Probability risk transmission matrix as a decision tool for assessing methods of transmission interruption of Wuchereria bancrofti infection

Abstract

Lymphatic filariasis continues to cause severe morbidity and economic loss. The World Health Assembly (WHA) has passed a resolution to eliminate this disease by 2020. The major thrust of the elimination strategy is interrupting transmission by anti-parasitic treatment of entire communities. However, both vector density and community microfilaria load (CMFL) influence the intensity of transmission. Therefore, using a logistic regression approach a relationship has been established between the Risk of Infection Index (RII), vector density and CMFL. The present analysis indicates that there is no risk of transmission as long as the CMFL is maintained below 5 microfilaria (mf)/60 mm3 and the vector density per man-hour (MHD) is 25 and CMFL is <5 mf/60 mm3. In situations where CMFL is very high, parasitic control by mass administration may be cost effective in interrupting transmission. But at lower level of CMFL (<4 mf) and higher level of vector density it might be more cost effective to use vector control methods. A RII value <0.2 is considered to be the threshold for confirming interruption of transmission. Thus, the relationship has been depicted in the form of a probability matrix, which could be used for selecting an appropriate control strategy.

Fig

Incidence of filarial infection in the 0–5 years age group by risk probability., Observed; —, predicted. Incidence=−0·76+4·1×risk, R²=0·59, P=0·013.