HOST FOR SWINE INFLUENZA VIRUS II. THE TP.ANSmSSlON OF SWINE IN:FLUENZA VIRUS BY THE SWINE LUNGWOI~

In the preceding paper (1) experiments have been described in which swine influenza virus infections were elicited in apparently normal swine by multiple intramuscular injections of suspensions of either living or heat-killed Hemophilus influemae suis. The findings suggested that the virus of swine influenza had been present somewhere in the pigs at the time of injection. In the present paper it will be shown that the swine lungworm is. capable of harboring swine influenza virus and of transmitting it from swine to swine. This discovery was made incidentally to observations on the possible r61e of the lungworm in transmitting hog cholera. Study of the possibility that the swine lungworm might serve as an intermediate host for hog cholera had as its basis the popular belief held by certain farmers and veterinarians in the Middle West that the earthworm is responsible, in some unvisualized fashion, for the persistence of cholera virus from one outbreak of the disease to the next. I The observations of the Hobmaiers (2) and Schwartz and Alicata (3) that the earthworm serves as intermediate host for the swine lungworm lent some plausibility to this belief, although it seemed more likely, if the earthworm were involved, that its r61e was indirect and that the lungworm in all probability was the actual carrier of the infectious agent. I t was decided to test the possibility experimentally. In the hope that findings with one agent might serve as controls for those with another, a study with the swine influenza virus was conducted in parallel with that of the hog cholera virus. The latter yielded negative results whereas that with the influenza virus clearly showed that the lungworm was capable of serving as the transmitting intermediate host. For this reason the findings with the influenza virus will be especially stressed.