Etiology. Influenza viruses are single-stranded negative sense RNA viruses of the family Orthomyxoviridae. Three types (A, B, and C) of influenza viruses infect humans. Type A and B viruses are known to cause significant human disease. The genome contains eight gene segments that code for 11 proteins, including the two main surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA). Type A viruses are further classified into subtypes based on their HA and NA proteins. Currently circulating human influenza A subtypes include A (H1N1) and A (H3N2) viruses. Human influenza viruses bind to and replicate primarily in epithelial cells of the upper respiratory tract.
Clinical picture. 
The incubation period lasts 1-2 days with variationsfrom a few hours to 3 days.Influenza can be mild, moderate and severe. The disease can havea typical or atypical clinical manifestations.
A typical influenza begins acutely with elevation of body temperatureand chilliness. In 4-5 hours the body temperature can be ashigh as 38.7-40 °C. If the disease is mild, the body temperature can besubfebrile. The condition of the patient worsens. He complains ofheadache, mostly frontal and retro-ocular, which is accentuated bythe movement of the eyes, pain in the muscles and bones, insomnia,cough, nasal obstruction, dry throat, sneezing, sweating, andweakness.
Examination reveals hyperaemic face and neck, and injectedscleral vessels. There are also tachypnoea and arterial hypotension;the heart sounds are dull; the pulse is slow (disagrees with bodytemperature). Nosebleed is possible. Among the respiratory symptomsare catarrh of the upper airways: stuffy nose, sneezing, hoarsevoice, dry cough. The fauces are hyperaemic, the tongue is coated.
Cough can persist in the young for 10-12 days, and in the elderly forlonger time. The influenza virus and its toxins affect the peripheralnervous system and bone marrow, which is manifested by neuralgia,neuritis and symptoms of encephalitis.
If influenza is not aggravated by complications, fever persists for2-4 days, less frequently 5 days, or it may be as short as 1 day.
A severe (toxic) form of influenza is characterized by markedsymptoms of toxaemia: severe headache, hyperpyrexia (to 40 °C),dyspnoea, cyanosis, hypotension, weak and fast pulse, insomnia orsomnolence, sometimes delirium, nausea, vomiting, loss of consciousness,muscular cramping, symptoms of meningitis; haemorrhages inthe skin can develop. Severe forms of influenza usually occur duringthe first two weeks of an epidemic.
Influenza is characterized by specific leucopenia with relativelymphocytosis and a neutrophilic shift to the left, and aneosinophilia.

by col3neg

published Date 2017-03-21