Hilary Way

Arbovirus infections in Sarawak, October 1968-February 1970.Tembusu and Sindbis virus isolations from mosquitoes.

Thirty isolations of Tembusu virus and four of Sindbis virus were obtained from approximately 280 000 mosquitoes collected between October 1968 and February 1970 in Sarawak, particularly from K. Tijirak, a Land Dyak village 19 miles South of Kuching. Twenty-two isolations of Tembusu virus and two of Sindbis virus were from Culex tritaeniorhynchus; two of Tembusu virus and two of Sindbis virus came from Culex gelidus. Tembusu virus was active throughout the year at K. Tijirak, the highest infection rates in C. tritaeniorhynchus being in January-March and May-August, when the C. tritaeniorhynchus population was declining and ageing. These results confirm that C. tritaeniorhynchus is the principal arthopod host of Tembusu virus in Sarawak. Antibody studies suggest that birds, particularly domestic fowl, are probably vertebrate maintenance hosts of Tembusu and Sindbis viruses in Sarawak.

Japanese encephalitis in Sarawak: virus isolation and serology in a Land Dyak village.

Abstract 55 viruses were isolated from approximately 174,300 mosquitoes collected in 2 areas of Sarawak between November 1968 and December 1969: 36 isolates, of which 4 have been provisionally identified as strains of Japanese encephalitis virus, came from C. tritaeniorhynchus and 7 isolates, of which 1 is a strain of Japanese encephalitis, from C. gelidus. The infection rate with Japanese encephalitis virus in the human population of Kampong Tijirak was estimated to be approximately 6% per annum. In pigs the infection rate was very much higher and was not uniform throughout the year. Pigs appear to become infected more frequently with increasing age and there was a considerable increase in the pig infection rate during the last quarter of the year coincident with the seasonal peak in C. tritaeniorhynchus population. The lower infection rate in man than in pigs is probably attributable to the considerably lower frequency with which man is bitten by C. tritaeniorhynchus. A considerable proportion of wild birds and of village dogs had Japanese encephalitis virus antibody and a few bats and ducks also had antibody. Fowls, geese and rodents do not appear to play a role in the maintenance of the virus.

Arbovirus infections in Sarawak: the role of the domestic pig

The possible role of pigs as arbovirus maintenance hosts and their importance as amplifier hosts was studied. Blood samples from 464 pigs of all ages collected in 1962 and 1964 were tested against 10 arboviruses. Antibodies to Japanese encephalitis and Getah viruses were particularly prevalent and their calculated monthly infection rates were 19-5% and 13-3% respectively. In 1969, 447 pigs were bled monthly throughout the year and the infection rates for Japanese encephalitis virus were calculated in pigs during the first year of life. Infection rates were not uniform throughout the year; the rate increases as the pig grew older and there was a marked seasonal increase in the infection rate in the period from November to January. This coincided with the seasonal major population peak of Culex tritaeniorhynchus following intense breeding of this mosquito prior to rice planting. It is suggested that, in Sarawak, the pig acts as a maintenance host of Japanese encephalitis in a cycle involving C. gelidus mosquitoes and also acts as an important amplifier host towards the end of the year in a cycle involving C. tritaeniorhynchus. It is further suggested that Getah virus is maintained in a similar cycle between C. tritaeniorhynchus and pigs.

Arbovirus infections in Sarawak, October 1968–February 1970: Human serological studies in a Land Dyak Village

449 human sera collected in a Land Dyak village were tested for antibodies to 11 arboviruses. Japanese encephalitis and dengue virus antibodies were particularly prevalent. The rates of infection with these viruses were estimated to be 5-2% per annum for Japanese encephalitis, 8-8% for dengue 1 and 4-3% for dengue 2. Chikungunya virus antibodies were quite common with an annual infection rate of the order of 5% per annum. Infections with other Group A and B and Bunyamwera group viruses were generally at a low level.

Arbovirus isolations from, and serological studies on, wild and domestic vertebrates from Kano Plain, Kenya

Arbovirus infection and presence of haemagglutination-inhibiting antibodies in small mammals, birds and livestock were examined over a period of five years on the Kano Plain in western Kenya. Eleven isolations were made from mammals and birds. The viruses were identified as Arumowot and Germiston while three different agents could not be shown to be related to 188 African arboviruses. Prevalence of antibodies against arboviruses suspected of occurring in the area was generally low.

Arbovirus infections in Sarawak, October 1968-February 1970: GETAH virus isolations from mosquitoes.

14 strains of Getah virus were isolated from a variety of mosquito species collected in Sarawak between October 1968 and February 1970. Ten strains were isolated from C. tritaeniorhynchus 7 of them at K. Tijirak. Single strains were isolated from C. gelidus, C. pseudovishnui, M. bonneae/dives and Aanopheles species. 6 of the isolates were obtained in October 1968 when Japanese encephalitis, Tembusu and Sindbis viruses were also very active. The available evidence suggest that Getah virus in Sarawak is maintained in a cycle similar to that of Japanese encephalitis virus and involves C. tritaeniorhynchus, C. gelidus and domestic pigs.

Arbovirus infections in Sarawak: serological studies in man.

Abstract 1. 1.2,118 human sera collected from all age groups in a wide variety of ecological zones in Sarawak during December 1962 and January 1963, April-May 1964 and September-December 1966, were tested for haemagglutination-inhibiting and neutralizing antibodies to 9 arboviruses. 2. 2.Japanese encephalitis and dengue virus antibodies were prevalent in all areas. The estimated annual infection rate with Japanese encephalitis virus varied from about 2% to over 9% with a mean of 6%. Estimated dengue virus infection rates varied from less than 1 % to over 11% with a mean of just over 5% per annum. 3. 3.There was only slight evidence of infection with group A, Bunyamwera and other group B arboviruses. 4. 4.No significant differences in the prevalence of arbovirus infections could be distinguished between any of the ecological zones. The wide distribution of Japanese encephalitis and dengue virus infections matched the distribution of the principal arthropod hosts of the viruses, C. tritaeniorhynchus, C. gelidus and Ae. albopictus . 5. 5.The general trend of arbovirus infections in Sarawak was of highest infection rates in coastal, estuarine and inland forest areas. Urban areas had the lowest rates while rural areas of settled cultivation had intermediate rates of infection.

Arbovirus isolations from mosquitoes: Kano Plain, Kenya

Arbovirus isolation attempts on 324,486 mosquitoes captured over a four-year period on the Kano Plain, Kenya, yielded 15 isolates including Pongola (six strains), Ilesha (three strains), Germiston (two strains), Sindbis (one strain), Barur (one strain) and two viruses which could not be characterized. Mansonia uniformis, Anopheles gambiae and Culex antennatus constituted 70% of the total collection and accounted for all of the isolates except one, which came from Anopheles funestus.