The yellow fever epidemic in Trinidad began with an epizootic in alouatta monkeys in November, 1978. Activity was detected by virus isolation from Alouatta monkeys and from Haemagogus mosquitoes between this date and July 1980. First reports of monkey deaths centered around the Guayaguayare forests of South Trinidad, following which the epizootic spread west to the Moruga area, and north through the Biche Forest reserve, eventually reaching the north-west Chaguaramas peninsula. Surveillance of febrile persons attending clinics and hospitals was intensified and 18 confirmed cases were identified, from 14 of whom yellow fever virus was isolated. In four cases, diagnoses were made on the basis of liver pathology only. Paired sera were obtained from 10 of 11 persons who survived, and in each case serological conversions were obtained by haemagglutination inhibition and mouse neutralization tests. Yellow Fever virus was isolated from 16 of 32 Alouatta monkeys and from 19 of 174 pools of Haemagogus mosquitoes.

Two systems were used for virus isolation:

the Aedes cell line AP-61 and suckling mice. The former proved to be more sensitive, detecting virus in 11.7 per cent of 725 specimens inoculated whereas suckling mice detected virus in 7.9 per cent of 724 specimens. In 11 instances virus was detected in an animal or mosquito pool by AP-61 but not initially by mouse inoculation whereas the converse was true in only one case.