Comparative studies on Mopeia viruses and other Arenaviridae, particularly Lassa virus

Abstract

Serologically related arenaviruses have been isolated from West Africa, Mozambique, Zimbabwe and the Central African Republic. Human disease is only associated with the West African isolates. The virulence of Mozambique, Zimbabwe and Central African Republic isolates in humans is not known. This Thesis is an account of work carried out by the author to compare the biological characteristics of isolates from West Africa, Mozambique and Zimbabwe. It describes the successful isolation and identification of the aetiological agents, their physicochemical and antigenic characteristics and describes in vivo studies using mice, guinea pigs and Rhesus monkeys. A direct comparison was made with a patient diagnosed as having Lassa fever. The disease in man and monkeys following infection with Lassa virus was similar. The Rhesus monkey and guinea pig proved suitable experimental models in which to study and compare the pathogenic responses and also to evaluate various aspects of protection. These animal models when immunised with the viruses from Mozambique and Zimbabwe were protected when subsequently challenged with Lassa virus. The Mozambique and Zimbabwe isolates proved to have morphological and physicochemical characteristics not dissimilar from West African Lassa viruses and those members of the arenavirus family from South America. Serological and immunochemical investigations suggest the existence of both common and unique antigenic determinants on the viruses from Mozambique, -Zimbabwe and West Africa. This grouping also coincides with the geographic separation of the viruses, i.e. Lassa - West Africa and Mopeia -southeast Africa. Similar differences in host susceptibility have also been demonstrated. Lassa virus produces a fatal haemorrhagic disease while Mopeia isolates produce only an asymptomatic infection. The combined data suggests the possibility of two virus groups within the 'Old World' arenavirus classification. The proposed name, 'Mopeia', forms one group and includes the viruses from Mozambique and Zimbabwe. The Lassa strains from West Africa form the second group. It is suggested that the Mopeia viruses are minor antigenic variants of Lassa and should be included within the arenavirus family.