Abstract
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. Keywords: Japanese encephalitis, California serogroup, Alphavirus, mosquito, Chandipura virus doi: 10.4038/cjsbs.v37i1.492 Cey. J. Sci. (Bio. Sci.) 37 (1): 7-14, 2008
Highlights
Arboviruses are a group of taxonomically diverse viruses that share a common mode of transmission between vertebrate hosts
The Japanese encephalitis (JE) viruses isolated from Cx.pseudovishnui in Kandy and from a patient with JE encephalitis in Anuradhapura have been genetically sequenced and found to be closely related suggesting that the lack of epidemic JE in Kandy is not due to differences in virus virulence (Chen et al, 1990) but is more likely due to abundance of vectors and amplifier hosts
Our studies suggested that bovine seroprevalence correlated better with human epidemic JE risk than does porcine seroprevalence, probably because bovines were a spillover host for JE virus just as humans are
Summary
Arboviruses (derived from arthropod-borne viruses) are a group of taxonomically diverse viruses that share a common mode of transmission between vertebrate hosts. These studies have included a) Virus isolation from live caught mosquitoes and ticks, b) sero-epidemiological studies using neutralization tests and c) studies on the ecology and epidemiology of Japanese encephalitis virus in different regions of Sri Lanka. These studies provided the first record of isolation of alphavirus Getah in the Indian subcontinent; the Bunyavirus Batai and the reovirus Arkonam from mosquitoes in Sri Lanka (Peiris et al, 1994) and Nairobi sheep disease (NSD) virus from pools of Haemaphysalis intermedia ticks (Perera et al, 1996) (Table 1).
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