Isolations of akabane virus from sentinel cattle and Culicoides brevitarsis

Revisiting the Importance of Orthobunyaviruses for Animal Health: A Scoping Review of Livestock Disease, Diagnostic Tests, and Surveillance Strategies for the Simbu Serogroup

Orthobunyaviruses (order Bunyavirales, family Peribunyaviridae) in the Simbu serogroup have been responsible for widespread epidemics of congenital disease in ruminants. Australia has a national program to monitor arboviruses of veterinary importance. While monitoring for Akabane virus, a novel orthobunyavirus was detected. To inform the priority that should be given to this detection, a scoping review was undertaken to (1) characterise the associated disease presentations and establish which of the Simbu group viruses are of veterinary importance; (2) examine the diagnostic assays that have undergone development and validation for this group of viruses; and (3) describe the methods used to monitor the distribution of these viruses. Two search strategies identified 224 peer-reviewed publications for 33 viruses in the serogroup. Viruses in this group may cause severe animal health impacts, but only those phylogenetically arranged in clade B are associated with animal disease. Six viruses (Akabane, Schmallenberg, Aino, Shuni, Peaton, and Shamonda) were associated with congenital malformations, neurological signs, and reproductive disease. Diagnostic test interpretation is complicated by cross-reactivity, the timing of foetal immunocompetence, and sample type. Serological testing in surveys remains a mainstay of the methods used to monitor the distribution of SGVs. Given significant differences in survey designs, only broad mean seroprevalence estimates could be provided. Further research is required to determine the disease risk posed by novel orthobunyaviruses and how they could challenge current diagnostic and surveillance capabilities.

Genetic and pathogenic characterisation of a virulent Akabane virus isolated from goats in Yunnan, China

Introduction

Akabane virus (AKAV) has been detected in a variety of host species in China, but there are only limited records of its occurrence in goats. However, more attention needs to be paid to understanding the diversity of viruses in this species. The aim of the study was to explore the genotype characteristics and variation trend of AKAV and their relationship with virulence in Yunnan, China.

Material and Methods

Blood samples were collected from goats during routine surveillance of goat diseases in Yunnan province in 2019. The AKAV CX-01 strain was isolated using BHK-21 cells. To understand pathogenicity, the virus was intraperitoneally (IP) and intracerebrally (IC) inoculated into suckling mice and tissue samples were subsequently analysed histopathologically and immunohistochemically.

Results

Akabane virus CX-01 strain induced encephalitis and impairment of the central nervous system with fatal consequences. Phylogenetic analysis based on the ORF sequences of the small segments indicated that the AKAV isolate used was most closely related to the GD18134/2018 Chinese midge and bovine NM BS/1strains, while phylogenetic analysis based on the medium segments showed a close relationship between CX-01 and the Chinese GLXCH01 strain.

Conclusion

The CX-01 isolate was related to AKAV genogroup Ia and probably originated from a recombination of different strains.

Evolutionary history of Simbu serogroup orthobunyaviruses in the Australian episystem

Orthobunyaviruses of the Simbu serogroup are transmitted by insects (primarily biting midges) and infect mammals and/or birds. Many have been associated with disease in livestock or humans. The orthobunyavirus genome comprises three negative-sense RNA segments (L, M and S). We report the complete coding sequences of 57 isolates of Simbu serogroup viruses collected in Australia during 1968-1984. Phylogenetic analysis identified novel genogroups of Akabane virus (AKAV), Aino virus (AINOV) and Peaton virus, and provided evidence of constrained movement of AKAV between epidemiological systems in the northern and eastern regions of the continent. Differential clustering of AKAV isolates in trees inferred from L, M and S segments was indicative of intratypic segment reassortment. Similarly, intertypic segment reassortment was detected between AKAV and Tinaroo virus, and between AINOV and Douglas virus. L segments representing novel genogroups were detected in AINOV reassortants, suggesting the presence of unidentified Simbu group viruses in the episystem.

Culicoides Biting Midges-Underestimated Vectors for Arboviruses of Public Health and Veterinary Importance

Culicoides biting midges, small hematophagous dipterans, are the demonstrated or putative vectors of multiple arboviruses of veterinary and public health importance. Despite its relevance in disease spread, the ceratopogonid genus Culicoides is still a largely neglected group of species, predominantly because the major human-affecting arboviruses are considered to be transmitted by mosquitoes. However, when a pathogen is detected in a certain vector species, a thorough search for further vectors often remains undone and, therefore, the relevant vector species may remain unknown. Furthermore, for many hematophagous arthropods, true vector competence is often merely suspected and not experimentally proven. Therefore, we aim to illuminate the general impact of Culicoides biting midges and to summarize the knowledge about biting midge-borne disease agents using the order Bunyavirales, the largest and most diverse group of RNA viruses, as an example. When considering only viruses evidentially transmitted by Culicoides midges, the Simbu serogroup (genus Orthobunyavirus) is presumably the most important group within the virus order. Its members are of great veterinary importance, as a variety of simbuviruses, e.g., the species Akabane orthobunyavirus or Schmallenberg orthobunyavirus, induces severe congenital infections in pregnant animals. The major zoonotic representative of this serogroup occurs in South and Central America and causes the so-called Oropouche fever, an acute febrile illness in humans.

Akabane, Aino and Schmallenberg virus-where do we stand and what do we know about the role of domestic ruminant hosts and Culicoides vectors in virus transmission and overwintering?

Akabane, Aino and Schmallenberg virus belong to the Simbu serogroup of Orthobunyaviruses and depend on Culicoides vectors for their spread between ruminant hosts. Infections of adults are mostly asymptomatic or associated with only mild symptoms, while transplacental crossing of these viruses to the developing fetus can have important teratogenic effects. Research mainly focused on congenital malformations has established a correlation between the developmental stage at which a fetus is infected and the outcome of an Akabane virus infection. Available data suggest that a similar correlation also applies to Schmallenberg virus infections but is not yet entirely conclusive. Experimental and field data furthermore suggest that Akabane virus is more efficient in inducing congenital malformations than Aino and Schmallenberg virus, certainly in cattle. The mechanism by which these Simbu viruses cross-pass yearly periods of very low vector abundance in temperate climate zones remains undefined. Yearly wind-borne reintroductions of infected midges from tropical endemic regions with year-round vector activity have been proposed, just as overwintering in long-lived adult midges. Experimental and field data however indicate that a role of vertical virus transmission in the ruminant host currently cannot be excluded as an overwintering mechanism. More studies on Culicoides biology and specific groups of transplacentally infected newborn ruminants without gross malformations are needed to shed light on this matter.

A large-scale serological survey of Akabane virus infection in cattle, yak, sheep and goats in China

Akabane virus (AKAV) is a member of the Simbu serogroup, classified in the genus Orthobunyavirus, family Bunyaviridae. AKAV infection can cause abortion, stillbirth, and congenital arthrogryposis and hydranencephaly in cattle and sheep. The distribution and prevalence of AKAV infection in China is still unknown. A total of 2731 sera collected from 2006 to 2015 in 24 provinces of China from cattle, sheep, goats and yak were examined by serum neutralisation test. The overall seroprevalence rates for AKAV antibodies were 21.3% in cattle (471/2215) and 12.0% (17/142) in sheep or goats, and 0% in yak (0/374). The results indicated widespread AKAV infection in China among cattle and sheep but yak appear to have a low risk of infection. Using a selection of 50 AKAV-positive and 25 AKAV-negative cattle sera, neutralisation tests were also conducted to detect antibodies to several other Simbu serogroup bunyaviruses and closely related Leanyer virus. Although inconclusive, the data suggest that both Aino virus and Peaton virus, which have been reported previously in Japan and Korea, may also be present in cattle in China.

Culicoides monitoring in Belgium in 2011: analysis of spatiotemporal abundance, species diversity and Schmallenberg virus detection

In 2011, Culicoides (Diptera: Ceratopogonidae) were collected at 16 locations covering four regions of Belgium with Onderstepoort Veterinary Institute (OVI) traps and at two locations with Rothamsted suction traps (RSTs). Quantification of the collections and morphological identification showed important variations in abundance and species diversity between individual collection sites, even for sites located in the same region. However, consistently higher numbers of Culicoides midges were collected at some sites compared with others. When species abundance and diversity were analysed at regional level, between-site variation disappeared. Overall, species belonging to the subgenus Avaritia together with Culicoides pulicaris (subgenus Culicoides) were the most abundant, accounting for 80% and 96% of all midges collected with RSTs and OVI traps, respectively. Culicoides were present during most of the year, with Culicoides obsoletus complex midges found from 9 February until 27 December. Real-time reverse-transcription polymerase chain reaction screening for Schmallenberg virus in the heads of collected midges resulted in the first detection of the virus in August 2011 and identified C. obsoletus complex, Culicoides chiopterus and Culicoides dewulfi midges as putative vector species. At Libramont in the south of Belgium, no positive pools were identified.

Bunyavirus-vector interactions

The Bunyaviridae family is comprised of more than 350 viruses, of which many within the Hantavirus, Orthobunyavirus, Nairovirus, Tospovirus, and Phlebovirus genera are significant human or agricultural pathogens. The viruses within the Orthobunyavirus, Nairovirus, and Phlebovirus genera are transmitted by hematophagous arthropods, such as mosquitoes, midges, flies, and ticks, and their associated arthropods not only serve as vectors but also as virus reservoirs in many cases. This review presents an overview of several important emerging or re-emerging bunyaviruses and describes what is known about bunyavirus-vector interactions based on epidemiological, ultrastructural, and genetic studies of members of this virus family.

The emergence of Schmallenberg virus across Culicoides communities and ecosystems in Europe

Schmallenberg virus (SBV), a novel arboviral pathogen, has emerged and spread across Europe since 2011 inflicting congenital deformities in the offspring of infected adult ruminants. Several species of Culicoides biting midges (Diptera: Ceratopogonidae) have been implicated in the transmission of SBV through studies conducted in northern Europe. In this study Culicoides from SBV outbreak areas of mainland France and Italy (Sardinia) were screened for viral RNA. The role of both C. obsoletus and the Obsoletus complex (C. obsoletus and C. scoticus) in transmission of SBV were confirmed in France and SBV was also discovered in a pool of C. nubeculosus for the first time, implicating this species as a potential vector. While collections in Sardinia were dominated by C. imicola, only relatively small quantities of SBV RNA were detected in pools of this species and conclusive evidence of its potential role in transmission is required. In addition to these field-based studies, infection rates in colony-derived individuals of C. nubeculosus and field-collected C. scoticus are also examined in the laboratory. Rates of infection in C. nubeculosus were low, confirming previous studies, while preliminary examination of C. scoticus demonstrated that while this species can replicate SBV to a potentially transmissible level, further work is required to fully define comparative competence between species in the region. Finally, the oral competence for SBV of two abundant and widespread mosquito vector species in the laboratory is assessed. Neither Aedes albopictus nor Culex pipiens were demonstrated to replicate SBV to transmissible levels and appear unlikely to play a major role in transmission. Other vector competence data produced from studies across Europe to date is then comprehensively reviewed and compared with that generated previously for bluetongue virus.

Schmallenberg virus circulation in culicoides in Belgium in 2012: field validation of a real time RT-PCR approach to assess virus replication and dissemination in midges

Indigenous Culicoides biting midges are suggested to be putative vectors for the recently emerged Schmallenberg virus (SBV) based on SBV RNA detection in field-caught midges. Furthermore, SBV replication and dissemination has been evidenced in C. sonorensis under laboratory conditions. After SBV had been detected in Culicoides biting midges from Belgium in August 2011, it spread all over the country by the end of 2011, as evidenced by very high between-herd seroprevalence rates in sheep and cattle. This study investigated if a renewed SBV circulation in midges occurred in 2012 in the context of high seroprevalence in the animal host population and evaluated if a recently proposed realtime RT-PCR approach that is meant to allow assessing the vector competence of Culicoides for SBV and bluetongue virus under laboratory conditions was applicable to field-caught midges. Therefore midges caught with 12 OVI traps in four different regions in Belgium between May and November 2012, were morphologically identified, age graded, pooled and tested for the presence of SBV RNA by realtime RT-PCR. The results demonstrate that although no SBV could be detected in nulliparous midges caught in May 2012, a renewed but short lived circulation of SBV in parous midges belonging to the subgenus Avaritia occured in August 2012 at all four regions. The infection prevalence reached up to 2.86% in the south of Belgium, the region where a lower seroprevalence was found at the end of 2011 than in the rest of the country. Furthermore, a frequency analysis of the Ct values obtained for 31 SBV-S segment positive pools of Avaritia midges showed a clear bimodal distribution with peaks of Ct values between 21–24 and 33–36. This closely resembles the laboratory results obtained for SBV infection of C. sonorensis and implicates indigenous midges belonging to the subgenus Avaritia as competent vectors for SBV.

Dynamics of Schmallenberg virus infection within a cattle herd in Germany, 2011

In late 2011, the insect-transmitted Schmallenberg virus (SBV) emerged in Europe. In this study, a cattle farm located in the core region of the epidemic was closely monitored between May 2011 and January 2012. Up to the end of September every tested serum sample was negative by an SBV-specific antibody ELISA, suggesting the absence of an infection before autumn 2011. Around the end of September/beginning of October SBV genome was detected in blood samples of some animals, and a few cows exhibited fever during that period. Starting at the end of September the first cows seroconverted; the within-herd prevalence reached 100% within barely 1 month. Consequently, SBV spread rapidly in the tested herd during the vector season of 2011.

Evaluation of two commercial enzyme-linked immunosorbent assay kits for the detection of serum antibodies against Akabane virus in cattle

In New Zealand, an arbovirus surveillance program has been operating for more than 20 years, which includes testing of cattle with the Akabane virus neutralization test. With the aim to replace this laborious test by an easier-to-perform enzyme-linked immunosorbent assay (ELISA), 2 commercial ELISA kits, ELISA-1 from France (originally from Australia) and ELISA-2 from Japan, were compared, using 334 serum samples from noninfected New Zealand cattle, and 548 serum samples from naturally infected cattle herds in Australia. Diagnostic specificities for the test methods were high, ranging from 99.4% to 100%. The diagnostic sensitivities varied considerably between the test methods and differed from the values reported by the manufacturers (94% for each ELISA). The diagnostic sensitivities relative to the virus neutralization test (n = 378) were 96.0% for ELISA-1 or 98.9% when suspect samples were included, and 78.0% for ELISA-2. Differences in the commercial ELISA kits may be explained by the presence of other Simbu serogroup viruses in Australian cattle herds, causing cross-reactions in ELISA-1. Both commercial ELISA kits would be fit for purpose and could replace the virus neutralization test for Akabane virus surveillance in New Zealand. ELISA-1 may be able to detect other Simbu serogroup viruses, should they be present. The current study shows that despite comparable ELISA test characteristics given by the manufacturers, evaluation on the target population revealed marked differences in the ELISA kits test methods' characteristics.

Detection of the Schmallenberg virus in nulliparous Culicoides obsoletus/scoticus complex and C. punctatus--the possibility of transovarial virus transmission in the midge population and of a new vector

The arthropod-borne Schmallenberg virus (SBV) emerged in Europe in the late summer/autumn of 2011. SBV spread across the continent until 2012. This paper presents SBV detection in female Culicoides spp. caught in UV traps located in 23 different locations in Poland. The midges were divided into pools containing 20.5 individual insects on average according to species and parity status. The study was based on duplex real-time reverse transcription PCR (RT-PCR) for the detection of the SBV S segment and culicoid 18S gene fragments. Forty-four out of 402 midge pools tested (10.9%) were found to be positive for the presence of viral RNA. The SBV positive Culicoides came from 10 traps spread randomly across the country and were collected between August and October 2012. The timing of the SBV positive midge collections and the locations of the traps corresponded to the epizootic situation of SBV in ruminants. SBV RNA was most frequently identified in gravid midges (36.4%), while in nulliparous, blood-fed and parous midges the percentages were 10.8% 13.0% and 8.1%, respectively. The majority (82%) of SBV positive pools belonged to Culicoides obsoletus/scoticus complex; however, viral RNA was also found in 8 out of the 149 (5.4%) Culicoides punctatus pools tested. While no statistical differences in the Ct values between different parity groups were found, the bimodal distribution observed at the Ct frequency plots suggested active SBV replication, especially in parous and gravid midge females, and sub-transmissible infection in nulliparous and blood-fed insects. The most important findings included identification of C. punctatus as a new possible vector of SBV and the recovery of viral RNA from the nulliparous females which may suggest transovarial transmission in C. obsoletus/scoticus complex and C. punctatus.

Schmallenberg virus in Culicoides spp. biting midges, the Netherlands, 2011

To determine which species of Culicoides biting midges carry Schmallenberg virus (SBV), we assayed midges collected in the Netherlands during autumn 2011. SBV RNA was found in C. scoticus, C. obsoletus sensu stricto, and C. chiopterus. The high proportion of infected midges might explain the rapid spread of SBV throughout Europe.

Seroprevalence of Schmallenberg virus antibodies among dairy cattle, the Netherlands, winter 2011-2012

Seroprevalence was highest in the eastern part of the country, bordering Germany, where the virus was first identified.

Infections with Schmallenberg virus (SBV) are associated with congenital malformations in ruminants. Because reporting of suspected cases only could underestimate the true rate of infection, we conducted a seroprevalence study in the Netherlands to detect past exposure to SBV among dairy cattle. A total of 1,123 serum samples collected from cattle during November 2011–January 2012 were tested for antibodies against SBV by using a virus neutralization test; seroprevalence was 72.5%. Seroprevalence was significantly higher in the central-eastern part of the Netherlands than in the northern and southern regions (p<0.001). In addition, high (70%–100%) within-herd seroprevalence was observed in 2 SBV-infected dairy herds and 2 SBV-infected sheep herds. No significant differences were found in age-specific prevalence of antibodies against SBV, which is an indication that SBV is newly arrived in the country.

Sequence analysis of the medium RNA segment of three Simbu serogroup viruses, Akabane, Aino, and Peaton viruses

The sequence analysis was carried out for the medium (M) RNA segment of the Akabane virus (AKAV), Aino virus (AINV), and Peaton virus (PEAV) of the Simbu serogroup of the genus Orthobunyavirus of the family Bunyaviridae. The complementary sequences of the M RNA segments of AKAV, AINV, and PEAV contain a single large open reading frame (ORF), like other orthobunyaviruses. The ORFs potentially encode 1401 amino acids (aa), 1404 aa, and 1400 aa polypeptides, respectively. The identity of the M segment among these viruses is remarkably low, although previous researchers reported that the small RNA segments are highly conserved. Because the M segment codes for the viral surface glycoproteins G1 and G2, the variability of the M segment may affect the antigenicity of these viruses. Phylogenetic studies based on the M and S segment sequences suggested that genetic reassortment has been occurring among ancestral viruses of the three Simbu serogroup viruses throughout their evolution.

Akabane and bovine ephemeral fever virus infections

Akabane and bovine ephemeral fever viruses are exotic to the American continent. Both viruses are spread by insect vectors, and each causes disease of varying severity in food-producing animals. However, there are few other similarities between the agents and the diseases that they cause. They do not share the same insect vectors, the mammalian host range is different, and the clinical manifestations of virus infection vary markedly. Akabane virus is a cause of severe congenital defects, but adult animals show no signs of infection. In contrast, bovine ephemeral fever virus causes a febrile illness affecting mainly mature animals. If introduced to North America, it is probable that there would be significant economic losses, at least until endemic virus transmission patterns were established. Subsequently, it is likely that there would be patterns of alternate disease outbreaks followed by interepidemic periods in which there is a minor clinical effect.

Culicoides biting midges: their role as arbovirus vectors

Culicoides biting midges are among the most abundant of haematophagous insects, and occur throughout most of the inhabited world. Across this broad range they transmit a great number of assorted pathogens of human, and domestic and wild animals, but it is as vectors of arboviruses, and particularly arboviruses of domestic livestock, that they achieve their prime importance. To date, more than 50 such viruses have been isolated from Culicoides spp. and some of these cause diseases of such international significance that they have been allocated Office International des Epizooties (OIE) List A status. Culicoides are world players in the epidemiology of many important arboviral diseases. In this context this paper deals with those aspects of midge biology facilitating disease transmission, describes the factors controlling insect-virus interactions at the individual insect and population level, and illustrates the far-reaching effects that certain components of climate have upon the midges and, hence, transmission potential.

Study of Akabane infection in Saudi Arabia by the use of sentinel ruminants

Two sentinel herds of calves (Eastern and Central regions of Saudi Arabia) and one of sheep and goats (South Western region) were established to study Akabane virus infection. The herd at the Al-Ahsa oasis (Eastern region) showed evidence of Akabane viral activity, as reflected by the presence of maternal (colostral) antibody, which had waned to insignificant concentrations by the time the calves had reached the age of 5 months. There was no evidence of subsequent seroconversion. The other two sentinel herds gave no indication of Akabane viral activity.

Rapid identification of Australian bunyavirus isolates belonging to the Simbu serogroup using indirect ELISA formats

The Bunyavirus genus, belonging to the Bunyaviridae family, is comprised of a large group of antigenically and geographically disparate arthropod-borne viruses of medical and veterinary significance. In Australia, viruses belonging to the Simbu serogroup of the Bunyavirus genus, Akabane, Tinaroo, Peaton, Aino, Douglas, Thimiri and Facey's Paddock have been isolated. In this communication we describe two indirect ELISAs, referred to as the Simbu serogroup ELISA (SG-ELISA), and the Simbu typing ELISA (ST-ELISA), for the identification of these Simbu serogroup viruses. Infected cell lysate antigens prepared from Simbu serogroup virus isolates were assessed in the SG-ELISA for reactivity with a mouse monoclonal antibody (4H9/B11/F1). The monoclonal antibody reacted strongly with all Australian members of Simbu serogroup reference viruses and is proposed for use as a serogrouping reagent for Simbu viruses. Furthermore, the ST-ELISA enabled specific identification of viruses from within this group by recognition of characteristic reaction patterns between infected cell lysate antigens and a panel of polyclonal antisera raised to Simbu serogroup viruses.

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.

The isolation of Akabane virus (Iriki strain) from calves in Taiwan

Nonsuppurative encephalitis in calves aged 4-12 months, cow abortion and fetal deformities were endemic in dairy farms in Taiwan in recent years. A virological investigation emphasizing on Arthpodborn virus (Arbovirus) was conducted. Total of 11 strains of Akabane virus were isolated from endemic districts between June and July of 1992. Among them, seven viruses were isolated from blood samples of 15 calves showing nervous signs. Another 4 Akabane viruses were isolated from clinically healthy calves from three of six dairy farms investigated. All the six investigated farms had a recent history of abortion and fetal deformities. The isolates caused prominent cytopathic effects in HmLu-1 cells and could reach a high virus titers (5 x 10(6) TCID50/ml). As demonstrated by a cross neutralization test, the isolates had identical antigenicity to Iriki strain of Akabane virus, but were antigenically more distant to JaGar-39 and OBE-1 strain of Akabane virus. This is the first report on the isolation of Akabane virus in Taiwan, and also the second report on the isolation of Iriki virus in the world.

Akabane virus

Akabane virus, an arthropod-borne Bunyavirus, is the major cause of epizootics of congenital malformations in ruminants in Australia, Japan, Korea, and Israel, and is suspected to be a cause of sporadic outbreaks elsewhere. Blood-sucking insects, such as biting midges, transmit the virus horizontally to vertebrates. Climatic factors influence the seasonal activity and geographic range of the vector population and, therefore, occurrence of related disease. Inoculated ruminants seroconvert rapidly after a short subclinical viremia. Infection is of consequence only if ruminants are pregnant and not protected by adequate specific neutralizing antibodies. In naive pregnant animals, virus may spread hematogenously to replicate and persist in trophoblastic cells of placental cotyledons and subsequently invade the fetus. A distinct tropism for immature rapidly dividing cells of the fetal central nervous system and skeletal muscle results in direct virus-induced necrotizing encephalomyelitis and polymyositis. If fetuses survive, such injury may manifest as arthrogryposis, hydranencephaly, porencephaly, microencephaly, hydrocephalus, or encephalomyelitis at term. The earlier in gestation that fetal infection occurs, the more severe the lesions, reflecting the large population of vulnerable cells and lack of fetal immunocompetency at earlier stages of pregnancy. Injury during the period of critical cell migration and differentiation in organogenesis may substantially disrupt structural development in target organs. Late gestational infections cause nonsuppurative inflammation in the brain and spinal cord, premature birth, or fetal death with stillbirth or abortion. Affected neonates are nonviable. Control is by vaccination but is not always justified economically. Akabane viral infections must be differentiated from infections with other teratogenic viruses (including related Bunyaviruses), inherited conditions, and maternal intoxications. Diagnosis is made by serology and viral isolation.

Isolation and identification of arboviruses from the Sultanate of Oman

Sentinel herds and a vector surveillance system were used to identify the presence of arboviruses in Oman. Two strains of bluetongue virus (BTV) serotype 4 and two strains of Akabane virus, were isolated and identified. Both BTV isolates and one Akabane virus isolate came from goats while the second Akabane isolate came from Culicoides imicola. This is the first isolation of an Akabane virus from Culicoides in Arabia. Vector competence studies with the Oman viruses in laboratory reared C. variipennis showed that after oral infection both viruses replicated in Culicoides and were maintained at high titre for at least 10 days post infection.

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.

Serological reactions in sheep and cattle experimentally infected with three Australian isolates of bluetongue virus

Serums from 103 sheep and 24 cattle experimentally infected with one of 3 serotypes of bluetongue virus isolated in Australia were tested for antibody to bluetongue virus in the serum neutralisation test and the agar gel diffusion precipitin test. Antibody to bluetongue virus was first detected by these tests 8 to 10 days after intravenous infection in 4 sheep that were bled daily for serum analysis. The agar gel diffusion test failed to detect antibody in 28% (29/103) of sheep which had seroconverted in the serum neutralisation test. A further 7% (7/103) of sheep serums were negative in both tests 14 to 22 d after infection. Both tests detected antibody to bluetongue virus in all cattle serums by 10 days after detection of viraemia. In comparison with the intravenous route of infection, extended prepatent periods for the commencement of viraemia resulting from intradermal, subcutaneous and intrauterine routes of infection in the cattle caused corresponding delays in the detection of antibody. For example, one cow that was infected by intrauterine inoculation did not become viraemic until 22 d after inoculation and antibody was not detected until 32 d after inoculation.

Investigations of bluetongue and other arboviruses in the blood and semen of naturally infected bulls

Small groups of bulls were exposed to natural infection with arboviruses. The bulls were bled and ejaculated regularly and the blood and semen were processed for virus isolation. Over a 5-year observation period, virus isolation and serology indicated that the 29 exposed bulls had experienced 79 viraemic episodes with the viruses of the bluetongue, epizootic haemorrhagic disease, Palyam and Simbu serogroups and an incompletely characterised rhabdovirus. In no instance was there unequivocal evidence of bluetongue virus contamination of semen, despite 18 infections in the study period.

Arboviruses recovered from sentinel cattle using several virus isolation methods

A group of 20 sentinel steers was bled weekly for 5 months in 1986 and the blood samples were examined for arboviruses by inoculation firstly into embryonated chicken eggs (ECE), baby mice, Aedes albopictus cells and BHK21 monolayers. A second group of cattle was similarly examined for virus in 1987, except that baby mice were not used. Viruses were recovered from 26% of the 878 weekly bleeds. The viruses identified consisted of 14 types belonging to the bluetongue, epizootic haemorrhagic disease (EHD), Palyam and Simbu groups with a single isolation of bovine ephemeral fever virus. The ECE system was found to be the best for isolating bluetongue and Simbu viruses, though the eggs were not usually killed by the inoculum. The ECE and A. albopictus systems were equally sensitive for recovering EHD viruses, while Palyam group viruses were most efficiently isolated in BHK21 monolayers.

Transmission of Akabane virus from the ewe to the early fetus (32 to 53 days)

The role of the placental junction in AKA virus infection in the ewe was examined during the time when the chorionic villi were first becoming firmly attached to the maternal caruncles. The studies were made over 21 days covering the period between 32 and 53 days of pregnancy. Viral tropism in the fetal membranes and tissues of the fetuses was identified by virus isolation and immuno-fluorescence studies. Areas of virus replication were noted from 24 h post-inoculation in the fetal membranes and persisted in these tissues throughout the experiment. Viral antigen was first detected in the fetus from day 5 post-inoculation by virus isolation and immuno-fluorescence. From this time on, viral activity increased in specific areas of the fetus, notably in the brain and, to a lesser extent, the skeletal muscles. Gross pathological changes occurred in the fetuses between day 14 and day 21 post-inoculation (46 to 53 days gestation). Despite the relatively high titres of AKA virus present in the placental tissues and the developmental changes occurring in the fetus due to the virus, the placental junction continued to carry out its physiological function of maintaining pregnancy.

Prevalence of neutralising antibodies to Akabane virus in the Arabian peninsula

Serum-neutralising antibodies to Akabane virus were found in a wide range of domestic animals in all countries of the Arabian Peninsula but the virus does not seem to be endemic there. Sentinel herds in Oman and N. Yemen did not detect any Akabane activity between August 1984-November 1986 and May 1983-November 1984, respectively. However, there is strong evidence to suggest that Akabane virus incursions have recently taken place in Kuwait, Saudi Arabia and Bahrain as neutralising antibodies were detected in 1-year-old cattle bled during 1986 in each of these countries. The possibility of windborne infected vectors, from virus-endemic areas, initiating these incursions into the Arabian Peninsula is discussed.

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 1981-82. 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.

Teratogenicity of Australian Simbu serogroup and some other Bunyaviridae viruses: the embryonated chicken egg as a model

The use of embryonated chicken eggs as a model for assessing the teratogenic potential of animal viruses was investigated with 12 members of the Bunyaviridae family. Infection of 4-day-old embryonated chicken eggs via the yolk sac with 10 of the viruses resulted in deaths or congenital deformities that were similar to those observed in Akabane virus infections of fetal ruminants and included arthrogryposis, scoliosis, mandible defects, and retarded development. Statistical analysis showed that the viruses fell into three main groupings, namely, those that caused both death and deformities (Akabane, Aino, Tinaroo, and Belmont viruses), those that mainly caused death (Peaton, Thimiri, and Facey's Paddock viruses), and those that required very high doses to cause either death or deformities (Douglas and CSIR0296 viruses). In addition, two viruses (Kowanyama and Mapputta viruses) caused neither death nor deformities. A difference in the pathogenic potential between two Akabane isolates (B8935 and CSIR016) in the embryonated chicken egg model was found to correlate with differences previously observed in experimentally infected sheep; Akabane CSIR016 was the more pathogenic. It is concluded that the embryonated chicken egg model should also be of value in assessing the teratogenic potential of other Bunyaviridae and attenuated vaccine viruses, although it does not assess the ability of the virus to cross the placenta.

Bluetongue virus serotype 20 infection in pregnant Merino sheep

Eleven maiden Merino ewes, free of antibody to bluetongue virus serotype 20 (BTV-20) in agar gel immunodiffusion and serum neutralisation tests, were mated once with a ram. Ten ewes were inoculated with BTV-20 35 to 42 days after service, and one ewe was left as an uninoculated control. One of the inoculated ewes and the control ewe remained uninfected throughout the experiment. Eight of the remaining 9 ewes showed clinical signs ranging from mild to moderate, and the other showed no clinical signs of infection. BTV-20 viraemia was detected in ewes between days 3 and 11 post inoculation, and the serum antibody response was followed. The control ewe and 5 of the 9 infected ewes were pregnant when examined 90 to 97 days after service. Each of these animals produced a normal lamb. There was no evidence of abortion in the remaining 5 ewes, and no transplacental transfer of virus was detected in the lambs of the 5 infected ewes. At necropsy, 46 days after the birth of the last lamb, no gross or microscopic lesions were observed in either the ewes or lambs.

Transmission of Oropouche virus from man to hamster by the midge Culicoides paraensis

Oropouche virus (arbovirus family Bunyaviridae, Simbu serological group) was experimentally transmitted from man to hamster by the bite of the midge Culicoides paraensis. Infection rates and transmission rates were determined after the midge had engorged on patients with viremia. The threshold titer necessary to enable infection or transmission by the midges was approximately 5.3 log10 of the median lethal dose of the virus in suckling mice per milliliter of blood. Transmission was achieved 6 to 12 days after C. paraensis had taken the infective blood meal. This represents conclusive evidence of transmission of an arbovirus of public health importance to man by a member of the Ceratopogonidae family.