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Influenza Viral Infection: Pathology, Clinical Presentations, Complications, Diagnosis, Prognosis And Treatment

Updated on March 25, 2014

Respiratory Tract Limitation Due To Flue VIrus


A General Overview Of Influenza Viral Infection

Influenza is a common viral disease which presents as an acute febrile illness. It is caused by three groups of myxoviruses, important among them being influenza virus A, B and C which are antigenically different. Influenza has occurred in pandemics on several occasions. During these pandemics, the antigenicity of the causative organisms has changed due to the development of new mutants. Influenza A, B and C consists of at least four subgroups each. The virus is spherical (80 to 120 nm in diameter) or filamentous in shape. Influenza A is involved in the pandemics. During epidemics, children and the elderly suffer more. Crowding together of people aids in the dissemination of the virus. Infection is through the respiratory tract.

Pathology: The virus multiplies in cells limiting the respiratory tract including the ciliated epithelium, alveolar cells, mucous gland cells and macrophages. The infected cells show degenerative changes like cytoplasmic granulation, vacuolation and swelling. Ultimately, the cells undergo necrosis and they slough away. The mucosa is hyperermic and edematous. Focal hemorrhages are common in these sites. Pneumonia may occur primarily due to viral infection, though it is more common to get secondary bacterial pneumonia. In viral pneumonia, the alveolar septa are thickened and intra-alveolar hemorrhage may occur. Secondary bacterial infection is common and it gives rise to suppurative inflammation.

Secondary Bacterial Infection Complicating Flu


Clinical Manifestations Of Influenza Viral Infection

The incubation period ranges from a few to 48 hours. Onset is sudden with fever, severe generalized myalgia and prostration. There is spasmodic non-productive cough. Conjunctiva is infected. Temperature varies from 380 to 400C and may last for 3 to 4 days. In the uncomplicated case, there is relative bradycardia. Severe complications may occur in few, especially at the extremes of age and in debilitrated subjects.


  1. Pulmonary complications: These include primary influenza virus pneumonia, influenza pneumonia with secondary bacterial infections, and bacterial pneumonia with multiple organisms.
  2. Primary influenza virus pneumonia: This is a serious condition associated with high mortality. These subjects present with high fever, cough with blood stained expectoration, dyspnea and cyanosis. Examination of the chest may reveal bilateral rhonchi and crepitations. Pulmonary involvement is diffused. Fever and respiratory signs persist despite antibiotic therapy and other symptomatic measures. The course is more acute and serous in those cases with rheumatic heart disease, myocardial infarction or chronic obstructive airway disease.
  3. Influenza pneumonia with secondary bacterial infection: In addition to viral pneumonia, localized consolidation may also develop.
  4. Bacterial pneumonia: This condition is caused by multiple organisms such as staphylococci, H. influenza, group A streptococci, and pneumococci. This type of pneumonia carries a grave prognosis.
  5. Cardiac complications: Toxic myocarditis may occur. This gives rise to tachycardia and cardiac failure. The ECG may be abnormal.
  6. Neurological complications: These include febrile convulsions, meningitis, meningo-encephalitis and encephalitis.

Pneumonia Is A Pulmonary Complication Of Flu


Diagnosis And treatment Of Influenza Viral Infection


The diagnosis is not difficult during an epidermic. Coryza may be mistaken for a mild attack of influenza. Nasal symptoms predominate in coryza but are less marked in influenza. Adenovirus infection, which may resemble influenza, can be diagnosed by the prominence of sore throat and pharyngitis. Primary atypical pneumonia has to be differentiated from influenza virus pneumonia. In primary atypical pneumonia, the sputum is more purulent. It is of gradual onset and the clinical course is milder.

Streptococcal pharyngitis may present at a short duration of fever with sore throat. Its incidence is higher in children. Cervical adenitis is higher in children. Cervical adenitis is present and blood shows neutrophil leucocytosis. The severe pain and bodyache of influenza may be mistaken for dengue fever and sandfly fever. Specific diagnosis can be made by isolating the virus from throat washings or sputum and by demonstration of rise in titers of antibodies in paired sera.

Prognosis: The disease runs a benign course without complication in the majority of cases. Uncomplicated cases recover within a week or two. Complications increased the mortality. In may cases, convalescence may be prolonged. Generalised vague ill health may persist for several weeks.


There is no specific curative treatment. Bed rest is essential during the period of illness and during convalescence. If there is secondary bacterial infection, a course of ampicillin should be given. Viral pneumonia has to be managed with intensive respiratory care. When meningitis or encephalitis occurs, corticosteroids may be indicated.

Specific prevention: Vaccines containing inactivated or live virus are available for use during pandemics or epidemics and these offer 90% protection. Since the viral characteristics change from time to time, the composition of the vaccine has also to be different at times. The general direction for the vaccine is given by WHO, taking into consideration the most prevalent viral strains. Usually, the vaccines contain A and B strains. One dose in previously exposed individuals and two doses in unprimed subjects give a 90% protection rate. Mild local and general side effects may occur in a few. Sensitivity to egg protein is a contraindication for the vaccine. Pregnancy is not a contraindication. Amantadine in a dose of 100 mg given twice daily for 10 to 14 days offers chemoprophylaxis.

© 2014 Funom Theophilus Makama


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