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Saturday, April 16, 2011

INFLUENZA

Influenza is a specific acute illness caused by a group of myxoviruses. It occurs in epidemics, and occasionally pandemics, often explosive in nature.

Aetiology
There are two common types of virus, A and B. At least four strains of influenza A, which is responsible for pandemics, have been identified. Influenza B is usually associated with smaller and less virulent outbreaks. The immunity follows infection is type-specific and of relatively short duration. This causes problems in providing effective immunisation.
Clinical features
Incubation:  24-48 h
Onset
Sudden pyrexia associated with headache, generalised aches and pains, anorexia, nausea and vomitting
Chest symptoms
cough- harsh and unproductive
Clinical signs
Fauces hyperaemic. Usually no abnormalities on examination of chest
white cell count: leucopenia
Course: When no complications acute symptoms subside within 3-5 days. Post-influenzal asthenia ,may persist for a few weeks.
The disease may spread rapidly throughout a house hold or institution. During epidemics, the diagnosis is usually easy. Most sporadic cases are identifiable only as respiratory viral infections unless the virus is isolated, or demonstrated by the fluorescent antibody technique or if serological tests for specific antibodies are positive.
Complications
The disease may be complicated by trcheitis, bronchitis, bronchiolitis and bronchopneumonia. Secondary bacterial invasion by Strep.Pneumoniae, H.influenzae and occasionally Staph. aureus may also occur.
Toxic cardiomyopathy may cause sudden death especially when there is pre-existing cardiac disease. Encephalitis and post-influenzal demyelinating encephalopathy and peripheral neuropathy are rare complications. Post-influenzal asthenia and depression are common, often marked, and may last for several weeks.
Management
Bed rest is advisable until the fever has subsided. A mild analgesic such as paracetamol 0.5-1 g every 4-6 hours usually relieves the headache and generalised pains. Pholcodine 5-10 mg 3-4 times daily may be used to suppress unproductive cough. Specific treatment of complications such as bronchitis and pneumonia may be necessary.
Prevention
Immunity is type-specific and if the antigenic constitution of a new strain can be detected early a specific vaccine may give about 70% protection. Annual winter vaccination is recommended for patients suffering from chronic pulmonary, cardiac or renal disease.

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