[The role of Anopheles anthropophagus in malaria transmission in in Xinyang City of Henan Province].

OBJECTIVE: To study the role of Anopheles anthropophagus in malaria transmission and transmission threshold so as to provide basis for vector surveillance and malaria control strategy. METHODS: Parasitological and entomological methods were used in the investigation at 5 villages of Xinyang City, Henan Province. RESULTS: From July to August, 1999, 74 febrile cases (10.9% of the total population) were examined. Among them 50 were infected, the incidence in the population of surveyed spots was 7.4%. Active detection was made in another randomly selected two villages and found that the parasite rate in the inhabitants was 2.0%, and the positive rate of IFA was 8.4%. Only vivax malaria was detected. An. anthropophagus and An. sinensis were collected, with An. anthropophagus as the predominant one in human dwellings. The estimated man-biting rate and the human blood index were 4.9388 and 0.7858 respectively. The vectorial capacity of An. anthropophagus was 5.5296. The critical man-biting rate of An. anthropophagus was 0.2407 as calculated by the formula (ma = -rlnP/abPh) according to Macdonald's model. The local man-biting rate was 20 times higher than that of the critical man-biting rate. CONCLUSION: The results demonstrated that An. anthropophagus is the principal vector in malaria transmission in the area. The findings imply that the critical man-biting rate is of practicable importance in vector surveillance.

[Practicability of IFAT using Plasmodium cynomolgi and Plasmodium falciparum antigens in different malarious areas].

OBJECTIVE: To compare the practicability of IFAT in different malarious areas using Plasmodium cynomolgi(P.c.) and Plasmodium falciparum(P.f.) antigens. METHODS: This survey was carried out in Yaliang Township of Sanya City, Hainan Province, where a mixed malaria is endemic, and in Tongbo County, Henan Province where only vivax malaria is endemic, and in Weihui City, Henan Province where vivax malaria has been under effective control since 1994-1998. RESULTS: In Yaliang Township, 310 blood samples were examined, the antibody positive rates with P.c. and P.f. were 37.4% and 31.3%, respectively, the rate of coincidence being 83.9%. In Tongbo County, 300 blood samples were examined. The antibody positive rates with P.c. and P.f. were 23.0% and 9.7%, respectively (P < 0.01). Another 245 blood samples from children were examined in Weihui City and the antibody positive rates were below 1% with two antigens, while the positive antibody rate was 3.3% with P.f. antigen. CONCLUSION: Both P.f. and P.c. antigens could be used in malaria antibody surveillance in mixted endemic areas, while in vivax malaria endemic areas, P.c. antigen was recommended.

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 mid-1980s indoor spraying and bednet impregnation with pyrethroids began. By 1992 only 318 cases were reported. In 1992 Henan declared "basic elimination of malaria" and in consequence spraying and bednet impregnation ceased after 1994. Subsequently, malaria broke out again in southern Henan. In 1995 we conducted a household survey for malaria transmission in southern Henan. Blood smears and serum samples for immunofluorescent 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 > or = 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, occurs mainly in southern Henan (S of latitude 33 degrees N) and was greatly 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 impregnation of bednets ceased. Over 10% of 9377 residents reported having malaria. The true number affected among the at-risk population of 700,000 must be larger. We conclude that impregnated bednets and malaria surveillance should continue even after an area is declared to have "basically eliminated" malaria.

PIP: As a result of an aggressive malaria control program initiated in China's Henan Province in 1970, including indoor spraying and bednet impregnation with pyrethroids, the "basic elimination of malaria" was declared in 1992 and spraying and bednet impregnation ceased in 1994. Subsequently, there was a resurgence of vivax malaria in southern Henan. In a 1995 household survey of malaria transmission in three counties in southern Henan, blood smears and serum samples were collected for immunofluorescent antibody testing from 2329 residents. 3.1% were positive for infection with Plasmodium vivax and 13% were positive for malaria (titre of 1:20 and above). More than 10% of 9377 residents in six counties reported having malaria at least once in 1994-95. Comparison of 1995 entomological data with historical data indicated that Anopheles anthropophagus increased in proportion to other anophelines after spraying activities and bednet impregnation ceased. Malaria control in Henan should not have led to withdrawal of protective measures, especially since there is extensive cross-border movement in this area.

Study of simplified measures for malaria surveillance in the late consolidation phase in China.

This paper presents the results of a study on simplified surveillance methods conducted in 23 pilot counties in 11 provinces and municipalities in China where reside 15 million people and malaria control has been in the late consolidation phase. Two simplified surveillance Schemes (A and B) taking treatment of clinical cases as the main measure were implemented in 1992-1994. The rate of annual blood examination for case detection was 1.0% in pilot Scheme A, while in areas of scheme B it was 0.3%. The implementation of both Scheme A and Scheme B, simplified or without treatment of infection foci and management of mobile populations, acquired satisfactory effects against malaria. Consequently, malaria incidence was declining steadily, only a few indigenous and introduced cases were detected. The parasite rate in residents and the IFA positive rate in children were very low. The results of pilot studies and cost-effectiveness analysis indicated that Scheme B is effective, rational and economic, and can be implemented to replace the routine surveillance measures in areas where malaria has been at the late consolidation phase in China.