Swine Influenza Virus H1N1

Viruses of the classical H1N1 lineage were the dominant cause of influenza among pigs in North America from their first isolation.

Classical H1N1 viruses have also been isolated from pigs in South America, Europe and Asia.

There is only limited evidence of maintenance of human H1N1 influenza viruses after natural introduction into swine populations but human H3N2 viruses have been recovered frequently from pigs in Asia and Europe.

Experimental infection studies have shown that pigs can be infected with a wide range of avian influenza virus (AIVs) and naturally acquired infections of pigs with AIVs have also been documented from multiple areas of the world.

In particular, an avian H1N1 virus introduction into pigs Europe in late 1970s spread throughout much of the European continent and United Kingdom and ultimately became a dominant cause of swine flu in these areas.

These avian-like H1N1 viruses have also undergone genetic/antigenic drift and have spread from pigs to domestic turkeys.

The occurrence of influenza virus infections in pigs poses two important public health issues: zoonotic infections of people with swine influenza viruses and the potential for pigs to serve as hosts for the creation of novel viruses of pandemic potential for the human population.

Infections with swine influenza viruses is generally limited to the respiratory tract, with virus replication demonstrated in epithelial cells of the nasal mucosa, tonsils, trachea, lungs and tracheobronchial lymph nodes.

Swine flu is an acute infections and virus clearance is extremely rapid. In most experimental studies, nasal virus shedding begins on day 1 postinoculation (P1) and ceases within 7 days.

Likewise, swine influenza virus could not be isolated from lungs or other respiratory tract tissues after day 7.

Infections with H1N1, H1N2 and H3N2 subtype viruses are clinically similar, and viruses of all subtypes have been associated with acute respiratory episodes in most European countries.

Disease onset is sudden, after an incubation period of 1 – 3 days. Disease signs typically appear in a large percentage of animals of all ages within a herd or epidemiological unit.
Swine Influenza Virus H1N1

The 1976 Swine Flu Fiasco

The 1976 Swine Flu Fiasco
Shortly after new army recruit and soldiers returning form the Christmas holidays arrived at Fort Dix, New Jersey, in January 1976, an outbreak of influenza ensued.

Most of the illness remained mild with only a few hospitalized victims. One sick recruit refuse to answer sick call died from influenza related pneumonia.

Tests showed that he and three others had been infected with and H1N1 swine virus, while all the others had been infected with a variant of the H3N2 virus hat had been circulating every year since it was introduced to human population in 1968.

There had been a few reported cases of human infection by the swine flu since 1974, but the virus had grown so adapted to pigs that it no longer adjusts well enough in the human host to be transmitted from person to person.

Fearful that the H1N1 subtype of 1918 had begun to resurface within the human population, with the prospect of a similar pandemic, scientist debated the issue and considered what should be done to prevent such a disaster.

Some scientists believed this was not the same type variant of 1918, while many others feared it could be.

President Ford at that time, following recommendations coming out of the debate announced in March the federal government’s intent to immunize the entire population of the United States against the swine flu to prevent a disastrous outbreak expected in the fall of 1976, similar to the 1918 pandemic.

Congress appropriated $135 million for the vaccination program.

Ten days after the vaccinations began, three elderly individuals with the heart conditions died shortly after receiving their shots. The news media jumped on this to create fear of the vaccine.

This prompted President Ford and his family to encourage people to take the shots by televising their own vaccinations.

Over 40 million people did receive the vaccine before the program ended in December.
The 1976 Swine Flu Fiasco