Swine Flu: Media Scare or Major Threat?
Think the current swine influenza scare is just a bit of media drama? Don’t be too sure. Pigs have the potential to serve as a genetic “mixing vessel” for influenza viruses carried by birds, pigs and humans. Most viruses tend to be species specific but not those of the Influenza type A viruses. These viruses can easily swap genetic code between traditional avian, pig and human infections. It is feared that this mixing of genetic code may someday result in a flu pandemic to rival that of the 1918 Influenza epidemic.
The flu epidemic of 1918 killed an estimated 50 million people worldwide which is more than were killed in World War I. In one year the flu epidemic of 1918 lowered the average life expectancy in the United States by 12 years. It is currently believed that the severe morbidity and mortality achieved by the human Influenza virus H1N1 in 1918 was through the mixing of especially avian genes and possibly swine genes.
Swine flue is actually an Orthomyxovirus of which there now four known subtypes. H1N1, H1N2 and H3N2 and the newly characterized H2N3. The newest H2N3 swine influenza strain is composed of avian and swine influenza genes.
In 2006, two separate groups of pig production facilities were found to be infected with the newly described H2N3 Influenza virus by researchers from Iowa State University, the University of Minnesota and St. Jude Children’s Hospital. Both of these pig production facilities used water obtained from ponds that were frequented by migrating water fowl. The newest swine flu was found to have a similar molecular composition to the H2N3 strain infecting mallard ducks. Exposure to bird flu was enough to create a new flu infecting pigs. Even mice and ferrets can be infected with the new H2N3 virus. How long before this genetic mixing creates another human flu epidemic?
Did you know swine influenza only appeared immediately after the 1918 influenza pandemic in humans? It is generally accepted that swine influenza was an adaptation of human influenza virus in pigs.
The natural reservoir of influenza A virus is aquatic birds. Pigs are susceptible to both human and avian viruses.
Young , growing pigs and pigs that are stressed are the most susceptible to infection. When an infection occurs almost all of the pigs in a herd will be infected within a few days.
Swine flu is traditionally described as an infection of the upper respiratory tract with the primary lesion being a viral interstitial pneumonia.
The incubation period for swine flu is from 1 to 7 days and is typically from 1 to 3 days. Viral shedding typically starts on day 1 of infection and continues through day 7 with peak shedding occurring within 24 hours of infection.
Clinical signs of infection include a fever, anorexia (not eating), sneezing, muscle stiffness pain and labored jerky breathing. A deep painful cough is possible. An ocular and nasal discharge is common. In severe cases there can be open mouth breathing and dyspnea. Morbidity is usually 100% but mortality is rarely above 1%. In 4 to 6 days pigs usually show signs of recovery. The H3N2 variety in the U.S. has been associated with spontaneous abortion and death of adult pigs in addition to respiratory disease.
Infection may be confirmed by serologic antibody testing. ELISA, virus isolation form nasopharyngeal swabs and PCR testing are all available.
There is no specific treatment currently available other than supportive care and treatment with antibiotics for secondary infection.
Control may be achieved by vaccination and biosecurity. Biosecurity can be difficult to completely isolate susceptible animals to people and birds.
Moellenberg, Dell Rae. “Avian Influenza Under the Microscope at CSU.” DVM News. November 2006. P. 10.
“New Swine Flu Subtype as Avian Flu Genes.” JAVMA. Vol. 232. No. 4 News. P. 497.
Radostits, Otto et al. Veterinary Medicine. 10th Ed. Saunders/Elsevier. 2007. Pp. 1331-1335.