EVIDENCE OF ARBOVIRUS INFECTION IN FIJI

Islands as Hotspots for Emerging Mosquito-Borne Viruses: A One-Health Perspective

During the past ten years, an increasing number of arbovirus outbreaks have affected tropical islands worldwide. We examined the available literature in peer-reviewed journals, from the second half of the 20th century until 2018, with the aim of gathering an overall picture of the emergence of arboviruses in these islands. In addition, we included information on environmental and social drivers specific to island setting that can facilitate the emergence of outbreaks. Within the context of the One Health approach, our review highlights how the emergence of arboviruses in tropical islands is linked to the complex interplay between their unique ecological settings and to the recent changes in local and global sociodemographic patterns. We also advocate for greater coordination between stakeholders in developing novel prevention and mitigation approaches for an intractable problem.

Ross River virus (Togaviridae: Alphavirus) infection (epidemic polyarthritis) in American Samoa

An outbreak of Ross River virus infection (epidemic polyarthritis), which occurred in American Samoa between August 1979 and January 1980, is described. On the basis of a serological survey performed near the end of the epidemic, it is estimated that at least 13,500 people were infected. Ross River virus was isolated from the blood of a single polyarthritis patient. Plaque reduction neutralization tests, using this virus strain, were done on 393 human and 143 animal sera collected on Tutuila island. Over-all, 43.8% of the people sampled had evidence of infection. Sera from 100 adult residents of the same island, collected in 1972, had no Ross River antibody, suggesting recent introduction of the virus. In contrast to the human serological data, the prevalence of Ross River antibodies among animals was relatively low. Dogs and pigs had the highest rates with 20% and 15%, respectively. Results of this study suggest that the Ross River virus cycle during the epidemic in American Samoa involved primarily humans and mosquitoes with animals less frequently infected. These observations plus the recent introduction of Ross River virus into new areas of the South Pacific suggest that a major change has occurred in the epidemiology of epidemic polyarthritis.

Mosquito-borne infections in Fiji. V. The 1971-73 dengue epidemic

A dengue epidemic due to type 2 virus involving some 3,400 cases began in Fiji early in 1971, had a peak during May, June and July, and cases have continued to occur with a low incidence during 1972 and 1973. Many of the notified cases showed classical dengue fever symptoms and there were no confirmed cases of haemorrhagic fever. A serological survey indicated that there had been at least 20,000 subclinical infections. It is probable that the virus was introduced to Fiji either through the port of Lautoka or Nadi international airport in February 1971. The normal travel patterns of residents must have spread the virus to all the more accessible localities but, with the exception of Rotuma, it caused infections only in areas where Aedes aegypti was available as a vector. There was no evidence that pre-existing dengue type 1 serum antibody gave any protection during this epidemic.

Mosquito-borne infections in Fiji. II. Arthropod-borne virus infections

Surveys of arbovirus activity in Fiji were conducted over a 10-year period from December 1959 to December 1969. No arboviruses were isolated from over 200,000 mosquitoes, 9000 ticks, or 575 serum samples. Eight thousand human and 1117 bird, bat and animal sera were tested for haemagglutination-inhibiting arbovirus antibody using a variety of group A, group B and Bunyamwera group antigens. Only a small number of low-titre reactions were found among the non-human sera, but 14% of all human sera were found to contain Group B antibody. The antibody prevalence increased with increasing age, from less than 1% for persons born since 1950, to 70% for persons born before 1900. The age differences in prevalence could be used to estimate the time and size of previous epidemics. Differences were found in antibody prevalence between the sexes, between ethnic groups and between persons from different regions. These differences could be explained in terms of climate, location and custom.Historical and serological evidence both suggest that all the antibody detected was due to past exposure to dengue virus. The very high proportion of the population with no dengue antibody makes Fiji a high-risk area for a further dengue epidemic. Dengue virus is known to be active in the Pacific and South-East Asia.

The isolation of Coxsackie A viruses from human sera and mosquitoes in Fiji

1. Coxsackie A6 virus was isolated in January 1963 from the circulating blood of four children in Suva, Fiji, suffering from fever, lymphadenitis and pharyngitis.

2. Nine strains of the same agent were isolated from Aedes (Stegomyia) poly-nesiensis mosquitoes caught over a period of 2 weeks near or in a village situated among mangrove swamps at the mouth of the Rewa river, in January 1963.

3. No virus was isolated from mosquitoes caught in Suva.

4. A serological survey indicated that Coxsackie A6 infections are common and widespread in Fiji.