Frederick Glyn Davies.

A vet who made a substantial contribution to tropical veterinary virology.

Efficacy of a canarypox-vectored recombinant vaccine expressing the hemagglutinin gene of equine influenza H3N8 virus in the protection of ponies from viral challenge.

OBJECTIVE: To determine onset and duration of immunity provided by a 2- or 3-dose series of a new canarypox-vectored recombinant vaccine for equine influenza virus (rCP-EIV vaccine) expressing the hemagglutinin genes of influenza H3N8 virus strains A/eq/Kentucky/94 and A/eq/Newmarket/2/93 in ponies. ANIMALS: Forty-nine 1- to 3-year-old male Welsh Mountain Ponies that were seronegative for equine influenza virus. PROCEDURES: Vaccinated and control ponies were challenged with aerosolized influenza virus A/eq/Sussex/89 (H3N8), representative of the Eurasian lineage of circulating influenza viruses. In trial 1, control ponies and ponies that received rCP-EIV vaccine were challenged 2 weeks after completion of the 2-dose primary vaccination program. In trial 2, ponies were challenged 5 months after 2 doses of rCP-EIV vaccine or 1 year after the first boosting dose of rCP-EIV vaccine, administered 5 months after completion of the primary vaccination program. After challenge, ponies were observed daily for clinical signs of influenza and nasal swab specimens were taken to monitor virus excretion. RESULTS: The challenge reliably produced severe clinical signs consistent with influenza infection in the control ponies, and virus was shed for up to 7 days. The vaccination protocol provided clinical and virologic protection to vaccinates at 2 weeks and 5 months after completion of the primary vaccination program and at 12 months after the first booster. CONCLUSION AND CLINICAL RELEVANCE: The rCP-EIV vaccine provided protection of ponies to viral challenge. Of particular importance was the protection at 5 months after the second dose, indicating that this vaccine closes an immunity gap between the second and third vaccination.

Experimental infection of ponies with equine influenza A2 (H3N8) virus strains of different pathogenicity elicits varying interferon and interleukin-6 responses.

The production of interferon (IFN), interleukin-6 (IL-6), and tumor necrosis factor (TNF) was monitored in horses during the course of influenza A2 virus infections. The effects of two virus strains, Newmarket/2/93 and Sussex/89, were compared, of which the latter is considered the more pathogenic in terms of clinical signs. Ten naive ponies were infected with influenza A/equine/Sussex/89 and 10 with influenza A/equine/Newmarket/2/93, respectively. As expected ponies infected with Sussex/89 showed the most pronounced clinical signs but there was no notable difference in viral excretion compared with Newmarket/2/93. IFN was detected in nasal secretions of all ponies infected with Sussex/89 but only in 2 ponies infected with Newmarktet/2/93. IFN was not detected in serum of any animal. IL-6 activity was detected in nasal secretions of all experimental animals from day 2 and onwards, but showed markedly higher IL-6 responses were observed in ponies infected with Sussex/89. No TNF activity was detected in any of the samples collected. In summary, equine influenza A 2 infections elicited local, and in some cases systemic, IFN and IL-6 responses in the ponies. Interestingly, there was some evidence that the duration and levels of cytokine responses may be related to the pathogenicity of the influenza strains.