Incidence of free-living amoebae in the nasal passages of local population in Zaria, Nigeria.

Following the observation of cases of primary amoebic meningoencephalitis (PAME) during the dusty harmattan period in Zaria, a survey was carried out in randomly selected local populations of Zaria, to find out the incidence of free-living amoebae in the nasal passages. The times of sampling were spaced so as to cover both the rainy (non-harmattan) abd dry (harmattan) seasons. In all 1250 individuals were sampled, and were grouped in the three age groups of above 18 years, between 4 and 18 years and below 4 years. The overall incidence was 4.2% (52 out of 1250). There was no marked difference in the three age groups studied. The incidence rate in males was 4.8% (30 of 630) and that in females was 3.5% (22 of 620). Nine different species of free-living amoebae were isolated. Six belonged to the Genus Hartmannella, two to the genus Naegleria, and one to the genus Schizopyrenus. Three species were found to be pathogenic for mice: H. culbertsoni, H. rhysodes and N. fowleri. It was observed from this study that a significant percentage of the Zaria population carry free-living amoebae in the nasal passages. The monthly incidence rate in population ranged from 1.8 to 3.1% during the rainy (non-harmattan) season whereas in the dry (harmattan) season it ranged from 4.2 to 7.9%. The highest incidence rate coincided with the peak of the dry (harmattan) season. The possible role of harmattan winds on the nasal carriage as well as the necessity to investigate fully the disease PAME in this environment is discussed.