The dispersal of Culicoides brevitarsis in eastern New South Wales and associations with the occurrences of arbovirus infections in cattle

Distributions of the vector Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae) (determined from light trap data) and 2 arboviruses (determined from seroconversions in sentinel cattle) were studied in eastern New South Wales in 1993–94. C brevitarsis was recorded progressively from endemic areas on the north coast, to Nowra on the south coast, and westward to Scone, in the Hunter Valley. C brevitarsis also survived through winter at Paterson, in the Hunter Valley. Its apparently focal reappearance in this marginal area had no obvious effect on the broad pattern of its progression or the dispersal of Akabane and bluetongue viruses. These viruses were first recorded from foci near Coffs Harbour, on the mid-north coast. Their first occurrences at different locations were associated with those of C brevitarsis, but not with each other. The viruses were found only within the recorded limits of the vector's distribution. Delays between the initial occurrence of C brevitarsis and first evidence of virus transmissions at locations ranged from 2 to 7 months. The delays decreased away from the points of focus and were negatively associated with the time of initial occurrence of the vector. Seroconversions to the viruses were related to the presence of C brevitarsis. However, the densities of C brevitarsis had no apparent effect on the initial numbers of cattle seroconverting to either virus. The results support the conclusion that the progressions of C brevitarsis and Akabane and bluetongue viruses were the result of gradual movements by the vector.     

Studies on the pathogenesis of bovine ephemeral fever in sentinel cattle. I. Virology and serology

Twenty-two sentinel cattle were observed daily during an outbreak of ephemeral fever on a dairy farm in eastern Australia in the summer of 1981–192. Of the 22 cattle, 9 developed clinical ephemeral fever. None developed sub-clinical infection. The pattern of the epidemic was a single index case followed 10 days later by the main epidemic wave which lasted for 7 days. This wave stopped when there were still 14 uninfected susceptible animals remaining in the sentinel group, and when biting flies were very active. Ten isolations of bovine ephemeral fever virus were made in Aedes albopictus tissue cultures from the blood of 5 clinical cases. One hundred and twelve isolations of CSIRO Village virus and one each of Kimberley and Akabane viruses were also made from various members of the sentinel group. There was serological evidence that infections with Tibrogargan, Tinaroo and Aino viruses also occurred in 6 cattle in the observation period. The 13 cattle undergoing a sub-clinical viraemia with CSIRO Village virus, Tibrogargan, Kimberley, Akabane or Aino viruses at the time of the main outbreak, appeared to be temporarily protected against ephemeral fever. However, 9 of the 11 still remaining in the herd were susceptible in a subsequent outbreak of ephemeral fever 2 years later. Evidence is presented that subclinical infections with other arboviruses may limit an ephemeral fever epidemic by providing temporary protection by interference.     

ANTIBODIES TO AKABANE VIRUS IN AUSTRALIA

SUMMARY Neutralising antibody to Akabane virus was shown to develop in cattle in northern Australia throughout the year and also on the east coast of New South Wales in the summer during 1975/1976. Other species found to have antibody to Akabane virus were buffaloes, horses, camels and sheep, but no antibody was found in domestic chickens, ducks, wallabies or man. The biting midge Culicoides brevitarsis has been detected in all the major areas where antibody was demonstrated in this study.     

A SURVEY OF ANTIBODY TO AINO VIRUS IN CATTLE AND OTHER SPECIES IN AUSTRALIA

SUMMARY A serological survey of healthy cattle in Australia showed that antibodies to Aino virus were present in serums from cattle in northern Australia and down the east coast as far as central New South Wales in 1975, 1976 and 1977, but occurred with a lower frequency than antibodies to Akabane virus. in contrast to the findings with Akabane virus, no neutralising antibodies to Aino virus were detected in serums from camels, dogs or horses. Antibodies to both viruses were detected in buffaloes and sheep, but not in humans or any of the Australian indigenous species so far tested. All positive serums originated from within the known range of Culicoides brevitarsis.     

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

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 10² to 10^5.5 TCID₅₀/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 IgG₁ 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 IgG₁ 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 IgG₁ or neutralising antibody to Akabane virus. No IgG₂ or IgA were detected in any foetal serum.     

The length of BTV-8 viraemia in cattle according to infection doses and diagnostic techniques

Four groups of BTV free Frisian and cross bred calves were used to determine the length of viraemia following infection with different doses of BTV-8 Italian isolate. The first group of five animals was infected with 10 TCID₅₀ of BTV-8, the second group of four animals with 10³ TCID₅₀ and the third group, which also included four animals, was infected with 10⁶ TCID₅₀. A placebo containing uninfected tissue culture medium was given to the four animals of the fourth group. The viraemia was evaluated by real time RT-PCR and virus isolation. In all infected groups, virus isolation was able to detect infectious virus up to 39 days post infection (dpi) while RT-PCR was positive up to 151–157 dpi. Infectious dose did influence neither the length nor the pattern of BTV-8 viraemia and confirmed that real time RT-PCR remains positive although no circulating virus is detectable in the peripheral circulation.     

Akabane virus infection in the pregnant ewe. 2. Pathology of the foetus

A strain of Akabane virus (CSIRO 16) isolated from Culicoides brevitarsis was given three different passage treatments in the laboratory and then inoculated into ewes that were 32 to 36 days pregnant. The foetuses from these ewes were examined between the 69th and 106th days of gestation. The 39 infected ewes produced 55 foetuses of which 44 (80%) had severe developmental defects. Arthrogryposis and agenesis of the brain or hydranencephaly, were present in 43 of the foetuses. Other gross defects affecting variable proportions of foetuses were porencephaly, brachygnathism, scoliosis, hypoplasia of the lungs and agenesis or hypoplasia of the spinal cord. Histopathological findings covered a wide spectrum of defects that have previously been considered to occur over an extended range of foetal ages. These defects included skeletal muscle atrophy and degeneration, and in the brain, particularly in the cerebrum, cystic areas and malacia, general oedema, subependymal gliosis, perivascular cuffing and mineralised plaques. Similar lesions were seen in the pons and cerebellum. Extensive lesions, with and without inflammation were seen in the spinal cord.     

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.     

Seroprevalence of five arboviruses in sentinel cattle as part of nationwide surveillance in South Korea, 2009?2012

To investigate the possible circulation of arboviruses in South Korea, nationwide surveillance of five arbovirues was conducted in sentinel calves during 2009−2012. We used serum neutralization tests to investigate the presence of antibodies for the Aino virus, Akabane virus, bovine ephemeral fever virus, Chuzan virus and Ibaraki virus. In 2009, 2011 and 2012, the seropositive rates for these five arboviruses were all less than 14.1%. In 2010, however, the seropositive rates for Aino virus and Akabane virus were 33.2% and 40.2%, respectively. High seropositive rates were also associated with a large-scale outbreak of Akabane viral encephalomyelitis in cattle in southern Korea in 2010. Continued seroprevalence surveillance will be useful for monitoring natural arboviral diseases.     

Replication of bovine viral diarrhoea virus in the bovine reproductive tract and excretion of virus in semen during acute and chronic infections.

Five mature bulls were studied during an acute transient infection with bovine viral diarrhoea virus (BVDV). The bulls had been infected experimentally by the intranasal instillation of blood and serum from a cow which was a persistent carrier of the virus. Infection was confirmed by the demonstration of a low titred viraemia in four of the five animals and by the seroconversion of all five. Semen samples were collected from each bull on four occasions between seven and 14 days after infection. The virus was isolated from the semen of three of the five bulls and from nine of 12 batches of semen from them. In contrast to other studies of the infection of semen, BVDV was isolated with similar efficiency from raw, unprocessed semen and from diluted, extended semen. The titres of virus in the semen ranged from 5 to 75 TCID50/ml. The infection did not appear to affect the quality of the semen. Shedding of virus continued after the end of the period of viraemia and appeared to be a consequence of the replication of the virus in the reproductive tract and its subsequent excretion in the seminal fluid. Virological studies of the reproductive tracts of these bulls suggested that the most productive sites of virus replication were the seminal vesicles and the prostate gland. Concurrent studies in a persistently infected bull supported these findings.     

A sentinel herd system for the study of arbovirus infections in Australia and Papua-New Guinea

The establishment, and development between 1969 and 1978, of a system of sentinel cattle in herds located in many areas of Australia and in Papua New Guinea is described. Though the system was established for the study of the epidemiology of a variety of viruses infecting cattle, the study has been limited since 1974 to arboviruses. By means of serology, it was established that bovine ephemeral fever virus was present in Australia in subclinical form between major epidemics but was not detected in Papua-New Guinea. The development of antibody to bovine ephemeral fever virus in individual cattle before they developed clinical signs in epidemics was clearly demonstrated. The sentinel technique was used to demonstrate that subclinical Akabane virus infection in cattle occurred at the time that virus was present in its suspected vector,Culicoides brevitarsis which had been collected nearby. The epidemiology of other Simbu group viruses, D'Aguilar virus, and bluetongue virus, (serotype 20) was also studied. A limited programme of arbovirus isolation in tissue cultures produced 0.8% of isolates from 2090 of the blood clots which accompanied sentinel herd serum samples.The most valuable aspect of the sentinel herd scheme has been the accumulation of a well documented representative set of serum samples for retrospective serology by the use of newly isolated or imported antigens.     

Infectivity of pestivirus following persistence of acute infection

Bovine viral diarrhoea virus (BVDV) is an endemic pathogen worldwide and eradication strategies focus on the identification and removal of persistently infected (PI) animals arising after in utero infection. Despite this, acute infections with BVDV can persist for months or years after the removal of the PI source despite repeated screening for PIs and tight biosecurity measures. Recent evidence for a prolonged duration of viraemia in the testicles of bulls following acute BVDV infection suggests the possibility of a form of chronic persistence that may more closely resemble the persistence strategies of hepatitis C virus (HCV). To investigate the potential for virus transmission from infected and recovered cattle to virus naïve hosts we established an acute infection of 5 BVDV-naïve calves and monitored animals over 129 days. Infectious BVDV was detected in white blood cells between days 3 and 7 post-challenge. The animals seroconverted by day 21 post-infection and subsequently were apparently immune and free from infectious virus and viral antigen.Animals were further monitored and purified white blood cells were stimulated in vitro with phytohaemagglutinin A (PHA) during which time BVDV RNA was detected intermittently.Ninety-eight days following challenge, blood was transferred from these apparently virus-free and actively immune animals to a further group of 5 BVDV-naïve calves and transmission of infection was achieved. This indicates that BVDV-infected, recovered and immune animals have the potential to remain infectious for BVDV-naïve cohorts for longer than previously demonstrated.     

Isolation of bovine herpesvirus-3 from African buffaloes (Syncerus caffer)

Eleven virus isolations were made from the blood of 45 free living healthy African buffaloes by long term cocultivation of their leucocytes with bovine thymus or spleen cells. The isolates were indistinguishable from each other or from herpesviruses isolated from a severely ill buffalo calf and from a dead buffalo. These viruses possessed the characteristics of the bovine herpesvirus-3 (BHV-3) group and were indistinguishable by serology and restriction endonuclease analysis from the BHV-3 type strains Movar 33/63 and DN599. There was a 93.6 per cent prevalence of indirect immunofluorescent antibody to BHV-3 in the sera of 94 buffaloes in the sample population. No clinical signs or viraemia were detected in five cattle inoculated with 10(8.7) log10 TCID50 of the isolate from the sick buffalo calf. Two of three cattle hyperimmunised with this virus resisted challenge with malignant catarrhal fever herpesvirus, which proved fatal for the other immunised animal and for three control cattle.     

Neutralising antibodies to Akabane virus in ruminants in Cyprus

Summary Neutralising antibodies to Akabane virus, a cause of arthrogryposis and hydranencephaly, were demonstrated in serum samples from 33 sheep, 3 goats and 1 bovine among 285 serum samples collected in south-eastern Cyprus from December 1970 onwards. Twenty-four of the 29 sheep having positive antibodies came from one farm in Liopetri. No positive sera came from animals born after 1969, no association with abortions or stillbirths was noted and no arthrogryposis or hydranencephaly was observed in Cypriot animals in 1969 or before. It is suggested that Akabane virus was carried to Cyprus from the eastern Mediterranean mainland by infected midges on the wind in 1969 and possibly also in 1968, but that no disease was observed since infection took place after 50 days of gestation when damage to the foetus was unlikely.

---

Anticuerpos Neutralizantes Del Virus Akabane En Rumiantes En Chipre

Resumen Se encontraron anticuerpos neutralizantes del virus Akabane, la causa de artrogriposis e hidranencefália, en muestras de suero de 33 ovejas, 3 cabras y 1 bovino, entre 285 muestras en total colectadas en la región suroriental de Chipre. El muestreo empezó en Diciembre de 1970. Veinticuatro de las 29 ovejas positivas se sangraron en una granja de Liopetri.No se encontraron anticuerpos específicos en animales nacidos después de 1969; tampoco se encontró asociación alguna con abortos o daños fetales. No se observó artrogriposis o hidranencefália en animales chipriotas en 1969 o anterior a esa fecha. Esto sugiere, que el virus Akabane llegó a Chipre de la región oriental mediterránea, en insectos del ordenDiptera, en 1969 y posiblemente también en 1968. La enfermedad en esa época no se vió, posiblemente debido a que la infección ocurrió después de los 50 días de gestación, cuando el feto es poco susceptible al virus.

---

Anticorps Neutralisants, Specifiques Du Virus Akabane, Chez Des Ruminants A Chypre

Résumé Des anticorps neutralisants, spécifiques du virus Akabane, agent de l'arthrogrypose et de l'hydrocéphalie, ont été mis en évidence dans des échantillons de sérum, provenant de 33 moutons, 3 chevres et 1 vache, sur 285 échantillons sérologiques prélevés dans la partie orientale de Chypre depuis décembre 1970.24 des 29 moutons positifs venaient d'une ferme de Liapetri. Aucun sérum ne provenait d'animaux nés en 1969 ou avant; de même aucun syndrome d'avortement ou de mortinatalité associé à des cas d'arthrogrypose ou d'hydrocéphalie n'avait été décelé chez les animaux de Chypre en 1969 on avant. On pense que le virus Akabane a pu être importé à Chypre depuis les rivages de la Méditerranée orientale par des moucherons infectés transportés par le vent en 1969 peut être aussi en 1968 mais qu'aucun cas n'avait été observé puisque l'infection s'était déclarée après 50 jours de gestation alors que l'atteinte du foetus était devenue peu probable.

     

Isolation of Akabane virus from the biting midge Culicoides oxystoma in Japan

Akabane virus was isolated from the biting midge, Culicoides oxystoma, collected in a cowshed in Kagoshima on Kyushu Island of Japan. This is the first report on the isolation of Akabane virus from biting midges of the genus Culicoides in Japan. Two calves kept as bait in the cowshed seroconverted to Akabane virus. These results strongly suggest that C. oxystoma may be a vector of Akabane virus.     

Culicoides: biological vectors of Akabane virus

Akabane virus replicated in Culicoides nubeculosus and Culicoides variipennis after intrathoracic inoculation and was maintained in both species of midge for at least 9 days post-infection. The virus also replicated to high concentration in C. variipennis after oral infection and was transmitted through a membrane by this species of midge 7-10 days after infection. The experiments described in this paper provided the first definitive evidence that Culicoides spp. are able to act as fully competent vectors of Akabane virus.     

A serological survey of Akabane virus infection in cattle and sheep in northwest China

Purpose

Akabane disease characterized mainly by fetal damage is a ruminant disease caused by insect-transmitted Akabane virus infection.

Methods

We investigated Akabane disease using serum neutralization tests in 446 blood samples collected from 187 cattle and 259 sheep of Xinjiang province, northwest China.

Results

(1) The overall prevalence rate of neutralizing antibody was 19.06?% (85/446), (2) the prevalence rates of Akabane disease in cattle and sheep were 20.32?% (38/187) and 18.15?% (47/259), respectively, (3) the disease prevalence rates were not significantly different between cattle and sheep, but significantly different among samples collected from different sampling months, (4) the disease was most prevalent in July when mosquitoes and culicoides were most active, and (5) the disease prevalence rates were significantly different between individuals with abortion experience and without abortion experience (P?<?0.05), suggesting that Akabane virus infection may significantly increase abortion risk in cattle and sheep.

Conclusions

To our knowledge, this is the first report confirming that Akabane virus infection is common in cattle and sheep of Xinjiang province, northwest China and providing useful epidemiological information for cattle and sheep abortion prevention and control.     

CONGENITAL BOVINE EPIZOOTIC ARTHROGRYPOSIS AND HYDRANENCEPHALY IN AUSTRALIA: Distribution of Antibodies to Akabane Virus in Australian Cattle after the 1974 Epizootic

At the end of the 1974 epizootic of bovine congenital arthrogryposis and hydranencephaly in south-eastern New South Wales, an Australia-wide serological survey (about 4,000 serums) was made to determine the ditribution of cattle possessing serum neutralising antibodies against Akabane virus. Eighty per cent of the serums from cattle in northern Australia (Western Australia, Northern Territory, and Queensland) were positive. A detailed study in the epizootic area in New South Wales (particularly around Bega) showed that 80 to 100% of serums from cows in herds in this area possessed neutralising antibodies. The animals possessing antibodies extended as far south as Genoa in north-eastern Victoria, and as far west as Darlington Point on the Murrumbidgee River. There were no positive herds along the Murray River, where an outbreak of the mosquito-borne disease Murray Valley encephalitis occurred in 1974. Serums tested from cows in the rest of Victoria, South Australia, south-western Western Australia, and Tasmania were negative. Arthrogrypotic calves born in Tasmania and south-western Western Australia were not associated with the presence of Akabane virus. In Papua New Guinea, serums collected from cattle at Boroka, Lae, and Goroka did not possess neutralising antibodies. The distribution of cattle possessing antibodies in Australia would fit a spread of the virus by Culicoides brevitarsis, a biting midge from which Akabane virus had been isolated on three occasions. The possibility of other vectors, as well as C. brevitarsis, was suggested by the presence of cows possessing antibodies at Alice Springs, where this biting midge has not been found. Possibly most cattle in northern Australia become infected early in life. The epizootics in New South Wales could occur when seasonal conditions allow a southerly extension of virus-infected C. brevitarsis which feed on susceptible pregnant animals. C. brevitarsis also bites sheep, and both neutralising antibodies to Akabane virus and congenitally deformed lambs have been observed in the epizootic area. An understanding of the distribtuion of Akabane virus and C. brevitarsis, a possible Australian vector for bluetongue virus, may prove useful if bluetongue should enter Australia.     

Subclinical pneumonia in lambs

Groups of lambs were either slaughtered at weekly intervals between November and June, or regularly sampled over this period. The number of isolations of Pasteurella haemolytica and Mycoplasma sp. from the lungs increased during the later part of two seasons, as did the incidence of lesions typical of enzootic pneumonia. P. haemolytica was frequently isolated after February from nasal swabs in spite of the presence of serum antibody titres against this organism. Serum antibody titre to two adenoviruses were found to fall to a low level, one in January, the other in May, and then to rise again. Virus isolations were made at the time the homologous antibody titres were lowest.