Flu still kills up to 650,000 people in a typical year
Influenza is viral respiratory illness ranging from mild aches to severe pneumonia. Four virus types—A, B, C, and D—occupy separate Orthomyxoviridae genera; aquatic birds seed influenza A that also infects mammals. Hand washing, masks, and yearly vaccines cut risk while seasons still sicken five to fifteen percent of people.
Global tallies count three to five million severe cases and as many as 650,000 respiratory deaths yearly, hitting the very young, elderly, and chronically ill hardest. Fever, sore throat, aching muscles, headache, cough and exhaustion typically begin about two days after exposure, within a one-to-four-day window, and last two to eight days; children may also vomit or have diarrhoea. Upper-airway illness can descend into viral or secondary bacterial pneumonia, and rarer complications include meningitis, encephalitis and acute respiratory distress.
Type A drives most severe disease, seasonal epidemics, and pandemics. Its subtypes are named after two surface proteins, haemagglutinin and neuraminidase, so H1N1 carries the first version of each. Type B, mostly human, splits into Victoria and Yamagata lineages instead of subtypes; C mainly causes mild or silent infections in children; D lives naturally in cattle but has turned up in pigs, horses, camels, goats and people.
Each virus carries a segmented genome of negative-sense single-stranded RNA: eight segments encoding ten main proteins in A and B, seven segments and nine proteins in C and D. Particles range from spheres to long filaments. Laboratories label every isolate with a formal code naming genus, host animal, place, lab number, year and, for A, its H and N types, as in an H5N1 strain taken from a chicken in Thailand.
Because type A mutates quickly, millions of samples are analysed each year and vaccines are reformulated, typically covering H1N1, H3N2 and one or two B strains. Diagnosis relies on antigen, antibody or PCR tests, and severe cases may get antivirals such as oseltamivir; in healthy people the illness usually resolves on its own.
Source: Influenza
