Antibody Response in Cattle Vaccinated Against Bluetongue Serotype 8 in Italy

Development of an inactivated combined vaccine for protection of cattle against lumpy skin disease and bluetongue viruses

Lumpy Skin Disease (LSD) and Bluetongue (BT) are the main ruminants viral vector-borne diseases. LSD is endemic in Africa and has recently emerged in Europe and central Asia as a major threat to cattle industry. BT caused great economic damage in Europe during the last decade with a continuous spread to other countries. To control these diseases, vaccination is the only economically viable tool. For LSD, only live-attenuated vaccines (LAVs) are commercially available, whilst for BT both LAVs and inactivated vaccines are available with a limited number of serotypes. In this study, we developed an inactivated, oil adjuvanted bivalent vaccine against both diseases based on LSDV Neethling strain and BTV4. The vaccine was tested for safety and immunogenicity on cattle during a one-year period. Post-vaccination monitoring was carried out by VNT and ELISA. The vaccine was completely safe and elicited high neutralizing antibodies starting from the first week following the second injection up to one year. Furthermore, a significant correlation (R = 0.9040) was observed when comparing VNT and competitive ELISA in BTV4 serological response. Following BTV4 challenge, none of vaccinated and unvaccinated cattle were registered clinical signs, however vaccinated cattle showed full protection from viraemia. In summary, this study highlights the effectiveness of this combined vaccine as a promising solution for both LSD and BT control. It also puts an emphasis on the need for the development of other multivalent inactivated vaccines, which could be greatly beneficial for improving vaccination coverage in endemic countries and prophylaxis of vector-borne diseases.

Alternative methods to reduce the animal use in quality controls of inactivated BTV8 Bluetongue vaccines

The acceptance of serology data instead of challenge for market release of new batches of commercial vaccine is under evaluation by regulatory agencies in order to reduce the use of animals and costs for manufacturers. In this study two vaccines for Bluetongue virus serotype 8 were submitted to quality controls required by the European Pharmacopoeia and tested on sheep in comparison with a commercial inactivated vaccine. Body temperature, antibody titres and viraemia of vaccinated and controls sheep were recorded. In addition IL4 and IFNγ in sera and supernatant derived from in vitro stimulation of blood cells were also quantified using two commercial ELISA kit. The outer-capsid protein VP2 contained in vaccine formulations was quantified using a home-made capture-ELISA. Results obtained indicates that in-lab evaluation of cell-mediated and humoral immune response are useful parameters to predict the efficacy of BTV inactivated vaccines avoiding the challenge phase required to release new batches of vaccines with proven clinical efficacy and safety. The correlation observed between serology data and VP2 protein concentration of final product could be useful in-process control to predict if a new vaccine batch of BTV must be discarded or released to the market.

Estimation of French cattle herd immunity against bluetongue serotype 8 at the time of its re-emergence in 2015

BACKGROUND

From 2006 to 2010, France experienced two bluetongue epidemics caused by serotype 1 (BTV-1) and 8 (BTV-8) which were controlled by mass vaccination campaigns. After five years without any detected cases, a sick ram was confirmed in August 2015 to be infected by a BTV-8 strain almost identical to that circulating during the previous outbreak. By then, part of the French cattle population was expected to be still protected, since bluetongue antibodies are known to last for many years after natural infection or vaccination. The objective of this study was to estimate the proportion of cattle in France still immune to BTV-8 at the time of its re-emergence in 2015.

RESULTS

We used BTV group-specific cELISA results from 8525 cattle born before the vaccination ban in 2013 and 15,799 cattle born after the ban. Samples were collected from January to April 2016 to estimate seroprevalence per birth cohort. The overall seroprevalence in cattle at national and local levels was extrapolated from seroprevalence results per birth cohort and their respective proportion at each level. To indirectly assess pre-immune status of birth cohorts, we computed prevalence per birth cohort on infected farms in autumn 2015 using 1377 RT-PCR results. These revealed limited BTV circulation in 2015. Seroprevalence per birth cohort was likely to be connected to past exposure to natural infection and/or vaccination with higher seroprevalence levels in older animals. A seroprevalence of 95% was observed for animals born before 2008, of which > 90% were exposed to two compulsory vaccination campaigns in 2008-2010. None of the animals born before 2008 were found to be infected, unlike 19% of the young cattle which had never been vaccinated. This suggests that most ELISA-positive animals were pre-immune to BTV-8. We estimated that 18% (from 12% to 32% per département) of the French cattle population was probably pre-immune in 2015.

CONCLUSIONS

These results strongly suggest a persistence of antibodies for at least 5-6 years after natural infection or vaccination. The herd immunity of the French cattle population probably limited BTV circulation up to 2015, by which time more than 80% of cattle were naive.

Indoor and outdoor winter activity of Culicoides biting midges, vectors of bluetongue virus, in Italy

Indoor and outdoor winter activity of Culicoides spp. (Diptera: Ceratopogonidae) in central Italy was investigated in order to evaluate whether indoor activity might account for the overwintering of bluetongue virus, as has been hypothesized by some authors. Weekly Culicoides collections were performed at three farms over three consecutive winter seasons. At each farm, two black-light traps were operated simultaneously, indoors and outdoors. Culicoides were identified using both morphological and molecular means. The Culicoides obsoletus group accounted for 98.2% of sampled specimens. Within this group, C. obsoletus s.s. accounted for 56.8% and Culicoides scoticus for 43.2% of samples. Nulliparous, parous and engorged females were caught throughout the entire winter, both indoors and outdoors. At times, indoor catch sizes outnumbered outdoor collections. A significant inverse correlation was found between minimum temperature and the proportion of indoor Culicoides of the total midge catch, thus indicating that lower outdoor temperatures drive Culicoides midges indoors. High rates of engorged females were recorded indoors, possibly as the result of the propensity of C. obsoletus females to feed indoors. Higher proportions of parous females were found in indoor than in outdoor catches, indicating higher survival rates indoors and, consequently, higher vectorial capacities of midges sheltering indoors compared with those remaining outdoors.

Vaccines for Prevention of Bluetongue and Epizootic Hemorrhagic Disease in Livestock: A North American Perspective

Bluetongue (BT) and epizootic hemorrhagic disease (EHD) are noncontagious, insect-transmitted diseases of domestic and wild ruminants caused by related but distinct viruses. There are significant gaps in our scientific knowledge and available countermeasures to control an outbreak of orbivirus-induced disease, whether BT or EHD. Both BT virus (BTV) and EHD virus (EHDV) cause hemorrhagic fevers in susceptible ruminants; however, BT is principally a disease of domestic livestock whereas EHD is principally a disease of certain species of wild, non-African ungulates, notably white-tailed deer. The live-attenuated (modified live virus [MLV]) vaccines available in the United States for use in small ruminant livestock do provide good protection against clinical disease following infection with the homologous virus serotype. Although there is increasing justification that the use of MLV vaccines should be avoided if possible, these are the only vaccines currently available in the United States. Specifically, MLVs are used in California to protect sheep against infection with BTV serotypes 10, 11, and 17, and a MLV to BTV serotype 10 is licensed for use in sheep throughout the United States. These MLV vaccines may need to continue to be used in the immediate future for protective immunization of sheep and goats against BT. There are currently no licensed vaccines available for EHD in the United States other than autogenous vaccines. If there is a need to rapidly develop a vaccine to meet an emerging crisis associated with either BTV or EHDV infections, development of an inactivated virus vaccine in a conventional adjuvanted formulation will likely be required. With two doses of vaccine (and in some instances just one dose), inactivated vaccines can provide substantial immunity to the epizootic serotype of either BTV or EHDV. This strategy is similar to that used in the 2006-2008 BTV serotype 8 outbreaks in northern Europe that provided vaccine to the field within 2 years of the initial incursion (by 2008). Further research and development are warranted to provide more efficacious and effective vaccines for control of BTV and EHDV infections.

A one-year follow-up of antibody response in cattle and sheep after vaccination with serotype 8- and serotype 1-inactivated BT vaccines

Sixteen sheep and 18 cattle were followed up during 1 year to estimate the duration of immunity induced by inactivated bluetongue virus serotype 8 (BTV-8) vaccines (sheep and cattle) and a bluetongue virus serotype 1 (BTV-1) vaccine (cattle) under field conditions using cELISA and seroneutralization test (SNT). Four sheep never seroconverted. Those that seroconverted were all seronegative by BTV-8 SNT at the date of last sampling [378 days post-vaccination (dpv)]. Eight sheep were still positive by competitive ELISA (cELISA) 378 dpv. All the cattle seroconverted. At the end of the study, eight and 11 cattle were still positive by BTV-8 SNT and cELISA, respectively (335 dpv); and nine were still positive by BTV-1 SNT (301 dpv).

Seroprevalence after vaccination of cattle and sheep against Bluetongue Virus (BTV) serotype 8 in Sweden

Sweden experienced its first outbreak of bluetongue virus (BTV) infection beginning in September 2008. Mandatory vaccination with an inactivated vaccine (BTVPUR Alsap8; Merial, Lyon, France) began 2 days after bluetongue was confirmed in the country. The aim of this study was to investigate whether the goal of 80% seroconversion by the susceptible population within the vaccination area was met during the initial phase of the Swedish vaccination campaign and whether there were discrepancies between subpopulations. Milk or blood samples were collected from 274 cattle randomly selected from the vaccinated population. Blood samples were also collected from ten ewes on each of 28 randomly selected vaccinated herds. The vaccination campaign in Sweden may be regarded as successful, as measured by apparent seroprevalence in the vaccinated population. The overall apparent seroprevalence was 77%, and in cattle, which constituted the majority of the susceptible population, the apparent seroprevalence was 82%. Factors that influenced the titres after vaccination were as follows: (i) the time span between vaccination and sampling and (ii) the age of the animals.