RESUMEN
Observations on transmission of the rat lung worm, Angiostrongylus cantonensis, from rats to the snail intermediate host. Achatina fulica, in a vacant lot in Bangkok are described. The prevalence of A. cantonensis increased with snail age until 200 days of age when it attained a plateau of 50-60%. The overall prevalence was 53%. The worm burden slowly rose with age until 200 days of age beyond which it remained relatively constant. The highest mean worm burden of 5,478 was observed in the oldest age group. The parasite distribution in the snail population was highly aggregated both within each age class and in the overall population. Experiments on susceptibility of snails to laboratory infection revealed that worm recovery was dependent on dose of first stage larval infection but was independent of snail size in the range of 4-8 cm. The percent worm recovery of third stage larvae was negatively correlated with dose of infection, and no density-dependent effects of worm burden on worm size were observed.