H. A. Standfast

Akabane virus infection in the pregnant ewe. 1. Growth of virus in the foetus and the development of the foetal immune response

Abstract Three different pools of the CSIRO 16 strain of Akabane virus differing in their laboratory passage histories were used to inoculate 39 ewes between 32 and 36 days pregnant; 22 pregnant ewes received inocula containing no virus. There was no difference in the development, duration and titre of the viraemia and neutralising antibody response between the three infected groups of ewes. Both infected and control ewes had 141% foetuses when autopsied at 69 to 105 days gestation. Of the 55 foetuses from infected ewes 44 (80%) had gross developmental abnormalities. At autopsy of the dams Akabane virus was isolated only from the uterine caruncle. From foetal samples virus was isolated from a wide range of tissues, from one foetus at 69 days and from the blood of four foetuses at 95 to 106 days gestation. Virus was also isolated from 24 of the choriolllantoic fluid samples and from 37 placentomes of the 44 foetuses with developmental defects, in concentrations ranging from 10 2 to 10 5.5 TCID 50 /ml or/g. No virus was isolated from the tissues of the control ewes or their foetuses. Neutralising antibody to Akabane virus was detected in 78% of the foetal sera from the infected group, titres ranging from 2 to 64. IgM and IgG 1 and neutralising antibody were detected in sera of 40 foetuses with developmental abnormalities including three that were of 76 to 78 days gestation. Neutralising antibody was detected only in serum that contained IgG 1 but may also have been associated with IgM in infected foetuses. IgM was detected in the serum of most foetuses including the non-infected controls, but sera from the control foetuses did not contain IgG 1 or neutralising antibody to Akabane virus. No IgG 2 or IgA were detected in any foetal serum.

Isolation of Tibrogargan virus, a new Australian rhabdovirus, from Culicoides brevitarsis.

CSIRO 132 virus, which is new to science in Australia, and probably the world, has been isolated from Culicoides brevitarsis. Electron micrographs show that it resembles a rhabdovirus. Antibodies to the new virus have been detected in water buffaloes and cattle, but not in 58 human beings, 14 camels, 21 dogs, 67 goats, 15 horses, 43 pigs, 154 sheep, 98 wallabies or 38 possums. The distribution of antibodies in cattle lies within the distribution range of C. brevitarsis. It has not so far been associated with disease. The name Tibrogargan is proposed for the new virus.