Inactivation of Paragonimus westermani metacercariae in soy sauce-marinated and frozen freshwater crabs.

Soy sauce-marinated freshwater crabs (Eriocheir japonicus) are a source of human paragonimiasis. The viability of Paragonimus westermani metacercariae (PwMc) in marinated crabs was investigated in an experimental setting. The PwMc collected from freshwater crayfish were inoculated into freshwater crabs, which were then frozen or marinated in soy sauce. All PwMc in the freshwater crabs were inactivated after freezing for 48 h at -20 °C and after freezing for 12 h at -40 °C. After marinating for 32 days, the survival rate of PwMc in 5% NaCl soy sauce was 50%, in 7.5% NaCl soy sauce it was 33.3%, and in 10.0% NaCl soy sauce it was 31.3%. When marinated for 64 days, all PwMc were inactivated in all experimental groups. These results revealed that freezing and soy sauce marination were detrimental to the survival of PwMc in freshwater crabs. Specifically, freezing crabs for more than 48 h or soaking them in soy sauce containing at least 5.0% NaCl for 64 days can inactivate PwMc. These results can inform the production of the traditional Korean soy sauce-marinated freshwater crabs known as gejang.

Effectiveness of mefloquine against Clonorchis sinensis in rats and Paragonimus westermani in dogs.

The aim of the study is to explore the effect of mefloquine against Clonorchis sinensis and Paragonimus westermani. For anti-C. sinensis study, a total of 71 rats were divided into four batches for oral infection of each rat with 50 C. sinensis metacercariae. Five to 7 weeks post-infection, groups of rats were treated orally with mefloquine at single doses or multiple daily doses while infected, but untreated rats served as control. All treated rats were euthanized 2 weeks post-treatment for assessment of efficacy. For anti-P. westermani study, two batches of eight and ten dogs were each infected intraperitoneally with 100 P. westermani metacercariae. Eighty-five to 96 days post-infection, groups of two or three dogs were treated orally with mefloquine and groups of two dogs were treated with praziquantel at a single dose or multiple doses. In each batch of test, three untreated but infected dogs served as control. All treated dogs were euthanized 26-30 days post-treatment for evaluation of efficacy. In rats infected with C. sinensis and treated orally with mefloquine at a single dose of 75 and 150 mg/kg, no effect against C. sinensis was observed. When the dose of mefloquine was increased to 250 mg/kg, one third (five out of 15) rats died 3-5 days post-treatment. Although the mean worm burden was lower than that of the control, the difference between the treated and control groups was not statistically significant (P>0.05) with worm burden reduction of 22.4%. Whereas, the group of infected rats received mefloquine at a daily dose of 100 mg/kg for 3 days, one out of five rats died after the last administration. The mean worm burden was significantly lower than that of the control with worm burden reduction of 67.6% (P<0.01). In the first test of mefloquine against P. westermani, three infected dogs received two oral doses of the drug, 50 mg/kg, given at a 4-h interval, the mean worm burden were similar to that of the control. While other two dogs were treated with praziquantel at the same dose schedule, the worm burden reduction of 78% was observed. In the second test, three and two dogs were treated with mefloquine 50 mg/kg daily for 5 days or 100 mg/kg daily for 2 days; the mean worm burdens of the two groups were lower than that of the control with worm burden reduction of 65.6% and 51.9%, respectively. However, only the difference of mean worm burdens between mefloquine 50 mg/kg given daily for 5 days and the control was statistically significant (P<0.05). Other two dogs treated with praziquantel at a single dose of 100 mg/kg were cured. The results indicate that under the appropriate dose schedule mefloquine exhibits less effect against C. sinensis in rats and P. westermani in dogs.

Artemether and tribendimidine lack activity in experimental treatment of Paragonimus westermani in the dog.

Artemether and tribendimidine are active against several trematode species, but no data are available regarding the lung fluke Paragonimus westermani. We infected six dogs with 100 P. westermani metacercariae each. At day 103 post-infection, four dogs were treated orally for 3 days with either artemether (total dose, 66.7 and 75 mg/kg) or tribendimidine (total dose, 100 mg/kg). The remaining dogs were left untreated and served as control. Sixteen days after the final dosing, dogs were killed, and P. westermani flukes were recovered from the lungs and counted. Neither artemether nor tribendimidine showed activity against P. westermani at this dose regimen in dogs.