HUMAN LOIASIS IN WESTERN NIGERIA

Abstract

An attempt has been made in this study to bridge some of the gaps in our knowledge of loiasis in Western Nigeria. At this same time, areas for future research which might lead to a better understanding of the disease pattern in loiasis are highlighted. This thesis is made up of both laboratory and field studies which were carried out at the University College Hospital, lbadan, and in villages in the Western State of Nigeria respectively. Tha sample population for the prevalence study comprised of 10830 school pupils and 1399 adults drawn from villages in divisions all over the Western State. Blood samples were examined parasitologically for microfilariae of Loa loa and the results obtained were analysed and utilised in determining the geographical distribution of loiasis within the state. Vectors of Loa Loa were determined in Ijebu and Remo divisions and the role of the common blood sucking mosquitoes in the transmission of loiasis was assessed in Ibadan city. The observation that Mansonia africana would allow the development of Mf Loa to the mature third stage larva raises the possibility that the Loa Loa population in Western Nigeria might be different from the other known population; therefore the local population was measured and compared with the Kumba (Cameroon) population. Some of the manifestations often associated with Loiasis were discussed on tho basis of the observations made in villages during the prevalence studies; furthermore the association that may exist between Loiasis, endomyocardial dibrosis, ABO blood groups and haemoglobulin genotypes, elephantiasis and hydrocoele were examined and discussed. The results of the present study show that loiaisis is endemic in the Western State of Nigeria, with most of the transmission taking place in the rain-forest and freshwater swamp zones. It has also been shown that, C.silacea and C.dimidiata are the vectors of Loa Loa in both the Ijebu and Remo divisions of the State. Even though M.aficana supportod the development of Mf Loa to the natural larval stage, this mosquito is not important as a vector in nature. The importance of M.africana lies in its possible use as a laboratory vector in preference to Chrysops species because of its short period of larval development. There is no preferential infection by Loa Loa of any of the groups and the haemoglobin genotypes studied. It has also been shown that there is no protective effect in any of the groups studied either in terms of preventing infestation or in the intensity of infection. Therefore none of the blood groups or haemoglobulin genotypes in this study is at an advantage or disadvantage with respect to loiasis. There is yet no conclusive evidence with which to incriminate loiasis with endomyocardial fibrosis, elephantiasis and hydrocoole formation in infected patients.