Do UK sheep farmers use orf vaccine correctly and could their vaccination strategy affect vaccine efficacy?

Abstract

Orf, a parapoxvirus, is a zoonosis causing a contagious pustular dermatitis, and has a high morbidity in sheep worldwide. Despite a vaccine being available, orf prevalence in England is estimated to be 2 per cent in ewes and 20 per cent in lambs​​. There is concern that farmers are not complying with the vaccination guidelines and therefore the objective of this study was to investigate if orf vaccine is used correctly on sheep farms in the UK and to identify barriers and motivators of sheep farmers to use the vaccine. The survey was completed by 570 respondents. The results show several areas of concern; only 27 per cent of respondents used the correct site (axilla), 37 per cent of respondents would use orf vaccine up to a week after opening a vial (shelf life is eight hours), 33 per cent of respondents would vaccinate their ewes too close to lambing and 73 per cent of respondents did not separate vaccinated and non-vaccinated animals (both leading to infection risk for non-vaccinated animals). When vaccinating, only 53 per cent of respondents were wearing gloves and 31 per cent washed their hands just before and immediately after vaccination. Results demonstrate that orf vaccination is not carried out correctly on all UK sheep farms, which is likely to affect vaccine efficacy. A concern around vaccine efficacy, the ‘hassle’ of the scratch administration, the ‘risk of making it worse’ and the zoonotic risk when vaccinating were the most common barriers for using orf vaccine, highlighting the importance of veterinary advice when prescribing orf vaccine.

Immunomodulatory Strategies for Parapoxvirus: Current Status and Future Approaches for the Development of Vaccines against Orf Virus Infection

“…However, the ability of the virus to repeatedly infect the susceptible host does not appear to be associated with the production of the desired memory T-cells as a promising hypersensitivity reaction to ORFV antigen, as reported by several recent publications [54,79,83,129]. Thus, such an immune response cannot be considered abnormal for ORFV infection, as significant levels of CD4 + T-cells have been detected among the infected animals when compared to CD8 + cytotoxic T-cells and/or B-cell response [115,[130][131][132][133][134][135]. On the other hand, the humoral immune response does not play an important role in protecting animals from ORFV infection [136].…”

“…More recent studies demonstrated that plasmid DNA-based ORFV vaccines derived from virulent strains induced protective T cells and ORFV-specific antibody responses in neonates [3,27,64,130,135]. The result indicated that the plasmid DNA-based vaccines induced similar responses in mice compared to live-attenuated vaccines [179].…”

“…This vaccination strategy offers some considerable advantages, not the least of which is a desirable immune response against viral diseases that can induce long-lived immunity [124]. Attenuated vaccines can usually elicit durable immunity after a single injection and additional boosters aren't required [130]. The ORFV D1701 strain is an excellent example of an efficient attenuated vaccine against ORFV infection in sheep that requires a single or two boosters to induce durable immunity [128,163].…”

“…Sheep/goats (1999,1996,1998,2008) attenuated vaccines e.g., D1701 goat vaccine Induce (4-8 months) humoral & cell-mediated immunity short-lived immunity, possible reversion to virulence strain Evokes broad immune responses; and CD4-T cells, CD8-T cells and the cytokine IFN-g (interferon-g) have been observed [5,14,25,78,129,175] Egg-based vaccine [ 25,130,160,183] However, the antibodies detected in the vaccinated animals are not considered significant for sustained protection against ORFV infection, but the presence of an antibody in the vaccinated sheep indicated prior exposure to ORFV [124,129,179,180,182]. On the other hand, live-attenuated ORFV vaccines based on cell culture elicited the desired immunity against originally virulent ORFV strain obtained from a British isolate of Orf virus [56,92,129,181].…”

NF-κB as an Important Factor in Optimizing Poxvirus-Based Vaccines against Viral Infections

“…Mortality due to ORFV infections is rarely associated with secondary infections and aspiration pneumonia. In general, orf disease is a threat to kids and lambs and may cause farms to suffer economic losses [90][91][92][93][94].…”