How long you are contagious with flu?

What makes flu an important public health problem is that it is a highly contagious disease, which can spread rapidly to take the shape of an epidemic or a pandemic, taking a heavy toll on human lives and economic productivity.

Flu or influenza is an acute respiratory illness caused by influenza viruses of three types- A, B and C, members of orthomyxoviridae family. It is a disease that is very common in the winter. Localized outbreaks or even global pandemics occur at variable intervals. A person with the disorder presents gradually with respiratory symptoms such as cough, sore throat and associated systemic features like fever, headache, chills, myalgia and malaise.

SOURCE OF INFECTION-

Source of infection is a person who is acutely infected with the virus. The virus is shed in the respiratory secretions of acutely infected individuals. A person who comes in contact with these secretions by any means gets infected. A person remains the source of infection as long as he keeps shedding the virus from his body primarily through his secretions.

MODES OF TRANSMISSION-

Influenza can spread in various ways from a person to another. The virus is transmitted mainly via aerosols generated during coughing or sneezing. Also hand-to-hand contact, other personal contact and even by common use of towels, handkerchiefs, toys and other inanimate objects transmission may take place. Coming in contact with contaminated surfaces like door handles is also another mode of transmission.

PERIOD OF INFECTIVITY AND COMMUNICABILITY-

The virus enters our body through the respiratory tract when the virus gets deposited on the respiratory epithelium. The virus infects the ciliated columnar epithelial cells and other nearby cells. Here they replicate within 4-6 hours and the viral progeny are released to infect other adjacent cells. The incubation period ranges from 1-3 days depending on the number of virus entered the body. The virus after multiplying is shed through the nasal secretions and in form of aerosols. Another individual who inhales these aerosolized virus particles or come in contact with the secretions get infected and by this way the virus spreads. So, a person remains contagious starting from day before the onset of symptoms until the virus shedding stops, generally 2-5 days after symptoms first appear.

The host immune system tries to put a check to the infection and induces inflammation and influx of leukocytes takes place. Interferon and cytokines are released that are responsible for the systemic features associated with influenza. The host response dominates and puts an end to the infection. This renders the person non-infective as virus shedding stops in 2-5 days.

ROLE OF ANTIVIRAL DRUGS IN REDUCING INFECTIVITY AND COMMUNICABILITY-

Treatment with antiviral drugs (oseltamivir and zanamivir) has been shown to reduce the severity and chances of developing complications only if taken within 48 hours of appearance of symptoms. These drugs act on the neuraminidase antigens and inhibit them, (Neuraminidase antigens on the virus surface are enzymes that help release of virus progenies from the cells and helps in the spread of the virus). As less viral particles are released in cough and sneezes, the chance of infecting others is also less. Oseltamivir and zanamivir are also used for chemoprophylaxis against flu as these drugs protect against being infected by flu virus during outbreaks.

PERSISTENCE OF INFECTIVITY-

In some cases, the infection remains active for longer periods in the body as in cases of immune-compromised individuals. The same holds good for those who suffer from primary influenza virus pneumonia. In such cases, virus shedding continues for longer periods as effective immune response cannot be initiated against the virus.

REDUCING CHANCES OF BEING INFECTED-

If you are infected by the flu virus and suffering from the disease, it is better that you avoid going places and meeting people and thus stop yourself being a source of infection to others. Washing your hands every time you cough or sneeze or handle your nasal secretions is another effective method to contain spread. Use of disinfectants is another option. Encouraging persons suffering from the disease to cover their face while sneezing and coughing is very helpful. Vaccination provides immunity against the virus and reduces the chances of getting infected only for a year's time as every year the virus undergoes mutation and renders the vaccine useless, making vaccination every year necessary. One needs to take these preventive measures to prevent the spread of the disease to other people around.

Also published by me at Helium under pen name Dev Senapati.