Paragonimus heterotremus and other Paragonimus spp. in Thailand: Pathogenesis, clinical features and treatment

Abstract

Six species of Paragonimus have been reported in Thailand: P. siamensis in cat, bandicoot and rat; P. bangkokensis in mongoose; P. harinasutai in cat and dog (experiment); P. macrochis in bandicoot and rat; P. westermani in tiger and P. heterotremus in cat, dog and man. It is interesting to note that in 1965 two immature P. heterotremus worms were recovered for the first time in man, namely in subcutaneous swellings in a boy; in 1981, 9 mature P. heterotremus worms were expectorated after praziquantel treatment. P. heterotremus has been postulated to be the main cause of human paragonimiasis in Thailand. The clinical manifestation of paragonimiasis heterotremus is similar to paragonimiasis westermani. In the 1960's and 1970's bithionol was used to treat paragonimiasis, the cure rate was only 50-60%, and side effects including urticaria, rash, abdominal pain, nausea, vomiting, diarrhoea and dizziness were common. In the past 4 years, niclofolan and praziquantel ((2-cyclohexylcarbonyl-1,2,3,6,7,11b-hexahydro-4H-pyrazino[2,1-a]isoquinol in-4-one, EMBAY 8440, Biltricide®) have been used. A single dose of 2 mg/kg body weight of niclofolan yielded a 100% cure rate. Praziquantel at dosages of 3 x 25 mg/kg body weight daily for 1 day and 2 days gave 80% and 100% cure rates, respectively. The eggs disappeared in 2-3 weeks with improvement of symptoms and signs, but radiologically lesions took a few months or more to clear, depending on size and severity. Side effects in the niclofolan group were higher; in the praziquantel group side effects were minimal and no toxic effects were detected.