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  • Author or Editor: Patricia Whitaker-Dowling x
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Objective—To develop and characterize a cold-adapted live attenuated equine-2 influenza virus effective as an intranasal vaccine.

Animals—8 ponies approximately 18 months of age.

Procedures—A wild-type equine-2 virus, A/Equine/ Kentucky/1/91 (H3N8), was serially passaged in embryonated chicken eggs at temperatures gradually reduced in a stepwise manner from 34 C to 30 C to 28 C to 26 C. At different passages, infected allantoic fluids were tested for the ability of progeny virus to replicate in Madin-Darby canine kidney (MDCK) cells at 34 C and 39.5 C. Virus clones that replicated at 26 C in eggs and at 34 C in MDCK cells, but not at 39.5 C in MDCK cells, were tested for stability of the coldadapted, temperature-sensitive (ts), and protein synthesis phenotypes. A stable clone, P821, was evaluated for safety, ability to replicate, and immunogenicity after intranasal administration in ponies.

Results—Randomly selected clones from the 49th passage were all ts with plaquing efficiencies of < 10-6 (ratio of 39.5 C:34 C) and retained this phenotype after 5 serial passages at 34 C in either embryonated eggs or MDCK cells. The clone selected as the vaccine candidate (P821) had the desired degree of attenuation. Administered intranasally to seronegative ponies, the virus caused no adverse reactions or overt signs of clinical disease, replicated in the upper portion of the respiratory tract, and induced a strong serum antibody response.

Conclusion and Clinical Relevance—A candidate live attenuated influenza vaccine virus was derived by cold-adaptation of a wild-type equine-2 influenza virus, A/Equine/Kentucky/1/91, in embryonated eggs. (Am J Vet Res 2001;62:1290–1294)

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in American Journal of Veterinary Research


Objective—To determine safety, efficacy, and immunogenicity of an intranasal cold-adapted modified- live equine influenza virus vaccine administered to ponies following induction of exercise-induced immunosuppression.

Design—Prospective study.

Animals—Fifteen 9- to 15-month old ponies that had not had influenza.

Procedure—Five ponies were vaccinated after 5 days of strenuous exercise on a high-speed treadmill, 5 were vaccinated without undergoing exercise, and 5 were not vaccinated or exercised and served as controls. Three months later, all ponies were challenged by nebulization of homologous equine influenza virus. Clinical and hematologic responses and viral shedding were monitored, and serum and nasal secretions were collected for determination of influenza-virus-specific antibody isotype responses.

Results—Exercise caused immunosuppression, as indicated by depression of lymphocyte proliferation in response to pokeweed mitogen. Vaccination did not result in adverse clinical effects, and none of the vaccinated ponies developed clinical signs of infection following challenge exposure. In contrast, challenge exposure caused marked clinical signs of respiratory tract disease in 4 control ponies. Vaccinated and control ponies shed virus after challenge exposure. Antibody responses to vaccination were restricted to serum IgGa and IgGb responses in both vaccination groups. After challenge exposure, ponies in all groups generated serum IgGa and IgGb and nasal IgA responses. Patterns of serum hemagglutination inhibition titers were similar to patterns of IgGa and IgGb responses.

Conclusions and Clinical Relevance—Results suggested that administration of this MLV vaccine to ponies with exercise-induced immunosuppression was safe and that administration of a single dose to ponies provided clinical protection 3 months later. (J Am Vet Med Assoc 2001;218:900–906)

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in Journal of the American Veterinary Medical Association