Influenza

Influenza

The flu virus is negative-sense single-strand RNA virus belonged to family orthomyxoviridae which contains seven genera, four of them cause influenza in vertebrates (influenza A, influenza  B, influenza C, influenza D).Influenza A contains H5N1 and which called avian influenza and H1N1 which called swine influenza that affects human, birds and some other mammals. Influenza A

 is the cause of all human influenza outbreaks. Influenza B and C also infect humans.

Influenza virus contains two types of receptors on its surface the hemagglutinin (HA) and neuraminidase (NA) so it takes symbols H and N. Influenza A contains hemagglutinin antigen varies from H1 till H16 and neuraminidase antigen vary from N1 till N9.

Influenza hemagglutinin and neuraminidase:

The hemagglutinin (HA) and neuraminidase (NA)  are influenza glycoproteins present in envelop and attache to sialic acid receptors in RBS (Red Blood Cells) and other cells .The viral infection starts with attachment of influenza receptors hemagglutinin (HA) and neuraminidase (NA) with sialic acid receptors on the target cells in tropism areas .and then the virus starts replication .

Hemagglutinin (HA) and neuraminidase (NA)  receptors are the site of antibodies interaction with influenza virus . After the immune system releases antibodies ,these antibodies block influenza receptors( hemagglutinin (HA) and neuraminidase (NA)) to stop infection of the cells .

Influenza type A vaccine induce antibodies against  hemagglutinin ,however it is found that neuraminidase  may be important target .

Hemagglutination test :

Hemagglutination is a test used for diagnosis of some viruses which have envelope .This test used in influenza diagnosis depending on hemagglutinin  antigen in influenza and sialic acid receptors in RBCs.

Influenza or flu symptoms:

Flu symptoms range from mild to severe cases. They mainly respiratory signs including cough, runny nose sore throat but other signs appear also as headaches, fatigue, body aches, fever( sometimes) and may some cases suffer from vomiting and diarrhea in case of gastroenteritis which some people called stomach flu and that is not true. Flu symptoms may take one or two weeks till recovery.

Severe influenza:

In some cases, complications can happen due to extreme inflammatory response or secondary bacterial infection that may reach to pneumonia .Other complications like inflammatory actions in heart muscles and respiratory and renal failure. In chronic cases, asthma and chronic cardiac disease occur.

How does influenza transmit?

The flue is a contagious disease. It transmits by migratory birds, life birds markets or from man to man when does not use a tissue during cough or sneezing and spreads aerosols in the air and it can infect people who stand in a short distance.Also by touching infected places then touch your mucous membranes ( eye, mouth even nose).

The WHO classified the outbreak into steps:

1-Animal infection with the virus.

2-Infection transmit from animal to human.

3-Infection spread between people.

4-Spreading of the outbreak in the whole world.

Influenza outbreaks:

Because the influenza virus is single-strand RNA virus, mutation and changes happen continuously causing outbreaks and transmission from other species to humans. In 1918 sever influenza outbreak ( Spanish flu outbreak ) happened because of avian influenza H1N1and it speeded widely and cause about fifty million death cases worldwide.

In 1957 new flu viruses appeared in Asia causing the Asian influenza outbreak. The first time where H2N2 virus appeared was in Singapore than in Hong Cong. The number of people who died in this outbreak estimated at 1.1 million in the whole world.

In 1968 H3N2 influenza virus appeared and caused by mutation of avian influenza causing H3. Its first appearance was in the USA on 9/1968. The number of people who died in this outbreak estimated with one million in the whole world most of them were sixty-five years old and over sixty-five.

In 2009 another type of influenza appeared(H1N1)pdm09 but it was different from type appeared in 1918 and not sever as H1N1 .firstly, it appeared in the USA then spread to other countries. Scientists found that the seasonal influenza vaccine could make little immunization against (H1N1) pdm09.

Avian influenza virus H5N1:

H5N1 is a very infective strain and is predicted to cause an outbreak in the future. The number of cases estimated with 861 cases from 2003 till now. The H5N1 virus caused many outbreaks in birds .these outbreaks estimated with 15000 worldwide or more. These outbreaks occur seasonally mostly from Jan to March. Low temperature is a good environment for this virus .it can stay in cold water for a long period. Some studies suggested that outbreaks related to the winter migration of birds.

People at risk:

Old people sixty-five years and more.

People have chronic diseases

Pregnant women and children less than five years old.

Influenza vaccine:

Because of continuous mutation and antigenic draft, influenza vaccine should be reviewed annually .Any minor change in influenza gen can affect the vaccine strength .Many studies showed that influenza vaccine has a good effect in reducing pneumonia and number of dead elderly people during outbreaks if influenza vaccine is the same or similar to the outbreak strain.

Flu treatment:

Antiviral drugs are very important to avoid severe complications. Some studies that made on oral oseltamivir proved that it has limited efficacy against H5N1 but it decreased the death rate from 90% to 60%.

Flu prevention:

Take the seasonal flu vaccine

Wash your hand s

Avoid contacting with ill people.

If you feel sick stay at home, during sneezing and coughing put a tissue on your mouth and nose.

Some diseases have symptoms similar to influenza as common cold and COVID-19.

If you are interested in microbiology courses you can start with this course Microbiology for beginners