A survey of the infective larvae of Gnathostoma spinigerum in swamp eels bought in a local market in Bangkok, Thailand.

The livers were separated from the viscera of 2738 swamp eels (Monopterus alba) purchased from Klong Toey market, the largest market in Bangkok, between June 1999 and May 2000. When these livers were digested in artificial gastric juice, 524 (19.1%) were found to be infected with the human-infective, third-stage larvae (L3) of Gnathostoma spp. All the identified larvae were confirmed morphologically to be G. spinigerum. Prevalence of the infection varied with season, from a high of 38.3% in September to a low of 7.0% in April, being generally high during the rainy season and winter (June-February). The mean (S.E.) number of L3 recovered/infected liver, which was 3.99 (0.52) overall, also varied with the season, peaking at 5.38 (1.89) in January, but the month-on-month variation was not statistically significant. Although the results of an earlier study had indicated that the prevalence of eel infection decreased in November, after the rainy season, the most abrupt decrease observed in the present study occurred at the beginning of summer (March). However, the period covered by the present study was unusually wet, and the prevalence of eel infection may depend on rainfall more than season.