Changing patterns of some trematode infections in Asia

Abstract

In certain areas of Asia the pattern of trematode infections in both man and animals seems to have changed in the recent past. On Taiwan, for example, paragonimiasis, fasciolopsiasis and schistosomiasis were at one time highly endemic in certain locations, but in recent years these parasitoses have been difficult to find in definitive, intermediate as well as reservoir hosts. Education, industrialization, alterations in the ecology and the use of modern agricultural practices have contributed to the changes. Conversely, it appears that human clonorchiasis is increasing in Taiwan while in Hong Kong, the disease, once highly prevalent, seems to be decreasing due to control measures implemented in China; the source of infected fish for Hong Kong residents has been China. Furthermore, Clonorchis sinensis infections are more common in higher income groups of Hong Kong since imported fish are more expensive. Along the same line, metagonimiasis is more common among the more affluent sports fishermen in Japan who eat mountain-stream trout as "sashimi" soon after the catch. One of the most dramatic changes in the prevalence of a trematode disease has been in the Lindu Lake region of Central Sulawesi, Indonesia. Echinostomiasis lindoensis was highly endemic in the area and human infection was acquired by eating infected Corbicular sp. clams. The fish Tilapia mossambica was subsequently introduced into the lake and competed for food with the clam and ate the glochidial larval stages of the clam. The clams are no longer present in the lake and consequently, the parasitosis has disappeared.(ABSTRACT TRUNCATED AT 250 WORDS)