D.I.H. Simpson

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.

Cross-neutralization study of seven California group (Bunyaviridae) strains in homoiothermous (PS) and poikilothermous (XTC-2) vertebrate cells.

Antigenic relationships among seven California group strains were studied by a plaque-reduction neutralization test (PRNT). Cross-reactions occurred in most cases but three subgroups were noted: (1) the major serogroup contained the viruses of California encephalitis, LaCrosse, Snowshoe Hare and Trahyna (including the Lumbo strain) whereas (2) Jamestown Canyon and (3) Trivittatus viruses were distinct. There was no significant difference between the PRNT results in mammalian (PS) cells incubated at 37 degrees C and amphibian (XTC-2) cells incubated at 28 degrees C. Trivittatus virus failed to produce plaques in XTC-2 cells.

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: 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.

Arbovirus isolations from ixodid ticks infesting livestock, Kano Plain, Kenya

In a study conducted on the Kano Plain, Kenya, virus isolation attempts were made on ixodid ticks collected, over a 14-month period, from livestock held in family enclosures (bomas) before releasing the animals for daily foraging. 8735 Amblyomma variegatum (Fabricius) were tested, 98.6% of which were taken from cattle, yielding 36 strains of Dugbe (DUG), four strains of Nairobi sheep disease (NSD), three strains of Bhanja (BHA), one strain of Thogoto (THO) and five strains of virus which could not be characterized. 6549 Rhipicephalus spp. ticks were collected (60.3% from cattle). NSD, DUG and BHA viruses were each isolated twice from ticks taken from cattle. One BHA virus strain was recovered from ticks from a sheep. One strain recovered from ticks on cattle could not be characterized.