ORUNGO ( UgMP 359) VIRUS: A HITHERTO UNDESCRIBED VIRUS, BIOCHEMICAL, BIOPHYSICAL AND EPIDEMIOLOGICAL STUDIES

Abstract

Orungo virus, a hitherto undescribed virus, first isoated from a pool of Anopheles mosquitoes caught off human bait in Uganda was studied by biochemical, biophysical and sero- epidemiological methods. These studies were conducted to classify orungo virus, determine antigenic differences between Orungo virus strains, and determine the host range and extent of infection of Orungo virus in man and animals in Nigeria. The techniques employed included reaction of Orungo virus to physical and chemical agents, electron microscopy, to determine the ultrastructure of the virus, neutralization tests in new-born-mice, complement fixation, homagglutination and agar gel precipitation tests. Other techniques used were plaque formation in tissue culture, experimental infection of laboratory animals and transmission studies with arthropods.

Orungo virus, with a virus particle size of 63nm and an icosahedral capsid construction was found to be similar in all details of morphology and morphogenesis to the orbivlruses - a group of viruses which are serologically unrelated but morpholo¬gically and morphogenetically identical. Orungo virus shares with the orbivlruses, the common property of relative stability to lipid solvents and soodiun desxycholate, lability at pH 3.0 and lack of antigenic relationship to any of the major serologic group A, B and Bumyamwera. Orungo virus was found to be thermo- labile at 56°C, sensitive to UV irradiation and treatment with BPL and formalin. The host range susceptibility include the Swiss albino mice, hamsters, lambs and rabbits. Sparrows and day old chicks neither circulated virus nor developed antibody following inoculation with Orungo virus.

0runco virus multiplies with resultant CPE in Vero and BHK-21 cell lines, but not in Aedes albopictus cell cultures. Experimental transmission of Orungo virus was achieved with Aedes albopictus and Aedes aegypti mosquitos inoculated by the intra-thoracic route.

Orungo virus docs not show homaggelutinating activity, however by CP, and N tests varying degrees of differences were demonstrated between the Orungo virus strains. In AGD tests, there was a complete line of identity with all the strains. Strain HG0974 previously reported as a strain of Orungo virus was found to be Tateguine virus.

Neutralizing antibodies to Orungo virus were detected in the sora of man and animal collected from different parts of Nigeria. There was an increasing trend in prevalence rate from the not forested area to the drier savannah regions. In addition the prevalence of antibody increased with age. The commonly described symptoms of Orungo virus infection are mild fever of short duration, myalgia, headache and occasional weakness of the lower extremities.