Saturday, 9 May 2009

Swine Flu Research

Swine flu (swine influenza) is a highly contagious respiratory disease of pigs, caused by one of several swine influenza A viruses. Since pigs can be infected with more than one virus type at a time, genes of several viruses from various sources (including humans) can mix, allowing the swine influenza viruses to cross species barrier and eventually cause disease in humans. The clinical symptoms then are similar to seasonal influenza and other acute upper respiratory tract infections, in some cases leading to severe pneumonia and resulting in death. However, since mild or asymptomatic cases may have escaped from recognition, the true extent of this disease among humans is still unknown. Currently, there is no human vaccine on the market which protects against swine influenza.

A new study by University of Maryland researchers suggests that the potential for an avian influenza virus to cause a human flu pandemic is greater than previously thought. Results also illustrate how the current swine flu outbreak likely came about.

As of now, bird flu viruses can infect humans who have contact with birds, but these viruses tend not to transmit easily between humans. However, in research recently published in the Proceedings of the National Academy of Sciences, Associate Professor Daniel Perez showed that after reassortment with a human influenza virus, a process that usually takes place in intermediary species like pigs, an avian flu virus requires relatively few mutations to spread rapidly between mammals by respiratory droplets.

"This is similar to the method by which the current swine influenza strain likely formed," said Perez, program director of the University of Maryland. "The virus formed when avian, swine, and human-like viruses combined in a pig to make a new virus. After mutating to be able to spread by respiratory droplets and infect humans, it is now spreading between humans by sneezing and coughing."

A virus vaccine is derived from the virus itself. The vaccine consists of virus components or killed viruses that mimic the presence of the virus without causing disease. These prime the body's immune system to recognize and fight against the virus. The immune system produces antibodies against the vaccine that remain in the system until they are needed. If that virus, or in some cases a closely similar one is later introduced into the system, those antibodies attach to viral particles and remove them before they have time to replicate, preventing or lessening symptoms of the virus.

The immune system also retains antibodies to a virus after being infected with it, so humans have general immunity to human strains of avian influenza strains. But humans do not generally have immunity to avian flu strains because they have not been infected by them before. The surface proteins are sufficiently different to escape the human immune response. Avian flu strains are therefore more dangerous for humans because the human immune system cannot recognize the virus or protect against it.