Yellow fever and other arthropod-borne viruses: A consideration of two serological surveys made in South Western Nigeria

Abstract

1. 1) Serological surveys employing mouse protection tests have been made in two places in south western Nigeria. 2. 2) A high incidence of antibodies was found against Bwamba fever, dengue, Uganda S., yellow fever and Zika viruses; a low incidence was found against Bunyamwera, Mengo, Semliki Forest and West Nile viruses. 3. 3) The association of positive results in different protection tests was analysed and significant associations were found at Ilobi between positive results in the following pairs of viruses: Zika and dengue, Zika and Uganda S., Zika and yellow fever but not between yellow fever and Uganda S., dengue and yellow fever or Uganda S. and dengue. However, at Ilaro, yellow fever and Uganda S. did show a positive association. Amongst triads taken from this complex of four Group B viruses, positive tests to Zika and Uganda S. were remarkably associated with a positive test to yellow fever. Thus a positive test to Zika virus was found in nearly all the significant associations. 4. 4) Possible causes of the associations are discussed and it is considered that serological overlap is the most likely. 5. 5) Although the serological overlaps may not occur with sufficient frequency to interfere seriously with the interpretation of epidemiological serological surveys, nevertheless their presence may account for certain observed abnormalities in the clinical epidemiology of yellow fever in Nigeria. 6. 6) The hypothesis is advanced that the low incidence of clinical yellow fever in certain parts of Nigeria is due to tolerance of this virus induced by prior infections with related virus.