Circadian periodicity of Wuchereria bancrofti in Liberia and its effect on the results of a prevalence study.

The Harmonic Wave curve of Sasa and Tanaka (1972), describing microfilarial periodicity, has been fitted to observations on 38 persons infected with W. bancrofti in Liberia, as well as to data previously obtained from the same country by other authors. The periodicity of the Liberian strain was similar to that of periodic forms of W. bancrofti in Southeast Asia and Japan. The effect of periodicity on microfilaraemia prevalence survey results has been examined, using data from a recent study in coastal Liberia. Although prevalence rates appear to be little affected the median microfilarial densities (MfD50) vary condiserably according as to whether a population is examined in the early evening or late at night.