Background

Influenza viruses type A, B and C are among the causes of respiratory tract infections in humans. Type A virus has 15 sub types some of which are predominant in pigs (swine influenza virus), in humans (human influenza virus), in horses (equine influenza virus) or in birds (avian influenza virus)1.

Human and animals can pass influenza virus from one to another. Humans can thus, become sick from avian or swine influenza when they pick up the virus from these animals2

In irregular intervals which can be as frequent as yearly, genetic particles of viruses from birds and pigs or humans are mixed (assortment) to produce novel sub types with increasing virulence. The theory of the pandemic flu is derived from the expectation that such a mixture of viral materials will produce a novel influenza that will spread early in humans unhindered by a non-existent human immunity

Peiris JS, de Jong MD,

Influenza A viruses are classified into sub types based on two surface proteins, the hemagglutinin (HA) and neuraminidase (NA). A virus that has a type 1 HA and type 2 NA, for example, would have the sub type H1N2. At least 16 types of hemagglutinins (H1 to H16), and 9 neuraminidases (N1 to N9) are known to exist in birds.

Symptoms

The symptoms of swine influenza and avian influenza in people are similar to the symptoms of regular human seasonal influenza infection and include: