Twenty-five swine, infested with lungworms infected with masked swine influenza virus, were exposed to adverse weather conditions on one or more occasions. Of these, 4 came down with apparent swine influenza, while 6 others developed serological evidence of infection with swine influenza virus. The remaining 15 prepared swine, as well as 8 lungworm-free control swine, failed to show evidence of swine influenza virus infection, despite repeated exposures to adverse weather.
The data presented indicate that, in the 10 swine in which swine influenza virus infections were elicited, some feature of the weather to which the animals were exposed was responsible for provoking masked influenza virus to infectivity. The exact constituent of the meteorological complex comprising "weather", responsible for the provocation, cannot be determined from the data obtained.