Population dynamics and host reactions in young foxes following experimental infection with the minute intestinal fluke, Haplorchis pumilio

Liver fluke infections by Amphimerus sp. (Digenea: Opisthorchiidae) in definitive and fish intermediate hosts in Manabí province, Ecuador

Amphimerus sp. is a fluke that dwells in the biliary tracts of vertebrate definitive hosts including humans, domestic, and wild mammals in Latin America. Opisthorchiid liver infections are rarely studied in the Americas confirming its status as a neglected tropical disease. In Ecuador, small trematode eggs were reported in human cases from the province of Manabí in 1949, and recently, Amphimerus sp. adults were recovered from human and reservoir hosts in the province of Esmeraldas. Due to the lack of research on the infectious sources of Amphimerus sp. in the continent, we have developed a series of epidemiological studies with parasitological and molecular techniques to elucidate the endemicity of opisthorchiid fluke infections. We developed a cross-sectional study in three communities at Pedro Pablo Gómez parish in the province of Manabí, Ecuador. We examined a total of 176 fecal samples to detect opisthorchiid eggs, and four fish species to find opisthorchiid metacercariae. To study adult worms, we treated and purged seven patients in a family and dissected the livers of a dog and a cat infected. We observed morphological features of adults and metacercariae and used polymerase chain reaction with restricted fragment length polymorphism (PCR-RFLP) and DNA sequencing of a section of the ITS2 gene for identification. Small trematode eggs were detected in 63 (35.8%) out of 176 fecal samples of residents in the three study sites. Adult opisthorchiid flukes were recovered from human patients, a dog and a cat, and they were morphologically and molecularly identified as Amphimerus sp. Opisthorchiid metacercariae were also identified molecularly as Amphimerus sp. in four fish species, i.e., Rhoadsia altipinna, Bryconamericus bucay, Andinoacara rivulatus, and Piabucina aureoguttata. Metacercariae of the heterophyid Haplorchis pumilio were also found in the four fish species examined. This is the first study to confirm the current endemicity of Amphimerus sp. in Pedro Pablo Gómez, Manabí, Ecuador. The adult worms isolated here shared morphological characteristics with previous Amphimerus sp. descriptions and were molecularly similar to Amphimerus sp. described in the province of Esmeraldas. Moreover, this study is the first to document four fish species as infection sources of Amphimerus sp. detected via a molecular protocol targeting the metacercariae of the parasite. Fish species identified here should be targeted for public health campaigns to avoid further human liver-fluke infections by Amphimerus sp. or potential intestinal-fluke infections by H. pumilio or others.

Among neglected tropical diseases, foodborne trematodiases rank among the least studied, especially in the Americas. In Ecuador, a parasite of the genus Amphimerus, family Opisthorchiidae, has been found in the biliary ducts of humans, cats, and dogs, in the northern province of Esmeraldas. Reports as old as 1949 document opisthorchiid infections in the coastal province of Manabí. Given a lack of studies elucidating the infective larval stage of these flukes in Ecuador, we decided to conduct parasitological and molecular experiments to characterize the presence of these human liver infections in the area. We found adult Amphimerus sp. flukes in humans and other domestic animals, and its metacercariae in four edible freshwater fish species: Rhoadsia altipinna, Bryconamericus bucay, Andinoacara rivulatus, and Piabucina aureoguttata. Moreover, we found a prevalence of 35.8% of small trematode eggs in humans. Finally, we also found the metacercariae of the intestinal fluke Haplorchis pumilio in all fish species examined. Our findings confirm the area of Pedro Pablo Gómez as an endemic region for opisthorchiid liver infections due to Amphimerus sp., and expand the human differential diagnosis of small trematode eggs to liver and intestinal flukes. Consumption of undercooked freshwater fish of the species identified here could lead to Amphimerus sp. infections. Surveillance in other areas known for raw fish consumption would likely unveil new cases of foodborne trematodiases in Ecuador and other regions.

Environmental contamination with Toxocara eggs: a quantitative approach to estimate the relative contributions of dogs, cats and foxes, and to assess the efficacy of advised interventions in dogs

Background

Environmental contamination with Toxocara eggs is considered the main source of human toxocariasis. The contribution of different groups of hosts to this contamination is largely unknown. Current deworming advices focus mainly on dogs. However, controversy exists about blind deworming regimens for >6-month-old dogs, as most of them do not actually shed Toxocara eggs. We aim to estimate the contribution of different non-juvenile hosts to the environmental Toxocara egg contamination and to assess the effects of different Toxocara-reducing interventions for dogs.

Methods

A stochastic model was developed to quantify the relative contribution to the environmental contamination with Toxocara eggs of household dogs, household cats, stray cats, and foxes, all older than 6 months in areas with varying urbanization degrees. The model was built upon an existing model developed by Morgan et al. (2013). We used both original and published data on host density, prevalence and intensity of infection, coprophagic behaviour, faeces disposal by owners, and cats’ outdoor access. Scenario analyses were performed to assess the expected reduction in dogs’ egg output according to different deworming regimens and faeces clean-up compliances. Estimates referred to the Netherlands, a country free of stray dogs.

Results

Household dogs accounted for 39 % of the overall egg output of >6-month-old hosts in the Netherlands, followed by stray cats (27 %), household cats (19 %), and foxes (15 %). In urban areas, egg output was dominated by stray cats (81 %). Intervention scenarios revealed that only with a high compliance (90 %) to the four times a year deworming advice, dogs’ contribution would drop from 39 to 28 %. Alternatively, when 50 % of owners would always remove their dogs’ faeces, dogs’ contribution would drop to 20 %.

Conclusion

Among final hosts of Toxocara older than 6 months, dogs are the main contributors to the environmental egg contamination, though cats in total (i.e. both owned and stray) transcend this contribution. A higher than expected compliance to deworming advice is necessary to reduce dogs’ egg output meaningfully. Actions focusing solely on household dogs and cats are unlikely to sufficiently reduce environmental contamination with eggs, as stray cats and foxes are also important contributors.

Towards improved diagnosis of neglected zoonotic trematodes using a One Health approach

Reaching the goal of control, elimination and eradication of the Neglected Tropical Disease in a foreseeable future provides significant challenges at the ground level especially regarding helminthiasis. Helminths are still mainly diagnoses by egg identification in stool, methods with low sensitivity and for most species low specificity. Cross-sectoral collaboration with regard to zoonoses is almost non-existing and cross-validation by inter-laboratory evaluation of diagnostic tests is not a common practice. The aim of this review was to elucidate the dilemma of helminth diagnosis using zoonotic trematodes as examples. Much progress has been made improving the diagnostic sensitivity of Opisthorchis and Clonorchis using DNA-based techniques but the specificity of these tests is still a challenge due to the many most common but neglected intestinal trematodes. The burden of these diseases and ways to control them remains to be elucidated. Although efficacious drugs are available, the effectiveness of mass drug administration remains to be assessed. The importance of animal reservoirs and ways to control the diseases in animals are yet unknown. Diagnostic challenges regarding Schistosoma japonicum and Schistosoma mekongi include the many light infections and the persisting influx from the animal reservoirs. The sensitivity of the faecal based techniques suited morbidity control but will be insufficient for elimination of the helminths. More accurate diagnostic tools are required and new algorithms for detection and progression of helminth elimination will be needed. Standardized inter-laboratory test validation, inter-sectoral collaboration and establishment of an international One Health diagnostic platform, sharing best practices on diagnosis of helminth zoonoses, could all significantly contribute to control and elimination of these diseases.

Reinfection of dogs with fish-borne zoonotic trematodes in northern Vietnam following a single treatment with praziquantel

Background

Fish-borne zoonotic trematodes (FZT) infections including liver- and minute intestinal flukes are common in Southeast Asia in both humans and domestic animals eating raw fish and since 2010, the liver flukes are recognised as neglected tropical diseases by WHO. Mass drug treatment with praziquantel is advised for humans, but no recommendations for control of the FZT in the reservoir hosts exist.

Methodology/Principal Findings

A study was conducted to assess the ability of praziquantel treatment for control of FZT in farm dogs in an endemic area in Northern Vietnam. Initially, 101 dogs from 73 households were examined for small trematode eggs in their faeces. Forty seven copro-positive dogs were included in the study. Thirty eight dogs received treatment with a single dose of 40 mg/kg of praziquantel. A group of nine dogs were left untreated. Coprological examination for small trematode eggs was performed on day 0, 3, 10, 30, 60, 90 and 120 post treatment. Farmers were questioned about dog keeping practises. All dogs were copro-negative for small trematode eggs on both day 3 and 10 post treatment. From day 30 onwards previously negative dogs became positive again. The reinfection rates were 26.3% (day 30), 45.5% (day 60), 53.1% (day 90), 61.3% (day 120).The nine untreated dogs remained positive throughout the study period. There was no difference in the intensity of infection at day 0 and 120 neither in the treated or untreated group.

Conclusion

Dogs had easy access to raw fish and did not receive treatment against flukes by their owner. More than 50% of the dogs were reinfected 3 months post treatment. We do not recommend controlling FZT infections in dogs by anthelmintic treatment alone since reinfection occurs fast under the existing farm management systems.

Fish-borne zoonotic trematodes (FZT) including liver and small intestinal flukes in humans and domestic animals are a growing problem in Southeast Asia. WHO has recently recognized the problem, listed the liver flukes as neglected tropical diseases and recommends mass drug treatment of humans to overcome the diseases. Domestic animals including dogs, cats and pigs contribute to transmission and the infection must be controlled in these animals if the transmission cycle shall be broken. We studied the effect of a single praziquantel treatment in a group of natural infected dogs in an FZT endemic area in Northern Vietnam. The dogs were followed over 4 months after treatment and management practices were described. We found that dogs had easy access to raw fish and did not receive treatment against flukes by their owners. More than fifty per cent of the dogs became reinfected with FZT within 3 months after treatment. We conclude that repeated mass treatments are not applicable and cannot stand alone for control of FZT in dogs. The reinfection pattern in humans treated for FZT needs to be investigated to monitor effect of mass drug treatments and avoid development of drug resistance.

Use of black carp (Mylopharyngodon piceus) in biological control of intermediate host snails of fish-borne zoonotic trematodes in nursery ponds in the Red River Delta, Vietnam

Background

The risks of fish-borne zoonotic trematodes (FZT) to human health constitute an important problem in Vietnam. The infection of humans with these trematodes, such as small liver trematodes (Clonorchis sinensis and Opisthorchis viverrini), intestinal trematodes (Heterophyidae) and others is often thought to be linked to fish culture in areas where the habit of eating raw fish is common. Juvenile fish produced in nurseries are often heavily infected with FZT and since fishes are sold to aquaculture facilities for growth, control of FZT in these fishes should be given priority. Controlling the first intermediate host (i.e., freshwater gastropods), would be an attractive approach, if feasible. The black carp, Mylopharyngodon piceus, is a well-known predator of freshwater snails and is already used successfully for biological control of snails in various parts of the world including Vietnam. Here we report the first trials using it for biological control of intermediate host snails in nursery ponds stocked with 1-week old fry (10–12 mm in length) of Indian carp, Labeo rohita.

Methods

Semi-field and field experiments were set up to test the effect of black carp on snail populations. In the semi-field experiment a known quantity of snails was initially introduced into a pond which was subsequently stocked with black carp. In the field trial in nursery ponds, density of snails was estimated prior to a nursing cycle and at the end of the cycle (after 9 weeks).

Results

The results showed that black carp affect the density of snail populations in both semi-field and field conditions. The standing crop of snails in nursery ponds, however, was too high for 2 specimens to greatly reduce snail density within the relatively short nursing cycle.

Conclusions

We conclude that the black carp can be used in nursery ponds in Northern Vietnam for snail control. Juvenile black carp weighing 100 - 200g should be used because this size primarily prey on intermediate hosts of FZT and other studies have shown that it does not prey on fish fry of other species. It may be necessary to use a high stocking density of black carp or to reduce snail density in the nursery ponds using other measures (e.g. mud removal) prior to stocking fry in order for the black carp to keep the density of intermediate host snails at a very low level.