Dracunculus and dracunculiasis

A new dracunculus species (Nematoda: Dracunculoidea) in neotropical otters (Lontra longicaudis) from Argentina: morphological and molecular characterization

A new species of Dracunculus is described in wild neotropical otters, Lontra longicaudis, occurring in Corrientes, Argentina, based on morphological and molecular characteristics. Worms were located in the subcutaneous tissue from two of five investigated otters. Dracunculus jaguape n. sp. is differentiated from the 14 species of Dracunculus described from mammals and reptiles by the prominent dorsal and ventral papillae on the head; deirids posterior to nerve ring; male with long needlelike spicules and presence of gubernaculum; and long first stage larva. Phylogenetic analysis using the 18S rRNA positioned Dracunculus jaguape n. sp. in an anterior position to the rest of Dracunculus sequences available and COI positioned it in a separated clade sister to Dracunculus lutrae sequences. This is the first report on the presence of this nematode in Lontra longicaudis in Argentina.

Evaluating the Effectiveness of Potential Interventions for Guinea Worm Disease in Dogs in Chad Using Simulations

Guinea worm (GW) disease (or dracunculiasis) is currently transmitted among dogs in Chad, which presents risks for the human population. We studied how interventions implemented at different levels might reduce the spread of GW disease (geographically and over time) and what levels of interventions might accelerate elimination. We built a multiple-water-source agent-based simulation model to analyze the disease transmission among dogs in Chad, as well as in geographic district clusters, and validated it using local infection data. We considered two interventions: 1) tethering, where infected dogs are kept on a leash during periods of infectivity, and 2) Abate®, under which the water source is treated to reduce infectivity. Our results showed that elimination (0 dog infections) is most likely achieved within 5 years with extremely high levels of tethering (95%) and Abate (90%), when intervention levels are uniform across district clusters. We used an optimization model to determine an improved strategy, with intervention levels which minimize the number of dogs newly infected in the 6th year, under limitations on intervention levels across clusters; the number of dogs infected after 5 years of intervention could be reduced by approximately 220 dogs with an optimized strategy. Finally, we presented strategies that consider fairness based on intervention resource levels and outcomes. Increased tethering and Abate resources above historical levels are needed to achieve the target of GW disease elimination; optimization methods can inform how best to target limited resources and reach elimination faster.

Copepod consumption by amphibians and fish with implications for transmission of Dracunculus species

Parasitic nematodes in the genus Dracunculus have a complex life cycle that requires more than one host species in both aquatic and terrestrial habitats. The most well-studied species, Dracunculus medinensis, is the causative agent of human Guinea worm disease (dracunculiasis). There are several other Dracunculus species that infect non-human animals, primarily wildlife (reptiles and mammals). The classic route of D. medinensis transmission to humans is through the ingestion of water containing the intermediate host, a cyclopoid copepod, infected with third-stage larvae (L3s). However, many animal hosts (e.g., terrestrial snakes, dogs) of other Dracunculus sp. appear unlikely to ingest a large number of copepods while drinking. Therefore, alternative routes of infection (e.g., paratenic or transport hosts) may facilitate Dracunculus transmission to these species. To better understand the role of paratenic and transport hosts in Dracunculus transmission to animal definitive hosts, we compared copepod ingestion rates for aquatic species (fish, frogs [tadpoles and adults], and newts) which may serve as paratenic or transport hosts. We hypothesized that fish would consume more copepods than amphibians. Our findings confirm that African clawed frogs (Xenopus laevis) and fish consume copepods, but that fish ingest, on average, significantly higher numbers (68% [34/50]) than adult African clawed frogs (36% [18/50]) during a 24-h time period. Our results suggest that amphibians and fish may play a role in the transmission of Dracunculus to definitive hosts. Still, additional research is required to determine whether, in the wild, fish or frogs are serving as paratenic or transport hosts. If so, they may facilitate Dracunculus transmission. However, if these animals simply act as dead-end hosts or as means of copepod population control, they may decrease Dracunculus transmission.

•

Copepod ingestion during 24 h was assessed for fish and amphibians.

•

Significant numbers of copepods were consumed by fish and adult Xenopus.

•

Tadpoles and newts did not consume large numbers of copepods during this time.

•

Fish and amphibians may facilitate Dracunculus transmission.

•

Further studies may elucidate how copepod ingestion impact parasite transmission.

Susceptibility of anurans, lizards, and fish to infection with Dracunculus species larvae and implications for their roles as paratenic hosts

Dracunculus spp. are parasitic nematodes that infect numerous species of mammals and reptiles. The life cycles of Dracunculus species are complex, and unknowns remain regarding the role of paratenic and transport hosts in transmission to definitive hosts. We had two primary objectives: to assess the susceptibility of several species of anurans, lizards, and fish as paratenic hosts for Dracunculus species, and to determine the long-term persistence of Dracunculus infections in African clawed frogs (Xenopus laevis). Animals were orally exposed to copepods infected with infectious third-stage larvae (L3s) of either Dracunculus insignis or D. medinensis. Dracunculus L3s were recovered from four anuran species, two lizard species, and one fish species, demonstrating that Dracunculus can infect tissues of a diversity of species. In long-term persistence trials, D. medinensis L3s were recovered from African clawed frogs tissues up to 58 days post-infection, and D. insignis L3s were recovered up to 244 days post-infection. Our findings regarding the susceptibility of novel species of frogs, lizards, and fish to infection with Dracunculus nematodes, and long-term persistence of L3s in paratenic hosts, address pressing knowledge gaps regarding Dracunculus infection in paratenic hosts and may guide future research regarding the transmission of Dracunculus to definitive mammalian hosts.

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.

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.

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.

Guinea worm eradication depends on detecting people and animals with the disease in order to prevent transmission. The situation in Chad is especially urgent because the number of domestic dogs with Guinea worm has been rapidly increasing in the past five years, and now represents the vast majority of Guinea worm cases globally. The global Guinea Worm Eradication Program, the Chad Guinea Worm Eradication Program, and the Chad Ministry of Public Health requested an investigation to evaluate the associations between Guinea worm knowledge, community engagement, and case detection and to investigate how the active surveillance system could be improved to more effectively detect and contain every Guinea worm case. We surveyed 627 people across 45 villages in Chad. We found that Chad’s system for monitoring Guinea worm operates unevenly, with some villagers receiving frequent visits by community volunteers and other villagers reporting never being visited. Villagers visited by a community volunteer at least twice per week had much better knowledge of Guinea worm symptoms and prevention, compared with villagers visited less frequently. Community volunteers are instrumental to Guinea worm eradication efforts in Chad because they transmit key educational messages that facilitate disease detection. More efforts should be made to increase volunteer accountability and to provide volunteers and their supervisors with targeted, high quality training.

Dracunculiasis in a domestic dog in Brazil

We report and discuss the surprising encounter of a dog naturally infected by Dracunculus sp. in Brazil, a brief clinical history of the animal and a procedure for removing the nematode. We also present details on the morphology of the fragments collected from the nematode and a phylogenetic comparison of the partial sequences of the mitochondrial 18S rRNA and cytochrome c oxidase subunit I (COI) genes, deposited with others in GenBank. The samples were an independent lineage forming a well-supported monophyletic assemblage with D. medinensis. We thus conclude that this species has not yet been sequenced or even described and will only be elucidated by more information because only two species of Dracunculus have been reported in Brazil, D. fuelleborni and D. brasiliensis.

Hopkins D, J. Weiss A. Correlates of Variation in Guinea Worm Burden among Infected Domestic Dogs

The Guinea Worm Eradication Program has been extraordinarily successful-in 2019, there were 53 human cases reported, down from the estimated 3.5 million in 1986. Yet the occurrence of Guinea worm in dogs is a challenge to eradication efforts, and underlying questions about transmission dynamics remain. We used routine surveillance data to run negative binomial regressions predicting worm burden among infected dogs in Chad. Of 3,371 infected dogs reported during 2015-2018, 38.5% had multiple worms. A multivariable model showed that the number of dogs in the household was negatively associated with worm burden (adjusted incidence rate ratio [AIRR] = 0.95, 95% CI: 0.93-0.97, P < 0.0001) after adjusting for dog age (AIRR = 0.99, 95% CI: 0.96-1.01, P > 0.1). This could relate to the amount of infective inocula (e.g., contaminated food or water) shared by multiple dogs in a household. Other significant univariable associations with worm burden included dog history of Guinea worm infection (IRR = 1.30, 95% CI: 1.18-1.45) and dog owners who were hunters (IRR = 0.78, 95% CI: 0.62-0.99, P < 0.05) or farmers (IRR = 0.83, 95% CI: 0.77-0.90, P < 0.0001). Further analysis showed that the number of dogs in the household was significantly and positively correlated with nearly all other independent variables (e.g., owner occupation: farmer, fisherman, or hunter; dog age, sex, and history of Guinea worm). The associations we identified between worm burden and dogs per household, and dogs per household and owner characteristics should be further investigated with more targeted studies.

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, R₀, 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.

Population genomic evidence that human and animal infections in Africa come from the same populations of Dracunculus medinensis

BACKGROUND

Guinea worm-Dracunculus medinensis-was historically one of the major parasites of humans and has been known since antiquity. Now, Guinea worm is on the brink of eradication, as efforts to interrupt transmission have reduced the annual burden of disease from millions of infections per year in the 1980s to only 54 human cases reported globally in 2019. Despite the enormous success of eradication efforts to date, one complication has arisen. Over the last few years, hundreds of dogs have been found infected with this previously apparently anthroponotic parasite, almost all in Chad. Moreover, the relative numbers of infections in humans and dogs suggests that dogs are currently the principal reservoir on infection and key to maintaining transmission in that country.

PRINCIPAL FINDINGS

In an effort to shed light on this peculiar epidemiology of Guinea worm in Chad, we have sequenced and compared the genomes of worms from dog, human and other animal infections. Confirming previous work with other molecular markers, we show that all of these worms are D. medinensis, and that the same population of worms are causing both infections, can confirm the suspected transmission between host species and detect signs of a population bottleneck due to the eradication efforts. The diversity of worms in Chad appears to exclude the possibility that there were no, or very few, worms present in the country during a 10-year absence of reported cases.

CONCLUSIONS

This work reinforces the importance of adequate surveillance of both human and dog populations in the Guinea worm eradication campaign and suggests that control programs aiming to interrupt disease transmission should stay aware of the possible emergence of unusual epidemiology as pathogens approach elimination.

Guinea worm in domestic dogs in Chad: A description and analysis of surveillance data

After a ten-year absence of reported Guinea worm disease in Chad, human cases were rediscovered in 2010, and canine cases were first recorded in 2012. In response, active surveillance for Guinea worm in both humans and animals was re-initiated in 2012. As of 2018, the Chad Guinea Worm Eradication Program (CGWEP) maintains an extensive surveillance system that operates in 1,895 villages, and collects information about worms, hosts (animals and humans), and animal owners. This report describes in detail the CGWEP surveillance system and explores epidemiological trends in canine Guinea worm cases during 2015-2018. Our results showed an increased in the number of canine cases detected by the system during the period of interest. The proportion of worms that were contained (i.e., water contamination was prevented) improved significantly over time, from 72.8% in 2015 to 85.7% in 2018 (Mantel-Haenszel chi-square = 253.3, P < 0.0001). Additionally, approximately 5% of owners of infected dogs reported that the dog had a Guinea worm-like infection earlier that year; 12.6% had a similar worm in a previous year. The proportion of dogs with a history of infection in a previous year increased over time (Mantel-Haenszel chi-square = 18.8, P < 0.0001). Canine cases were clustered in space and time: most infected dogs (80%) were from the Chari Baguirmi (38.1%) and Moyen Chari Regions (41.9%), and for each year the peak month of identified canine cases was June, with 78.5% occurring during March through August. Findings from this report evoke additional questions about why some dogs are repeatedly infected. Our results may help to target interventions and surveillance efforts in terms of space, time, and dogs susceptible to recurrent infection, with the ultimate goal of Guinea worm eradication.

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.

The wild world of Guinea Worms: A review of the genus Dracunculus in wildlife

Nematodes are an extremely diverse and speciose group of parasites. Adult dracunculoid nematodes (Superfamily Dracunculoidea) occur in the tissues and serous cavities of mammals, fish, reptiles, amphibians and birds. Of the dracunculid group, perhaps best known is Dracunculus medinensis, the human Guinea Worm. Considerable work has been done on D. medinensis; however recent infections in peri-domestic dogs and the finding of naturally-infected paratenic hosts (previously unreported for D. medinensis) indicate we still have much to learn about these parasites. Furthermore, among eight species in the Old World and six species in the New World there is a lack of general life history knowledge as well as questions on species occurrence, host diversity, and transmission dynamics. Herein, we provide a comprehensive review of the genus Dracunculus, in order of a theoretical evolutionary progression from reptilian to mammalian hosts. Species descriptions, where available, are provided but also show where gaps occur in our knowledge of various species. Additionally, many first reports of Dracunculus spp. were done prior to the development and use of molecular tools. This is especially important for this group of parasites as speciation based on morphology is only applicable to males of the genus, and males, given their size, are notoriously difficult to recover from definitive hosts. Therefore, we also discuss current molecular tools used in the investigation of this group of parasites. Given recent host-switching events, the dracunculids are of increasing importance and require further work to expand our understanding of this genus.

A mathematical study to control Guinea worm disease: a case study on Chad

Global eradication of Guinea worm disease (GWD) is in the final stage but a mysterious epidemic of the parasite in dog population makes the elimination programme challenging. There is neither a vaccine nor an effective treatment against the disease and therefore intervention strategies rely on the current epidemiological understandings to control the spread of the disease. A novel mathematical model can predict the future outbreaks and it can quantify the dissemination rates of control interventions. Due to the lack of such novel models, a realistic mathematical model of GWD dynamics with human population, dog population, copepod population and the worm larvae is proposed and analyzed. Considering case data from Chad, we calibrate the model and perform global sensitivity analysis of the basic reproduction number with respect to the control parameters and copepod consumption rates. Furthermore, we investigate the impact of three control interventions: awareness of humans, isolation of infected dogs and copepod clearance from contaminated water sources. We also address the impact of combination interventions which leads to the conclusion that the combination of isolating the infected dogs and treating the contaminated ponds is a plausible way for eliminating the burden of GWD from 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.

What It Means to Be Guinea Worm Free: An Insider's Account from Ghana's Northern Region

Despite several periods of stagnating guinea worm disease (GWD) incidence in Ghana during its national eradication campaign in the 1990s and early 2000s, the last reported case of GWD was in May 2010. In July 2011, Ghana celebrated the interruption of guinea worm (GW) transmission. Although it has been established that GWD causes disability, pain, and socioeconomic hardship, there is a dearth of population-based evidence collected in post-GW-endemic countries to document the value attributed to GWD eradication by residents in formerly endemic communities. Given Ghana's recent history of GWD and a concentrated burden of the disease in its Northern Region, a pattern which remained true through to the final stage of the eradication campaign, seven villages in the Northern Region were targeted for a retrospective, cross-sectional study to detail the perceptions, attitudes, and beliefs about the impact of eradication of GWD in northern Ghana. The study revealed that respondents from the sampled communities felt GW eradication improved their socioeconomic conditions, as the impact of infection prohibited the pursuit of individual and social advancement. The value residents placed on the absence of GWD highlights both the impact infection had on the pursuit of social and economic advancement and the newfound ability to be disease-free and productive. Of the 143 respondents, 133 had GWD in the past and were incapacitated for an average of 6 weeks annually per GW infection, with each infected person affected nearly four times in his or her lifetime.

Possible Role of Fish and Frogs as Paratenic Hosts of Dracunculus medinensis, Chad

Tadpoles fed infected copepods can harbor infective D. medinensis larvae and thus serve as potential paratenic hosts.

Copepods infected with Dracunculus medinensis larvae collected from infected dogs in Chad were fed to 2 species of fish and tadpoles. Although they readily ingested copepods, neither species of fish, Nile tilapia (Oreochromis niloticus) nor fathead minnow (Pimephalis promelas), were found to harbor Dracunculus larvae when examined 2–3 weeks later. Tadpoles ingested copepods much more slowly; however, upon examination at the same time interval, tadpoles of green frogs (Lithobates [Rana] clamitans) were found to harbor small numbers of Dracunculus larvae. Two ferrets (Mustela putorius furo) were fed fish or tadpoles that had been exposed to infected copepods. Only the ferret fed tadpoles harbored developing Dracunculus larvae at necropsy 70–80 days postexposure. These observations confirm that D. medinensis, like other species in the genus Dracunculus, can readily survive and remain infective in potential paratenic hosts, especially tadpoles.

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.

Guinea worm: from Robert Leiper to eradication

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

The endoparasites of Liasis fuscus (Serpentes : Boidae) from the Adelaide River floodplain, Northern Territory, Australia

This study documents the parasite assemblage of Liasis fuscus Peters, 1873 from the Adelaide River flood plain, Northern Territory, Australia. In total, nine species of helminth (comprising three cestodes and six nematodes), one pentastome and one protozoan were found in 180 water pythons, with the Nematoda being the dominant and most diverse group, and a cestode, Bothridium ornatum Maplestone & Southwell, 1923, the most prevalent species. In spite of the hosts being present in high numbers the helminth assemblage was depauperate, characterised by low prevalence, intensity, frequency and abundance of species, with neither season nor sex of host affecting abundance. There were, however, significant differences between ages of hosts, juveniles having fewer parasites, and seasonal diversity, with the wet season of 2004 and the dry of 2005 the most similar. Of the Australian python species analysed Morelia spilota (Lacépède, 1804) had the highest species richness. The lower species richness found in L. fuscus was possibly due to its unusual biology. Biogeographic relationships of the parasite fauna of L. fuscus are diverse, connections with Africa, Asia, and South America being noted.

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.

Dracunculiasis eradication and the legacy of the smallpox campaign: what's new and innovative? What's old and principled?

Coming on the heels the declaration of smallpox eradication in 1980 was the launch of the dracunculiasis (Guinea worm) eradication program, as a key outcome indicator of the success of the United Nations 1981-1990 International Drinking Water Supply and Sanitation Decade (IDWSSD). The dracunculiasis eradication campaign has carried on well beyond the close of the IDWSSD largely due to the efforts of President Jimmy Carter and The Carter Center, to assist the national Guinea Worm Eradication Programs in collaboration with partner organizations, including the Centers for Disease Control and Prevention (CDC), UNICEF, and the World Health Organization. Dracunculiasis eradication efforts have as primary tools health education, filter distribution for drinking water filtration, and case containment, all guided by rigorous village based surveillance. Additional tools are treatment of selected water sources with ABATE(R) (temephos) larvicide and provision of protected drinking water supplies. Village volunteers provide monthly reporting of cases (including reports of zero cases). The global campaign has made remarkable progress through both innovation and adherence to eradication principles. Annual cases of dracunculiasis have decreased from 3.5 million in 1986 to less than 2000 in 2010. The challenge is to reach zero cases. The task, so often faced by eradication programs, is to finish the 'final inch' in some of the most difficult places on earth to work. In the case of dracunculiasis, that is the new Republic of South Sudan.

Dracunculiasis in tribal region of southern Rajasthan, India: a case report

Although the Rajasthan state was declared rid off from dracunculiasis in 1997, nevertheless two cases in succession 2002 and 2003 were reported and the present is third one which is being reported from Dungarpur district of Rajasthan, India.

Dracunculus brasiliensis sp. n. (Nematoda: Dracunculidae) from the anaconda, Eunectes murinus (Ophidia: Boidae)

Dracunculus brasiliensis sp. n. (Dracunculidae), is described based on a single female specimen found in the body cavity of the anaconda, Eunectes murinus (L.) (Ophidia: Boidae), from the Mexiana Island, Amazon River delta, Brazil and one female previously recorded from the subcutaneous tissue of this host species imported from South America into Europe (ZOO in the Czech Republic). The new species is characterised mainly by markedly large, anteriorly protruding dorsal and ventral double papillae of the internal circle and small lateral papillae of the same circle, a widely rounded caudal end, the excretory pore situated just posterior to the nerve ring, a distinctly transversely striated cuticle and by the length (396-429 mum) of larvae from uterus. This is the first species of Dracunculus described from reptiles in South America.

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.

Dracunculus mulbus n. sp. (Nematoda: Spirurida) from the water python Liasis fuscus (Serpentes: Boidae) in northern Australia

A new species of Dracunculus Reichard, 1759 (Nematoda: Spirurida) is described from the tissues surrounding organs in the body-cavity of the water python Liasis fuscus Peters in northern Australia. One to 14 worms were recovered from 22% (27/120) of pythons examined. Males were located principally around the lungs, liver and heart of the hosts, and females were recovered from peritoneal tissue surrounding the intestines and lining the body-cavity. This species differs from previously described species of Dracunculus in the position of the papillae at the posterior end in males, and in the possession of thick, narrow caudal alae. Submedian cephalic papillae are single in both sexes. Dorsal and ventral anterior cephalic papillae are absent in males. This is the first report of a species of Dracunculus from the Australian region.

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.

Differentiating Dracunculus medinensis from D. insignis, by the sequence analysis of the 18S rRNA gene

This study, undertaken as a component of the global Dracunculiasis Eradication Program (DEP), was designed to provide molecular tools to distinguish Dracunculus medinensis, the nematode causing human dracunculiasis, from other tissue-dwelling nematodes, including other Dracunculus species that infect humans and other animals. DNA was extracted from D. medinensis and from a closely related species that infects North American carnivores, D. insignis, so that the genes coding for the small-subunit ribosomal RNA (18S rRNA) of the parasites could be amplified, sequenced and compared. Sequences were obtained for 20 specimens of D. medinensis (from humans in Pakistan, Yemen and six African countries endemic for dracunculiasis) and three of D. insignis (from raccoons trapped in the state of Georgia in the southern U.S.A.). All of the D. medinensis 18S-rRNA sequences were found to be 1819 bases long and identical. The three D. insignis 18S-rRNA sequences were also found to be identical to each other but were 1821 bases long and differed from the D. medinensis 18S- rRNA sequence at eight positions (representing a difference of 0.44%). The 18S-rRNA coding region of a Guinea worm extracted from a dog in Ghana was indistinguishable from that of the D. medinensis isolates from human cases. These results provide the basis for the molecular differentiation of D. medinensis that will permit the DEP to determine, rapidly and accurately, whether a worm recovered from an area considered dracunculiasis-free is a specimen of D. medinensis or not.

Global eradication of Guinea worm

Little more than a decade ago, it was estimated that over three million cases of dracunculiasis occurred worldwide. Since then, the numbers have fallen dramatically, thanks to the water supply initiatives of the 1980s and, more recently, the national guinea worm eradication programmes implemented in a score of endemic countries. Hervé Periès and Sandy Cairncross discuss how eradication will require the containment of cases in the remaining endemic areas, together with the simultaneous strengthening of surveillance to permit the certification of eradication. This aim requires existing strategies to be adapted to maintain their efficacy and also to improve their sustainability and cost-effectiveness. Sudan with its civil war, and more than a hundred thousand reported cases, remains a major obstacle to rapid achievement of the goal.

Redescription of Dracunculus globocephalus Mackin, 1927 (Nematoda: Dracunculidae), a parasite of the snapping turtle, Chelydra serpentina

Dracunculus globocephalus Mackin, 1927 (Nematoda: Dracunculoidea) is redescribed from specimens collected from the mesentery of the snapping turtle, Chelydra serpentina (L.), in Louisiana, USA. The use of scanning electron microscopy, applied for the first time in this species, made it possible to study details in the structure of the cephalic end and the arrangement of male caudal papillae that are difficult to observe under the light microscope. This species markedly differs from all other species of Dracunculus in having the spicules greatly unequal in size and shape, in the absence of a gubernaculum, and in the disposition of male caudal papillae. The validity of D. globocephalus is confirmed, but the above mentioned morphological differences are not sufficient for listing it in a separate genus. This is the first record of D. globocephalus in Louisiana.

Some aspects of the taxonomy and biology of dracunculoid nematodes parasitic in fishes: a review

The nematode superfamily Dracunculoidea includes 166 recognized species, of which 150 (90%) are parasitic in about 300 species of freshwater, brackish-water and marine fishes. Fish dracunculoids are placed in 31 genera (86% of all dracunculoid genera) belonging to eight of the nine dracunculoid families: Anguillicolidae, Daniconematidae, Guyanemidae, Lucionematidae, Micropleuridae, Philometridae, Skrjabillanidae, and Tetanonematidae; the genus Lockenloia is considered incertae sedis. Because of difficulties in studying fish dracunculoids, associated with their morphological and biological peculiarities, most species of these largely histozoic parasites are poorly known and males of the majority of species and of eight genera have not yet been discovered. It is apparent that the present classification system of dracunculoids as a whole does not reflect phylogenetic relationships and a taxonomic revision of this nematode group, based on detailed morphological (including SEM and TEM), life history and molecular studies of individual species, is quite necessary. Data on the biology of fish dracunculoids is scarce. In known cases, their life cycles involve copepods, ostracods or branchiurids as intermediate hosts and, sometimes, fish paratenic hosts are known to occur in dracunculoid species parasitizing as adults piscivorous definitive hosts. However, nothing is known about the life cycles of representatives of 20 genera. Some species of dracunculoids, particularly of philometrids, are highly pathogenic and are known as agents of serious fish diseases. During recent years, especially the importance of Philometra spp. parasitizing the gonads of many species of marine fishes has increased due in particular to the rapid development of marine aquaculture, because they may significantly decrease fish reproduction or even cause full parasitic castration. Therefore, further detailed studies on fish dracunculoids are significant not only from the theoretical viewpoint, but they may also have practical implications.

Dracunculiasis (Guinea worm disease) and the eradication initiative

Dracunculiasis, also known as guinea worm disease, is caused by the large female of the nematode Dracunculus medinensis, which emerges painfully and slowly from the skin, usually on the lower limbs. The disease can infect animals, and sustainable animal cycles occur in North America and Central Asia but do not act as reservoirs of human infection. The disease is endemic across the Sahel belt of Africa from Mauritania to Ethiopia, having been eliminated from Asia and some African countries. It has a significant socioeconomic impact because of the temporary disability that it causes. Dracunculiasis is exclusively caught from drinking water, usually from ponds. A campaign to eradicate the disease was launched in the 1980s and has made significant progress. The strategy of the campaign is discussed, including water supply, health education, case management, and vector control. Current issues including the integration of the campaign into primary health care and the mapping of cases by using geographic information systems are also considered. Finally, some lessons for other disease control and eradication programs are outlined.

Rheumatic manifestations of parasitic diseases

OBJECTIVES

To consolidate the spectrum and frequency of parasite-related rheumatic syndromes, which have largely been regarded as exceedingly rare by the general medicine, infectious disease, and rheumatology literature.

METHODS

A MEDLINE search was performed for articles on rheumatic syndromes related to parasitic infections published from 1966 through December 2000. Identified articles included clinical and epidemiologic studies describing cases of rheumatic syndromes associated with verified parasitic infection.

RESULTS

Rheumatologic syndromes, including inflammatory arthritis, inflammatory myositis, and vasculitis, have been described among multiple different parasite infections of all parasitic divisions, including Protozoa, Nematoda, and Platyhelminthes. Individual parasitic divisions are often associated with particular rheumatic syndromes, such as reactive arthritis and spondyloarthropathy, inflammatory or infectious myositis, and reactive or parainfectious vasculitis.

CONCLUSIONS AND RELEVANCE

Parasitic infection may underlie the clinical presentation of some rheumatic conditions. Given the continued and growing number of patients at risk for parasitosis by virtue of their country of origin, travel habits, and an immunocompromised state, potential parasitosis must be considered in patients undergoing evaluation for rheumatic complaints.

Studies on immunodiagnosis of dracunculiasis. II. Search for circulating antigens

Sera from individuals living in a dracunculiasis endemic area of northern Ghana were examined for circulating Dracunculus medinensis antigens by applying protocols previously developed for detection of circulating antigens in other helminth infections. Antisera from rabbits immunised with homogenized first stage D. medinensis larvae were used for antigen capture and detection in three different forms, namely non-treated, biotinylated and horseradish peroxidase (HRP)-labelled. Three different preparations of human sera were examined, namely non-treated, pre-treated with polyethylene glycol/ethylenediaminetetra-acetic acid (PEG/EDTA) for analysis of precipitated immune complexes, and pre-treated with trichloroacetic acid (TCA) for analysis of isolated glycoproteins. In both SDS-PAGE/Western blotting and ELISA, significant reactivity was observed between non-treated and treated rabbit-antisera on the one hand and non-treated and treated human sera on the other. However, no significant response differences were observed between sera obtained from individuals with dracunculiasis and non-endemic controls. The reasons are analysed and possible explanations presented. The study provided no evidence that D. medinensis-specific circulating antigens, detectable by relatively simple means, occur in infected individuals.

Studies on immunodiagnosis of dracunculiasis. I. Detection of specific serum antibodies

To explore the possibility for development of an immunodiagnostic test for Dracunculus medinensis infections, the antibody responses (IgG1, IgG2, IgG3, IgG4 and IgE) to antigen preparations made from adult female worms (ADGW) and first stage larvae (LVGW) of D. medinensis were analysed. By sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE)/Western blotting, sera from individuals with patent D. medinensis infection reacted extensively and similarly with ADGW and LVGW over a broad molecular weight range (5-200 kDa). Sera from individuals infected with Onchocerca volvulus (the major cross-reacting infection) had a more pronounced reaction with ADGW than LVGW, and only with antigens of molecular weights above 23 kDa. These findings were used to design an enzyme-linked immunosorbent assay (ELISA) with high sensitivity and specificity for D. medinensis infection. The most promising results were obtained when detecting for specific IgG4. Thus, when using LVGW, the assay had a sensitivity of 83% and a specificity of 97%. Refining the antigen into a low molecular weight filtrate improved the sensitivity to 92%, and the sensitivity was further improved (to 96%) when combining the results from two or more antibody types measured simultaneously, without affecting the specificity. The results were encouraging for the prospects for developing an applicable immunodiagnostic test for patent D. medinensis infections based on detection of specific serum antibodies.

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.

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.