ECOLOGY OF ARBOVIRUSES IN SRI LANKA: A SUMMARY OF STUDIES FROM 1984-1990

Studies on arboviruses carried out between 1984-1990 at the University of Peradeniya are summarized here. The isolation of Nairobi sheep disease virus, Getah, Batai and Arkonam and serological evidence of the circulation of California encephalitis serogroup and Chandipura viruses have been reported for the first time in Sri Lanka. The ecology of Japanese encephalitis (JE) in areas with epidemic disease and sylvatic infection has been compared. A synchronous pattern of seroconversion in pigs and seroprevalence in cattle are more predictive of epidemic JE risk than overall porcine seroprevalence which is a good indicator of the presence of sylvatic JE rather than of human epidemic risk. Relatively modest changes in vector abundance associated with rainfall or agricultural practices have dramatic changes on the emergence of epidemic JE. Chandipura virus which is known to cause major outbreaks of encephalitis in India is endemic in Sri Lanka as are viruses belonging to the California encephalitis serogroup. Both these viruses are potential causes of human encephalitis and should be sought in patients with undiagnosed encephalitis. Nairobi sheep disease virus is endemic in animals (especially goats) and infects humans working closely with such livestock. Arboviruses remain an under-recognised cause of human and animal disease and an inter-sectoral multidisciplinary approach is needed to confront such emerging infectious disease threat