Infectious disease: Dog diets may drive transmission cycles in human Guinea worm disease.

Domestic dogs have an important role in the ecology of transmission of the Guinea worm, a debilitating human parasite. A new study documents how fish content in dogs' diets can predict Guinea worm infection status, suggesting additional avenues for control.

Ecology of domestic dogs (Canis familiaris) as a host for Guinea worm (Dracunculus medinensis) infection in Ethiopia.

The global programme for the eradication of Guinea worm disease, caused by the parasitic nematode Dracunculus medinensis, has been successful in driving down human cases, but infections in non-human animals, particularly domestic dogs (Canis familiaris), now present a major obstacle to further progress. Dog infections have mainly been found in Chad and, to a lesser extent, in Mali and Ethiopia. While humans classically acquire infection by drinking water containing infected copepods, it has been hypothesized that dogs might additionally or alternatively acquire infection via a novel pathway, such as consumption of fish or frogs as possible transport or paratenic hosts. We characterized the ecology of free-ranging dogs living in three villages in Gog woreda, Gambella region, Ethiopia, in April-May 2018. We analysed their exposure to potential sources of Guinea worm infection and investigated risk factors associated with infection histories. The home ranges of 125 dogs and their activity around water sources were described using GPS tracking, and the diets of 119 dogs were described using stable isotope analysis. Unlike in Chad, where Guinea worm infection is most frequent, we found no ecological or behavioural correlates of infection history in dogs in Ethiopia. Unlike in Chad, there was no effect of variation among dogs in their consumption of aquatic vertebrates (fish or frogs) on their infection history, and we found no evidence to support hypotheses for this novel transmission pathway in Ethiopia. Dog owners had apparently increased the frequency of clean water provision to dogs in response to previous infections. Variations in dog ranging behaviour, owner behaviour and the characteristics of natural water bodies all influenced the exposure of dogs to potential sources of infection. This initial study suggests that the classical transmission pathway should be a focus of attention for Guinea worm control in non-human animals in Ethiopia.

Investigation of Dracunculiasis Transmission among Humans, Chad, 2013-2017.

Dracunculiasis, slated for global eradication, typically is acquired by drinking stagnant water containing microscopic crustaceans (copepods) infected with Dracunculus medinensis larvae, causing clusters of case persons with worms emerging from the skin. Following a 10-year absence of reported cases, 9-26 sporadic human cases with few epidemiologic links have been reported annually in Chad since 2010; dog infections have also been reported since 2012. We conducted an investigation of human cases in Chad to identify risk factors. We conducted a case-control study using a standardized questionnaire to assess water and aquatic animal consumption, and links to dog infections. Case persons had laboratory-confirmed D. medinensis during 2013-2017. Each case person was matched to one to three controls without history of disease by age, gender, and residency in the village where the case person was likely infected. We estimated odds ratios (ORs) using simple conditional logistic regression. We enrolled 25 case persons with 63 matched controls. Dracunculiasis was associated with consumption of untreated water from hand-dug wells (OR: 13.4; 95% CI: 1.7-108.6), but neither with consumption of aquatic animals nor presence of infected dogs in villages. Unsafe water consumption remains associated with dracunculiasis. Education of populations about consuming safe water and using copepod filters to strain unsafe water should continue and expand, as should efforts to develop and maintain safe drinking water sources. Nevertheless, the peculiar epidemiology in Chad remains incompletely explained. Future studies of dogs might identify other risk factors.

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.

Dracunculus Species in Meso-mammals from Georgia, United States, and Implications for the Guinea Worm Eradication Program in Chad, Africa.

The prevalence and diversity of parasitic nematodes in wildlife have been well studied for certain species, yet for others considerable gaps in knowledge exist. The parasitic nematode Dracunculus insignis infects North American wildlife, and past research on this species has led to an increased understanding of the potential host diversity and transmission of the closely related human Guinea worm, Dracunculus medinensis (which is currently the focus of a global eradication program). Many definitive hosts have been documented for D. insignis; however, the life cycle has been studied only in laboratories, and only a single phylogenetic study has been conducted on D. insignis (from Canada). The goals of the present study were to investigate the prevalence of infections with Dracunculus species among wildlife at a single site (Di-Lane plantation) in the southeastern United States, evaluate the genetic diversity of parasites at this site, and investigate potential paratenic hosts that may be involved in transmission. Over 3 yr, we sampled 228 meso-mammals, reporting an overall prevalence of infection with Dracunculus insignis of 20% (46/228). Amphibians and fish were sampled in the same geographic area as infected meso-mammals. Dracunculus insignis third-stage larvae were recovered from 2 different species of amphibians, but all fish sampled were negative. Phylogenetic analysis of the partial cytochrome c oxidase I (COI) gene showed very little diversity of Dracunculus at Di-Lane; however, we did recover a single nematode from a Virginia opossum (Didelphis virginiana) that falls outside of the D. insignis clade, more closely aligns with Dracunculus lutrae, and may represent an undescribed species. This work documents the occurrence of D. insignis in frogs, a potential transmission pathway for D. insignis at a single geographic site in nature. When applied to the global Guinea Worm Eradication Program, and Chad, Africa, in particular, this work increases our knowledge of the potential role of aquatic animals in the transmission of Dracunculus species and informs on potential intervention strategies that may be applied to the eradication of Guinea worm in Africa.

Challenges in the last mile of the global guinea worm eradication program.

OBJECTIVE: The objective of this study was to identify the existing challenges in the last mile of the global Guinea Worm Eradication Program. METHODS: Systematic Review of articles published from 1 January 2000 until 31 December 2019. Papers listed in Cochrane Library, Google Scholar, ProQuest PubMed and Web of Science databases were searched and reviewed. RESULTS: Twenty-five articles met inclusion criteria of the study and were selected for analysis. Hence, relevant data were extracted, grouped and descriptively analysed. Results revealed 10 main challenges complicating the last mile of global guinea worm eradication: unusual mode of transmission; rising animal guinea worm infection; suboptimal surveillance; insecurity; inaccessibility; inadequate safe water points; migration; poor case containment measures, ecological changes; and new geographic foci of the disease. CONCLUSION: This systematic review shows that most of the current challenges in guinea worm eradication have been present since the start of the campaign. However, the recent change in epidemiological patterns and nature of dracunculiasis in the last remaining endemic countries illustrates a new twist. Considering the complex nature of the current challenges, there seems to be a need for a more coordinated and multidisciplinary approach of dracunculiasis prevention and control measures. These new strategies would help to make history by eradicating dracunculiasis as the first ever parasitic disease.

OBJECTIF: L'objectif de cette étude était d'identifier les défis existants sur le dernier kilomètre du programme mondial d'éradication de la dracunculose. MÉTHODE: Revue systématique des articles publiés du 1er janvier 2000 au 31 décembre 2019. Les articles répertoriés dans les bases de données Cochrane Library, Google Scholar, ProQuest PubMed et Web of Science ont été recherchés et examinés. RÉSULTATS: Vingt-cinq articles répondaient aux critères d'inclusion de l'étude et ont été sélectionnés pour l'analyse. Par conséquent, les données pertinentes ont été extraites, regroupées et analysées de manière descriptive. Les résultats ont révélé 10 principaux défis compliquant le dernier kilomètre de l'éradication mondiale du ver de Guinée: mode de transmission inhabituel, infection animale croissante du ver de Guinée, surveillance sous-optimale, insécurité, inaccessibilité; points d'eau salubres inadéquats, migration, mauvaises mesures de confinement des cas, changements écologiques et de nouveaux foyers géographiques de la maladie. CONCLUSION: Cette revue systématique montre que la plupart des défis actuels de l'éradication du ver de Guinée ont été présents depuis le début de la campagne. Cependant, le changement récent des profils épidémiologiques et de la nature de la dracunculose dans les derniers pays d'endémie restants illustre une nouvelle tournure. Compte tenu de la nature complexe des défis actuels, il semble nécessaire d'adopter une approche plus coordonnée et multidisciplinaire des mesures de prévention et de lutte contre la dracunculose. Ces nouvelles stratégies contribueraient à faire l'histoire en permettant l'éradication de la dracunculose en tant que toute première maladie parasitaire.

Agent-Based Simulation for Seasonal Guinea Worm Disease in Chad Dogs.

The campaign to eradicate dracunculiasis (Guinea worm [GW] disease) and its causative pathogen Dracunculus medinensis (GW) in Chad is challenged by infections in domestic dogs, which far outnumber the dwindling number of human infections. We present an agent-based simulation that models transmission of GW between a shared water source and a large population of dogs. The simulation incorporates various potential factors driving the infections including external factors and two currently used interventions, namely, tethering and larvicide water treatments. By defining and estimating infectivity parameters and seasonality factors, we test the simulation model on scenarios where seasonal patterns of dog infections could be driven by the parasite's life cycle alone or with environmental factors (e.g., temperature and rainfall) that could also affect human or dog behaviors (e.g., fishing versus farming seasons). We show that the best-fitting model includes external factors in addition to the pathogen's life cycle. From the simulation, we estimate that the basic reproductive number, R 0, is approximately 2.0; our results also show that an infected dog can transmit the infection to 3.6 other dogs, on average, during the month of peak infectivity (April). The simulation results shed light on the transmission dynamics of GWs to dogs and lay the groundwork for reducing the number of infections and eventually interrupting transmission of GW.

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.

Cooking copepods: The survival of cyclopoid copepods (Crustacea: Copepoda) in simulated provisioned water containers and implications for the Guinea Worm Eradication Program in Chad, Africa.

INTRODUCTION: The global Guinea Worm Eradication Program has reduced numbers of human infections of Guinea worm disease (dracunculiasis) to 49 cases in four countries. However, infections of domestic animals (dogs and cats) have recently been recognized and are increasing. Typically, Guinea worm (Dracunculus medinensis) transmission occurs via the ingestion of copepods from water. Despite several interventions, including tethering of dogs while worms emerge, the number of infected dogs continue to increase. One hypothesis is that dogs could be infected through the ingestion of copepods in provisioned water. OBJECTIVES: The purpose of this study was to determine whether copepods can survive in water containers under typical Chadian temperatures. METHODS: Four container types (plastic, glass, gourd, and metal) were seeded with copepods and exposed to simulated Chadian temperatures. RESULTS: All copepods in the metal containers died within 4 h. Conversely, after 8 h live copepods were still present in plastic, glass, and gourd containers. CONCLUSIONS: If provisioned water is provided to potential hosts of D. medinensis, metal containers create the most inhospitable environment for copepods. Plastic containers have little effect on copepod mortality. The use of metal containers for water provisions could be a useful tool assisting with the interruption of D. medinensis transmission among dogs.

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.

Dracunculiasis: water-borne anthroponosis vs. food-borne zoonosis.

Dracunculiasis is the first parasitic disease set for eradication. However, recent events related to the Dracunculus medinensis epidemiology in certain African countries are apparently posing new challenges to its eradication. Two novel facts have emerged: the existence of animal reservoirs (mainly dogs but also cats and baboons), and possibly a new food-borne route of transmission by the ingestion of paratenic (frogs) or transport (fish) hosts. Therefore, instead of being exclusively a water-borne anthroponosis, dracunculiasis would also be a food-borne zoonosis. The existence of a large number of infected dogs, mainly in Chad, and the low number of infected humans, have given rise to this potential food-borne transmission. This novel route would concern not only reservoirs, but also humans. However, only animals seem to be affected. Dracunculus medinensis is on the verge of eradication due to the control measures which, classically, have been exclusively aimed at the water-borne route. Therefore, food-borne transmission is probably of secondary importance, at least in humans. In Chad, reservoirs would become infected through the water-borne route, mainly in the dry season when rivers recede, and smaller accessible ponds, with a lower water level containing the infected copepods, appear, whilst humans drink filtered water and, thus, avoid infection. The total absence of control measures aimed at dogs (or at other potential reservoirs) up until the last years, added to the stimulating reward in cash given to those who find parasitized dogs, have presumably given rise to the current dracunculiasis scenario in Chad.

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.

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.