The effects of strain heterology on the epidemiology of equine influenza in vaccinated population

Equine influenza (Horse flu) is the disease caused by strains influenza that are endemic in horse species. Equine influenza occurs globally ,and is caused by two mainstrains of virus equine -1 (H7N7) and equine-2 (H3N8).The disease has nearly 100% infection rate in an unvaccinated horse population that has not been previously exposed to the virus. While equine influenza is known to affect humans historically ,the impact of an outbreak amongst even the animal population was devastating because horseswere heavily relied upon for communication the social and economic impact of widespread equine disease was devastating today. We assess the effects of strain heterology (strains that are immunologically similar but not identical) on equine influenza in vaccinated population. Using data relating to individual animals, for both homologous and heterologous vaccines ,we estimate distributions for the latent and infectious periods, quantify the risk of becoming infected in terms of the quantity of cross-reactive antibodies to key surface protein of the virus (haemagglutinin) and estimate the probability of excreting virus (i.e. becoming infectious) given that infection has occurred. The data suggest that the infectious period, the risk of becoming infected (for given vaccine-induced level of cross-reactive antibodies) and the probability of excreting virus are increased for heterologously vaccinated animals when compared with homologously vaccinated animals. The data are used to parameterize modified susceptible, exposed, infectious and recovered/resistant) SEIR) model, which shows that these relatively small differences combine to have large effect at the population level, where populations of heterologous vaccinees face significantly increased risk of an epidemic occurring

Keywords:

stochasticmodel , equine influenza :epidemiology , Heterology