Schmallenberg virus: emergence of an Orthobunyavirus among ruminants in Western Europe

Recently, a novel virus has been identified among ruminants in Western Europe. This virus, the so-called Schmallenberg virus, belongs to the family Bunyaviridae, genus Orthobunyavirus, serogroup Simbu and is closely related to Akabane, Aino and Shamonda virus. In cattle, acute symptoms in the dam and adult animals generally include high fever, milk drop and diarrhea among others. More importantly, infection during gestation may lead to abortion, stillbirth and congenital malformations. As all bunyaviruses, Schmallenberg virus also uses vectors for efficient transmission. Closely related viruses causing similar symptoms, such as Akabane and Akabane-like viruses, are mainly transmitted by Culicoides. It is very likely that Schmallenberg virus is transmitted by similar vectors. This review provides an overview of Bunyaviridae, their epidemiology, symptoms, prevention and control. Special emphasis is put on the Simbu serogroup of the Orthobunyavirus genus pointing out the similarities between them and closely related members

Reduced virulence of a pseudorabies virus isolate from wild boar origin in domestic pigs correlates with hampered visceral spread and age-dependent reduced neuroinvasive capacity

Morbidity and mortality associated with pseudorabies virus (PRV) infection are dependent on the age of the pig and the virulence of the strain. PRV strains circulating in wild boar are considered to be low virulent, but no mechanistic explanation for their reduced virulence is available. Here infection of 2-and 15-week-old domestic pigs with the PRV wild boar strain BEL24043 did not induce clinical symptoms in 15-week-old pigs, but resulted in important neurological and respiratory disease in 2-week-old piglets. A detailed study of the (neuro) pathogenesis and associated cytokine mRNA expression showed that the reduced virulence of the wild boar strain, compared to what was previously reported for the virulent domestic NIA3 strain, is due to a severely hampered spread to visceral organs in pigs of both age categories and to an efficient suppression of viral replication at primary replication sites of 15-week-old pigs and to a lesser extent in those of 2-week-old piglets. The age-dependent difference in induced symptoms seems to be due to an immature development state of the immune and/or nervous system in 2-week-old pigs. An extensive viral replication associated with a robust expression of cytokine-related mRNA was found in the olfactory bulb of 2-week-old piglets, correlating with observed neurological disease. Neuroinvasion also occurred via the trigeminal route in 2-week-old pigs, but viral replication was efficiently suppressed in the trigeminal ganglion in the presence of a moderate induction of cytokine-related mRNA. Viral replication in the peripheral and central nervous system of 15-week-old pigs was limited and efficiently suppressed

Follow-Up of PRRSv-Vaccinated Piglets Born from PRRSv-Vaccinated, ELISA-Seropositive and ELISA-Seronegative Sows

Vaccination against the porcine reproductive and respiratory syndrome virus (PRRSv) is widely used to prevent production losses in the swine industry. In this study, piglets born from both PRRSv-vaccinated ELISA-seropositive sows (E+ piglets) and PRRSv-vaccinated ELISA-seronegative sows (E− piglets) were followed-up pre-vaccination, 3 weeks post-vaccination (wpv) and 8 wpv in two Belgian farrow-to-finish herds. The aim of the study was to analyze the presence of PRRSv-specific maternally-derived antibodies (MDAs) and the PRRSv vaccine response in both groups of piglets. The E− piglets lacked the presence of PRRSv-specific MDAs (0% seropositive), while these were present in the E+ piglets (97% seropositive). Due to this, the E− piglets showed a strong initial vaccine response (72–80% seroconversion) and vaccine viremia (65–75% PCR positive) at 3 wpv. In contrast, the E+ piglets showed only limited initial vaccine responses (25–61% with increased ELISA values) and vaccine viremia (30–31% PCR positive) at 3 wpv. By 8 wpv, the proportion of seropositive E− piglets (78–100%) and seropositive E+ piglets (55–90%) increased in both herds. However, a difference in vaccine viremia duration was observed between both herds at 8 wpv, with a decrease in the proportion of PCR positive piglets in herd 1 (E−: 47%; E+: 25%) and an increase in the proportion of PCR positive piglets in herd 2 (E−: 85%; E+: 92%). This study identified clear differences in the presence of PRRSv-specific maternally-derived antibodies and PRRSv vaccine responses between E− and E+ piglets. Further research is warranted to elicit the biological relevance of these observed differences

Follow-Up of PRRSv-Vaccinated Piglets Born from PRRSv-Vaccinated, ELISA-Seropositive and ELISA-Seronegative Sows

Vaccination against the porcine reproductive and respiratory syndrome virus (PRRSv) is widely used to prevent production losses in the swine industry. In this study, piglets born from both PRRSv-vaccinated ELISA-seropositive sows (E+ piglets) and PRRSv-vaccinated ELISA-seronegative sows (E− piglets) were followed-up pre-vaccination, 3 weeks post-vaccination (wpv) and 8 wpv in two Belgian farrow-to-finish herds. The aim of the study was to analyze the presence of PRRSv-specific maternally-derived antibodies (MDAs) and the PRRSv vaccine response in both groups of piglets. The E− piglets lacked the presence of PRRSv-specific MDAs (0% seropositive), while these were present in the E+ piglets (97% seropositive). Due to this, the E− piglets showed a strong initial vaccine response (72–80% seroconversion) and vaccine viremia (65–75% PCR positive) at 3 wpv. In contrast, the E+ piglets showed only limited initial vaccine responses (25–61% with increased ELISA values) and vaccine viremia (30–31% PCR positive) at 3 wpv. By 8 wpv, the proportion of seropositive E− piglets (78–100%) and seropositive E+ piglets (55–90%) increased in both herds. However, a difference in vaccine viremia duration was observed between both herds at 8 wpv, with a decrease in the proportion of PCR positive piglets in herd 1 (E−: 47%; E+: 25%) and an increase in the proportion of PCR positive piglets in herd 2 (E−: 85%; E+: 92%). This study identified clear differences in the presence of PRRSv-specific maternally-derived antibodies and PRRSv vaccine responses between E− and E+ piglets. Further research is warranted to elicit the biological relevance of these observed differences

A survey on biosecurity and management practices in selected Belgian cattle farms

&lt;p&gt;The shift from cure towards prevention in veterinary medicine involves the implementation of biosecurity, which includes all measures preventing pathogens from entering a herd and reducing the spread of pathogens within a herd. In Belgium no studies have considered the implementation of biosecurity measures in the daily management of cattle farms. Therefore the aim of the study was to map the current application of biosecurity measures in Belgian cattle farms in the prevention of disease transmission within and between farms. Between March 2011 and April 2013 the data were collected as part of a larger cross-sectional study, conducted to identify risk factors for reinfection with BVDV in cattle herds assumed free from BVDV. Questionnaire data from 33 dairy farms, 16 beef farms and 25 mixed (dairy and beef cattle) farms were analyzed using a combination of a linear scoring system, a categorical principal component analysis and a two-step cluster analysis to differentiate these farms based on their biosecurity levels and visit frequencies. Further enhancement of preventive measures considering external and internal biosecurity was still possible for each farm, as none of the farms obtained an overall high biosecurity level. Three groups of cattle farms were differentiated with a biosecurity level varying from low to high-medium, of which the group with the lowest biosecurity level mainly consisted of mixed farms. Animal-to-animal contacts with cattle from other herds were frequently possible as only 12% of the farmers purchasing cattle quarantined purchased animals at least three weeks and contacts over fences on pasture were possible in 70% of the herds. Basic biosecurity measures such as farm-specific protective clothing and boots were present in the majority of the farms, but they were insufficiently or incorrectly used. Cattle farms were very often visited by professional visitors of which the herd veterinarian, the AI technician and the cattle salesman most frequently entered the farm. It can be concluded that few biosecurity measures were undertaken by Belgian cattle farmers, thereby exposing themselves to the risk of disease transmission within and between farms. Especially in regions with a high cattle density, small distances to neighbouring farms and high frequencies of professional visits, a farm-specific preventive strategy should be developed, thereby using the facilities often already present on the farm.&lt;/p&gt;</p

Pseudorabies virus isolates from domestic pigs and wild boars show no apparent in vitro differences in replication kinetics and sensitivity to interferon-induced antiviral status

Pseudorabies virus is the causative agent of Aujeszky's disease. Domestic pigs and wild boars are its natural hosts, and strains circulating within both populations differ in their capacity to induce clinical disease. Cell biological and molecular explanations for the observed differences in virulence are, however, lacking. Different virulence determinants that can be assessed in vitro were determined for five domestic swine strains, four wild boar strains and the NIA3 reference strain. Replication kinetics and plaque formation capacity in continuous swine testicular cells and different primary porcine cell lines were highly similar for isolates from both populations. Treatment of these cell lines with IFN alpha, IFN gamma or a combination of both provoked similar plaque-reducing effects for all strains. In conclusion, our results indicate that isolates from domestic swine and wild boar differ neither in intrinsic replication and dissemination capacity nor in sensitivity to antiviral effects of IFNs

Virulence comparison and quantification of horizontal bovine viral diarrhoea virus transmission following experimental infection in calves

&lt;p&gt;Bovine viral diarrhoea virus (BVDV) causes persistent infections by infecting the fetus of susceptible animals during gestation. These persistently infected (PI) animals are important sources of infection. On the contrary, transiently infected (TI) animals are believed to be less important, but transient infections with a severe BVDV-2 strain can spread explosively. To assess the importance of TI cattle in the epidemiology of BVDV, two experimental infections were performed to determine basic reproduction ratios (R0). In each experiment three calves were infected via intranasal inoculation and housed together with seven susceptible animals. Two strains isolated in Belgium were used, a virulent BVDV-1b and a virulent BVDV-2a field isolate, resulting in an R0 of 0.25 (95% CI 0.01; 1.95) and 0.24 (95% CI 0.01; 2.11), respectively. A PI animal was then introduced to the remaining uninfected animals and produced an R of +∞ (95% CI 1.88; +∞). These results support the suggestion that TI animals, compared to PI animals, contribute only a limited amount to BVDV spread. Additionally, the severe clinical symptoms observed in the field with these isolates could not be reproduced during these experiments, suggesting that other factors besides strain virulence influence the clinical manifestations evoked by BVDV.&lt;/p&gt;</p

Effect of saliva stabilisers on detection of porcine reproductive and respiratory syndrome virus in oral fluid by quantitative reverse transcriptase real-time PCR

&lt;p&gt;This study evaluated the effect of extraction-amplification methods, storage temperature and saliva stabilisers on detection of porcine reproductive and respiratory syndrome virus (PRRSV) RNA by quantitative reverse transcriptase real-time PCR (qRT-PCR) in porcine oral fluid. The diagnostic performance of different extraction-amplification methods was examined using a dilution series of oral fluid spiked with PRRSV. To determine RNA stability, porcine oral fluid, with or without commercially available saliva stabilisers, was spiked with PRRSV, stored at 4°C or room temperature and tested for the presence of PRRSV RNA by qRT-PCR. PRRSV RNA could be detected in oral fluid using all extraction-amplification combinations, but the limit of detection varied amongst different combinations. Storage temperature and saliva stabilisers had an effect on the stability of PRRSV RNA, which could only be detected for 7 days when PRRSV spiked oral fluid was kept at 4°C or stabilised at room temperature with a commercial mRNA stabiliser.&lt;/p&gt;</p

PRRSV-Vaccinated, Seronegative Sows and Maternally Derived Antibodies (II): Impact on PRRSV-1 Vaccine Effectiveness and Challenge Outcomes in Piglets

Vaccination against the Porcine Reproductive and Respiratory Syndrome virus (PRRSV) is widely practiced in both sows and piglets. However, it has been shown that multivaccinated sows sometimes lack a detectable antibody response, testing seronegative in ELISA (non-responders). Moreover, PRRSV-vaccinated piglets can remain seronegative as well, which is mainly attributed to the interference of maternally derived antibodies (MDAs). The current study investigated the impact of the sow’s immune status on the PRRSV vaccine effectiveness in the progeny. The experimental trial included forty-eight piglets (n = 48) originating from a commercial Belgian breeding herd, with twenty-four piglets born from PRRSV vaccinated responder sows (E+ piglets) and twenty-four piglets born from PRRSV vaccinated non-responder sows (E− piglets). Eight piglets in each group were either non-vaccinated (NoVac piglets; n = 8), intramuscularly vaccinated (IM piglets; n = 8), or intradermally vaccinated (ID piglets; n = 8), with the same PRRSV-1 vaccine as used in the sow population. Vaccination was performed at weaning at three weeks of age, and all study piglets were challenged with a high dose of the PRRSV-1 07V063 strain at 6 weeks of age. A clear interference of MDAs was observed in the E+ piglets: 66.7% of the vaccinated E+ piglets lacked an antibody response at 3 weeks post-vaccination (non-responders). Consequently, post-challenge, only the responding E+ piglets had a significantly reduced serum viremia compared to the E+ NoVac piglets. The observed viremia in the non-responding E+ piglets was similar to the viremia of the E+ NoVac piglets. In the vaccinated E− piglets, a lack of antibody response at 3 weeks post-vaccination was observed in 18.8% of the piglets. Interestingly, despite the lack of a vaccine antibody response, the non-responding E− piglets had a significantly reduced serum viremia compared to the NoVac E− piglets. In contrast, the viremia of the responding E− piglets was only numerically reduced compared to the NoVac E− piglets. Finally, some clear differences were observed in both the kinetics of infection and the immune responses post-challenge between the E+ and E− piglets. The results of this study confirm the consequences of the MDA interference on the induced partial protection of PRRSV vaccination in experimentally challenged piglets. More research is warranted to understand the immunological mechanisms behind MDA interference in PRRSV vaccination and to explain the observed differences between E+ and E− piglets