The emergence of vampire bat rabies in Uruguay within a historical context.

Pathogen spillover from wildlife to humans or domestic animals requires a series of conditions to align with space and time. Comparing these conditions between times and locations where spillover does and does not occur presents opportunities to understand the factors that shape spillover risk. Bovine rabies transmitted by vampire bats was first confirmed in 1911 and has since been detected across the distribution of vampire bats. However, Uruguay is an exception. Uruguay was free of bovine rabies until 2007, despite high-cattle densities, the presence of vampire bats and a strong surveillance system. To explore why Uruguay was free of bovine rabies until recently, we review the historic literature and reconstruct the conditions that would allow rabies invasion into Uruguay. We used available historical records on the abundance of livestock and wildlife, the vampire bat distribution and occurrence of rabies outbreaks, as well as environmental modifications, to propose four alternative hypotheses to explain rabies virus emergence and spillover: bat movement, viral invasion, surveillance failure and environmental changes. While future statistical modelling efforts will be required to disentangle these hypotheses, we here show how a detailed historical analysis can be used to generate testable predictions for the conditions leading to pathogen spillover.

Perinatal immuno/inflammatory responses in the presence or absence of bovine fetal infection.

BACKGROUND: It is known that the bovine fetus can mount an immune and inflammatory reaction to infection, but it is not known whether there is a contemporaneous maternal response. Nor is it known whether the response of calves which die perinatally, with or without infection, differs from that of live perinates. Hence, the objective of this study was to determine if acute phase reactant and immunoglobulin concentrations differed between calves (and their dams) in three groups: live calves (CC; n = 21) and dead calves with (PM INF+; n = 22) or without (PM INF-; n = 89) in utero infection. In calf plasma, serum amyloid A, haptoglobin, immunoglobulins M, G1 and G2 and interleukin-6 were measured. In dam serum, SAA and Hp was measured and in amniotic and abomasal fluid, IL-6 was measured. RESULTS: Live calves had higher plasma concentrations of SAA and IL-6 than dead calves with (PM INF+) or without (PM INF-) in utero infection. Calves in the PM INF-, but not PM INF+ group, had higher Hp concentrations than calves in the CC group. Calves in the PM INF+ group had higher IgG1 concentrations than calves in the PM INF- and CC groups. Except for higher IgG1 and IgG2 concentrations, biomarker values did not differ significantly between dead calves with or without in utero infection. Live calves had higher IL-6 concentrations in abomasal fluid compared to PM INF- calves. There were no significant differences in blood biomarker concentrations between dams of the three groups of calves. Amniotic fluid IL-6 concentrations were higher from the dams of control calves than the dams of uninfected calves. CONCLUSIONS: Differences in biomarkers (higher Hp and IgG1; lower SAA and IL-6) between perinatal mortalities and live perinates probably reflect differences between these two groups in age at sampling (SAA and IL-6) and in utero infection (IgG1). Out of the six analytes measured in calves, only IgG1 and IgG2 were biomarkers of (chronic) in utero infection.

Isolation of Neospora caninum from kidney and brain of a bovine foetus and molecular characterization in Brazil.

Bovine neosporosis has become a disease of international concern as it is among the main causes of abortion in cattle. Viable N. caninum has been isolated from brains of fetuses and neonatal calves, and there is no report of isolation of tachyzoites from kidney. Also, detailed information about the genetic diversity of N. caninum is scarce. N. caninum tachyzoites were isolated from the kidney and the brain of an aborted 4-month-old bovine foetus. The parasite was confirmed to be N. caninum by PCR. The tachyzoites of the new isolate, named BNC-PR4, were propagated in Vero cell cultures. Pathogenicity of the parasite was examined in BALB/c mice. Mice inoculated intraperitoneally with BNC-PR4 failed to yield clinical signs of disease and did not induce severe brain lesions, suggesting a bovine isolate with low virulence. The N. caninum-positive DNA sample was further analyzed by multilocus microsatellite (MS) genotyping for MS4, MS5, MS6A, MS6B, MS7, MS8, MS10, MS12, and MS21. Multilocus-microsatellite genotyping revealed a unique genetic profile that differed from previously reported isolates.

Detection of Coxiella burnetii DNA and anti-Coxiella burnetii IgG antibodies in precolostral blood samples of stillborn calves in an endemically infected Holstein dairy herd.

Coxiella burnetii (C. burnetii), an intracellular zoonotic bacterium causing Q fever, occurs widely in cattle herds. After invasion of the pregnant uterus and initial localization in the placenta, active C. burnetii infections may spread to the fetus hematogenously or by the amniotic-oral route and thus may cause abortion, premature delivery, stillbirth, and weak offspring (APSW) complex. In a case-control study, we investigated precolostral blood samples of 56 stillborn calves and 30 live births from a dairy herd endemically infected with C. burnetii "C-cluster" strains and an increased stillbirth rate in primiparous cows. Within the group of the stillborn calves, four precolostral blood samples (7.1%) were tested positive for C. burnetii DNA by PCR and one serum sample (1.8%) positive for anti-C. burnetii IgG antibodies by a commercial ELISA test, respectively. Neither C. burnetii DNA nor anti-C. burnetii IgG antibodies were detected in the samples of calves being born alive. In conclusion, we demonstrated that coxiellaemia and precolostral seroconversion occurred sporadically in stillborn calves from this endemically infected herd. Due to the low detection rates, C. burnetii could not be confirmed to be the cause of the increased stillbirth rate.

Hydrops associated with chondrodysplasia of the fetus in a miniature Scottish Highland cow.

CASE DESCRIPTION A 2-year-old primiparous miniature Scottish Highland cow with an unknown breeding date was evaluated for suspected hydrops. CLINICAL FINDINGS Transabdominal and transrectal ultrasonographic examination identified a large amount of hypoechoic fluid within an enlarged uterus; the fetus could not be identified. Presence of a severely distended uterus and concerns regarding associated health risks to the cow led to the decision to induce labor. Although fluids were expelled, parturition did not progress further over the following 48 hours. Vaginal examination revealed a partially dilated cervix and an abnormally shaped fetus that was too large to pass vaginally. TREATMENT AND OUTCOME Supportive care was provided to the cow, and a stillborn bull calf was delivered by cesarean section. Grossly evident chondrodystrophic dwarfism with hydrocephalus, compatible with so-called bulldog calf malformations, was confirmed by diagnostic imaging and histopathologic evaluation. The cow recovered from surgery uneventfully and was discharged from the hospital the following day. Genetic analysis of DNA from hair roots collected from the sire and dam confirmed both were carriers of an aggrecan-1 gene mutation (bulldog dwarfism1) previously associated with dwarfism and bulldog calf malformations in Dexter cattle. CLINICAL RELEVANCE To our knowledge, this is the first reported case of bulldog calf malformations associated with an aggrecan-1 gene mutation in miniature Scottish Highland cattle, confirming that at least 1 genetic mutation associated with this condition is found in cattle breeds other than Dexter. The findings highlighted the clinical importance of testing for known genetic diseases in breeding cattle, particularly among miniature breeds.

Programmed cell death-associated gene transcripts in bovine embryos exposed to bovine Herpesvirus type 5.

In vitro-produced bovine embryos become infected after exposure to bovine Herpesvirus type 5 (BoHV-5), yet no changes in developmental rates, mitochondrial activity and inhibition of apoptosis are detected in comparison to unexposed embryos. Thus, the aim of the present study was to assess the transcription of mitochondria-mediated apoptosis genes using TaqMan real-time polymerase chain reaction. Transcripts of mcl-1, caspase-2, -3, Apaf-1 and Bax genes were measured after exposure to BoHV-5 in vitro. Mitochondrial dehydrogenase activity was evaluated by MTT test and compared between groups of exposed and unexposed embryos, at day 7 of development. The rate of oocyte maturation was assessed by the extrusion of the first polar body. In summary, BoHV-5 exposed embryos retained their viability, mitochondrial dehydrogenase activity and displayed up-regulation of transcription of survival mcl-1 gene and down-regulation of Bax transcription in relation to mitochondria-mediated pathway which might improve embryo viability. These findings demonstrate that BoHV-5 exposed embryos maintain their viability and mitochondrial dehydrogenase activity with no compromise of embryos produced in vitro.

Invited review: heat stress effects during late gestation on dry cows and their calves.

In dairy cattle, late gestation is a critical period for fetal growth and physiological transition into the next lactation. Environmental factors, such as temperature and light, exert dramatic effects on the production, health, and well-being of animals during this period and after parturition. The aim of this review was to introduce effects of heat stress during late gestation on dairy cattle, and discuss the biological mechanisms that underlie the observed production and health responses in the dam and her fetus. Relative to cooled cows, cows that are heat stressed during late gestation have impaired mammary growth before parturition and decreased milk production in the subsequent lactation. In response to higher milk yield, cows cooled prepartum undergo a series of homeorhetic adaptations in early lactation to meet higher demand for milk synthesis compared with heat-stressed cows, but no direct effect of environmental heat stress on metabolism exists during the dry period. Prepartum cooling improves immune status of transition cows and evidence suggests that altered prolactin signaling in immune cells mediates the effects of heat stress on immune function. Late-gestation heat stress compromises placental development, which results in fetal hypoxia, malnutrition, and eventually fetal growth retardation. Maternal heat stress may also have carryover effects on the postnatal growth of offspring, but direct evidence is still lacking. Emerging evidence suggests that offspring from prepartum heat-stressed cows have compromised passive immunity and impaired cell-mediated immune function compared with those from cooled cows.

Evaluation of developmental changes in bovine in vitro produced embryos following exposure to bovine Herpesvirus type 5.

BACKGROUND: Bovine Herpesvirus type-5 (BoHV-5) is a neurovirulent α-Herpesvirus which is potentially pathogenic for cows and suspected to be associated with reproductive disorders. Interestingly, natural transmission of BoHV-5 by contaminated semen was recently described in Australia. Additionally, BoHV-5 was also isolated from the semen of a healthy bull in the same country and incriminated in a natural outbreak of reproductive disease after artificial insemination. In contrast with BoHV-1, experimental exposure of in vitro produced bovine embryos to BoHV-5 does not affect embryo viability and seems to inhibit some pathways of apoptosis. However, the mechanisms responsible for these phenomena are poorly understood. In this study, we examined mitochondrial activity, antioxidant protection, stress response and developmental rates of in vitro produced bovine embryos that were exposed and unexposed to BoHV-5. METHODS: For this purpose, bovine embryos produced in vitro were assayed for cell markers after experimental infection of oocytes (n = 30; five repetitions), in vitro fertilization and development. The indirect immunofluorescence was employed to measure the expression of superoxide dismutase 1 (SOD1), anti-oxidant like protein 1 (AOP-1), heat shock protein 70.1 (Hsp 70.1) and also viral antigens in embryos derived from BoHV-5 exposed and unexposed oocytes. The determination of gene transcripts of mitochondrial activity (SOD1), antioxidant protection (AOP-1) and stress response (Hsp70.1) were evaluated using the reverse transcriptase polymerase chain reaction (RT-PCR). MitoTracker Green FM, JC-1 and Hoechst 33342-staining were used to evaluate mitochondrial distribution, segregation patterns and embryos morphology. The intensity of labeling was graded semi-quantitatively and embryos considered intensively marked were used for statistical analysis. RESULTS: The quality of the produced embryos was not affected by exposure to BoHV-5. Of the 357 collected oocytes, 313 (+/- 6.5; 87.7%) were cleaved and 195 (+/- 3.2; 54.6%) blastocysts were produced without virus exposure. After exposure, 388 oocytes were cleaved into 328 (+/- 8.9, 84.5%), and these embryos produced 193 (+/- 3.2, 49.7%) blastocysts. Viral DNA corresponding to the US9 gene was only detected in embryos at day 7 after in vitro culture, and confirmed by indirect immunofluorescence assay (IFA). These results revealed significant differences (p < 0.05) between exposed and unexposed oocytes fertilized, as MitoTracker Green FM staining Fluorescence intensity of Jc-1 staining was significantly higher (p < 0.005) among exposed embryos (143 +/- 8.2). There was no significant difference between the ratios of Hoechst 33342-stained nuclei and total cells in good-quality blastocysts (in both the exposed and unexposed groups). Using IFA and reverse transcriptase polymerase chain reaction (RT-PCR) for the set of target transcripts (SOD1, AOP-1 and Hsp 70.1), there were differences in the mRNA and respective proteins between the control and exposed embryos. Only the exposed embryos produced anti-oxidant protein-like 1 (AOP-1). However, neither the control nor the exposed embryos produced the heat shock protein Hsp 70.1. Interestingly, both the control and the exposed embryos produced superoxide dismutase (SOD1), revealing intense mitochondrial activity. CONCLUSION: This is the first demonstration of SOD1 and AOP-1 production in bovine embryos exposed to BoHV-5. Intense mitochondrial activity was also observed during infection, and this occurred without interfering with the quality or number of produced embryos. These findings further our understanding on the ability of α-Herpesviruses to prevent apoptosis by modulating mitochondrial pathways.

Non-classical major histocompatibility complex class makes a crucial contribution to reproduction in the dairy cow.

The aim of this study was to evaluate the effect of classical and non-classical major histocompatibility complex (MHC) on the reproduction in the dairy cow. Nine pairs of MHC-I genes were chosen according to their homology and possible function, and their transcription levels in maternal peripheral blood mononuclear cells (PBMCs) from all three trimesters and transcription levels in fetal tissues were compared to evaluate their contributions to cattle reproduction. The results showed that three non-classical genes were variably expressed in PBMCs of pregnant cows. MICB was downregulated in the first and second trimesters (P<0.05), but recovered back to the level in replacement heifers in the last trimester (P>0.05). BoLA-NC1* was upregulated in the first and last trimesters (P<0.001) but no different in the second trimester (P>0.05). BoLA-NC3* was upregulated in all trimesters (P<0.001). On the other hand, MICB was upregulated in fetal ear tissues (P<0.001), and BoLA-NC1* was almost silent in both fetal placenta and ear tissues (P<0.001); however, BoLA-NC3* was upregulated in both the fetal placenta and ear tissues (P<0.001). These results suggested that non-classical gene BoLA-NC1* increased maternal immunity against the fetus, which was inhibited by BoLA-NC3*. BoLA-NC3* also inhibited fetal autoimmunity. Apoptosis of the fetal placenta could reduce itself expressing MICB, and upregulated expression of MICB in ear tissues was favorable for the fetus to escape autoimmunity. On the other hand, downregulated expression of MICB in the fetal placenta allows for placental decoherence from the maternal placentome, which was beneficial to fetus delivery. Although classical genes were expressed differentially, their effects were restricted because of heavy chain deficiency.

Embryo transfer: a comparative biosecurity advantage in international movements of germplasm.

This paper uses cattle as a model to provide an overview of the hazards involved in the transfer of in vivo-derived and in vitro-produced embryos. While scientific studies in recent decades have led to the identification of pathogens that may be associated with both in vivo- and in vitro-derived embryos, those studies have also been the basis of appropriate disease control measures to reduce the risks to a negligible level. These disease control measures have been identified and assessed by the International Embryo Transfer Society's (lETS) Health and Safety Advisory Committee, the expert body that advises the World Organisation for Animal Health (OIE) on matters related to the safety of embryo transfer. Through the OIE's processes for developing and adopting international standards, the disease control measures identified by the IETS have been incorporated into the Terrestrial Animal Health Code. The basic principles rely on the crucial ethical roles of the embryo collection team and embryo transfer team, under the leadership of approved veterinarians. Decades of experience, with nearly 10 million embryos transferred, have demonstrated the very significant biosecurity advantage that embryo transfer technology has when moving germplasm internationally, provided that the international standards developed by the IETS and adopted by the OIE are strictly followed.

Apoptotic and developmental effects of bovine Herpesvirus type-5 infection on in vitro-produced bovine embryos.

Bovine Herpesvirus type-5 (BoHV-5), which is potentially neuropathogenic, was recently described to be related with reproductive disorders in cows. The objective was to elucidate mechanisms involved in propagation of BoHV-5 in embryonic cells. For this purpose, bovine embryos produced in vitro were assayed for apoptotic markers after experimental infection of oocytes, in vitro fertilization, and development. Host DNA fragmentation was detected with a TUNEL assay, expression of annexin-V was measured with indirect immunofluorescence, and viral DNA was detected with in situ hybridization. Infective BoHV-5 virus was recovered from embryos derived from exposed oocytes after two consecutive passages on Madin-Darby bovine kidney (MDBK) cells. The viral DNA corresponding to US9 gene, localized between nucleotides 126243 to 126493, was detected in situ and amplified. There was no significant difference between the ratio of TUNEL stained nuclei and total cells in good quality blastocysts (0.87 ± 0.05, mean ± SD), but there were differences (P < 0.05) between infected (0.18 ± 0.05) and uninfected blastocysts (0.73 ± 0.07). The Annexin-V label was more intense in uninfected embryos (0.79 ± 0.04; P < 0.05). The quality of infected and uninfected embryos was considered equal, with no significant effect on embryonic development. In conclusion, we inferred that BoHV-5 infected bovine oocytes, replicated, and suppressed some apoptotic pathways, without significantly affecting embryonic development.

Thymic hypoplasia in Japanese black calves with stillbirth/perinatal weak calf syndrome.

To investigate the relationship between the decreased immunity associated with infirmity and low body weight at birth as a consequence of intrauterine growth retardation in Japanese Black calves with stillbirth/perinatal weak calf syndrome, the thymuses and spleens of 13 calves with this syndrome, weighing less than 20 kg at birth, were examined histopathologically. Cytokeratin staining of the thymus was also carried out to examine its composition. The thymus and spleen were classified as grades 0-4 and I-III according to their hypoplasia, respectively. All calves showed a decreased number of thymocytes. One calf was classified as grade 1, which was characterized by a starry sky appearance. Five calves were classified as grade 2, demonstrating a reversion of the cortex-to-medulla ratio, and the rest were classified as grades 3 and 4 showing an indistinguishable boundary between the cortex and medulla. The thymuses of grade 3 and 4 were occupied by stroma cells, and their Hassall bodies and other structures were rarely observed. Six of 13 calves showed a decreased number of splenocytes, grade II or III, and their red and white pulp regions were unclear. The intrauterine growth retardation caused by lack of growth factors during the fetal period might have induced thymic hypoplasia associated with decreased immunity in the calves with stillbirth/perinatal weak calf syndrome. Therefore, intrauterine growth retardation might be associated with one of the causes of decreased immunity involved in infirmity in this syndrome.

Muscular pseudohypertrophy (steatosis) in a bovine fetus.

Muscular pseudohypertrophy was diagnosed in the cervical musculature of a full-term crossbred Simmental fetus delivered by fetotomy. Only head and cervical regions were submitted for pathologic examination; the rest of the fetal body was reportedly normal. The neck musculature of the fetus was markedly deformed by 23 cm and 18 cm in diameter, firm, spherical masses that consisted of enlarged and pale left splenius and right serratus ventralis cervicis muscle, respectively, covered by intact skin. Additionally, lipomatous masses were present within the cervical vertebral canal, compressing the spinal cord. Microscopically, the prominent muscular enlargement was due to massive adipose and fibrous connective tissue replacement of atrophic muscle. Focal myelodysplasia and astrocytosis affecting the grey matter was detected in the mid-cervical region of the spinal cord, accompanied by degeneration in the ascending and descending tracts of the remaining cord segments. Abnormal spinal cord development as a result of severe spinal cord compression by the lipomatous masses within the spinal canal leading to replacement of muscle by fat and fibrous tissue was considered to be the cause of the muscular malformation in this fetus.

Genetic diagnosis of band 3 deficiency and sexing in bovine preimplantation embryos.

Band 3 deficiency with hereditary spherocytosis and hemolytic anemia in Japanese black cattle, band 3(Bov.Yamagata), is caused by a total lack of band 3 protein with an autosomal dominant inheritance. Genotyping for band 3 deficiency and sexing were successfully achieved in biopsied embryo cells with efficiencies of 98.4% and 97.4%, respectively. Transfer of the embryo that was determined as homozygous for the mutant allele into a recipient cow resulted in the production of a fetus exhibiting the genotype and red cell phenotypes characteristic of band 3(Bov.Yamagata). These results demonstrate that our procedure is reliable and applicable to produce animals free from or homozygous for the mutant allele by breeding carrier animals.

DNA extraction from bovine mummified fetuses and detection of factor XI gene deficiency in the mummies.

Genomic DNA extracted from bovine mummified tissue is valuable material for detection of some genes that may contribute to fetal abnormalities. In this study bovine genomic DNA was extracted from the hardened tissue samples of ten bovine mummified fetuses. The amount of genomic DNA extracted from 2 g of the mummified tissues by the phenol/chloroform-ethanol method was low (less than 4 microg/ml) for all samples. The extracted DNA was then amplified by the GenomiPhi DNA amplification system. After amplification, the amount of DNA was increased to more than 100 microg/ml for all samples. This amplification system was shown to be a good tool for amplifying the genomic DNA of the mummified fetuses. The amplified genomic DNA was used for testing the mummies for Factor XI gene deficiency, an autosomal recessive deficiency involved in the early stages of the intrinsic blood coagulation pathway. Exon 12 of the Factor XI gene of the mummies was amplified by PCR. Two of the ten mummified fetuses were heterozygous for the Factor XI gene as indicated by the presence of two amplified DNA fragments of 320 bp and 244 bp. Factor XI deficiency has already been described in Holstein cattle. However, no report is available for bovine fetus. In this study, DNA was extracted and amplified from the bovine mummified fetuses, and the samples were successfully tested for Factor XI gene deficiency in the mummies.

Humoral immune response to infectious agents in aborted bovine fetuses in Argentina.

The purpose of this study was to characterize the exposure of bovine aborted fetuses from beef and dairy herds of the humid pampas of Argentina to different infectious agents by the evaluation of fetal fluid antibodies. Presence of fetal antibodies to bovine viral diarrhea virus genotype 1 (BVDV-1), bovine herpes virus type 1 (BHV-1), Leptospira interrogans, Brucella abortus, and Neospora caninum was determined. Of the 95 fetuses processed, 66 came from 49 beef herds and 29 from 12 dairy herds. The average gestational age of the aborted fetuses was 7.1 months. Antibodies to the mentioned agents were detected in 65 of the 95 fetal fluids (68.4%). In addition, antibodies to more than one infectious agent were detected in 32 fetuses (33.7%), suggesting fetal exposure to multiple antigens during gestation. There were antibodies to BVDV-1, BHV-1, N. caninum and Leptospira interrogans in 43 (45.2%), 29 (30.5%), 26 (27.4%) and 5 (5.2%) specimens, respectively. Antibodies to B. abortus were not detected in any of the fetal fluids. The results of this study provide information on the determination of antibodies in fluids from bovine aborted fetuses exposed to different infectious agents in the region.

Limited demethylation leaves mosaic-type methylation states in cloned bovine pre-implantation embryos.

Cloning by nuclear transfer (NT) has been riddled with difficulties: most clones die before birth and survivors frequently display growth abnormalities. The cross-species similarity in abnormalities observed in cloned fetuses/animals leads us to suspect the fidelity of epigenetic reprogramming of the donor genome. Here, we found that single-copy sequences, unlike satellite sequences, are demethylated in pre-implantation NT embryos. The differential demethylation pattern between genomic sequences was confirmed by analyzing single blastocysts. It suggests selective demethylation of other developmentally important genes in NT embryos. We also observed a reverse relationship between methylation levels and inner cell mass versus trophectoderm (ICM/TE) ratios, which was found to be a result of another type of differential demethylation occurring in NT blastocysts where unequal methylation was maintained between ICM and TE regions. TE-localized methylation aberrancy suggests a widespread gene dysregulation in an extra-embryonic region, thereby resulting in placental dysfunction familiar to cloned fetuses/animals. These differential demethylations among genomic sequences and between differently allocated cells produce varied overall, but specified, methylation patterns, demonstrating that epigenetic reprogramming occurs in a limited fashion in NT embryos.

Bovine neosporosis: immunoblot improves foetal serology.

The purpose of the study is the comparative evaluation of the immunofluorescent antibody test (IFAT) and an immunoblot (IB) test for the examination of foetal fluids for specific antibodies against Neospora caninum. Peritoneal and pleural fluids as well as abomasal contents were analysed. The results of the serological examinations were compared to those obtained by histological, immunohistochemical, and PCR analysis of foetal tissues as well as to the results of maternal serological examinations. Fluids were used undiluted in the IB and reactions against six immunodominant antigens were recorded. When the recognition of at least two immunodominant antigens was regarded as positive, the agreement of the IB with other diagnostic methods was good to moderate as characterised by kappa-values of 0.76 (histology/immunohistochemistry), 0.69 (maternal serology) and 0.54 (PCR on foetal tissues). The IB results agreed better with the results of the other diagnostic methods than those of the IFAT. The higher relative sensitivity of the IB was regarded as the main reason for the better agreement. However, also the specificity of the IB was superior to that of the IFAT in relation to histology/immunohistochemistry, maternal serology and PCR.

Preferential infection of neuronal and astroglia cells by Akabane virus in primary cultures of fetal bovine brain.

Akabane virus is a member of the genus Bunyavirus; it is pathogenic for ruminants and transmitted by arthropod vectors. Infection of adult cattle and sheep causes a transient viremia without obvious clinical signs, while infection of pregnant animals often causes fetal abnormalities including hydranencephaly, poliomyelitis and arthrogryposis. Infectious virus or viral antigens is present in the brain, spinal cord and skeletal muscle of infected fetuses. To understand the interaction between Akabane virus and bovine brain cells, we investigated the viral tropism using primary cultures of fetal bovine brain. The cultured neuronal cells, astroglia cells and microglia cells were distinguished by cell type specific antisera. Akabane virus was found to infect neuronal cells and astroglia cells, which led to degenerative death. No microglia cells were found infected. In some brain cultures, we observed different sensitivities of the cells to two Akabane virus strains: an attenuated strain infected and spread more readily than wild type virus. This difference was not observed in a hamster fibroblast cell line. Both viral and host determinants might be involved in the different susceptibility of brain cells to Akabane virus infection.