Mode of Transmission
The human to human mode of transmission of the deadly swine flu virus is likely to occur when an infected person coughs or sneezes in the presence of uninfected people.
One infected person can transmit the virus to hundreds of people and it is this “viral” spread that is worrying the WHO officials. Ban Ki-moon, UN secretary- general, observed “We are concerned that this virus could cause a new influenza pandemic. It could be mild in its effect or potentially be severe. We don’t know which way it will go.” Another possible mode of transmission is when an uninfected person touches any item that that has the virus on it.
A single droplet of 0.5 to 5 µm in diameter or a single virus is enough to infect a person. A single sneeze releases over 40,000 droplets. The droplets can either remain as aerosol or settle on objects.
The avian influenza virus can survive indefinitely when frozen. The virus can survive for one to two days on surfaces such as plastic or metal and for about fifteen minutes on dry paper tissues but only five minutes on skin.
In the mucus secretions, it can survive longer. The virus is inactivated by heating to 56 °C (133 °F) for a minimum of 60 minutes and also by pouring acids (at pH <2) on the infected surfaces.
In an interesting study done on the survival of the human influenza viruses on banknotes that are dispensed in billions daily it was found that Influenza A viruses can survive in high concentrations for up to 3 days. The same inoculum in the presence of respiratory mucus showed a striking increase in survival time (up to 17 days). They concluded that the unexpected stability of influenza virus should be considered in the setting of pandemic preparedness.
Level of humidity and UV radiation can influence the survival of the virus. Low humidity combined with lack of sunlight (during winters) can be optimal for the virus to survive longer and this accounts for the higher prevalence of flu during winter months.
Influenza is known to occur commonly in pigs and the major route of transmission in these animals is also through direct contact between the infected and the uninfected animals. Pigs are raised and transported in close proximity and this increases the risk of transmission. Direct touching or transmission through air is also possible. Wild animals play a role in transmitting the disease between farms.
Farm hands who work with poultry and swine are at an increased risk of acquiring a zoonotic infection. The others at risk, albeit at a lower scale include veterinarians and those involved in meat processing.
Continuous public health surveillance and vaccination against swine flu are paramount to protect these people and to prevent the spread of the disease.
