Disease Carriers

Viruses: Influenza A

Influenza A is an important respiratory pathogen of humans. It re-emerges annually, causing significant morbidity and mortality in the world's population. In addition to humans, Influenza A also infects species such as birds, pigs, horses and marine mammals.

Influenza A virus has a heterogeneous morphology, giving it a diverse structural appearance. Some viruses are spherical while others have a filamentous shape. Two surface glycoproteins known as the hemagglutinin (H or HA) and neuraminidase (N or NA) are embedded in a lipid membrane and radiate from the particle. These are the protruding white spikes that are most easily seen on the magnified spherical particles (left). The HA and NA are major targets of our immune system. Influenza viruses continually change the amino acids and carbohydrates that make up these glycoproteins to evade the antibodies produced against previously circulating strains of the virus. This process is known as "antigenic drift" and it is the primary reason we have to annually modify the influenza vaccine.

A transmission electron micrograph of influenza A, negatively stained to enhance contrast