Kelly Lager, a veterinary researcher with the USDA Agricultural Research Service’s National Animal Disease Center in Ames, Iowa, provides the following definitions for terms frequently used in discussions relating to porcine respira-tory and reproductive syndrome virus transmission.

  • Horizontal transmission. Transmission of virus from one pig to another pig requires close contact between them. The use of PRRS-virus-contaminated semen collected from virus-positive boars can be included in this definition.
  • Vertical transmission. Trans-mission of virus from one generation to the next. For example, PRRS virus transmission from sow to piglet.
  • Fomite. An object that can harbor a pathogen and serve as an agent of transmission.
  • Vector. A carrier of infectious agent from one host to another host. It can be mechanical (which would just transmit the agent) or biological (the vector replicates the agent before transmitting it to a susceptible host.)
  • Area spread. Recognition of virus infection among swine herds in a selected geographical region, occurring about the same time.
  • Direct-area spread. Transmission of virus among herds in an area rela-ted to horizontal or vertical transmission.
  • Indirect-area spread. Trans-mission of virus among herds in an area not related to direct-area spread, assumed transmission via fomites, aerosol or vectors.