A note from the Team at SCTAOL: We received this helpful and friendly primer on influenza AH-1-N1, formerly known as the swine flu, from Dwight Ramos, who had received it as a forwarded message from his contacts. In light of the current global situation with regards to this illness, we thought it would be worth sharing with you, our readers. 

Influenza AH-1-N1, or “swine flu”, is a highly contagious acute respiratory disease of pigs, caused by one of several influenza AH-1-N1 viruses. Morbidity tends to be high and mortality low (1-4%). The virus is spread among pigs by aerosols, direct and indirect contact, and asymptomatic carrier pigs. 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 influenza AH-1-N1.

 Influenza AH-1-N1 viruses are most commonly of the H1N1 subtype, but other subtypes are also circulating in pigs (e.g., H1N2, H3N1, H3N2). Pigs can also be infected with avian influenza viruses and human seasonal influenza viruses, as well as by influenza AH-1-N1 viruses. 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. Although influenza AH-1-N1 viruses are normally species-specific and only infect pigs, they do sometimes cross the species barrier to cause disease in humans.

 What are the implications for human health?

 Outbreaks and sporadic human infection with influenza AH-1-N1 have been occasionally reported. Generally clinical symptoms are similar to seasonal influenza but reported clinical presentation ranges broadly from asymptomatic infection to severe pneumonia resulting in death. Since typical clinical presentation of influenza AH-1-N1 infection in humans resembles seasonal influenza and other acute upper respiratory tract infections, most of the cases have been detected by chance through seasonal influenza surveillance. Mild or asymptomatic cases may have escaped recognition; therefore the true extent of this disease among humans is unknown. 

Where have human cases occurred? 

Since the implementation of IHR(2005) in 2007, WHO has been notified of influenza AH-1-N1 cases from the United States and Spain. 

How do people become infected? 

People usually get influenza AH-1-N1 from infected pigs; however, some human cases lack contact history with pigs or environments where pigs have been located. Human-to-human transmission has occurred in some instances but was limited to close contacts and closed groups of people. 

Is it safe to eat pork and pork products? 

Yes. influenza AH-1-N1 has not been shown to be transmissible to people through eating properly handled and prepared pork (pig meat) or other products derived from pigs. The influenza AH-1-N1 virus is killed by cooking temperatures of 160°F/70°C, corresponding to the general guidance for the preparation of pork and other meat. 

Which countries have been affected by outbreaks in pigs? 

Influenza AH-1-N1 is not notifiable to international animal health authorities (OIE, www.oie.int). Therefore its international distribution in animals is not well known. The disease is considered endemic in the United States. Outbreaks in pigs are also known to have occurred in North America, South America, Europe (including the UK, Sweden, and Italy), Africa (Kenya), and in parts of eastern Asia including China and Japan. 

What about the pandemic risk? 

It is likely that most people, especially those who do not have regular contact with pigs, do not have immunity to influenza AH-1-N1 viruses that can prevent the virus infection. If a swine virus establishes efficient human-to human transmission, it can cause an influenza pandemic. The impact of a pandemic caused by such a virus is difficult to predict: it depends on virulence of the virus, existing immunity among people, cross-protection by antibodies acquired from seasonal influenza infection and host factors. 

Is there a human vaccine to protect from influenza AH-1-N1? 

There are no vaccines that contain influenza AH-1-N1, the current virus causing illness in humans. It is not known whether current human seasonal influenza vaccines can provide any protection. Influenza viruses change very quickly. It is important to develop a vaccine against the currently circulating virus strain for it to provide maximum protection. This is why WHO needs access to as many viruses as possible in order to select the most appropriate candidate vaccine virus.