Field and laboratory findings implicated Culex pipiens as a vector of Rift Valley fever (RVF) virus during the 1977-1978 epizootics/epidemics in Egypt. This study evaluated changes in infection and transmission rates, and viral titers in F1 through F16 generation Cx. pipiens mosquitoes orally infected with RVF virus. Infection and transmission rates of RVF virus by this species changed significantly during the colonization process. However, the ultimate viral titers of either the transmitting or the infected nontransmitting mosquitoes were not affected by the colonization process. Following ingestion of virus, Cx. pipiens could be separated into three distinct subpopulations, an uninfected group and two types of infected mosquitoes--transmitters and nontransmitters. Transmitters contained significantly more virus (approximately 100-fold) than nontransmitters. These results demonstrated that not every infected female mosquito should be considered a competent vector, even if the species (population) is known to be a primary vector. Transmission was also accomplished by probing mosquitoes which were unsuccessful in obtaining a blood meal. These data document the long-held suspicion that vector competence studies based upon laboratory-colonized specimens may not represent the field situation.

Fever and myalgia are non-specific clinical manifestations of illness which commonly occur in patients with arboviral disease. In Egypt, such illness is often mis-diagnosed as "influenza". To determine arboviral aetiology in patients admitted with fever and myalgia, acute and convalescent sera samples were obtained from 55 patients admitted with these clinical manifestations to the Imbaba Fever Hospital, Giza, Egypt, during October and November 1984. Based on viral isolation, and a comparison of acute and convalescent sera, 4 patients (7%) had acute arboviral infections. Haemagglutination inhibition and indirect immunofluorescence tests showed that one had West Nile virus (WNV) infection, 2 had sandfly fever virus-Naples (SFN), and 1 had sandfly fever virus-Sicilian (SFS) infection. SFN was isolated from the acute serum sample of 1 of the 2 patients with SFN infection.

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Plasmodium infection rates determined by enzyme-linked immunosorbent assay (ELISA) were compared for Anopheles sergentii (Theobald) and An. multicolor Cambouliu in Siwa Oasis, Egypt, an area with low-level Plasmodium vivax transmission, and in Bahariya and Farafra, two other Egyptian oases which appear to be free of malaria. Initial testing indicated that 4.4% (23 of 518) and 0.8% (4 of 518) of the An. sergentii were positive for P. vivax and P. falciparum, respectively, and that 1.4% (1 of 71) of the An. multicolor were positive for P. falciparum. However, after two confirmational tests, only 1.2% (6 of 518) of the An. sergentii remained consistently positive for P. vivax. Initial ELISA absorbance was not a useful predictor of potential false positive reactions in the P. vivax assay. Paradoxically, the six ELISA-positive An. sergentii were from the two malaria-free oases. This study raises the question of whether ELISA-positive reactions for anopheline vector species provides unequivocal evidence for transmission in areas of low malaria endemicity.