Influenza - Symptoms, Diagnosis, Treatment and Prevention

Introduction:

Types A, B, C, and D are the four subtypes of seasonal influenza viruses. The influenza A and B viruses spread and result in yearly illness outbreaks.

• Influenza A Virus: Hemagglutinin (HA) and neuraminidase (NA), two proteins found on the surface of influenza A viruses, are combined to form different subtypes. The influenza viruses of subtypes A (H1N1) and A (H3N2) are now present in humans. The A (H1N1) virus is often referred to as A (H1N1) pdm09 since it started the pandemic in 2009 and then displaced the seasonal A (H1N1) virus that had been in circulation before 2009. The only viruses known to have triggered pandemics are those of influenza type A.

• Influenza B Virus: Although influenza B viruses can be divided into lineages, they are not classified into subtypes. Two lineages of influenza type B viruses are currently in circulation: B/Yamagata and B/Victoria.

• Influenza C Virus: It rarely causes serious infections and is therefore not of significant concern for public health.

• Influenza D Virus: They are known to infect cattle primarily; they are not known to infect or afflict humans.

What Are the Signs and Symptoms of Influenza Virus?

Seasonal flu symptoms include:

1. A quick onset of fever.

2. Sore throat.

3. Runny nose.

4. Headache.

5. Muscle and joint discomfort.

6. Cough that is typically dry.

The cough may be strong and linger for two weeks or more. Most people get through a fever and other symptoms in a week or less without seeing a doctor. Nonetheless, influenza can lead to severe illness or even death, especially in persons already at high risk.

Mild, severe, and even fatal illnesses are all possible. Most hospitalizations and fatalities involve high-risk categories. These yearly epidemics are predicted to cause 290,000 and 650,000 respiratory deaths and three to five million episodes of severe disease globally.

The majority of influenza-related deaths in industrialized nations involve adults 65 and older. High rates of absenteeism from school and decreased productivity can occur from epidemics. At times of increased disease, clinics, and hospitals may become overburdened.

Although the impacts of seasonal influenza epidemics in poor nations are poorly understood, research indicates that these nations account for 99 % of all lower respiratory tract infection-related mortality in children under five.

What Is the Epidemiology of the Influenza Virus?

All age groups are susceptible. However, some are at more risk than others.

Pregnant women, children under 59 months, the elderly, people with chronic medical conditions (such as established cardiac, pulmonary, renal, metabolic, neurodevelopmental, liver, or hematologic diseases), and people with immunosuppressive conditions (such as HIV/AIDS, receiving chemotherapy or steroids, or having cancer) are all at higher risk of developing severe disease or complications when infected.

Due to their frequent contact with patients and the potential for subsequent infection, healthcare professionals are at significant risk of contracting the flu virus.

Seasonal influenza is easily transmitted and spreads quickly in crowded settings, such as nursing homes and schools. Infectious droplets, which can travel up to one meter in the air when an infected person coughs or sneezes, are released into the air and can infect people nearby who breathe them in.

Moreover, hands exposed to influenza viruses might spread the infection. People should often wash their hands and cover their mouths and nose when coughing to stop the spread of germs.

Seasonal epidemics primarily occur in the winter in temperate climate, although influenza may circulate all year round in tropical areas, leading to more sporadic outbreaks. The incubation period, which is the period between an infection and a disease, lasts roughly two days.

How to Diagnose the Influenza Virus?

Clinical diagnosis is used to determine the majority of human influenza cases. However, other respiratory viruses such as rhinovirus, respiratory syncytial virus, parainfluenza, and adenovirus infection can also present as influenza-like illness (ILI) in times of low influenza activity and outside of epidemic situations, making it challenging to distinguish influenza from other pathogens clinically.

Collecting the right respiratory samples and running a laboratory diagnostic test is necessary to ascertain the diagnosis. The crucial first step in the laboratory identification of influenza virus infections is the appropriate collection, storage, and transportation of respiratory specimens. It is usual practice to use direct antigen detection, viral isolation, or reverse transcriptase polymerase chain reaction to detect influenza-specific RNA in secretions from the throat, nose, nasopharynx, tracheal aspirate, or washings (RT-PCR). The WHO regularly updates and publishes several guidelines on laboratory procedures.

The use of rapid diagnostic tests for influenza (RIDTs) in clinical settings is every day. Still, their sensitivity is lower than that of RT-PCR techniques, and their reliability primarily depends on the circumstances in which they are applied.

What Is the Treatment of Influenza Virus?

Patients who do not belong to a high-risk group should receive symptomatic care, and they should be recommended to stay at home if they are symptomatic to reduce the danger of spreading the illness to others in the neighborhood. The goal of treatment is to minimize influenza symptoms like fever. People should monitor themselves to see if their condition worsens and seek medical help.

Antiviral therapy should begin as soon as possible for patients who are known to be in a group at high risk for developing a severe or complicated illness, in addition to symptomatic care.

The antiviral medication should be administered as soon as possible to patients with a severe or worsening clinical illness linked to a suspected or confirmed influenza virus infection (such as clinical syndromes of pneumonia, sepsis, or exacerbation of chronic underlying disorders).

• To maximize treatment advantages, neuraminidase inhibitors, such as Oseltamivir, should be prescribed as soon as feasible (preferably within 48 hours after symptom onset). Those who present later during the illness should also be considered while administering the medication.

• It is advised to continue treatment for a least five days, although this can be done if necessary to achieve good clinical improvement.

• As corticosteroids have been linked to extended viral clearance and immunosuppression that might result in bacterial or fungal superinfection, they should not be used frequently unless suggested for other reasons (such as asthma and other particular illnesses).

• Adamantane antiviral medications (such as Amantadine and Rimantadine) are ineffective as monotherapies against any of the influenza viruses that are currently circulating.

How to Prevent Influenza Virus?

Vaccination is the best method of illness prevention. Safe and reliable vaccines have been in use for more than 60 years. It is advised to get vaccinated annually to prevent influenza because vaccination-induced immunity deteriorates over time. The most widely used influenza vaccinations around the world are inactivated injections.

The influenza vaccine protects healthy adults even when the circulating viruses do not precisely match the vaccine viruses. The influenza vaccination, however, may be less successful in preventing illness in the elderly, but it does lessen the severity of the disease and the likelihood of complications and fatalities. Vaccination is crucial for those who live with or care for those at high risk for influenza complications.

Conclusion:

The development of influenza vaccines and antiviral drugs to prevent and treat influenza has made significant progress, and procedures are in place to provide early warning for the emergence of pandemic viruses.