Amirabad Pathobiology and Virology Laboratory


Everything about the Influenza virus!

Date: 3 سال قبل

author: AmirAbad

The influenza viruses are characterized by segmented  RNA genomes requiring an RNA-dependent RNA polymerase of viral origin for replication. The particular structure of the influenza virus genome and function of its viral proteins enable antigenic drift and antigenic shift. Influenza virus is in the virus family Orthomyxoviridae.
The Influenza A and B consists of eight segments of linear , single-stranded RNA. The multipartite genome is encapsidated, each segment in a separate nucleocapsid, and the nucleocapsids are surrounded by one envelope.
Influenza A and B are major causes of respiratory infection.
Influenza A viruses are classified into many subtypes based on specific proteins on the surface of the virus. As influenza viruses circulate, they undergo genetic changes that can affect their infectiousness and severity.
Influenza C and influenza D viruses have only seven RNA segments and do not seem to cause substantial disease in humans. However, influenza C virus infections can cause influenza-like illness and hospitalizations in some instances, especially in children. Influenza D viruses mainly affect cattle and do not seem to infect humans.
What Is Influenza?
Influenza is a respiratory disease caused by infection with the influenza type A, B, C or D virus. Influenza viruses are spread among people primarily through airborne droplets released when you talk, cough, or sneeze.
Influenza A and influenza B are the only types of influenza that can cause seasonal flu epidemics.
The flu is a common disease that is believed to affect around 8% of people in any given year. Flu viruses tend to spread more frequently during colder months and can lead to local seasonal epidemics.
Flu symptoms can range from mild to severe, and they vary from person to person.
Common symptoms of the flu include:
·       fatigue
·       nasal congestion
·       a cough
·       headaches
·       a sore throat
·       body aches
·       chills
·       a fever
·       vomiting or diarrhea, which are more common in children
Some people experience severe symptoms, which can include:
·       chest pain
·       shortness of breath
·       severe pain
·       severe weakness
·       a high fever
·       seizures
·       severe dizziness
·       loss of consciousness
A person who experiences any severe symptom should receive medical attention.
For most people, flu symptoms are mild and short-lived. In others, though, the flu can cause life-threatening complications. Children, older adults, pregnant women, and people with certain coexisting medical problems are at a higher risk of serious complications from an influenza virus infection.
According to researchersTrusted Source, influenza A viruses are responsible for about 75% of confirmed flu cases, while influenza B viruses are behind approximately 25% of confirmed cases.
For a person who is generally healthy, the flu is not typically dangerous. However, it can severely affect certain groups of people, who should seek medical attention as soon as they suspect that they have flu symptoms.
Those most at riskTrusted Source of developing flu complications include:
·       women who are pregnant
·       people with certain chronic medical conditions
·       children younger than 5
·       adults aged 65 or over
Many people believe that influenza A is more severe than influenza B. However, this is not always the case.
The following can help prevent a person from catching or spreading the flu:
·       limiting contact with sick people
·       staying home when ill
·       covering the nose and mouth when sneezing or coughing
·       washing the hands often
·       disinfecting surfaces that may contain flu germs
·       avoid touching the eyes, nose, and mouth
·       wearing a mask when leaving the house
·       The best method of prevention is to receive a flu vaccination every year. The flu vaccine can come as an injection or a nasal spray.
According to a 2017 studyTrusted Source, the vaccine may reduce the risk of in-hospital deaths from the flu, prevent associated intensive care unit hospitalization, and reduce the duration of related hospital stays.
A flu vaccine is developed every year based on the strains of influenza viruses that are expected to be circulating most widely in the colder months. Vaccination can reduce the impact of the flu but is not 100% effective. As a result, diagnosis and treatment of influenza can be important for many people.
Types of Influenza Tests
The first step in diagnosing influenza is almost always a physical examination that includes a review of any active flu-like symptoms. During seasonal flu epidemics, additional testing beyond a physical exam may not be needed to diagnose influenza.
When other tests are needed, they focus on identifying signs of an influenza infection. There are several different tests that can check for the presence of an influenza virus. The choice of which test to prescribe depends on the purpose of testing, how quickly results are needed, test availability, and laboratory capabilities.
Antigen test: Antigen tests use a sample from the respiratory tract and look for antigens of an influenza virus. Antigens exist on the surface of the virus and trigger an immune response. The presence of influenza antigens can be an indication of an active flu infection.
Molecular flu test: Molecular flu tests look for traces of genetic material, or DNA, from the influenza virus in a sample from your respiratory tract. These may also be called nucleic acid amplification tests (NAATs) or referred to by a specific laboratory method, such as reverse transcription polymerase chain reaction, (RT-PCR).
Serology test: Serology tests look for antibodies to influenza viruses in a blood sample. Antibodies are developed as part of the immune system’s reaction to a viral infection. It can take time for antibodies to form, though, so serology tests are used to identify a prior infection.

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