A brief survey of free-living amebae in Thailand and Hamamatsu District, Japan.

The aim of this study was to determine the presence of free-living amebae in aquatic habitats of human environments in Thailand and Hamamatsu district, Japan. Genus identification was based on the morphology of cyst and trophozoite forms and a flagellation test for genus Naegleria. The pathogenic potential was tested in mice by nasal instillation for genus Naegleria and Acanthameba. In 14 provinces of Thailand, amebae were isolated in 43 from 95 water samples and 67 from 120 soil swabs. Amebae of 49 isolates from waters were identified as Acanthameba (36.7%), Naegleria (28.6%), Hartmannella (20.4%), Vahlkampfia (12.2%) and Vannella (2%). Soil samples have significantly higher levels of Acanthameba and Hartmannella (p<0.05) but lower for Naegleria (p<0.05) and 7 unidentified amebae were found. In Hamamatsu district, Japan, 62 amebae of the same genera were isolated from 47 of 95 water samples. There were significantly higher levels of Acanthameba (22.6%) (p<0.05) but lower for Naegleria (4.8%) (p<0.05) than those of Thailand which each of them caused death in mice. Three unidentified amebae were isolated. This finding serves as additional evidence for the presence of free-living amebae under natural and the difference in distribution between tropic and subtropic areas.

In vivo efficacy of levamisole against larval stages of Angiostrongylus cantonensis and A. costaricensis.

Anti-larval effects of levamisole were examined on A. cantonensis in rats and A. costaricensis in mice. 1) In rats inoculated with 40 infective larvae of A. cantonensis: Compared with a non-treated control group, a significant reduction in number of worms recovered was seen in the group receiving a single dose of 1.0 mg/kg or more. A significant decrease in host lung-body weight ratio was seen in the group receiving drug of 3.0 mg/kg or more. 2) In mice inoculated with 20 infective larvae of A. costaricensis. In the non-treated control group, a severe loss in body weight and death of host animals were observed. A single dose of 30 mg/kg on 3, 4 or 5 days post-infection remarkably inhibited these changes. At 30 mg/kg for 3 or 7 days levamisole was more effective than a single dose of the drug. These results suggest that levamisole has conspicuous in vivo effects against larval stages of A. costaricensis as well as A. cantonensis.

Motility and drug susceptibility of Angiostrongylus cantonensis developing from gamma-irradiated first-stage larvae.

The effects of neuropharmacological agents on the motility of irradiated and non-irradiated Angiostrongylus cantonensis adult females were studied. GABA induced complete paralysis in non-irradiated and 5,000 R-irradiated worms, but caused only slight paralysis on 10,000 R-irradiated worms. The paralytic effect of GABA was antagonised by picrotoxin. The reason for low susceptibility of heavily irradiated worms to GABA is not known. There was no difference in susceptibility of non-irradiated and irradiated worms to other neuropharmacological agents including eserine, phenylephrine and dibenamine.