bird flu: a new emerging pandemic threat and its pharmacological intervention

ABSTRACT

Bird flu is an infection caused by avian influenza viruses, which are of different types A, B and C. Type A avian influenza viruses are the most frequently associated with avian influenza epidemics and pandemics. There are 16 hemagglutinin [H1 to H16] and 9 neuraminidase types [N1 to N9] identified till date. A peculiar characteristic of influenza A viruses is their propensity for genetic change by two main processes antigenic drift [small, gradual changes] and antigenic shift [abrupt, major change producing a novel influenza A virus subtype]. There are various modes of transmission of human influenza including inhalation, direct or indirect [fomite] contact etc., can have manifestations ranging from mild to severe or fatal disease, depend on the viral subtype causing the disease. Avian influenza A [H5N1] results in high death rate amongst infants and young children. The first outbreak of human infection by avian influenza viruses [H5N1] was observed in 1997 in Hong Kong. Since then a large number of outbreaks have been reported in different parts of the world. In fact, the spread of avian influenza H5N1 in various species including humans has lead to a current pandemic threat. Human avian influenza infections in persons at high risk of exposure can be prevented by adopting a series of protective measures, anti-viral vaccination and health monitoring. Drugs currently available for the treatment or prophylaxis of influenza infections include the adamantanes [amantadine and rimantadine] and the newer class of neuraminidase inhibitors [zanamivir, oseltamivir and peramivir]. However, vaccines are considered the first line of defense for reducing the excess morbidity and mortality that invariably accompany pandemics and a number of clinical trials are under way to test them