The role of domestic dogs in the transmission of zoonotic helminthes in a rural area of Mekong river basin

Distribution and prevalence of Taenia hydatigena, Taenia multiceps, and Mesocestoides spp. in Mongolian sheepdogs

Gastrointestinal parasite infections in livestock and companion animals in Mongolia have not been investigated sufficiently. This study aimed to determine the prevalence of cyclophyllid cestodes (Taeniidae and Mesocestoididae) in Mongolian sheepdogs using copro-DNA analysis. Sheepdog fecal samples (n = 1242) were collected from five ecological zones (mountain taiga, forest-steppe, steppe, desert-steppe, and desert) and four geographical regions (Western, Khangai, Central, and Eastern) within 20 of the country's 21 provinces. Among the 1242 samples, 201 (16.2%) tested positive for mitochondrial cytochrome c oxidase subunit 1 (cox1) and ribosomal 12S rRNA encoding genes of cyclophyllid cestodes. Prevalence in the mountain taiga, forest-steppe, steppe, desert-steppe, and desert zones was 29.2%, 15.4%, 15.1%, 20.1%, and 9.1%, respectively. Prevalence in the Western, Khangai, Central, and Eastern regions was 19.9%, 18.6%, 12.1%, and 12.8%, respectively. Taenia hydatigena, Taenia multiceps, and two Mesocestoides species (Mesocestoides sp.1 and Mesocestoides sp.2) were identified. T. hydatigena was found in the samples from all 20 provinces (all five zones and four regions), while T. multiceps was detected in the samples from 19 provinces (all five zones and four regions). Mesocestoides sp.1 infection was detected in the samples from all zones (except desert) and regions; it was detected in 14 provinces. Mesocestoides sp.2 infection was detected in the samples from all zones (except mountain taiga) and regions and found in seven provinces. Cyclophyllidea infection in sheepdogs is highly prevalent across Mongolia, representing a zoonotic risk. Implementation of a surveillance program for sheepdogs and their owners, and the wild animals in all ecological zones should be considered. In addition, control measures, including public awareness campaigns, especially for sheepdog owners, and periodic deworming of sheepdogs are warranted.

Current status of human liver fluke infections in the Greater Mekong Subregion

The Greater Mekong Subregion (GMS) is a trans-national region of the Mekong River basin in Southeast Asia comprising Cambodia, the People's Republic of China (specifically Yunnan Province and Guangxi Zhuang Autonomous Region), Lao People's Democratic Republic (Lao PDR), Myanmar, Thailand, and Vietnam home to more than 340 million people or almost 4.5% of the global population. Human liver fluke infections caused by Opisthorchis viverrini and Clonorchis sinensis have been major public health problems in this region for decades. Opisthorchiasis caused by O. viverrini is prevalent in Thailand, Lao PDR, Cambodia and central-southern Vietnam with more than 12 million people infected. Clonorchiasis caused by C. sinensis is endemic in northern Vietnam and Guangxi with estimated 3.5 -5 million infected. The infections can cause several liver and biliary diseases such as cholangitis, periductal fibrosis, gallstones, and cholangiocarcinoma (CCA), a fatal bile duct cancer. Key determinants of the geographical distribution differences of the two liver fluke species are snail species and geographic barriers. Main risk behaviour of the infections is the culture of eating raw fish "the raw attitude" of people in the GMS, especially the Tai/Dai/Thai/Laos ethnic groups, the major population in the GMS. Over the past 20 years, there is a big change in prevalence of the infections. Opisthorchiasis has long been endemic, particularly in northern and northeastern Thailand and Lao PDR with over 8-10 million cases estimated. However, after several rounds of national campaign against opisthorchiasis using integrated control approach in Thailand over the past three decades, the prevalence of O. viverrini infection has reduced from over 15% in 1996 to 2.2% in 2019. High prevalence of O. viverrini infection continues in Lao PDR and central Vietnam. Emerging high prevalence, up to a maximum of 47.5%, has been noted in Cambodia during the past 10 years possibly due to more studies being conducted rather than increasing prevalence. O. viverrini infection has now also been reported in Lower Myanmar in recent years. Clonorchiasis has been known in northern Vietnam and southern China for a long time. Several surveys have reported infections in Guangxi in the last 10 years, and until now liver fluke infected cases have not been reported in Yunnan. Overall, nowadays, there is a shift in high risk areas for GMS liver fluke infection from northeastern Thailand to Lao PDR, Cambodia, Vietnam, Myanmar, and Guangxi P.R. China. Urgent systematic disease mapping and integrated liver fluke control using One Health approaches should be implemented nationwide in GMS countries.

The Role of Nile Tilapia (Oreochromis niloticus) in the Life Cycle of Toxocara spp

The present study aimed to experimentally assess Nile tilapia as potential paratenic host of Toxocara spp. A total of 15 Nile tilapia (Oreochromis niloticus) were fed with 300 embryonated Toxocara canis eggs by oral gavage, while five others of the control group received distilled water. The fish were individually analyzed at 16, 24, 48, 72, and 240 h after inoculation. Water contamination was assessed, and tissue migration by liver, gastrointestinal tract (GIT), eyes, and central nervous system. A murine model was used as the paratenic host for egg infectivity assessment. Eggs and larvae were found in plastic tank water and fish GIT, ranging from 23 to 86% per fish. Eggs and larvae were recovered from the tank water (76.3%) and fish GIT (23.7%). The counting of eggs and larvae observed was negatively correlated with number of eggs and larvae in the water tank (rho = -0.698, p = 0.003). Shedding of embryonated eggs was first detected at 16 and up to 240 h, with significant egg and larvae yield decrease on water-shedding (p = 0.001) and in the GIT (p = 0.007). Although no T. canis larva was recovered in fish tissues, egg infectivity after fish GIT transit was experimentally confirmed by mice assessment. In conclusion, despite shedding viable embryonated eggs through the gastrointestinal tract, tilapias may not play a role as a suitable paratenic hosts for Toxocara spp., posing low risk of zoonotic transmission by fish meat consumption.

Human toxocariasis, a silent helminthic disease revealed in Savannakhet, Lao PDR

Toxocariasis is a zoonotic helminthiasis caused by the migrating larvae of Toxocara canis and T. cati, common roundworms of dogs and cats. Our previous study in Savannakhet Province of Lao PDR showed an infection rate of 44.1% of Toxocara spp. in dogs. Thus, we investigate if this previous high prevalence in the definitive hosts influenced the occurrence of human toxocariasis. For that we used a 38 kDa recombinant protein derived from T. canis larvae excretion secretion products in ELISA. Human serum samples were collected in the Lahanam area of Savannakhet province. The population attending the study in Lahanam village were aged from 7 to 59 years old (y/o) 65.9% (54/82) were male and 34.1% (28/82) were female. The total percentage of seropositivity to Toxocara sp. was 30.4% (25/82). Males were more likely to test positive for toxocariasis with a risk ratio of 2.70 (CI95 0.87–4.93). No significant differences between ages were seen. However, it was possible to observe an increase of optical density (OD) values in ELISA according to age. The awareness of the health system on the high prevalence of seropositivity to Toxocara sp. in Savannakhet can prevent irreversible consequences as permanent vision loss and seizures caused by this silent chronic disease revealed in the Lahanam area.

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The first survey for human toxocariasis was carried out in Savannakhet, Lao-PDR.

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Seropositivity was higher in males than females.

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Despite no reported clinical cases of toxocariasis 30.4% of seropositivity was found.

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People are at risk of exposure to Toxocara sp. larvae in Savannakhet, Lao-PDR.

Seroprevalence of Toxocara spp. infection in Southeast Asia and Taiwan

Human toxocariasis is a worldwide neglected zoonotic parasitic disease and caused mainly by Toxocara canis, and to a lesser event, by T. cati. There are only 16 epidemiological studies and 5 clinical toxocariasis case reports in 11 Southeast Asia countries and Taiwan (SEAT) that were found by searching data from PubMed in the period from January 1992 to August 2019. The overall seroprevalence in SEAT varied from 3.9% to 84.6% chiefly detected by using T. canis larval excretory-secretory antigen (TcES)-based ELISA. Playing with dogs or contacting Toxocara eggs from the contaminated soil or vegetables or eating raw meats/viscera containing encapsulated larvae seem likely the major risk factors leading to human toxocariasis in SEAT. Nevertheless, undertaking comprehensive seroepidemiological studies to establish the baseline data and beware of clinical toxocariasis cases by physicians as well as establishing adequate serodiagnostic methods in detection of Toxocara infection, e.g., TcES-based immunoblotting method in helminth endemic SEA are strongly required.

Zoonotic transmission of intestinal helminths in southeast Asia: Implications for control and elimination

Intestinal helminths are extremely widespread and highly prevalent infections of humans, particularly in rural and poor urban areas of low and middle-income countries. These parasites have chronic and often insidious effects on human health and child development including abdominal problems, anaemia, stunting and wasting. Certain animals play a fundamental role in the transmission of many intestinal helminths to humans. However, the contribution of zoonotic transmission to the overall burden of human intestinal helminth infection and the relative importance of different animal reservoirs remains incomplete. Moreover, control programmes and transmission models for intestinal helminths often do not consider the role of zoonotic reservoirs of infection. Such reservoirs will become increasingly important as control is scaled up and there is a move towards interruption and even elimination of parasite transmission. With a focus on southeast Asia, and the Philippines in particular, this review summarises the major zoonotic intestinal helminths, risk factors for infection and highlights knowledge gaps related to their epidemiology and transmission. Various methodologies are discussed, including parasite genomics, mathematical modelling and socio-economic analysis, that could be employed to improve understanding of intestinal helminth spread, reservoir attribution and the burden associated with infection, as well as assess effectiveness of interventions. For sustainable control and ultimately elimination of intestinal helminths, there is a need to move beyond scheduled mass deworming and to consider animal and environmental reservoirs. A One Health approach to control of intestinal helminths is proposed, integrating interventions targeting humans, animals and the environment, including improved access to water, hygiene and sanitation. This will require coordination and collaboration across different sectors to achieve best health outcomes for all.

Broad tapeworms (Diphyllobothriidae), parasites of wildlife and humans: Recent progress and future challenges

Tapeworms of the family Diphyllobothriidae, commonly known as broad tapeworms, are predominantly large-bodied parasites of wildlife capable of infecting humans as their natural or accidental host. Diphyllobothriosis caused by adults of the genera Dibothriocephalus, Adenocephalus and Diphyllobothrium is usually not a life-threatening disease. Sparganosis, in contrast, is caused by larvae (plerocercoids) of species of Spirometra and can have serious health consequences, exceptionally leading to host's death in the case of generalised sparganosis caused by 'Sparganum proliferum'. While most of the definitive wildlife hosts of broad tapeworms are recruited from marine and terrestrial mammal taxa (mainly carnivores and cetaceans), only a few diphyllobothriideans mature in fish-eating birds. In this review, we provide an overview the recent progress in our understanding of the diversity, phylogenetic relationships and distribution of broad tapeworms achieved over the last decade and outline the prospects of future research. The multigene family-wide phylogeny of the order published in 2017 allowed to propose an updated classification of the group, including new generic assignment of the most important causative agents of human diphyllobothriosis, i.e., Dibothriocephalus latus and D. nihonkaiensis. Genomic data of selected representatives have also begun to accumulate, promising future developments in understanding the biology of this particular group of parasites. The list of nominal species of taxonomically most complicated genus Spirometra as well as host-parasite list of 37 species of broad tapeworms parasitising marine mammals (pinnipeds and cetaceans) are also provided.

Odds, challenges and new approaches in the control of helminthiasis, an Asian study

The time is passing, and the worms are still a major struggle for local people in Asian countries, especially the less empowered and in a situation of social vulnerability. We are working in the field in Laos, Thailand, and the Philippines where the usual control programs based only on human treatment are partially effective. Areas with mass drug administration could diminish, but not eliminate STHs of endemic areas. The persistence of helminthic NTDs in the environment and animal hosts makes the eradication a very difficult task. Great changes in the landscapes of endemic areas, such as construction of dams, can change the fauna and the lifestyle of local people. Those changes can improve infrastructure, but it can also lead to social vulnerability. The challenge, then, is to conceive new and directed control programs for helminthiasis based on multi- and transdisciplinary approaches diminishing the health gap in a globalized world. In this short review, we summarize the actual scenario concerning the main helminths in Southeast Asia and how an environmental DNA approach and the use of GIS could contribute to surveillance and control programs.

Taenia solium, Taenia saginata, Taenia asiatica, their hybrids and other helminthic infections occurring in a neglected tropical diseases' highly endemic area in Lao PDR

Most part of Southeast Asia is considered endemic for human-infecting Taenia tapeworms; Taenia solium, T. saginata, and T. asiatica. However, until now there was no report of the occurrence of human cases of T. asiatica in Lao PDR. This study, conducted in Savannakhet Province, Lao PDR, microscopically examined a total of 470 fecal samples by Kato Katz method and found 86% of people harboring at least one helminth. Hookworms were detected in 56% of the samples besides Opisthorchis like eggs (42%), Trichuris trichiura (27%), Ascaris spp. (14%), and Taenia spp. (4%) eggs. Serology for cysticercosis showed 6.8% positives with results varying from 3% to 14.3% in Ethnic School students and Kalouk Kao village respectively. Species-specific PCR targeting mitochondrial DNA (mtDNA) of 28 tapeworms, recovered from 16 patients, revealed T. solium (n = 2), T. saginata (n = 21), and T. asiatica (n = 5). Two patients were confirmed to be coinfected with T. saginata and T. asiatica, indicating the endemicity of the 3 human Taenia in Lao PDR. However, nucleotide sequencing of a nuclear DNA gene, DNA polymerase delta (pold) revealed that all the tapeworms identified as T. asiatica using mtDNA had T. saginata type allele at pold locus, demonstrating that they are not "pure T. asiatica" but the hybrid descendants between the two species, confirming the wide distribution of hybrids of T. saginata/ T. asiatica in Southeast Asia. The high prevalence of several helminthic NTDs in east Savannakhet area even with conventional control measures indicates the importance to establish wide and multifaceted health programs to sustainably improve the quality of life of the populations living in these communities.

Reservoir Animals and Their Roles in Transmission of Opisthorchis viverrini

Although any fish-eating mammals could be potential definitive hosts of Opisthorchis viverrini, only a few, especially cats and dogs, are actually known reservoir hosts for this parasite. Both animals usually get infected via consuming raw or undercooked contaminated fish, fish dishes or food remains from households. The infected animals sustain parasite egg spread via open environment defecation. Cats are the most important reservoir with higher prevalence rates of O. viverrini infection than dogs in endemic areas. Usually Opisthorchis-infected animals do not exhibit apparent clinical symptoms or specific abnormalities in laboratory examinations. Pathological findings in these animal reservoirs are basically similar to those seen in humans and experimental animals, namely periductal inflammation, biliary hyperplasia and periductal fibrosis. However, O. viverrini-associated cholangiocarcinoma has not yet been reported in the reservoir animals at present. Praziquantel is a treatment of choice not only for humans but also for animal reservoirs. Integrated control of opisthorchiasis in animal reservoirs is based on holistic approaches such as EcoHealth/One Health concepts. In fact integrated control of opisthorchiasis in humans in ecosystem has also proved successful, for example, the Lawa model for opisthorchiasis control in the endemic area of Khon Kaen, Thailand. Other feral and wild animals in endemic areas might also be potential reservoirs, and this requires more investigation. In addition, genetic diversity and evolution of the flukes might also influence zoonotic capability.