RESURGENCE OF VIVAX MALARIA IN HENAN PROVINCE, CHINA

Henan Province (population, 90 million) in China has nonstable endemic malaria. After 1970 when 10.2 million cases of malaria were reported in the province, a huge control programme was undertaken, and in the m id-1980s indoor spraying and bednet impregnation with pyrethroids bega n. By 1992 only 318 cases were reported. In 1992 Henan declared ''basi c elimination of malaria'' and in consequence spraying and bednet impr egnation ceased after 1994. Subsequently, malaria broke out again in s outhern Henan. In 1995 we conducted a household survey for malaria tra nsmission in southern Henan. Blood smears and serum samples for immuno fluorescent antibody (IFA) testing were collected from 2329 people and 3.1 % (73/2329) were positive for infection with Plasmodium vivax and 13% (301/2329) positive for malaria (titre greater than or equal to 1 :20). All age groups were affected Exophilic Anopheles sinensis occurs throughout the province; endo-anthropophilic A. anthropophagus, whose vectorial capacity is 20 times greater than that of A. sinensis, occu rs mainly in southern Henan (S of latitude 33 degrees N) and was great ly reduced in numbers during 1985-92. Comparison of 1995 entomological data with historical data showed that A. anthropophagus increased in proportion to other anophelines after spraying activities and impregna tion of bednets ceased. Over 10% of 9377 residents reported having mal aria. The true number affected among the at-risk population of 700 000 must be larger. We conclude that impregnated bednets and malaria surv eillance should continue even after an area is declared to have ''basi cally eliminated'' malaria.