Critical analysis of an epidemetrons model for the assessment of bancroftian filariasis endemicity in some areas in Egypt.

This study attempted a trial fit of observed epidemiological data in Egypt using the Sasa-WHO-Southgate epidemetrons model to quantify the endemicity and risk of transmission of filariasis. The geometric and arithmetic means (GM, AM) were tried in addition to the recommended four epidemetrons of the model, prevalence rate (PR); median microfilaria density (MfD50); and linear regression coefficients (a and b). Data were based on microfilaria counts in 20 mm3 finger-prick night blood samples from all individuals 6 years of age and older of both sexes in a cluster of eight filaria-endemic villages. The study results showed that the model fits satisfactorily in each individual village but major discrepancies occurred when comparisons were made between the villages. PR was closely but by no means perfectly correlated with MfD50, was more closely correlated with GM but less with AM, and showed a rather weak negative correlation with each of a and b by linear regression and by rank order. A possible explanation for these discrepancies is that in areas of recent importation or increase of transmission of filariasis and in areas of great population mobility, observed microfilaria prevalences and microfilaria intensities will not conform to the PR, MfD50, a and b epidemetrons recommended by Sasa (1967), WHO (1967) and Southgate (1974) as descriptive epidemetrons of microfilaraemia. Further studies are warranted.