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A serological survey of the Seminole Indians in south Florida for evidence of exposure to arbovirus infection indicated not only past infection with the recognized North American encephalitis viruses-a high incidence for St. Louis encephalitis-but exposure to a Bunyamwera group agent and to Venezuelan equine encephalitis virus, activity of which had not been previously recognized north of Panama.
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The haemagglutination-inhibition test has been used to assess the frequency of arbovirus infections in the population of Ceylon, by age-group, and also in some animals. The antigens used were: chikungunya, JE, dengue 1, 2, 3, 4, and Tahyna.The percentage of positive reactors to the group-B viruses ranged from 16.3% to 84.6% and was lower in the mountainous part of the country. Infections with the chikungunya (group-A) virus were less frequent (from 0 to 37%) and were considered to be recent infections. The prevalence of antibodies was found to increase with age.From a comparison of the antibody titres of the indigenous Ceylonese population with those of a group of immigrant Yugoslav workers it was concluded that a titre of 1:640 would represent a significant titre for a recent infection.The animals examined included goats, cattle, bandicoots, pigs and sheep; virus infections were most frequent in the bandicoots, pigs and sheep.
Serological studies for arboviruses were conducted on 725 animal sera collected in 22 Ontario townships between 1975 and 1980 including 44 coyote (Canis latrans), 277 red fox (Vulpes vulpes), 192 raccoon (Procyon lotor) and 212 striped skunk (Mephitis mephitis). Hemagglutination inhibition antibodies to two flaviviruses, namely St. Louis encephalitis and Powassan were found in 50% of coyote, 47% of skunk, 26% of fox and 10% of raccoon sera. Similarly, hemagglutination inhibition antibodies to a California serogroup virus, snowshoe hare, were found in 12% of fox, 7% of skunk, 7% of raccoon and 5% of coyote sera. No antibodies were detected to two alphavirus, namely eastern equine encephalitis and western equine encephalitis, antigens. This study affirms the endemic presence of Powassan and snowshoe hare virus and further delineates the scope of St. Louis encephalitis activity in Ontario.
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Mosquito longevity and blood-feeding behaviour are very important but neglected factors in the dynamics of arbovirus infections as changes in them affect transmission rates exponentially. Some mosquito species feed on a narrow range of vertebrates, some on a wide range, both influenced by host-availability and other environmental and behavioural factors. Only those which feed on maintenance hosts contribute to maintenance of the infection. Some species change their feeding pattern with season. The frequency of blood-feeding depends inter alia on environmental temperature. Longevity is perhaps most important: the majority of mosquitoes infected probably do not survive long enough to become infective; it is influenced by relative humidity, temperature and predation. Longevity, feeding frequency and the extrinsic incubation period are all temperature dependent and are therefore important rate determinants in seasonal epizootics or epidemics. Equally, their relative stability in the tropics contributes to the equilibrium of an enzootic or endemic.
A survey of the frequency of hepatitis B markers in 258 subjects from Kavango, northern South West Africa/Namibia, was undertaken during February - May 1983. The hepatitis B surface antigen and hepatitis B e antigen carrier rates were 13,6% and 2,7% respectively. Only 1,9% of the subjects were negative for all the markers tested, indicating that infection had been present at some stage in 98,1% of the sample. No known transmission method of the virus seems to fit this high exposure rate. The possibility that arthropod transmission of the virus may play a role in the epidemiology of the disease in Kavango is being investigated. All subjects tested for antibodies to hepatitis A virus were found to give a positive result. Of the arboviruses tested for, West Nile virus was usually predominant and was probably responsible for most of the arbovirus infections. Antibodies to the Sindbis, Chikungunya, Germiston and Rift Valley fever viruses were also found.
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Lust, George (Fort Detrick, Frederick, Md.). Alterations of protein synthesis in arbovirus-infected L cells. J. Bacteriol. 91:1612-1617. 1966.-Cellular protein synthesis and ribonucleic acid (RNA) synthesis in mouse L cells were markedly depressed 1 hr after infection with Venezuelan equine encephalomyelitis virus. Host RNA and protein synthesis were inhibited more rapidly by the virus infection than by actinomycin D. In cells infected 4 hr, a cytoplasmic RNA polymerase was demonstrated which was absent in uninfected cells. At this time, deoxyribonucleic acid-directed RNA synthesis catalyzed by the nuclear RNA polymerase was inhibited in vitro in enzyme preparations from nuclei of virus-infected cells. For optimal activity, the cytoplasmic RNA polymerase required the four nucleoside triphosphates, Mg(++), and RNA. The enzyme was insensitive to actinomycin D and deoxyribonuclease, indicating that it catalyzed RNA-directed RNA synthesis. Attempts to purify the induced polymerase further were unsuccessful. Fresh preparations had to be used because the enzymatic activity was unstable.
Buggy Creek (BCR) virus is an arthropod-borne alphavirus that is naturally transmitted to its vertebrate host the cliff swallow (Petrochelidon pyrrhonota) by an invertebrate vector, namely the cimicid swallow bug (Oeciacus vicarius). We examined how the prevalence of the virus varied with the group size of both its vector and host. The study was conducted in southwestern Nebraska where cliff swallows breed in colonies ranging from one to 3700 nests and the bug populations at a site vary directly with the cliff swallow colony size. The percentage of cliff swallow nests containing bugs infected with BCR virus increased significantly with colony size at a site in the current year and at the site in the previous year. This result could not be explained by differences in the bug sampling methods, date of sampling, sample size of the bugs, age structure of the bugs or the presence of an alternate host, the house sparrow (Passer domesticus). Colony sites that were reused by cliff swallows showed a positive autocorrelation in the percentage of nests with infected bugs between year t and year t+1, but the spatial autocorrelation broke down for year t+2. The increased prevalence of BCR virus at larger cliff swallow colonies probably reflects the larger bug populations there, which are less likely to decline in size and lead to virus extinction. To the authors' knowledge this is the first demonstration of arbovirus infection increasing with group size and one of the few known predictive ecological relationships between an arbovirus and its vectors/hosts. The results have implications for both understanding the fitness consequences of coloniality for cliff swallows and understanding the temporal and spatial variation in arboviral epidemics.
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