English
Indonesia
Swine Influenza : Pigs, a place for influenza virus gene “coalition”
After the absence of avian influenza cases for quite some time, we are shocked by the emergence of swine influenza in Mexico. Since March 2009, 103 people have been reported dead because of swine influenza. World Health Organization (WHO) Director General, Margaret Chan, had warned about the potential of a pandemic. International mobility of human and agriculture product could very much likely contribute to the movement of viruses causing this disease.
Researchers are working hard to analyze characteristics of the virus. In general, many viruses could meet in pigs, ranging from swine, avian, until human viruses.
“Borrowing a political term, a perfect coalition between flu viruses could occur inside a pig’s body. It could result in the creation of a new virus that contains genetic materials from its predecessors and carries new characteristics,” said CA Nidom, researcher from the Tropical Disease Center and professor at Airlangga University in East Java, Indonesia.
Pigs are mixing vessels for these viruses. In the pig’s body, many different types and subtypes of viruses could mix and produce virus “offsprings” with new characteristics.
Nidom explains that easy mixing of avian influenza virus genes is only known to occur in pigs. Pigs have biological structures which enables it to mix virus genes. Nidom is doing research on the possibility of that process occurring in other mammals such as cats and dogs. But until now he hasn’t found any evidence of such process in both cats and dogs.
Replication
Genetic mixing starts when a virus enters the body of a pig. Human influenza and swine influenza viruses enter epithelial cells through alpha 2,6 sialic acid receptors while avian influenza viruses enters through alpha 2,3 sialic acid receptors. Pigs have both receptors.
In swine cells, these viruses replicate. During the process, some of the viruses could swap genes or conduct a process known as antigenic shift. Each virus has eight gene fragments. The fragments are HA, NA, PA, PB1, PB2, M, NP, and NS. These fragments could swap and form virus “offsprings” with different characteristics.
In the case of Mexican swine flu, reassortment produces a virus with an outer structure similar to its main contributor, the swine influenza virus (hence the virus is referred to as H1N1 subtype swine influenza), but the genetic material inside contains fragments of human influenza and avian influenza viruses.
Besides genetic exchange, there is a possibility of antigenic drift, where fragments mutate. If this really occurred, then genes of virus “offsprings” will be more complex.
“If antigenic shift and antigenic drift both occurred in swine influenza in Mexico, then it would be perfect alteration,” said Nidom.
Nidom believes that if swine influenza and avian influenza wants to infect humans, it must go through several steps. In Mexico, he suspects the virus went through reassortment in pigs and then infected humans. Virus adaptation occurred in the first human infected and then it spread to other people in full speed.
Until now, the known “building blocks” of the swine influenza virus in Mexico are low pathogenic swine influenza virus subtype H1N1, human influenza virus subtype H1N1 and H3N2, and avian influenza subtype H5N2.
In truth, the virulence of H5N1 avian influenza which reached 80 percent is far greater than the virulence of swine influenza which is 15 percent. But because of the fast spread rate, swine influenza had caused alarm among experts.
With the virus fragments still in study, there is intensive discussion among animal health experts whether it is appropriate to call the virus as swine influenza.
Nidom explained the basic structure of the virus is swine influenza, but the virus’s fragments are human and avian influenza.
“That’s why there is still debate on the appropriate term for this virus,” said Nidom. (MAR)
Source : Kompas