Orthomyxoviridae

Today’s post is about the flu. Orthomyxovirus gets its name from the Greek word ‘myxo’ which means mucus. In Orthomyxoviridae, there are 5 genera. But I would talk about the taxonomy of flu and more specifically on Influenza A. But I will first give a brief introduction on influenza.

Influenza virus types A and B are both common causes of acute respiratory illnesses. Both virus types may cause epidemics of considerable morbidity and mortality but influenza B infections are often limited to localized outbreaks whereas influenza A viruses are the principal cause of larger epidemics including worldwide pandemics. Influenza can be contracted throughout the year in tropical regions and its contribution to overall morbidity and mortality is less well defined. Orthomyxoviridae is typically spherical, enveloped and can appear in many forms. It is a single stranded RNA in 8 segments.

Influenza A viruses are further classified, based on the viral surface proteins hemagglutinin(HA or H) and neuraminidase(NA or N). Sixteen H subtypes (or serotypes) and nine N subtypes of influenza A virus have been identified.

Diagram of influenza nomenclature

http://www.ipedia.net/information/Orthomyxoviridae

Further variation exists; thus, specific influenza strain isolates are identified by a standard nomenclature specifying virus type, geographical location where first isolated, sequential number of isolation, year of isolation, and HA and NA subtype. Some examples are (A/Moscow/10/99) and (B/Hong Kong/330/2001)

The type A viruses are the most virulent human pathogens among the three influenza types and causes the most severe disease. The serotypes that have been confirmed in humans, ordered by the number of known human pandemic deaths, are H1N1, H2N2, H3N2, H5N1 and H7N7 just to name a few. Below is a chart on the latest flu pandemics.

Chart on latest flu pandemics

Name of pandemic	Date	Deaths	Subtype involved
Asiatic(Russian) Flu	1889-90	1 million	possibly H2N2
Spanish Flu	1918-20	40 million	H1N1
Asian Flu	1957-58	1 to 1.5 million	H2N2
Hong Kong Flu	1968-69	0.75 to 1 million	H3N2

Elderly and premmies are more immunocompromise, therefore they are more likely to get infected with influenza. Similar to rhinovirus, influenza occurs throughout the year. It has short incubation period of 1-4 days. There are few serotypes circulating simultaneously like rhinovirus. Take flu vaccine or antiviral medicines as treatment for influenza. Most importantly is drinking lots of water and have plenty of rest.

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This video is about the influenza virus H5N1 pandemic. It serves as a warning to people that H5N1 is not a small matter as many people have died due to this avian influenza. It also tells us the measures to take.