The overall incidence rate among children aged 6 months to 10 years was 2.7 per 100 person-months in the IRS area and 6.8 per 100 person-months in the control area. However, there was no significant difference in malaria incidence between the two sites during the first two months (July–August) and after the rainy season (December–February) (see Figure 4).
Kaplan-Meier survival curves for children aged 1 to 10 years in the study area after 8 months of follow-up
This study compared malaria prevalence and incidence in two districts using integrated malaria control strategies to assess the additional effect of IRS. Data were collected in two districts through two cross-sectional surveys and a 9-month passive case-finding survey at health clinics. Results from cross-sectional surveys at the beginning and end of the malaria transmission season showed that malaria parasitaemia was significantly lower in the IRS district (LLTID+IRS) than in the control district (LLTIN only). Since the two districts are comparable in terms of malaria epidemiology and interventions, this difference could be explained by the added value of IRS in the IRS district. In fact, both long-lasting insecticidal nets and IRS are known to significantly reduce malaria burden when used alone. Thus, many studies [7, 21, 23, 24, 25] predict that their combination will result in a greater reduction in malaria burden than either alone. Despite IRS, Plasmodium parasitaemia increases from the beginning to the end of the rainy season in areas with seasonal malaria transmission, and this trend is expected to peak at the end of the rainy season . However, the increase in the IRS area (53.0%) was significantly lower than that in the control area (220.0%). Nine years of consecutive IRS campaigns undoubtedly helped to reduce or even suppress the peaks of virus transmission in the IRS areas. Moreover, there was no difference in the gametophyte index between the two areas at the beginning. At the end of the rainy season, it was significantly higher in the control site (11.5%) than in the IRS site (3.2%). This observation partly explains the lowest prevalence of malaria parasitemia in the IRS region, since the gametocyte index is a potential source of mosquito infection leading to malaria transmission .
The results of the logistic regression analysis show the real risk associated with malaria infection in the control area and highlight that the association between fever and parasitemia is overestimated and that anaemia is a confounding factor.
As with parasitaemia, malaria incidence among children aged 0–10 years was significantly lower in the IRS than in the control areas. Traditional transmission peaks were observed in both areas, but they were significantly lower in the IRS than in the control area (Figure 3). In fact, while pesticides last for about 3 years in LLINs, they last for up to 6 months in the IRS. Therefore, IRS campaigns are conducted annually to cover transmission peaks. As shown by the Kaplan–Meier survival curves (Figure 4), children living in the IRS areas had fewer clinical cases of malaria than those in the control areas. This is consistent with other studies that have reported significant reductions in malaria incidence when expanded IRS is combined with other interventions . However, the limited duration of protection from residual effects of IRS suggests that this strategy may need to be improved by using longer-lasting insecticides or increasing the annual frequency of application .
Differences in the prevalence of anemia between IRS and control areas, between different age groups and between participants with and without fever may serve as a good indirect indicator of the strategy used .
This study shows that pirimiphos-methyl IRS can significantly reduce the prevalence and incidence of malaria in children under 10 years of age in the pyrethroid-resistant Koulikoro region, and that children living in IRS areas are more likely to develop malaria and remain malaria-free longer in the region. The studies have shown that pirimiphos-methyl is a suitable insecticide for malaria control in areas where pyrethroid resistance is common.
Post time: Dec-09-2024