Flu overview and Definition

Flu is a respiratory distress that occurs from a viral infection. It mainly focuses the respiratory system which includes nose, throat and lungs.

Structure of Flu

Structure of virus:

The virus belong to the Orthomyxoviridae. The following are the four genera of the virus. They include :

Influenza A

Influenza B

Influenza C

Influenza D

Influenza viruses negative sense, single-stranded RNA genome that is segmented. The negative sense of the genome means it can be used as a template to synthesize  messenger RNA. (mRNA). IAV and IBV have eight genome segments that encode 10 major proteins. ICV and IDV have seven genome segments that encode nine major proteins. Three segments encode three subunits of a RNA dependent RNA polymerase(RdRp) complex: PB1, a transcriptase, PB2, which recognizes 5' caps, and PA (P3 for ICV and IDV), an endonuclease. The matrix protein (M1) and membrane protein (M2) share a segment, as do the non-structural protein (NS1) and the nuclear export protein (NEP). For IAV and IBV, hemagglutinin (HA) and neuraminidase (NA) are encoded on one segment each, whereas ICV and IDV encode a hemagglutinin-esterase fusion (HEF) protein on one segment that merges the functions of HA and NA. The final genome segment encodes the viral nucleoprotein (NP). Influenza viruses also encode various accessory proteins, such as PB1-F2 and PA-X, that are expressed through alternative reading frames and which are important in host defense suppression, virulence, and pathogenicity.

The virus particle, called a virion, is pleomorphic and varies between being filamentous, bacilliform, or spherical in shape. 



Chronic flu is described as an chronic infection which shows inflammation in the pulmonary airway and bronchial hyperresponsiveness to an allergen resulting in asthmatic condition .inflammatory cells are accumulated in respiratory bronchioles.

Physiologically, allergen inhaled results in provocation of the inflammatory system of the respiratory system resulting in increased secreation of inflammatory mediators such as methacalmine and histamine. Release of histamine from the mast cells results in activation of the prostaglandins and leukotrienes.In addition to that cytokines are also released from the mast cells which leads to Increased vascular permeability, mucosal irritation, bronchospasm.

Triggering factors that results in  blockage of the pulmonary airway include flu air, exercise, viral upper respiratory infection, cigarette smoke, and respiratory allergens. Bronchial provocation with allergen induces a prompt early phase immunoglobulin E (IgE)-mediated decrease in bronchial airflow. Initially there is an increase in the leukocyte count in the pulmonary ares with help of CD4+ cells. The activated T-lymphocytes also direct the release of inflammatory mediators from eosinophils, mast cells, and lymphocytes. The cross-linkage of two IgE molecules by allergen causes mast cells to degranulate, releasing histamine, leukotrienes, and other mediators that perpetuate the airway inflammation. Histolopathology of the bronchial airway might shows  an inflammatory infiltrate consisting of neutrophils, mast cells, lymphocytes, macrophages and monocytes.

  • Pneumonia
  • Bronchitis
  • Asthma flare-ups
  • Heart problems
  • Ear infections
  • Acute respiratory distress syndrome


Clinical signs & symptoms


Throat infection

Redness or inflammation around the nose region

Nasal congestion

Post Nasal drip


Itching in eyes, nose and throat


Difficulty breathing, cough.

Swelling of your face, throat or mouth tissue.

Wheezing or difficulty swallowing.

Restlessness and anxiety.

Symptoms of flu:

  • breathing difficulties
  • pain or pressure in the chest or abdomen
  • dizziness, confusion, or loss of alertness
  • seizures
  • not urinating, which may indicate dehydration
  • severe pain, weakness, and unsteadiness
  • a fever or cough that goes away and then comes back
  • a worsening of other existing health conditions

Differential Diagnosis

Chest Xray:

The chest x ray predicts any abnormal area in the lungs

Computed tomography:

It reveals the slice of the lung. It uses both the combination of x ray and computer aided device.

It helps to analyse the size, shape and position of any lung tumour and also it helps in the detection of enlarged lymph nodes.

A nasal endoscopy: It is the instrument where a thin tube with a light source and visualizing unit at one end (endoscope) is inserted up to your nose so the physician can view the internal structure of nose clearly

A nasal inspiratory flow test:

A small device is placed over the mouth and nose to measure the air flow when you inhale the air through the nose.


It is a type of lung function test that measures how hard a person can blow air out of their lungs. It can determine the level of obstruction in the airway. The test is performed using a machine called a spirometer

Polymerase chain reaction:

This test can be used for DNA amplification and to detect the diagnosis.


The immunofluorescence test gives the antigen antibody reaction.



 It might take 1-2 weeks for the flu to get subside.

The flu symptoms might subside within 5-7 days


Stay away from contaminated areas.

Stay away from the triggering factors

If any surgical correction is indicated do it early

Follow healthy lifestyle

Use a vacuum cleaner fitted with a high efficiency particulate air such as HEPA filter- it can remove more dust than ordinary vacuum cleaners.

Wash the hands properly while coming indoors. It might reduces the infection and also the spread.

Follow healthy diet