an estimated 3.5 million cases occurred annually in 20 countries in Africa and Asia and 120 million persons were at risk for the disease. Because of slow mobilization in countries with endemic disease, the global dracunculiasis eradication program did not meet the 1995 target date for eradicating dracunculiasis set by WHA in 1991. In 2004, WHA established a new target date of 2009 ; despite considerable progress toward global eradication, that target date also will not be met. This report updates continued progress toward global eradication of dracunculiasis since January 2008. At the end of December 2008, dracunculiasis was endemic in six countries (Ethiopia, Ghana, Mali, Niger, Nigeria, and Sudan). The number of indigenous cases of dracunculiasis had decreased 52%, from 9,585 in 2007 to 4,619 in 2008. Of the 1,446 cases that occurred during January-June 2009, 1,413 (98%) were reported from Sudan and Ghana. Currently, insecurity (e.g., sporadic violence or civil unrest) in areas of Sudan and Mali where dracunculiasis is endemic poses the greatest threat to the success of the global dracunculiasis eradication program.

[Imported dracunculiasis: four cases confirmed in the south of Algeria]

The authors report for the first time, in the south of Algeria, four imported cases of dracunculiasis in Malian Touaregs. The patients came from Mali. They remained two months in Tamanrasset before settling in Illizi where they have been working illegally for more than nine months. In August 2007, because of infected lesions appearing on their legs a month earlier, the patients decided to go to the Illizi hospital for treatment The diagnosis of dracunculiasis was made by direct observation of worms emerging from lesions and by microscopic examination of larvae. The patients were then isolated and treated. The Ministry of Health immediately took measures to avoid local transmission of the disease, never seen in the region. The measures consisted in increasing awareness campaign among medical and paramedical staff about dracunculiasis and in pointing out the importance of detection of new cases among nomadic populations. The risk of emergence of a new dracunculiasis indigenous focus in the south of Algeria should be seriously considered, especially as the number of immigrants from endemic countries is increasing considerably

Dracunculiasis eradication: neglected no longer

This report summarizes the status of the global Dracunculiasis Eradication Program as of early 2008. By the end of 2007, dracunculiasis (Guinea worm disease) transmission had been eliminated from 15 of the 20 countries where the disease was endemic in 1986, only 9,585 cases were reported worldwide, and 2,016 villages still had indigenous cases of the disease. Two of the remaining affected countries (Nigeria and Niger) reported < 100 cases in 2007 and are on the verge of eliminating dracunculiasis if they have not stopped transmission already. Sudan, Ghana, and Mali are addressing their final challenges to interrupting all remaining transmission by the end of 2009.

Potential Vector Species of Guinea Worm (Dracunculus medinensis) in Northern Ghana

Guinea worm disease, also known as dracunculiasis (or dracunculosis), is caused by the large female of the nematode Dracunculus medinensis. It normally lives and grows in various places in the human body, before migrating to subcutaneous tissue and eventually emerging slowly from the skin, usually on the lower limbs. If the affected portion of the body comes into contact with water, first-stage juveniles (L(1)) are expelled in large numbers from the ruptured uterus. For further development, the juveniles need to be ingested by suitable predatory species of copepods. In this study, infectivity studies on the relative importance of various copepod species in the transmission of the Guinea worm disease was carried out. The infection potentials of the vectors were evaluated based on their ability to ingest the first stage juveniles (L(1)), and to remain alive for these juveniles to develop to the infective, third-stage juveniles (L(3)). The adults of the relatively larger species recorded very high mortality rates upon infection with the first stage juveniles (L(1)) of the parasite. The highest copepod mortality rate was recorded by M. kieferi (94%). However, the copepodid stages of these species were able to withstand infection for extremely longer periods. The smaller genera did not record any remarkable mortalities on ingesting parasite juveniles. The most important implicated potential vectors of Dracunculus medinensis evaluated in the area are Mesocyclops kieferi --> M. aspericornis --> Thermocyclops incisus --> T. inopinus --> T. oblongatus.

The other ‘neglected’ eradication programme: achieving the final mile for Guinea worm disease eradication?

Guinea worm disease is one of two diseases targeted for eradication, the other being polio. Since the late 1980s, the number of new cases per year has been reduced from approximately one million to some 25 000 in 2006. However, there was an increase from 2005 owing to improved surveillance in Sudan and problems in Ghana. The International Commission argues that more resources are required to ensure that the goal of eradication is completed. Elimination of transmission throughout Asia has now been confirmed and the disease is now confined to a small number of African countries requiring increased efforts to achieve the global goal.

Dracunculiasis eradication

Dracunculiasis is a disease caused by a parasite transmitted through infected drinking water. The International Drinking Water Supply and Sanitation Decade (1981-1990), provided a unique opportunity to eliminate the disease. The strategy of the eradication campaign was based on provision of safe drinking water supply, intensified case containment and health education. An appropriate epidemiological surveillance system was established to guide and evaluate the eradication effort. From an estimated 3.2 million people affected by the disease at the beginning of the campaign, the number of cases dropped to 10,674 by the end of year 2005. Currently the transmission of the disease takes place in 9 sub-Saharan countries only and another 7 countries are in the pre-certification stage. So far, 168 countries and territories have been certified free of transmission. However; eradication of the disease requires that all countries be certified free of transmission. With the support of the international community and the work of national dracunculiasis eradication programmes of affected countries, dracunculiasis may well be the first parasitic disease to be eradicated.

Waterborne Infectious Diseases--Could They Be Consigned to History?

The development of water resources, particularly in Africa, has changed the face of the continent, opening up land for agriculture, providing electric power, encouraging settlements adjacent to water bodies, and bringing prosperity to poor people. Unfortunately, the created or altered water bodies provide ideal conditions for the transmission of waterborne diseases and a favorable habitat for intermediate hosts of tropical parasitic infections that cause disease and suffering. The recent progress in control of these waterborne and vector-borne diseases, such as guinea worm, schistosomiasis, lymphatic filariasis, and onchocerciasis, suggests that many of them could be controlled effectively by 2015, which is the target for reaching the Millennium Development Goals. Donations of safe and effective drugs by several pharmaceutical companies, funds for delivering these donated drugs from foundations and bilateral donors, and effective global health partnerships should make these diseases history.

Uganda's successful Guinea Worm Eradication Program

Having begun its national Guinea Worm Eradication Program (UGWEP) in 1991 (1991 population, 16.6 million) with the third-highest number of cases reported by any endemic country, and ranked as the second-highest endemic country in the world in 1993, by 2004, Uganda celebrated its first full calendar year with no indigenous cases of the disease. Systematic interventions began in 1992 and were gradually intensified until the final indigenous case occurred in July 2003. The favorable concentration of most cases in relatively few northern districts of the country was partly offset by chronic insecurity in much of the endemic area and by repeated importations of cases from neighboring Sudan. Strong support and dedicated leadership by government officials and external partners were keys to this program's dramatic success. This program cost approximately US dollar 5.6 million.

Dracunculiasis (Guinea Worm Disease) Eradication

Since the seminal review by Ralph Muller about Dracunculus and dracunculiasis in this serial publication in 1971, the Centers for Disease Control and Prevention and The Carter Center forged, during the 1980s, a coalition of organizations to support a campaign to eradicate dracunculiasis. Eighteen of 20 countries were known in 1986 to have endemic dracunculiasis, i.e., Benin, Burkina Faso, Cameroon, Chad, Côte d'Ivoire, Ethiopia, Ghana, India, Kenya, Mali, Mauritania, Niger, Nigeria, Pakistan, Senegal, Sudan, Togo, and Uganda. Transmission of the disease in Yemen was documented in 1995, and the World Health Organization (WHO) declared Central African Republic endemic in 1995. As of the end of 2004, a total of 16026 cases of dracunculiasis were reported from 12 endemic countries (91% of these cases were reported from Ghana and Sudan, combined), a reduction greater than 99% from the 3.5 million cases of dracunculiasis estimated in 1986 to occur annually; the number of endemic villages has been reduced by >91%, from the 23475 endemic villages in 1991; disease transmission has been interrupted in 9 of the 20 endemic countries; and WHO has certified 168 countries free of dracunculiasis, including Pakistan (1996), India (2000), Senegal and Yemen (2004). Asia is now free of dracunculiasis.

[Water contacts in dracunculiasis-infected patients in Mali: transmission risk activities]

The aim of this study lies in the identification of human activities responsible for the transmission of the Guinea worm in an endemic village in Diema Region in Mali. Human water contacts observations started after a census followed by the implementation of a bi-monthly notification system, carried out from May to November 1993. Water contacts were noticed and observed from the mid-July to the end of November of the same year. The first case of dracunculiasis observed was randomly drawn out of a list of the families with obvious cases. The patent case activities involving either surface water, traditional wells or bore-hole water were recorded for 10 consecutive days. During this observation period, contacts made by other patients with the same water sources were also recorded. After 14 days, the case list was updated and a new case selected out of families previously selected. This cycle was repeated until the end of the study period. A "contact at risk for transmission" was defined by a close correspondence between the location of the worm's emergence and the surface of the skin exposed to water, within two weeks following emergence. Contacts were described according to water sources, activities in relation to water, date, gender and age. Observations were made on 103 patients who had 2506 activities in relation with a water body: 1132 of these activities implied a skin contact with the water. Only 133 (9%) of these water contacts were at risk for transmission, 75% took place during the months of August and September, 80% were related to surface waters and 20% to traditional wells. Woman household activities and boys games were the major activities at risk, in contrast to economic activities (watering cattle). The low proportion of "at risk activities" evaluated in this study suggests that a small number of water contacts is sufficient to maintain the transmission. The case implications of the current eradication strategy might not be sufficient alone to break the transmission and should therefore be associated with a reinforcement of the use of filters for drinking water together with an health education.

Tropical environments, human activities, and the transmission of infectious diseases

Throughout recent history, the tropical regions of the world have been affected more severely by infectious diseases than the temperate world. Much of the success of infectious diseases in that region is due to both biological and environmental factors that encourage high levels of biodiversity in hosts, vectors, and pathogens, and social factors that compromise efforts to control diseases. Several of these factors are described. Discussion then shifts to specific types of host-pathogen relationships. The most important of these in the tropics is the relationship between humans, a pathogen, and a vector that carries the pathogen from one human to another. Mosquitoes are the vector responsible for the transmission of many vector-borne human diseases. Characteristics of mosquito-human interactions are described, including cultural behaviors humans have developed that both increase the chances of transmission and help to limit that transmission. The transmission of water-borne diseases, fecal-oral transmission, zoonotic diseases, respiratory illnesses, and sexually transmitted diseases are also discussed. Attention is paid to how diseases with these modes of transmission differ in characteristics and importance in tropical human populations compared to those in temperate regions. Following this general discussion, three case studies are presented in some detail. The diseases chosen for the case studies include cholera, lymphatic filariasis, and dracunculiasis (guinea worm). These three case studies taken together provide examples of the diversity of human host-pathogen interactions as well as ways that human activities have both promoted their spread and helped to control them. The transmission of all three diseases is related to the nature and quality of water sources. The transmission of cholera, a water-borne disease, is related to sanitation practices, physical characteristics of the environment such as temperature and humidity, and modern shipping practices. Lymphatic filariasis, a mosquito-borne disease, has increased in frequency in parts of Africa in recent decades as a consequence of large-scale agricultural development projects that have shifted the nature and quantity of water sources and potential mosquito breeding sites. Dracunculiasis is transmitted by a small crustacean that contaminates sources of drinking water. Because its transmission can be prevented by a simple change in human behavior, filtering all water with a small piece of cloth before using it, dracunculiasis has been the focus of a major eradication effort that is near success.

Dracunculiasis eradication. Certification of absence of transmission

Dracunculiasis transmission is now confined to the African continent. Eradication efforts must be intensified in the countries that are still endemic: Benin, Burkina Faso, Central African Republic, Côte c'Ivoire, Ethiopia, Ghana, Mali, Mauritania, Niger, Nigeria, Sudan, Togo and Uganda. In these countries provision of safe drinking-water, containment of cases and health education for the exposed populations remain key measures for the interruption of transmission++ and for success. The Commission felt that particular attention should be given to Ghana, Nigeria and Sudan where eradication activities have been facing difficulties. In countries where transmission has recently ceased (Chad, Senegal and Yemen) or where no indigenous cases were reported in 1999 (Cameroon, Kenya), surveillance must be intensified over a period of 3 consecutive years and should include coverage of non-endemic regions at risk. In addition, reporting should continue and be reinforced to ensure the provision of monthly reports to WHO.

Guinea worm cause of adult onset asthmatic attack, a radiological diagnosis

A case report of a fifty years old Hausa male from Sokoto town, Nigeria an endemic region of guinea worm infestation, who presented with sudden adult onset of asthmatic attack and was evaluated radiologically and the diagnosis of acute obstructive airway disease was confirmed. It was noted, that there were associated calcified chain of guinea worms in the lung parenchyma. A rare association of acute asthmatic attack. Patient responded there-after to an anti-asthmatic regime of management.

Immunoepidemiology of Dracunculus medinensis infections II. Variation in antibody responses in relation to transmission season and patency

The serum antibody responses (specific IgG1, IgG4, and IgE, and total IgE) to Dracunculus medinensis infection in humans from a highly endemic area of northern Ghana were examined regularly by ELISA over a period of one year in cohorts of individuals who developed a patent D. medinensis infection during the study period (actively infected category), or who claimed to have never had a patent infection (endemic normal category). The results were analyzed in relation to seasonality and time of patency of infection. For individuals in the actively infected category, a clear seasonal variation in the mean levels of specific IgG1 and IgG4 was found, with the highest levels late in the dry season and early in the rainy season, when transmission is high, and the lowest levels late in the rainy season and early in the dry season. Endemic normal individuals responded with low and fluctuating levels of specific IgG1 and with low and nonfluctuating levels of specific IgG4. For specific and total IgE, no seasonal variation was observed in any of the two infection status categories. In relation to time of patency of infection (only involving the category of actively infected individuals), the mean levels of specific IgG1 and IgG4 increased from two months before patency of infection, peaked during patency, and then gradually decreased for four months until a constant level was reached. No significant fluctuations in the levels of specific and total IgE were observed in relation to time of patency. The present study thus showed extensive variation in levels of D. medinensis-specific IgG1 and IgG4 (but not IgE) over time. Seasonal variations in antibody responses may also occur in other helminth infections, especially those with seasonal transmission, and these should be taken into consideration when interpreting the results of immunologic studies.

Vector-borne parasitic diseases--an overview of recent changes

This paper summarises the impact of different changes (environmental, ecological, developmental) on the one hand, with the impact of control measures on the other. The former group of changes have tended to exacerbate the incidence and prevalence of vector-borne parasitic diseases while the reduced public funds available for the health sector have reduced disease surveillance systems. However, some vector control/eradication programmes have been successful. Vector control in onchocerciasis and Chagas' disease and immediate host control in Guinea worm have reduced the public health importance of these disease. This contrasts, with malaria, where the complexity of different ecological situations and the variable vector ecology have made control difficult and epidemics frequent and unpredictable. Advances in our knowledge of how to implement and sustain insecticide-impregnated bednets which reduce morbidity and mortality in under 5-year olds will be a key issue for the coming years. In African trypanosomiasis and leishmaniasis, where control is dependent on effective diagnosis and surveillance followed by high-cost drug treatment, the health services are faced with major challenges--lack of drug availability and diagnostics no vector control--the diseases in some areas assuming epidemic status yet health services are unable to respond. Human African trypanosomiasis and visceral leishmaniasis are fatal if untreated, and require an emergency response approach. Changing vector distribution of Glossina is related to the ability of riverine flies of Glossina palpalis group to adapt to new vegetation patterns. In leishmaniasis changes have occurred in the distribution of the disease associated with development impact, urbanisation, civil unrest and changed agroforestry practice.

An ancient scourge: the end of dracunculiasis in Egypt

This paper addresses the question of when guinea worm disease was last found in Egypt, and how written sources from the nineteenth and twentieth centuries which mention the disease should be evaluated. This enquiry is relevant to the global eradication campaign now in progress, and the need for countries in which dracunculiasis was once present to prepare a certification of eradication. Sudan, the country which has the largest number of cases today, is Egypt's southern neighbour. Because of the nature of the disease (in endemic areas it is most common among poor, rural people), it may not have come to the attention of urban-based health personnel. In the period before the details of the transmission cycle were known, the attitudes and mindsets of physicians and travellers also have to be taken into account in interpreting written reports of the disease. An examination of documentary sources from the nineteenth and twentieth centuries in European languages does not show any clear evidence for dracunculiasis transmission in Egypt during that period. Cases noted in Egypt, especially by the much quoted Dr Clot Bey in the 1820s, most likely originated beyond the borders of the country, in Sudan and, to a lesser extent, from endemic areas in the Middle East. However, many later commentators merely repeated what Clot Bey had written. A further difficulty is that some published reports which apparently concern dracunculiasis in Egypt, actually refer to cases in animals rather than humans.

The acceptability and effectiveness of a polyester drinking-water filter in a dracunculiasis-endemic village in northern region, Ghana

In the global effort to eradicate dracunculiasis (guinea-worm disease) one of the main tools is the use of filters for filtering unsafe drinking-water. The expensive and high-quality monofilament nylon filters, which for many years were donated to all dracunculiasis-endemic countries, are now mainly reserved for highly endemic countries. Polyester cloth is less expensive, and we investigated the user acceptability and effectiveness of this material as a drinking-water filter in a dracunculiasis-endemic village in Northern Region, Ghana, over a 3-month period. The polyester cloth completely retained the stages of copepods that are responsible for transmitting dracunculiasis. Over the 3-month study period a majority of respondents found that the new cloth was superior to the nylon filter with regard to strength (83%), filtering time (80%), and the ease with which the filter could be cleaned (87%). Inspection revealed that the filters were used intensively and that the new cloth was damaged after 2-3 months of use, which is also the case for the monofilament nylon filters.

An introduction to guinea worm on the eve of its departure: dracunculiasis transmission, health effects, ecology and control

A broad ranging discussion of the basic nature of guinea worm disease, fused with personal field observations in Ghana, shows its long-overlooked serious clinical aspects, and the many environmental and social influences that explain its persistence in the face of control efforts. It is a disease of neglect par excellence in remote rural areas. The global eradication campaign (which is not reviewed here) may be expected to come to closure over the next half decade. This account offers an overview, synthesis, and interpretation of a fascinating example in disease ecology at the time of its global vanishing.

Guinea worm disease in Ayod, Upper Nile Province, southern Sudan: a cross-sectional study

Upper Nile Province is one of the four main endemic areas for Guinea worm disease in the Sudan. In December 1994, a survey was conducted in the village of Ayod where the disease is endemic, to investigate morbidity and local knowledge of transmission and prevention. Interviews were conducted in households selected by standard cluster sampling procedures and of the 759 people examined, 156 (20.6%) had Guinea worm lesions. Adjusted odds ratios were used to estimate the relative risk for people with different personal or household characteristics in a multivariate analysis. After controlling for the possible confounding effects of other study variables, having a filter in the household, gender, and lack of knowledge about transmission and about prevention, were not associated with lesions. Only two variables were significantly associated with Guinea worm disease: getting water from a source other than a well increased the risk by a factor of 2.3, and being aged 5 years or more increased the risk by a factor of 31.1. This study demonstrates the clear association between the source of water for drinking and Guinea worm disease found elsewhere. We suggest the provision of reliable sources of pure drinking water and health education are the most suitable long-term preventive measures. The Sudan now represents the greatest challenge to the goal of global eradication of Guinea worm disease, following the reduction in cases in Nigeria. The continuing civil war and insecurity in southern Sudan hinder the implementation of an effective water programme and other control measures, but the potential benefits through reduced incapacity and improved agricultural productivity are considerable.

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.