| Abstract: | The temporal dynamics of microfilariae (mf) in human blood, and the biting activity and mf density in the vector were studied. Finger-prick blood samples (in duplicate) were collected from 14 microfilaraemic subjects at two-hourly intervals over a single 24-hour timescale. Samples were taken from 39 subjects at 22:00 in the first week of every month for a period of 17 consecutive months. The blood slides were dried, stained and examined for presence of microfilariae. Data were analyzed with cosinor rhythmometry. A statistically validated circadian rhythm was detected in mf density in 86% of the microfilaraemic subjects. For the circannual rhythm, the peak timing for microfilariae density was recorded in July, although the spread of the peak between subjects was quite wide, extending between May 17 and September 07. In a separate study, temporal variations in biting activity, mf density in the vector and in human blood were studied. The dynamics of parasite transmission were found to be sequential, with the peaks in the circadian rhythms appearing in the order: mf in human blood, biting activity and mf density in the vector. The biting periodicity appeared to be much more stable in all subjects; the peak appeared at 02:37 with a range between 00:39 and 03:22. The peak in mf frequency was earlier by 3 hours and 25 minutes, whereas the peak in mf frequency in the vector was later by about 2 hours 4 minutes. The observed synchronization between the rhythms of vector and host appears to be essential for effective transmission of diseases. Therefore, the application of chronobiologic principles may have a bearing in the success and failure of any future strategies aimed at the prevention, cure and management of filariasis. |
