Malaria N° 4 - Subject N° 7

AN ECOLOGICAL OBSERVATION ON MALARIA PARASITE PREVALENCE IN GHANA
W.A. Chinery

SUMMARY
This study considers the effects of ecological factors like rainfall, soil and vegetation types and urbanization rate on malaria parasite prevalence in Ghana comprising six bioclimatically different regions during the eight-year period 1950-51 and 1957-61. Mean annual parasite rates were computed from results of routine blood film examinations in 24 hospitals in the regions. Mean annual rainfall figures were similary computed. The mean parasite rate (parasite rate), graded as high, moderate and low were compared statically, by correlation coefficient and scattergraphs with mean annual rainfall (rainfall level) also similarly graded, under the ecological factors listed above. The highest parasite rate was significantly higher than the lowest parasite rate. Regional parasite rates were not significantly different and there was no difference between the effects of different vegetation types on parasite rates and by implication on vector longevity. The parasite rate was appreciably higher in moderate urbanization rate aeras (p = 0.01; t = 1.172166).

Correlation between parasite rate and rainfall level was significant in moderate urbanization rate aeras, low rainfall grade aeras and in three soil types namely oxysols, ochrosols ans sodium vleisols. It is concluded that soil type is one of the most important determinants on parasite rate, either potentiating or antagonizing the effect of rainfall on parasite rate. However, because this potentiating effect is not great in low rainfall aeras there was no significant difference between parasite rates in the congenial soil types (e.g. ochrosols and sodium vleisols soils) and other soil types. The antagonistic effect of rainfall on parasite rate in oxysols areas may be compensated for, probably by several running water bodies present, ipso facto accounting for the moderate to high parasite rates in oxysols soils aeras. Other complicating factors either potentiating e.g. fresh water bodies, stored water, will indirectly increase the parasite rate, or antagonistic e.g. polluted water bodies, adequate piped water supply, use of mosquito repellents and antimalaria prophylaxis will directly or indirectly depress the parasite rate.

KEY-WORDS: Ecological, Malaria prevalence, Ghana