Bluetongue, epizootic haemorrhagic disease of deer and related viruses: current situation in Australia.

Since 1975 3 serotypes of bluetongue (BT) virus (BTV) have been identified in Australia: BTV1 (CSIRO156), BTV20 (CSIRO19) and BTV21. At present 2 further BT viruses (DPP90 and DPP192) have been isolated from the blood of healthy cattle in the Northern Territory (NT) and are undergoing identification. There is serological evidence for BTV15 infection in Western Australia (WA) and the NT, and a background level of serological activity to BTV serotypes 1 to 17. In addition, over 50 isolations of epizootic hemorrhagic disease of deer (EHD) viruses (EHDV) have been made and can be divided into 5 main serotypes, CSIRO157, CSIRO439, CSIRO753, CSIRO775 and DPP59. All 5 serotypes occur within the ecological range of Culicoides brevitarsis, however, as for BTV, the high prevalence of antibodies in cattle in the Kimberley region of WA and the top end of the NT suggests other vectors may also be responsible. CSIRO439 has been shown to be closely related serologically to Ibaraki virus while the other EHD viruses were distinct from Ibaraki and from each other. The complex serological relationships between BTV, EHDV and Palyam virus groups are currently being examined using serological and biochemical techniques. It is often difficult to determine the differences between BTV and EHDV serogroup members. Antibodies to both BTV and EHDV have been found in cattle, buffaloes and deer but there has been no evidence of clinical disease in any of these species or in sheep under field conditions in Australia.

Serological studies of Australian and Papua New Guinean cattle and Australian sheep for the presence of antibodies against bluetongue group viruses.

Following isolation of a virus (CSIRO19) from insects in Australia and its identification as bluetongue virus serotype 20 (BTV20), a nationwide survey of antibodies in cattle and sheep sera was undertaken. Initial studies using the serum neutralization (SN) test showed that the distribution of BTV20 antibodies in cattle was confined to the northern part of Australia. Group-reactive antibody tests (agar gel diffusion precipitin, AGDP, and complement-fixation, CF) showed group-reactive cattle sera south of the BTV20 zone (northern Australia), and southwards from Queensland to New South Wales. Very few group-reactive sheep sera (45 out of 16213) were found and these were of doubtful epidemiological significance. Some of these BTV group-reactive, BTV20-negative, sera were tested in SN tests against BTV1 to 17 and Ibaraki (IBA) virus. The results indicated that BTV1, or a closely related orbivirus, was active in cattle in Queensland, northern Western Australia, and New South Wales, and that antibody to BTV15 was present in some of the cattle sera in northern Western Australia and the Northern Territory. Antibody to IBA virus was present in some cattle sera in Queensland, northern Western Australia and New South Wales. SN antibody titres greater than or equal to 60 were also found to a number of other BTV serotypes in cattle sera in northern Western Australia and Queensland (principally, BTV2 and BTV7). Low level reactions were commonly observed against these and a number of other BTV serotypes, often in the same serum samples. Further, 22% of the group-reactive cattle sera did not react with any of the viruses in the SN tests. Such results were difficult to interpret in terms of known Australian BTV or BTV-related isolates.

Experimental infection of bulls with Akabane virus.

Eight bulls were inoculated with Akabane virus and the clinical effects, development of viraemia and serological response to infection were followed. In addition semen was collected regularly from each bull both before and after inoculation. The bulls had a viraemia which occurred between days 2 and 9 after inoculation and which lasted for three to five days. Virus neutralising antibodies were detected in the serum of all bulls by days 7 to 10. Semen samples were tested for virus by inoculation of tissue cultures and by subcutaneous injection of susceptible cattle. Akabane virus was not detected in the semen using either method. The semen was usually of a standard acceptable for artificial breeding. The results of this study suggest that Akabane virus infection of the bull would not affect reproduction.

Developmental disorders of the fetus in some arthropod-borne virus infections.

A number of arboviruses have been associated with congenital defects in domestic aminals and man. In this review comparison is made of the temporal association between epidemics of arboviruses affecting man and animals in which there is an obvious relationship between the infection and the fetal defects, and arboviruses which cause no overt clinical symptoms in the vertebrate host but result in deformities of the fetus. The danger to the fetus following the use of live attenuated virus vaccines against several important arbovirus diseases is also examined. It is concluded that arboviruses which are capable of infecting humans or animals without producing overt clinical signs, and attenuated vaccine viruses pose the greatest threat to the fetus.

Congenital abnormalities in newborn lambs after infection of pregnant sheep with Akabane virus.

Akabane virus (a Bunyavirus) has been associated with epizootics of congenital deformities in cattle, sheep, and goats. Experimental studies using mouse-adapted virus inoculated intravenously into pregnant sheep gave an inapparent infection. Neutralizing antibodies were detected on day 5, and peaks in the titer were seen at days 10 and 48. Ewes infected at day 30 to 36 of pregnancy produced five (31% incidence) deformed lambs. Sera from four of these possessed neutralizing antibodies to Akabane virus before ingesting colostrum. Two lambs had arthrogryposis, hydranencephaly, kyphosis, scoliosis, and brachygnathia; one had micrencephaly; and the other two had porencephaly. The two lambs with arthrogryposis and hydranencephaly also had extensive lesions in other tissues. In the spinal cord there was a marked decrease in the number of ventral horn neurones and a depletion of myelin. Skeletal muscles showed marked atrophy. The medulla of the thymus possessed large Hassall's corpuscles and a reduced number of thymocytes in the cortex. It would appear that the pathogenic effects of Akabane virus are related to the gestational age (30 to 36 days) at which the fetus is infected. Akabane virus can now be included in the growing list of teratogenic viruses and provides an interesting system for studying such congenital diseases.

The role of wild animals in the spread of exotic diseases in Australia.

The distributions of the following feral animals are given -- cattle, buffalo, pig, goat, deer, camel, horse, donkey, fox, dog and cat -- and the native dingo. The possible role these and the native rodents, marsupials and monotremes would play should an exotic disease of livestock enter Australia is discussed. It is considered that feral animals would be important in creating foci from which the disease would spread.

The effect of natural and artificial breeding using bulls infected with, or semen contaminated with, infectious bovine rhinotracheitis virus.

Ten cows and heifers (Group B) were inoculated into the uterus at oestrus with semen followed by IBR virus for the first insemination and semen alone if a second insemination was necessary. All animals developed infectious pustular vulvo-vaginitis (IPV), and 2 cows conceived to the first and 2 to the second insemination (pregnancy rate of 40 percent requiring 4.5 services per conception). This group was compared with 10 control animals (Group A) which were treated similarly but received tissue culture fluid instead of virus at the first insemination. Group A had a pregnancy rate of 90 percent requiring 1.7 services per conception. Natural mating of 4 bulls with preputial infections due to infectious bovine rhinotracheitis (IBR) virus with 9 susceptible cows and heifers (group D), resulted in the production of lesions of IPV. The IPV infection did not affect their fertility (pregnancy rate of 89 percent requiring 1.4 services per conception) when it was compared to a similar group of females (group C) mated to the same bulls prior to infection with IBR virus (pregnancy rate of 100 percent requiring 1.2 services per conception). The 6 animals in Group B that were not pregnant and returned to oestrus 3 times were found on slaughter to have endometritis, salpingitis and vaginitis. A high incidence, 5 out of 18 (28 percent), of shortened oestrous cycles (less than 18 days) was a feature of the breeding pattern of this group. The undesirable consequences of distributing semen contaminated with IBR virus from artificial insemination centres are apparent.