Epidemiology of clonorchiasis in Ninh Binh Province, Vietnam.

Clinical and stool examinations for clonorchiasis were carried out in an endemic area, Kim Son District, Ninh Binh Province, Vietnam. Stool examination with the Kato-Katz technic revealed that in 306 residents selected randomly, 42 people (13.7%) were infected with Clonorchis sinensis. The rate was biased towards men (23.4%) as opposed to women (1.5%) and increased with age. No children younger than 10 years old were infected, reflecting difference in a chance for acquisition of infection through a habit of eating raw fish. Few clinical abnormalities were found by blood and urine examinations of the patients. Treatment with praziquantel decreased the infection rate to 5.3% at 6 weeks later. Snails, Melanoides tuberculatus, collected from ponds around the settlements were infected with cercariae at a rate of 13.3%. Farmed fish (Hypophthalmichtys molitrix) in the ponds were infected with metacercariae at rates of 56.4% in small individuals and 100% in large ones. The life cycle of C. sinensis is exclusively completed in the ponds and the traditional habit of eating raw fish in summer was thought to be a major route of infection.