Studies on some aspects of the biology of the intermediate hosts of Dracunculus Medinensis (Linnaeus) in Tamale Municipality, Northern Region, Ghana

The study was to identify the various species of cyclopoid copepods in six reservoirs in the Tamale Municipality suspected as transmission sites, and to determine which of the species acts as the intermediate host of dracunculiasis as well as the infection rates of this host. The seasonal and diurnal fluctuations of the cyclopoid copepod populations, the prevalence of dracunculiasis in the area as well as the physical characteristics such as temperature, pH, conductivity, and turbidity of the various reservoirs were also studied. The study was carried out in six artificial water reservoirs which are large enough to survive severe drought in the area. The reservoirs are situated in Adubiliyili, Kalariga, Lahagu, Tampion, Vittin and Zuo villages and are all within thirty kilometer radius from Tamale, Northern Region of Ghana. They are the most common type of water source for the rural communities in this part of the country. Seven species and two subspecies of cyclopoid copepods were found in the study area Six of these were species/subspecies of Thermocyclops, two were species of Mesocyclops and one was species of Cryptocyclops. The cyclopoid copepods found are: Thermocyclops emini, Thermocyclops crassus consimilis, Thermocyclops incisus, Therinocyclops inopinus, Thermocyclops neglectus decapiens: Mesocyclops kieferi, Mesocyclops major, Mesocyclops ogunnus, and Cryptocyclops linjanticus. Only three of the reservoirs, namely Kalariga, Lahagu and Tampion, were found to have infected cyclopoid copepods. Infection rates varied between 0.05% and 0.3%. The infected cyclopoids were T. incisus, T. inopinus, T. n. decipiens, and M. kieferi. The prevalence rates of Guinea worm disease from June 1991 to May 1992 for Adubiliyili, Kalariga, Lahagu, Tampion, Vittin and Zuo were 3.1%, 4.9%, 8.7%, 4.7%, 2.7%, and 1.8% respectively. The study showed that variations in cyclopoid copepod populations throughout the year differed in the six reservoirs. Two peaks of cyclopoid copepod populations were observed in Adubiliyili, one before the rains and one shortly after the rains. Kalariga had high populations of cyclopoid copepods before the peak of the rains and low populations during the dry season. The variation in cyclopoid copepod populations in Lahagu was rather erratic with low populations in the dry season. One peak of cyclopoid copepod population was noted at the onset of the rainy season in Tampion. Low population numbers were recorded in Vittin during the peak of the rainy season. The variations in the cyclopoid copepod population in Zuo reservoir were rather erratic and with no clear seasonal pattern. There was a strong positive correlation between the occurrence of high populations of cyclopoids copepods and the prevalence of guinea worm disease. The occurrence of high population densities of cyclopoid copepods during the dry season and at the onset of the rainy season coincided with the high prevalence of guinea worm disease in the surrounding villages. Transmission of dracunculiasis thus appears to occur predominantly during the dry season and the onset of the rainy season (March to July). The amplitude of variation in the physico-chemical factors was very low; there were apparently some correlations between these variations and the changes in cyclopoid copepod populations. Diurnal variation of cyclopoid copepod populations showed two peaks in the dry and hot seasons; the first peak occurred between 08.00 hours to 10.00 hours GMT and the second from 16.00 hours to 18.00 hours GMT. In the rainy season, only one peak occurred at 16.00 to 18.00 hours GMT. Inhabitants, who fetch water during the dry and hot season from the Vittin reservoir, collect water mostly in the morning between the hours of 09.30 to 10.30 and in the evening between 16.00 and 18.00 hours GMT. In the wet season collection of water is mostly done in the evenings. There was thus a positive coincidence between the time of water fetching by the inhabitants and the peaks of the diurnal cyclopoid copepod populations.

Source: KNUST