Influenza is the common viral infection, which is commonly called “the flu”. This infection is common to mammals as well as birds. The viruses are all belong to the group orthomyxoviridae. There are three types of influenza viruses. They are type A, B and C. Even though the virology may differ from one infection to the other, general features, symptoms, investigations and diagnosis, treatment, prevention and prognosis go along similar principles.
Virus shedding from an infected individual starts one day before the onset of symptoms. The patient remains infective for four to seven days. Patients are most infective around the third day of virus shedding. Virus shedding runs hand in hand with fever; therefore, the patient is more infective during the bouts of fever than during the afebrile period. The children are more infectious compared to adults. Influenza viruses can spread via droplets or direct contact. En route, the virus is susceptible to sunlight and drying. However, it can survive for a considerable time outside the body in low humidity and shade. Once the virus enters the body, it is thought to inhibit adreno-cortico-trophic hormone and the viral hemagglutinin proteins get cleaved by human proteases. Virulent strains like H5N1 hemagglutinins can be cleaved by a wide variety of proteases thus it spreads slowly, but widely. Production of cytokines is responsible for the clinical features. Patients present with fever, blocked nose, body pain, joint pain, ill health, lack of energy, red eyes, tearing, skin rashes, diarrhea and abdominal pain (especially in children). Common cold and influenza may be indistinguishable during early stages. However, high fever, excessive fatigue, and ill health set influenza apart. (Read more: Difference Between Common Cold and Influenza)
Full blood count may show a response to infection. Viral cultures may be used to confirm the diagnosis if doubts are there. Drinking a lot of fluids, bed rest, and good nutrition are very important to aid recovery. Antivirals are needed only in severe disease. Neuraminidase inhibitors and M2 inhibitors are the most commonly used antiviral drug classes. Prevention of influenza is difficult because of it can spread along many pathways. Good hygiene, hand washing, using separate utensils, and wearing masks may go a long way towards limiting spread. There is a flu vaccine available. It is recommended to healthcare workers, children, elderly, and people with long standing diseases. This vaccine can even be given to HIV/AIDS patients, post-transplant patients, and those who are on immuno-suppressive drugs. Because influenza viruses mutate and change rapidly, vaccination does not confer lifelong immunity. The protection lasts for about two to three years.
Influenza A virus usually lives in aquatic birds. They may get into the domestic animals and cause devastation in poultry or cause human pandemics. Spanish flu, Asian flu, Hong Kong flu, bird flu, and swine flu are a few such examples. General features, investigations, treatment, prevention, and prognosis of influenza A virus infection are similar to other viruses.
Influenza B virus Infects humans almost exclusively and the only other beings susceptible to influenza B infection is the seal and the ferret. It is less common than Influenza A. Influenza B mutates and changes slower than influenza A.
What is the difference between Influenza A and B?
• Influenza A can come from wild birds while influenza B almost always comes from another human being.
• Influenza A is commoner than B.
• The protection conferred by vaccination lasts longer for influenza B than A.
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