Viral emergence in marine mammals in the North Pacific may be linked to Arctic sea ice reduction.

Climate change-driven alterations in Arctic environments can influence habitat availability, species distributions and interactions, and the breeding, foraging, and health of marine mammals. Phocine distemper virus (PDV), which has caused extensive mortality in Atlantic seals, was confirmed in sea otters in the North Pacific Ocean in 2004, raising the question of whether reductions in sea ice could increase contact between Arctic and sub-Arctic marine mammals and lead to viral transmission across the Arctic Ocean. Using data on PDV exposure and infection and animal movement in sympatric seal, sea lion, and sea otter species sampled in the North Pacific Ocean from 2001-2016, we investigated the timing of PDV introduction, risk factors associated with PDV emergence, and patterns of transmission following introduction. We identified widespread exposure to and infection with PDV across the North Pacific Ocean beginning in 2003 with a second peak of PDV exposure and infection in 2009; viral transmission across sympatric marine mammal species; and association of PDV exposure and infection with reductions in Arctic sea ice extent. Peaks of PDV exposure and infection following 2003 may reflect additional viral introductions among the diverse marine mammals in the North Pacific Ocean linked to change in Arctic sea ice extent.

Bluetongue virus serotype 26: infection kinetics, pathogenesis and possible contact transmission in goats.

The aim of this study was to assess the pathogenicity and infection kinetics of Bluetongue virus serotype 26 (BTV-26) in goats. Out of a group of six goats housed in insect free accommodation, five were experimentally infected with BTV-26 and one was kept uninfected as an in-contact control. Samples taken throughout the study were used to determine the kinetics of infection using a pan specific BTV real time RT-PCR assay and a group specific ELISA. The five infected goats did not show clinical signs of BTV, however high levels of viral RNA were detected and virus was isolated from the blood of all 5 goats. Antibodies against BTV were first detected between 7 and 11 dpi in all 5 experimentally infected goats. Interestingly at 21 dpi viral RNA was detected in, and virus was isolated from, the blood of the in-contact control goat, which also seroconverted. These results suggest that BTV-26 replicates to high levels in goats, causing no obvious clinical disease, suggesting that goats may be the natural host for this virus. Preliminary evidence also indicates that BTV-26 may be spread by contact transmission between goats, however a more detailed study is required in order to confirm this observation.

Bluetongue and epizootic haemorrhagic disease virus in local breeds of cattle in Kenya.

The presence of bluetongue virus (BTV) and Epizootic Haemorrhagic Disease virus (EHDV) in indigenous calves in western Kenya was investigated. Serum was analysed for BTV and EHDV antibodies. The population seroprevalences for BTV and EHDV for calves at 51 weeks of age were estimated to be 0.942 (95% CI 0.902-0.970) and 0.637 (95% CI 0.562-0.710), respectively, indicating high levels of circulating BTV and EHDV. The odds ratio of being positive for BTV if EHDV positive was estimated to be 2.57 (95% CI 1.37-4.76). When 99 calves were tested for BTV and EHDV RNA by real-time RT-PCR, 88.9% and 63.6% were positive, respectively. Comparison of the serology and real-time RT-PCR results revealed an unexpectedly large number of calves that were negative by serology but positive by real-time RT-PCR for EHDV. Eight samples positive for BTV RNA were serotyped using 24 serotype-specific real-time RT-PCR assays. Nine BTV serotypes were detected, indicating that the cattle were infected with a heterogeneous population of BTVs. The results show that BTV and EHDV are highly prevalent, with cattle being infected from an early age.

Bluetongue virus serotype 26: infection kinetics and pathogenesis in Dorset Poll sheep.

Bluetongue virus serotype 26 (BTV-26) has recently been isolated from sheep in Kuwait. The aim of this study was to assess the pathogenicity and infection kinetics of BTV-26 in Dorset Poll sheep. Six sheep were experimentally infected with BTV-26 and samples taken throughout the study were used to determine the kinetics of infection using a pan specific BTV real time RT-PCR assay and two group specific ELISAs. Five of the six sheep showed mild clinical signs characteristic of bluetongue including conjunctivitis, reddening of the mouth mucosal membranes, slight oedema of the face and nasal discharge. Viral RNA was detected in 5 of the 6 sheep by real time RT-PCR, however the levels of viral RNA detected in the samples were lower and of shorter duration than seen with other field strains of BTV. Virus was isolated from the blood of infected animals at the peak of viraemia at around 9 dpi. Antibodies against BTV were first detected by 7 dpi using the early detection BTV ELISA and a little later (7-14 dpi) using a BTV specific competitive ELISA. Four of the five remaining sheep developed neutralising antibodies to BTV-26, measured by a serum neutralisation test (SNT), with titres (log(10)) ranging from 1.40 to 2.08.

Experimental infection of camels with bluetongue virus.

Three camels aged 4-5 years were experimentally infected with Bluetongue virus serotype 1 (BTV-1) and were observed for 75 days. No clinical signs of disease were observed throughout the experiment, however all three animals seroconverted and developed BTV-1 specific neutralising antibodies after challenge. All three camels developed a viraemia from 7 days post infection albeit at a lower level than that usually observed in experimental infections of sheep and cattle. Virus was isolated from the blood of all three animals suggesting that camels may act as a reservoir for BTV and play an important role in its transmission.

Infection kinetics of Epizootic Haemorrhagic Disease virus serotype 6 in Holstein-Friesian cattle.

Epizootic Haemorrhagic Disease virus serotype 6 (EHDV-6) has recently caused serious outbreaks of Epizootic Haemorrhagic Disease (EHD) on the edges of Europe, in Turkey, Israel and Morocco. The aim of this study was to assess the pathogenicity and infection kinetics of EHD in Holstein-Friesian cattle infected with the two distinct strains of EHDV-6 isolated from the recent Turkish and Moroccan outbreaks. Samples taken throughout the study were used to validate two recently developed diagnostic assays that detect EHDV antibodies and viral genome. Two groups of five Holstein-Friesian cattle were experimentally infected with either the Moroccan or the Turkish isolate of EHDV-6. Cattle in both groups remained clinically unaffected throughout the study, but displayed high levels of viral RNA and virus in their blood, confirming that sub-clinical infection of cattle is likely to play an important role in EHDV transmission. A recently developed and commercialised real-time RT-PCR assay detected viral RNA as early as 2 days post infection (dpi) in both infection studies and viral RNA persisted for the course of the study. Antibodies against EHDV were first detected by 9dpi using a recently developed EHDV blocking ELISA and antibodies persisted up to the end of the study. All animals developed high levels of neutralising antibodies to EHDV-6, measured by a serum neutralisation test (SNT), with titres (log(10)) ranging from 2.20 to 2.38 at the end of the study. Virus was isolated from the blood of infected animals from as early as 2dpi up to 28dpi.

Colostral antibody protection and interference with immunity in lambs born from sheep vaccinated with an inactivated Bluetongue serotype 8 vaccine.

Widespread vaccination programmes against Bluetongue virus serotype 8 (BTV-8), using inactivated vaccines, are being carried out across many countries in northern, western and southern Europe. This study investigates the extent and length of colostral antibody protection, as well as the degree of colostral antibody induced interference of the immune response to BTV-8, in sheep. Significantly lower titres of neutralising antibodies were transferred in colostrum to lambs born from sheep vaccinated once as opposed those vaccinated twice (single vaccine in the first year and a booster vaccine in the second year). On BTV-8 challenge, lambs born from sheep vaccinated on two occasions, with the second booster vaccine given approximately 1 month prior to lambing, were protected from clinical disease for up to 14 weeks. BTV-8 was isolated from 5 of the 22 challenged lambs, although only one of these lambs showed a transient rise in body temperature with no other clinical signs. Lambs born from ewes given a second booster vaccine 1 month prior to lambing, are likely to be protected from clinical disease for at least 14 weeks, whereas lambs born from ewes vaccinated once are likely to be protected for a shorter time. Colostral antibodies present in the 13-14-week-old lambs appeared to interfere with the humoral response to challenge virus. These results suggest that colostral antibodies may interfere with vaccination in lambs up to at least 14 weeks of age.

Seroconversion, neutralising antibodies and protection in bluetongue serotype 8 vaccinated sheep.

Bluetongue virus serotype 8 (BTV-8) has caused a major outbreak of disease in cattle and sheep in several countries across northern and western Europe from 2006 to 2008. In 2008 the European Union instigated a mass-vaccination programme in affected countries using whole virus inactivated vaccines. We evaluated vaccinal responses in sheep and the ability of the vaccine to protect against experimental challenge. Sheep vaccinated 10 months previously under field conditions were challenged with BTV-8. One of 7 vaccinated sheep became infected, as evidenced by detection of viral RNA by real-time RT-PCR and by virus isolation. The remaining 6 sheep appeared fully protected from virus replication. None of the vaccinated sheep showed clinical signs of BTV and there was a good correlation between the presence of neutralising antibodies on challenge and protection. Commercially available ELISAs were evaluated for their ability to detect antibodies in sheep vaccinated on a single occasion. The sandwich (double antigen) ELISA assays were found to be more sensitive at detecting antibodies in vaccinated sheep than the competitive ELISAs.

Emergence of bluetongue serotypes in Europe, part 2: the occurrence of a BTV-11 strain in Belgium.

An EDTA-blood sample from a cow without clinical signs, which gave early birth to a newborn calf that died soon after delivery, was shown to be positive for bluetongue virus (BTV)-RNA using a group-specific real-time RT-PCR (RT-qPCR). In-house serotype-specific RT-qPCR assays for bluetongue virus serotype 1 (BTV-1), -6 and -8 all gave negative results. Subsequent assays were carried out using conventional (gel-based) RT-PCR primers for all 25 BTV serotypes and only two primer sets, both specific for BTV-11, gave bands of the expected size. The cDNAs generated were sequenced and comparisons of the genome segment 2 sequence with that of the modified 'live' vaccine strain of BTV-11 from South Africa showed 100% identity. A survey of all ruminants in a 1-km area around the first positive farm using a BTV-11 serotype-specific RT-qPCR revealed five other holdings with in total nine BTV-11 positive animals. A cross-sectional monitoring of dairy cattle in Belgium showed an overall prevalence of 3.8% on herd level and 0.2% on animal level. A BTV-11 has been introduced into the Belgian cattle herd during the 2008 vector season. The source of the infection and the way by which the virus was introduced are unknown.