An Intestinal Threadworm as a Reservoir and Intermediate Host for Swine Influenza Virus

A laboratory model exemplifying Shope's concept of virus carriage by helminths was developed using Strongyloides ratti (Sandground, 1925), swine influenza virus, and caesarean-originated, barrier-sustained (COBS) mice and rats. It was shown that S. ratti can act as a carrier of swine influenza virus and infect mice, despite the fact that the nematode has undergone a complete life cycle after exposure to virus in infected rats. COBS rats were inoculated with the virus via the intranasal route and subsequently infected with S. ratti. The larvae and eggs found in the feces collected from these rats were allowed to develop in vitro. These second generation filariform larvae were then inoculated subcutaneously into COBS mice. At necropsy, 5-8 days postinoculation, swine influenza virus was isolated from 15% of the mouse lungs. In control studies, swine influenza virus was not isolated from the feces of the COBS rats which served as a source of both unexposed and exposed S. ratti. Swine influenza virus was recovered in vitro from S. ratti homogenates. It is suggested that this laboratory model be used to study more closely the various aspects of the ecology of virus-helminth relationships in vertebrate hosts.