B. PATHOGENICITY OF SFV 
1. Naturally Occurring SFV Infections 
First isolated and identified in 1942 (Smithbum and Haddow, 1944), SFV has 
been isolated in the wild from sentinel mice, wild birds, and several species of 
mosquitoes in sites widely distributed throughout Africa (Berge,1975). In 
addition, at least one isolate of SFV has been reported from Surinam, South 
America (Bradish,1971). Antibodies against SFV have been detected commonly 
in chimpanzees, wild rodents, and domestic animals in South Africa. 
Serological surveys indicate that SFV infection is common in human populations 
(5%-17%) of several regions within central and southern Africa (Berge, 1975; 
McIntosh et al., 1961). Neutralizing antibodies for SFV also have been detected 
in the peoples of India, Thailand, Vietnam, Malaya, Borneo, and the Philippines 
(Berge, 1975). Nevertheless, for more than forty years, human SFV infection in 
nature was considered to be mild and largely asymptomatic. 
The first, and only, report of naturally occurring, symptomatic SFV infection in 
man appeared in 1990 (Mathiot et al, 1990). During an outbreak of febrile illness 
in the Central African Republic, sera were drawn from 163 individuals presenting 
with acute, viral-like illness. From 23 of these patients’ sera, SFV was isolated. 
Most of the SFV-positive sera isolated were from Europeans, particularly soldiers 
recently arrived from France; only three positive samples were obtained from 
Africans. 
Virus identification by cross-neutralization assays indicated that the isolated 
strains were all identical, and related to known strains of SFV, including the 
prototype virus (Smithbum and Haddow, 1944). 
The symptoms in all cases included fever, headache, arthritis, and myalgia, and 
were "...generally mild and undifferentiable during the acute phase from other 
febrile illnesses, such as malaria and influenza (Mathiot et al,1990)." However, 
headaches in some cases, lasted up to 15 days. The acute symptomatic phase, of 
2-4 days, was followed by a prolonged period of convalescence. No fatalities 
were recorded. 
Whether this outbreak of illness in the Central African Republic was due to an 
unusually virulent strain of SFV is unknown. But this study established for the 
first time that naturally occurring SFV occasionally can cause symptomatic 
infection in man. No other examples of naturally occurring, overt SFV infection 
in humans have been reported. 
Recombinant DNA Research, Volume 18 
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