Progress Toward Eradication of Dracunculiasis - Worldwide, January 2022-June 2023.

The effort to eradicate Dracunculus medinensis, the etiologic agent of dracunculiasis, or Guinea worm disease, commenced at CDC in 1980. In 1986, with an estimated 3.5 million cases worldwide in 20 African and Asian countries, the World Health Assembly called for dracunculiasis elimination. The Guinea Worm Eradication Program (GWEP) was established to help countries with endemic dracunculiasis reach this goal. GWEP is led by The Carter Center and supported by partners that include the World Health Organization, UNICEF, and CDC. In 2012, D. medinensis infections were unexpectedly confirmed in Chadian dogs, and since then, infections in dogs, cats, and baboons have posed a new challenge for GWEP, as have ongoing civil unrest and insecurity in some areas. By 2022, dracunculiasis was endemic in five countries (Angola, Chad, Ethiopia, Mali, and South Sudan), with only 13 human cases identified, the lowest yearly total ever reported. Animal infections, however, were not declining at the same rate: 686 animal infections were reported in 2022, including 606 (88%) in dogs in Chad. Despite these unanticipated challenges as well as the COVID-19 pandemic, countries appear close to reaching the eradication goal. GWEP will continue working with country programs to address animal infections, civil unrest, and insecurity, that challenge the eradication of Guinea worm.

Participating in eradication: how Guinea worm redefined eradication, and eradication redefined Guinea worm, 1985-2022.

Guinea worm disease (dracunculiasis) is a debilitating waterborne disease. Once widespread, it is now on the brink of eradication. However, the Guinea Worm Eradication Programme (GWEP), like guinea worm itself, has been under-studied by historians. The GWEP demonstrates an unusual model of eradication, one focused on primary healthcare (PHC), community participation, health education and behavioural change (safe drinking). The PHC movement collided with a waterborne disease, which required rapid but straightforward treatment to prevent transmission, creating a historical space for the emergence of village-based volunteer health workers, as local actors realigned global health policy on a local level. These Village Volunteers placed eradication in the hands of residents of endemic areas, epitomising the participation-focused nature of the GWEP. This participatory mode of eradication highlights the agency of those in endemic areas, who, through volunteering, safe drinking and community self-help, have been the driving force behind dracunculiasis eradication. In the twenty-first century, guinea worm has become firstly a problem of human mobility, as global health has struggled to contain cases in refugees and nomads, and latterly a zoonotic disease, as guinea worm has shifted hosts to become primarily a parasite of dogs. This demonstrates both the potential of One Health approaches and the need for One Health to adopt from PHC and the GWEP a focus on the health of humans and animals in isolated and impoverished areas. Guinea worm demonstrates how the biological and the historical interact, with the GWEP and guinea worm shaping each other over the course of the eradication programme.

Responding to Africa's burden of disease: accelerating progress.

Although Africa is home to about 14% of the global population (1.14 billion people), it is growing three times faster than the global average [1]. The continent carries a high burden of disease, but there has been real progress in eradication, elimination, and control since 2015. Examples are the eradication of wild polio in 2020 [2] and the eradication or elimination of neglected tropical diseases, such as dracunculiasis in Kenya in 2018; Human African trypanosomiasis in Togo in 2022; and trachoma in Togo, Gambia, Ghana, and Malawi in 2022 [3]. New HIV infections reduced by 44% in 2021 compared to 2010 [4], and in 2021 the African region passed the 2020 milestone of the End TB Strategy, with a 22% reduction in new infections compared with 2015 [5].

Progress Toward Global Eradication of Dracunculiasis - Worldwide, January 2021-June 2022.

Dracunculiasis (Guinea worm disease), caused by the parasite Dracunculus medinensis, is acquired by drinking water containing small crustacean copepods (water fleas) infected with D. medinensis larvae. Recent evidence suggests that the parasite also appears to be transmitted by eating fish or other aquatic animals. About 1 year after infection, the worm typically emerges through the skin on a lower limb of the host, causing pain and disability (1). No vaccine or medicine is available to prevent or treat dracunculiasis. Eradication relies on case containment* to prevent water contamination and other interventions to prevent infection, including health education, water filtration, treatment of unsafe water with temephos (an organophosphate larvicide), and provision of safe drinking water (1,2). CDC began worldwide eradication efforts in October 1980, and in 1984 was designated by the World Health Organization (WHO) as the technical monitor of the Dracunculiasis Eradication Program (1). In 1986, with an estimated 3.5 million cases† occurring annually in 20 African and Asian countries§ (3), the World Health Assembly called for dracunculiasis elimination. The Guinea Worm Eradication Program (GWEP),¶ led by The Carter Center and supported by partners that include WHO, UNICEF, and CDC, began assisting ministries of health in countries with endemic disease. In 2021, a total of 15 human cases were identified and three were identified during January-June 2022. As of November 2022, dracunculiasis remained endemic in five countries (Angola, Chad, Ethiopia, Mali, and South Sudan); cases reported in Cameroon were likely imported from Chad. Eradication efforts in these countries are challenged by infection in animals, the COVID-19 pandemic, civil unrest, and insecurity. Animal infections, mostly in domestic dogs, some domestic cats, and in Ethiopia, a few baboons, have now surpassed human cases, with 863 reported animal infections in 2021 and 296 during January-June 2022. During the COVID-19 pandemic all national GWEPs remained fully operational, implementing precautions to ensure safety of program staff members and community members. In addition, the progress toward eradication and effectiveness of interventions were reviewed at the 2021 and 2022 annual meetings of GWEP program managers, and the 2021 meeting of WHO's International Commission for the Certification of Dracunculiasis Eradication. With only 15 human cases identified in 2021 and three during January-June 2022, program efforts appear to be closer to reaching the goal of eradication. However, dog infections and impeded access because of civil unrest and insecurity in Mali and South Sudan continue to be the greatest challenges for the program. This report describes progress during January 2021-June 2022 and updates previous reports (2,4).

Development and validation of a quantitative PCR for the detection of Guinea worm (Dracunculus medinensis).

Dracunculus medinensis (Guinea worm) is a parasitic nematode that can cause the debilitating disease dracunculiasis (Guinea worm disease) in humans. The global Guinea Worm Eradication Program has led intervention and eradication efforts since the 1980s, and Guinea worm infections in people have decreased >99.99%. With the final goal of eradication drawing nearer, reports of animal infections from some remaining endemic countries pose unique challenges. Currently, confirmation of suspected Guinea worm infection relies on conventional molecular techniques such as polymerase chain reaction (PCR), which is not specific to Guinea worm and, therefore, requires sequencing of the PCR products to confirm the identity of suspect samples, a process that often takes a few weeks. To decrease the time required for species confirmation, we developed a quantitative PCR assay targeting the mitochondrial cytochrome b (cytb) gene of Guinea worm. Our assay has a limit of detection of 10 copies per reaction. The mean analytical parameters (± SE) were as follows: efficiency = 93.4 ± 7.7%, y-intercept = 40.93 ± 1.11, slope = -3.4896 ± 0.12, and the R2 = 0.999 ± 0.004. The assay did not amplify other nematodes found in Guinea worm-endemic regions and demonstrated 100% diagnostic sensitivity and specificity. Implementation of this quantitative PCR assay for Guinea worm identification could eliminate the need for DNA sequencing to confirm species. Thus, this approach can be implemented to provide more rapid confirmation of Guinea worm infections, leading to faster execution of Guinea worm interventions while increasing our understanding of infection patterns.

Dracunculiasis Eradication: End-Stage Challenges.

This report summarizes the status of the global Dracunculiasis Eradication Program as of the end of 2021. Dracunculiasis (Guinea worm disease) has been eliminated from 17 of 21 countries where it was endemic in 1986, when an estimated 3.5 million cases occurred worldwide. Only Chad, Ethiopia, Mali, and South Sudan reported cases in humans in 2021. Chad, Ethiopia, and Mali also reported indigenous infections of animals, mostly domestic dogs, with Dracunculus medinensis. Insecurity and infections in animals are the main obstacles remaining to interrupting dracunculiasis transmission completely.

Epidemiological and molecular investigations of a point-source outbreak of Dracunculus medinensis infecting humans and dogs in Chad: a cross-sectional study.

BACKGROUND: Dracunculiasis (also known as Guinea worm disease), caused by the Dracunculus medinensis nematode, is progressing towards eradication, with a reduction in cases from 3·5 million cases in the mid-1980s to only 54 human cases at the end of 2019. Most cases now occur in Chad. On April 19, 2019, a 19-year-old woman presented with D medinensis in an area within the Salamat region of Chad, where the disease had not been previously reported. We aimed to investigate the connection between this case and others detected locally and elsewhere in Chad using a combination of epidemiological and genetic approaches. METHODS: In this cross-sectional field study, we conducted household case searches and informal group interviews in the Bogam, Liwi, and Tarh villages in Chad. All community members including children were eligible for participation in the outbreak investigation. Adult female D medinensis associated with this outbreak were collected for genetic analysis (18 from humans and two from dogs). Four mitochondrial genes and 22 nuclear microsatellite markers were used to assess relatedness of worms associated with the outbreak in comparison with other worms from elsewhere in Chad. FINDINGS: Between April 12 and Sept 6, 2019, we identified 22 human cases and two canine cases of dracunculiasis associated with 15 households. Six (40%) of the 15 affected households had multiple human or canine cases within the household. Most cases of dracunculiasis in people were from three villages in Salamat (21 [95%] of 22 cases), but one case was detected nearly 400 km away in Sarh city (outside the Salamat region). All people with dracunculiasis reported a history of consuming fish and unfiltered water. Worms associated with this outbreak were genetically similar and shared the same maternal lineage. INTERPRETATION: Molecular epidemiological results suggest a point-source outbreak that originated from a single female D medinensis, rather than newly identified sustained local transmission. The failure of the surveillance system to detect the suspected canine infection in 2018 highlights the challenge of canine D medinensis detection, particularly in areas under passive surveillance. Human movement can also contribute to dracunculiasis spread over long distances. FUNDING: The Carter Center.

Effects of Temephos (Abate®), Spinosad (Natular®), and Diflubenzuron on the Survival of Cyclopoid Copepods.

Dracunculus medinensis, also known as the African Guinea worm, is the causative agent of dracunculiasis and the focus of the global Guinea Worm Eradication Program (GWEP). Transmission of D. medinensis to humans occurs primarily by drinking water containing cyclopoid copepods infected with third-stage D. medinensis larvae. A common intervention to interrupt transmission and decrease the number of copepods in infected water bodies is the application of the organophosphate larvicide Abate® (temephos). However, the use of alternative compounds to help decrease copepod populations would be beneficial to the GWEP. We compared the immobilization of copepods by three compounds: Abate, Natular® (spinosad), and diflubenzuron. Our results confirm that neither diflubenzuron nor Natular immobilized copepods as quickly or as effectively as Abate. However, doubling or tripling the suggested concentration of Natular resulted in immobilization rates similar to Abate over 72 hours of continuous exposure. Further research on the possible effects of higher concentrations of Natular on the environment and nontarget organisms is necessary to determine whether this compound can be used safely to control the copepod population.

Seasonal fishery facilitates a novel transmission pathway in an emerging animal reservoir of Guinea worm.

Exploitation of natural resources is a driver of human infectious disease emergence. The emergence of animal reservoirs of Guinea worm Dracunculus medinensis, particularly in domestic dogs Canis familiaris, has become the major impediment to global eradication of this human disease. 93% of all Guinea worms detected worldwide in 2020 were in dogs in Chad. Novel, non-classical pathways for transmission of Guinea worm in dogs, involving consumption of fish, have been hypothesized to support the maintenance of this animal reservoir. We quantified and analyzed variation in Guinea worm emergence in dogs in Chad, across three climatic seasons, in multiple villages and districts. We applied forensic stable isotope analyses to quantify dietary variation within and among dogs and GPS tracking to characterize their spatial ecology. At the end of the hot-dry season and beginning of the wet season, when fishing by people is most intensive, Guinea worm emergence rates in dogs were highest, dogs ate most fish, and fish consumption was most closely associated with disease. Consumption of fish by dogs enables a non-classical transmission pathway for Guinea worm in Chad. Seasonal fisheries and the facilitation of dogs eating fish are likely contributing to disease persistence and to this key impediment to human disease eradication. Interrelated natural resource use, climatic variation, companion animal ecology, and human health highlight the indispensability of One Health approaches to the challenges of eradicating Guinea worm and other zoonotic diseases.

Progress Toward Global Eradication of Dracunculiasis, January 2020-June 2021.

Dracunculiasis (Guinea worm disease), caused by the parasite Dracunculus medinensis, is traditionally acquired by drinking water containing copepods (water fleas) infected with D. medinensis larvae, but in recent years also appears increasingly to be transmitted by eating fish or other aquatic animals. The worm typically emerges through the skin on a lower limb of the host 1 year after infection, causing pain and disability (1). There is no vaccine or medicine to prevent or medicine to treat dracunculiasis; eradication relies on case containment* to prevent water contamination and other interventions to prevent infection: health education, water filtration, treatment of unsafe water with temephos (an organophosphate larvicide), and provision of safe drinking water (1,2). The eradication campaign began in 1980 at CDC (1). In 1986, with an estimated 3.5 million cases† occurring annually in 20 African and Asian countries§ (3), the World Health Assembly called for dracunculiasis elimination (4). The Guinea Worm Eradication Program (GWEP), led by The Carter Center and supported by the World Health Organization (WHO), UNICEF, CDC, and other partners, began assisting ministries of health in countries with endemic disease. With 27 cases in humans reported in 2020, five during January-June 2021, and only six countries currently affected by dracunculiasis (Angola, Chad, Ethiopia, Mali, South Sudan, and importations into Cameroon), achievement of eradication appears to be close. However, dracunculiasis eradication is challenged by civil unrest, insecurity, and epidemiologic and zoologic concerns. Guinea worm infections in dogs were first reported in Chad in 2012. Animal infections have now overtaken human cases, with 1,601 reported animal infections in 2020 and 443 during January-June 2021. Currently, all national GWEPs remain fully operational, with precautions taken to ensure safety of program staff and community members in response to the COVID-19 pandemic. Because of COVID-19, The Carter Center convened the 2020 and 2021 annual GWEP Program Managers meetings virtually, and WHO's International Commission for the Certification of Dracunculiasis Eradication met virtually in October 2020. Since 1986, WHO has certified 199 countries, areas, and territories dracunculiasis-free. Six countries are still affected: five with endemic disease and importations into Cameroon. Seven countries (five with endemic dracunculiasis, Democratic Republic of the Congo, and Sudan) still lack certification (4). The existence of infected dogs, especially in Chad, and impeded access because of civil unrest and insecurity in Mali and South Sudan are now the greatest challenges to interrupting transmission. This report describes progress during January 2020-June 2021 and updates previous reports (2,4,5).

Assessment of the Chad guinea worm surveillance information system: A pivotal foundation for eradication.

BACKGROUND: In the absence of a vaccine or pharmacological treatment, prevention and control of Guinea worm disease is dependent on timely identification and containment of cases to interrupt transmission. The Chad Guinea Worm Eradication Program (CGWEP) surveillance system detects and monitors Guinea worm disease in both humans and animals. Although Guinea worm cases in humans has declined, the discovery of canine infections in dogs in Chad has posed a significant challenge to eradication efforts. A foundational information system that supports the surveillance activities with modern data management practices is needed to support continued program efficacy. METHODS: We sought to assess the current CGWEP surveillance and information system to identify gaps and redundancies and propose system improvements. We reviewed documentation, consulted with subject matter experts and stakeholders, inventoried datasets to map data elements and information flow, and mapped data management processes. We used the Information Value Cycle (IVC) and Data-Information System-Context (DISC) frameworks to help understand the information generated and identify gaps. RESULTS: Findings from this study identified areas for improvement, including the need for consolidation of forms that capture the same demographic variables, which could be accomplished with an electronic data capture system. Further, the mental models (conceptual frameworks) IVC and DISC highlighted the need for more detailed, standardized workflows specifically related to information management. CONCLUSIONS: Based on these findings, we proposed a four-phased roadmap for centralizing data systems and transitioning to an electronic data capture system. These included: development of a data governance plan, transition to electronic data entry and centralized data storage, transition to a relational database, and cloud-based integration. The method and outcome of this assessment could be used by other neglected tropical disease programs looking to transition to modern electronic data capture systems.

Quantifying conflict zones as a challenge to certification of Guinea worm eradication in Africa: a new analytical approach.

OBJECTIVES: To quantify conflict events and access across countries that remain to be certified free of transmission of Dracunculus medinensis (Guinea worm disease) or require postcertification surveillance as part of the Guinea Worm Eradication Programme (GWEP). SETTING AND PARTICIPANTS: Populations living in Guinea worm affected areas across seven precertification countries and 13 postcertification sub-Saharan African countries. OUTCOME MEASURES: The number of conflict events and rates per 100 000 population, the main types of conflict and actors reported to be responsible for events were summarised and mapped across all countries. Chad and Mali were presented as case studies. Guinea worm information was based on GWEP reports. Conflict data were obtained from the Armed Conflict Location and Event Data Project. Maps were created using ArcGIS V.10.7 and access was measured as regional distance and time to cities. RESULTS: More than 980 000 conflict events were reported between 2000 and 2020, with a significant increase since 2018. The highest number and rates were reported in precertification Mali (n=2556; 13.0 per 100 000), South Sudan (n=2143; 19.4), Democratic Republic of Congo (n=7016; 8.1) and postcertification Nigeria (n=6903; 3.4), Central Africa Republic (n=1251; 26.4), Burkina Faso (n=2004; 9.7). Violence against civilians, protests and battles were most frequently reported with several different actors involved including Unidentified Armed Groups and Boko Haram. Chad and Mali had contracting epidemiological and conflict situations with affected regions up to 700 km from the capital or 10 hours to the nearest city. CONCLUSIONS: Understanding the spatial-temporal patterns of conflict events, identifying hotspots, the actors responsible and their sphere of influence is critical for the GWEP and other public health programmes to develop practical risk assessments, deliver essential health interventions, implement innovative surveillance, determine certification and meet the goals of eradication.

Alternative transmission pathways for guinea worm in dogs: implications for outbreak risk and control.

Guinea worm (Dracunculus medinensis) has exerted a high human health burden in parts of Africa. Complete eradication of Guinea worm disease (dracunculiasis) may be delayed by the circulation of the parasite in domestic dogs. As with humans, dogs acquire the parasite by directly ingesting infected copepods, and recent evidence suggests that consuming frogs that ingested infected copepods as tadpoles may be a viable transmission route (paratenic route). To understand the relative contributions of direct and paratenic transmission routes, we developed a mathematical model that describes transmission of Guinea worm between dogs, copepods and frogs. We explored how the parasite basic reproductive number (R0) depends on parameters amenable to actionable interventions under three scenarios: frogs/tadpoles do not consume copepods; tadpoles consume copepods but frogs do not contribute to transmission; and frogs are paratenic hosts. We found a non-monotonic relationship between the number of dogs and R0. Generally, frogs can contribute to disease control by removing infected copepods from the waterbody even when paratenic transmission can occur. However, paratenic transmission could play an important role in maintaining the parasite when direct transmission is reduced by interventions focused on reducing copepod ingestion by dogs. Together, these suggest that the most effective intervention strategies may be those which focus on the reduction of copepods, as this reduces outbreak potential irrespective of the importance of the paratenic route.

Linked surveillance and genetic data uncovers programmatically relevant geographic scale of Guinea worm transmission in Chad.

BACKGROUND: Guinea worm (Dracunculus medinensis) was detected in Chad in 2010 after a supposed ten-year absence, posing a challenge to the global eradication effort. Initiation of a village-based surveillance system in 2012 revealed a substantial number of dogs infected with Guinea worm, raising questions about paratenic hosts and cross-species transmission. METHODOLOGY/PRINCIPAL FINDINGS: We coupled genomic and surveillance case data from 2012-2018 to investigate the modes of transmission between dog and human hosts and the geographic connectivity of worms. Eighty-six variants across four genes in the mitochondrial genome identified 41 genetically distinct worm genotypes. Spatiotemporal modeling revealed worms with the same genotype ('genetically identical') were within a median range of 18.6 kilometers of each other, but largely within approximately 50 kilometers. Genetically identical worms varied in their degree of spatial clustering, suggesting there may be different factors that favor or constrain transmission. Each worm was surrounded by five to ten genetically distinct worms within a 50 kilometer radius. As expected, we observed a change in the genetic similarity distribution between pairs of worms using variants across the complete mitochondrial genome in an independent population. CONCLUSIONS/SIGNIFICANCE: In the largest study linking genetic and surveillance data to date of Guinea worm cases in Chad, we show genetic identity and modeling can facilitate the understanding of local transmission. The co-occurrence of genetically non-identical worms in quantitatively identified transmission ranges highlights the necessity for genomic tools to link cases. The improved discrimination between pairs of worms from variants identified across the complete mitochondrial genome suggests that expanding the number of genomic markers could link cases at a finer scale. These results suggest that scaling up genomic surveillance for Guinea worm may provide additional value for programmatic decision-making critical for monitoring cases and intervention efficacy to achieve elimination.

Surveillance of Human Guinea Worm in Chad, 2010-2018.

The total number of Guinea worm cases has been reduced by 99.9% since the mid-1980s when the eradication campaign began. Today, the greatest number of cases is reported from Chad. In this report, we use surveillance data collected by the Chad Guinea Worm Eradication Program to describe trends in human epidemiology. In total, 114 human cases were reported during the years 2010-2018, with highest rates of containment (i.e., water contamination prevented) in the years 2013, 2014, 2016, and 2017 (P < 0.0001). Approximately half of case-patients were female, and 65.8% of case-patients were aged 30 years or younger (mean: 26.4 years). About 34.2% of case-patients were farmers. Cases were distributed across many ethnicities, with a plurality of individuals being of the Sara Kaba ethnicity (21.3%). Most cases occurred between the end of June and the end of August and were clustered in the Chari Baguirmi (35.9%) and Moyen Chari regions (30.1%). Cases in the northern Chari River area peaked in April and in August, with no clear temporal pattern in the southern Chari River area. History of travel within Chad was reported in 7.0% of cases, and male case-patients (12.5%) were more likely than female case-patients (1.7%) to have reported a history of travel (P = 0.03). Our findings confirm that human Guinea worm is geographically disperse and rare. Although the proportion of case-patients with travel history is relatively small, this finding highlights the challenge of surveillance in mobile populations in the final stages of the global eradication campaign.

Community-based Guinea worm surveillance in Chad: Evaluating a system at the intersection of human and animal disease.

BACKGROUND: Guinea worm is a debilitating parasitic infection targeted for eradication. Annual human cases have dropped from approximately 3,500,000 in 1986 to 54 in 2019. Recent identification of canine cases in Chad threatens progress, and therefore detection, prevention, and containment of canine cases is a priority. We investigated associations between disease knowledge, community engagement, and canine cases in Chad to identify opportunities to improve active surveillance. METHODS: We surveyed 627 respondents (villagers, local leaders, community volunteers, and supervisors) across 45 villages under active surveillance. Descriptive statistics were analyzed by respondent category. Logistic regression models were fitted to assess the effects of volunteer visit frequency on villager knowledge. RESULTS: Knowledge increased with respondents' associations with the Guinea worm program. Household visit frequency by community volunteers was uneven: 53.0% of villagers reported visits at least twice weekly and 21.4% of villagers reported never being visited. Villagers visited by a volunteer at least twice weekly had better knowledge of Guinea worm symptoms (OR: 1.71; 95% CI: 1.04-2.79) and could name more prevention strategies (OR: 2.04; 95% CI: 1.32-3.15) than villagers visited less frequently. The primary motivation to report was to facilitate care-seeking for people with Guinea worm. Knowledge of animal "containment" to prevent contamination of water, knowledge of rewards for reporting animal cases, and ability to name any reasons to report Guinea worm were each positively correlated with village canine case counts. CONCLUSIONS: Community volunteers play crucial roles in educating their neighbors about Guinea worm and facilitating surveillance. Additional training and more attentive management of volunteers and supervisors could increase visit frequency and further amplify their impact. Emphasizing links between animal and human cases, the importance of animal containment, and animal rewards might improve surveillance and canine case detection. The surveillance system should be evaluated routinely to expand generalizability of data and monitor changes over time.

A mathematical model of Guinea worm disease in Chad with fish as intermediate transport hosts.

Guinea-worm disease (GWD) was thought to be almost eliminated in Chad when it reemerged in 2010. The disease now shows a peculiar pattern of spreading along Chari River and its tributaries, rather than clustering around a particular drinking water source. We create a mathematical model of GWD that includes the population dynamics of the parasite as well as the dynamics of its hosts (copepods, fish, humans, and domestic dogs). We calibrate our model based on data from the literature and validate it on the recent GWD annual incidence data from Chad. The effective reproduction number predicted by our model agrees well with the empirical value of roughly 1.25 derived directly from the data. Our model thus supports the hypothesis that the parasite now uses fish as intermediate transport hosts. We predict that GWD transmission can be most easily interrupted by avoiding eating uncooked fish and by burying the fish entrails to prevent transmission through dogs. Increasing the mortality of copepods and even partially containing infected dogs to limit their access to water sources is another important factor for GWD eradication.