H5N1 Avian influenza has not become an epidemic till now. What is the most important reason for this?
Correct Answer: Human to human transmission is rare
Description: Ans. c. Human to human transmission is rare (Ref: Park 23/e p156; Robbins 8/e p715)H5N1 Avian influenza has not become an epidemic till now. Human to human transmission is rare; this is the most important reason.'Fortunately, the transmission of the current H5N1 virus is inefficient (Human to human transmission is rare). Most patients with H5N1 infection present with pneumonia. However, if antigenic recombination occurs between H5N1 influenza and a strain of influenza, which is highly infectious for humans, sustained human-to-human transmission could give rise to a pandemic, similar to the Spanish pandemic of 1918. This concern has spurred efforts to develop a vaccine. '- Robbins 8/e p715Avian InfluenzaAvian influenza refers to strains of influenza, which primarily infect birdsQ.One such strain with the antigenic type H5N1 is of greater concern because infection is frequently lethal in humans (approximately 60%) and since 2003 the virus is spreading throughout the world in wild and domestic birds.Also known as 'Bird flu' or 'Highly pathogenic avian influenza'Causative agentQ: H5N1 (Type A Influenza virus)Avian Influenza is a Pandemic: Origin from Hong Kong (1997)Nearly all cases of H5N1 influenza in humans have been acquired by close contact with domestic birdsQ.The severity of the disease results from the ability of the virus to cause widespread infection in the human body, instead of infection being limited to the lungQ.Pathophysiology:The tissue tropism of H5N1 influenza is increased due to the unusual structure of its hemagglutinin protein.Cleavage of viral hemagglutinin by host proteases is required for the influenza virus to enter host cells.The hemagglutinin protein of H5N1 influenza virus, and other highly pathogenic influenza viruses, is unusual in that it can be cleaved by ubiquitous proteases in the human, white the hemagglutinin of less virulent influenza virus stains can be cleaved by proteases found in limited organs, including the lung.Fortunately, the transmission of the current H5N1 virus is inefficientQ.However, if antigenic recombination occurs between H5N1 influenza and a strain of influenza, which is highly infectious for humans, sustained human-to-human transmission could give rise to a pandemic, similar to the Spanish pandemic of 1918.Treatment:Drug of choiceQ: Oseltamivir (Tamiflu) 75 mg BD x 5 days (contraindicated in infants)
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