Malaria in the highlands of Madagascar after five years of indoor house spraying of DDT

The central region of Madagascar is a vast area of highlands (altitude 700- 2000 m). Malaria transmission has re-established itself here since the last epidemic of 1985-90 and has caused the deaths of 40 000 persons according to the Minister of Health. To combat the main malaria Vector in the region, Anopheles funestus, annual programmes of indoor house spraying of DDT were carried out between December 1993 and January 1998 in most rural areas at altitude 1000-1500 m. A parasitological and serological study was then cond ucted in the highland schools to evaluate the impact of the programme and s et: up a database on the region. Using a cluster-sampling method 2 independ ent selections were conducted (one of 130 sites, the other of 40 sites). Du ring the study, 13 462 schoolchildren were examined, 71% living in sprayed villages. Parasite: prevalence among schoolchildren declined as altitude in creases, from 11% at: 700-900 m to 0.4% at > 1500 m. Below 1500 m, the impa ct of the spraying on the prevalence of the parasite was very clear (an ave rage decrease of from 20% to 2.7% below 1000 m and of from 4.5% without spr aying to 0.8% at 1000-1500 m). Geographical analysis of the data showed tha t the marginal regions remained the most affected by malaria (especially ou tside spraying zones), and persistence of pockets of transmission' at 1000- 1500 m, essentially in areas where spraying has never been used. In 9 schoo ls, anti-Plasmodium antibodies were sought by indirect immunofluorescence o n thick smears of parasitized red blood cells. The seroprevalence ranged fr om 22% to 63%, which suggests that the parasite is still circulating in the region. Even though our data show that vector control continues to be very successful in the Madagascan highlands, rapid reinfection could occur and must be monitored following spraying. To this end, the Minister for Health, with the support of the Italian Co-operation, has placed the region under epidemiological surveillance since 1997. An alert system for the timely det ection of the sources of epidemics and the targeting of the anti-vectoral c ampaign is also in operation. Our study suggests that this strategy should be reinforced by the spraying of DDT in the marginal zones in order to cons olidate the results obtained at higher altitudes.