Evidence of widespread natural recombination among field isolates of equine herpesvirus 4 but not among field isolates of equine herpesvirus 1.

Recombination in alphaherpesviruses allows evolution to occur in viruses that have an otherwise stable DNA genome with a low rate of nucleotide substitution. High-throughput sequencing of complete viral genomes has recently allowed natural (field) recombination to be studied in a number of different alphaherpesviruses, however, such studies have not been applied to equine herpesvirus 1 (EHV-1) or equine herpesvirus 4 (EHV-4). These two equine alphaherpesviruses are genetically similar, but differ in their pathogenesis and epidemiology. Both cause economically significant disease in horse populations worldwide. This study used high-throughput sequencing to determine the full genome sequences of EHV-1 and EHV-4 isolates (11 and 14 isolates, respectively) from Australian or New Zealand horses. These sequences were then analysed and examined for evidence of recombination. Evidence of widespread recombination was detected in the genomes of the EHV-4 isolates. Only one potential recombination event was detected in the genomes of the EHV-1 isolates, even when the genomes from an additional 11 international EHV-1 isolates were analysed. The results from this study reveal another fundamental difference between the biology of EHV-1 and EHV-4. The results may also be used to help inform the future safe use of attenuated equine herpesvirus vaccines.

Foot-and-mouth disease virus infection in fetal lambs: tissue tropism and cytokine response.

Foot-and-mouth disease virus (FMDV) can cause transplacental infection and death in fetal lambs. This study investigates the pathogenesis of FMDV infection in ovine fetuses using in-situ hybridization (ISH) to detect viral transcripts in tissue and real-time reverse transcriptase polymerase chain reaction (RT-PCR) assays to quantify the fetal cytokine response to infection. FMDV ribonucleic acid (RNA) was localized mainly to the heart and skeletal muscles of fetuses and was only occasionally expressed in the lingual epithelium, demonstrating that FMDV has a different tissue tropism in the fetus compared with that in adult sheep. There was early expression of genes encoding anti-viral cytokines (IFN-alpha and IFN-beta) in fetuses at 2 and 4 days post-infection (dpi), followed by a marked rise in the transcription of pro-inflammatory cytokine genes (IFN-gamma, TNF-alpha and IL-1alpha) from 7 to 18 dpi, particularly in the heart. The degree of cytokine mRNA expression correlated with fetal infection and was likely to be a factor in fetal death. In contrast, cytokine gene expression in infected neonatal lambs was much less and mainly occurred between 2 and 4 dpi. This study identifies two key factors in the pathogenicity of FMDV in fetal lambs: viral tropism for cardiac and skeletal muscles, and a marked cytokine response following infection.

Foot-and-mouth disease virus crosses the placenta and causes death in fetal lambs.

Eighteen pregnant sheep, six at 45 days gestation and twelve at 75 days gestation, were infected with foot-and-mouth disease virus (FMDV) type O UKG 34/2001. Two sheep from each gestational group were killed at 2, 4, and 7 days post-inoculation (dpi). Three sheep, pregnant for 75 days at infection, were killed at 17 and 18 dpi. Real-time reverse-transcriptase polymerase chain reaction (RT-PCR) and virus isolation (VI) were used to detect viral RNA and infectious virus, respectively, in fetal tissues taken post mortem. Eleven fetuses were obtained from the six sheep inoculated at day 45 of gestation. Of these, two of three fetuses at 2 dpi had viral RNA detected by RT-PCR and virus was detected in one by VI. Viral RNA was detected in two of four fetuses at 4 dpi, while viral RNA and virus were detected in all four fetuses at 7 dpi. No gross abnormalities were evident in these fetuses. In the group inoculated at day 75 of gestation, viral RNA was detected in three of four fetuses at 4 dpi. Virus and viral RNA were detected in three of four fetuses at 7 dpi. Of the seven fetuses examined at 17 and 18 dpi, viral RNA was detected in five, and four of these had died in utero. Gross abnormalities including haemorrhage and oedema in a number of tissues were evident in many of the fetuses in this group, but no vesicular lesions were found. Viral RNA and virus were detected in the amniotic fluid associated with infected fetuses. This study is the first to demonstrate that FMDV may cause transplacental infection and fetal death.

Cytokine and Toll-like receptor mRNAs in the nasal-associated lymphoid tissues of cattle during foot-and-mouth disease virus infection.

The pharyngeal region is known to play an important role in foot-and-mouth disease virus (FMDV) infection in relation to acute disease and viral persistence. In this study, the local mucosal immune response in nasal-associated lymphoid tissue (NALT) of cattle infected with FMDV (strain O UKG 34/2001) was examined. Quantitative "real-time" RT-PCR assays were used to measure mRNA expression of cytokines (IFN-alpha, beta and gamma, IL-2, IL-1alpha and TNF-alpha) and Toll-like receptors (TLR)-3 and -4. NALTs from dorsal soft palate were collected from cattle at 7 days post-infection (dpi) and from carriers and non-carriers at 64 dpi. Expression of IFN-alpha mRNA was significantly greater in NALT during acute disease than in uninfected animals. Increased expression of IFN-gamma and IL-1alpha mRNA was also observed but was much lower than IFN-alpha expression. There was a slight increase in mRNA expression of TNF-alpha and IL-2. During persistence, TNF-alpha mRNA expression in carrier cattle was much higher than in non-carrier cattle. Expression of TLR-4 in NALT during the acute stage of infection was greater than in uninfected animals. Carrier and non-carrier cattle did not differ in respect of expression of TLR-3 and -4 mRNA in NALT.