Public Health Importance and Pandemic Potentials/Threats of Influenza Viruses

Abstract

Influenza A viruses of different subtypes, infect a variety of animal species and with their ability to undergo reassortments and mutations readily, are a potential public health risk. The significant carriers as well as sources of viruses are poultry birds (ducks, wild/migratory birds, chickens) and pigs, and sharing of ponds having discharged household wastewater with the excreta of humans, pigs and birds, contribute to the development of a reassortant virus through evolutionary mechanisms within ‘mixing vessels’. Pandemic threat to humans in case of bird flu is limited to 4 HA types, viz. H5, H7, H9 and H10 (AIV subtypes H5N1, H7N2, H7N3, H7N7, H7N9, H9N2, H10N8 and H10N7). Handling of infected birds or infected eggs/meat causes serious trouble in relation to transmission of bird flu rather than eating poultry products. Few authenticated cases of human-to-human transmission of avian influenza (bird flu) have been documented. However, the bird flu virus has not yet learnt the capability to be spread in a rapid and vicious manner from human-to-human in a pandemic way. This kind of human-to-human transmission of bird flu virus can trigger a human pandemic claiming millions of lives, as happened during the earlier pandemics of the twentieth century. The chance of H5N1 human pandemic virus may arise some time in the near future because of mixed infection with a bird flu (H5N1) virus and a currently circulating H3 or H1 subtype human influenza virus. If a severe pandemic occurs with a pandemic flu virus having a lethal killing weapon like that of bird flu (H5N1) virus and rapid spread like that of recent/current swine flu (H1N1) virus, then this deadly evolving influenza virus could cause serious socio-economic and public health consequences. More than 208 countries have been affected with swine flu during the last 4 years taking lives of nearly 13,600 people. Pigs act as a ‘mixing vessel’ and have played an important role in the evolution of a novel subtype of Swine flu (H1N1 subtype) virus that has enormous pandemic potential. Interestingly, transmission of swine origin influenza A viruses (H1N1, H1N2 and H3N2) can occur between humans and animals, especially in children.