Swine influenza viruses are influenza viruses that commonly circulate in (and infect) swine, and in recent years have included certain H1N1, H1N2, and H3N2 viruses. Swine influenza viruses do not normally infect humans. However, sporadic human infections with swine influenza viruses do occur, and when this happens, these particular swine-origin viruses are called variant influenza viruses, and are denoted with a “v” – for example, influenza A (H3N2)v. Thus for nomenclature purposes, influenza viruses that circulate in swine are called swine influenza viruses when isolated from swine, but are called variant influenza viruses (or variant viruses) when isolated from humans.



General Information


(See also the Laboratory Testing and Infection Control sections.)

Laboratory Testing

Clinicians evaluating ill patients suspected to be cases of probable H3N2v virus infection should obtain a nasopharyngeal swab or aspirate (or a combined nasal swab and throat swab) from the patient, place the swab or aspirate in viral transport medium, and contact the Missouri Department of Health and Senior Services at 573-751-6113 or 800-392-0272 (24/7) for testing approval, and to arrange transport and testing for H3N2v virus at the Missouri State Public Health Laboratory (MSPHL). (Specific testing for H3N2v can only be obtained at state public health laboratories, and prior approval must be obtained before a specimen can be sent to MSPHL. Influenza sample collection procedures are available online.) Cases of probable H3N2v infection would generally be persons with influenza-like illness who had recent exposure to swine, to an ill person who had swine exposure, or to a person with confirmed H3N2v infection.

Infection Control

Public Health Response

(see also Infection Control)

Swine Influenza in Swine