Swine influenza, or “swine flu”, is a highly contagious acute respiratory disease of pigs, caused by one of several swine influenza A viruses. Morbidity tends to be high and mortality low (1-4%). The virus is spread among pigs by aerosols and direct and indirect contact, and asymptomatic carrier pigs exist. Outbreaks in pigs occur year round, with an increased incidence in the fall and winter in temperate zones. Many countries routinely vaccinate swine populations against swine influenza (WHO, 2009).
Many in the infectious disease community believe that pigs can be infected with more than one type of avian and human seasonal virus at the same time (CDC, 2002, 2004, 2008). For example, Swine influenza viruses are most commonly of the H1N1 subtype, but other subtypes are also circulating in pigs (e.g., H1N2, H3N1, H3N2). There are also biological similarities with H5N1. The H3N2 swine virus was thought to have been originally introduced into pigs by humans. Sometimes pigs can be infected with more than one virus type at a time, which can allow the genes from these viruses to mix. This can result in an influenza virus containing genes from a number of sources, called a “reassortant” virus (WHO, 2009). The “reassortant” virus means dual infection. Furthermore, the biology and chemistry of influenza has emerged since 1977. Since 1977, influenza A (H1N1) viruses, influenza A (H3N2) viruses, and influenza B viruses have been in global circulation. Influenza A (H1N2) viruses that probably emerged after genetic reassortment between human A (H3N2) and A (H1N1) viruses have been detected recently in many countries. Both influenza A and B viruses are further separated into groups on the basis of antigenic characteristics. New influenza virus variants result from frequent antigenic change (i.e., antigenic drift) resulting from point mutations that occur during viral replication. Influenza B viruses undergo antigenic drift less rapidly than influenza A viruses (MMWR, 2002).
The emergennce of influenza virology has created opportunities for pharamaceutical companies to address the antigenetic characteristics of the emerged influenza. Hence, the birth of chemoprophylaxis. This class of drugs do not subsitute vaccination. However, these antiviral agents have proven effective in the reduction of circulating influenza viruses. Antiviral agents like oseltamivir and zanamivir, when administered within two days of the onset of illness may reduce the lifecycle of the influenza and may prevent subclinical infection.
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Centers for Disease Control. [Online]. Swine influenza. Retrieved from http://www.cdc.gov/swineflu/ on April 20, 2009.
World Health Organization. [Online]. Epidemic and Pandemc Alert and Response (EPR): Swine influenza. Retrieved from http://www.who.int/csr/diseas e/swineflu/en/index.html on April 20, 2009.
MMWR. [Online]. Prevention and control of influenza. Retrieved from http://www.cdc.gov/mmwr/previ ew/mmwrhtml/rr5103a1.htm on April 21, 2009.