Flu
Influenza
Influenza (or as it is commonly known, the flu or the grippe) is a contagious disease, caused by an RNA virus of the orthomyxoviridae family. It rapidly spreads around the world in seasonal epidemics. The name comes from the old medical belief that unfavourable astrological influences cause the disease.

Types

There are three types of the virus, identified by antigenic differences in their nucleoprotein and matrix protein:

Influenza A viruses that infect mammals and birds

Influenza B viruses that infect only humans

Influenza C viruses that infect only humans

The A type of influenza virus is the type most likely to cause epidemics and pandemics. This is because the influenza A virus can undergo antigenic shift and present a new, immune target to susceptible people. Populations tend to have more resistance to influenza B and C, because they only undergo antigenic drift, and have more similarity with previous strains.

The term superflu is used to refer to a strain of flu that spreads unusually quickly, is unusually virulent, or is for which the host is uncommonly unresponsive to treatment. Thus, there is a tendency to apply the term to strains which cause epidemics or pandemics. There is no exact scientific definition of a superflu.

Symptoms

The virus attacks the respiratory tract, is transmitted from person to person by saliva droplets expelled by coughing, and causes the following symptoms:

Fever
Headache
Tiredness (can be extreme)
Dry cough
Sore throat
Nasal congestion
Sneezing
Irritated eyes
Body aches
Extreme coldness
Fatigue

Flu season
Influenza reaches peak prevalence in winter, and because the Northern and Southern Hemisphere have winter at different times of the year, there are actually two flu seasons each year. Hope-Simpson (1981) observed that influenza outbreaks are globally ubiquitous, and consistently occur six months following the time of maximum solar radiation in an area. Therefore, the World Health Organization makes two vaccine formulations every year; one for the Northern, and one for the Southern Hemisphere.

While most influenza outbreaks in the Northern Hemisphere tend to peak in January or February, not all do. For example, the influenza pandemic of 1918 and 1919 reached peak virulence during late spring and summer worldwide, and not until October in the US. It remains unclear why outbreaks of the flu occur seasonally rather than uniformly throughout the year. One possible explanation is that, because people are indoors more often during the winter, they are in close contact more often, and this is enough to trigger the outbreak. Another is that the cold weakens the immune system; however, the virus is contracted in a warm indoor environment in which it can thrive.

Prevention
It is possible to get vaccinated against influenza. However, due to the high mutability of the virus, a particular flu vaccine formulation usually only works for about a year. The World Health Organization co-ordinates the contents of the vaccine each year, to contain the most likely strains of the virus which probably will attack the next year. The flu vaccine is usually recommended for anyone in a high-risk group, who would be likely to suffer complications from influenza.

Treatment
Antiviral treatments that have proven effective in influenza are amantadine, rimantadine, zanamivir, oseltamivir and ribavirin. As most of these substances are expensive, various healthcare organisations and insurers only support their use where this would make a significant difference, e.g. in the elderly.

A trademarked elderberry extract may aid in shortening the duration of an episode of influenza once contracted, though it has no notable preventive effects (Zakay-Rones et al 1995).

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