- An acute infectious respiratory disease, caused by i. viruses, which are in the family Orthomyxoviridae, in which the inhaled virus attacks the respiratory epithelial cells of susceptible persons and produces a catarrhal inflammation; characterized by sudden onset, chills, fever of short duration (3–4 days), severe prostration, headache, muscle aches, and a cough that usually is dry and may be followed by secondary bacterial infections that can last up to 10 days. The disease commonly occurs in epidemics, sometimes in pandemics, which develop quickly and spread rapidly; mortality rate is usually low, but may be high in cases with secondary bacterial pneumonia, particularly in the elderly and those with underlying debilitating diseases; strain-specific immunity develops, but mutations in the virus are frequent, and the immunity usually does not affect antigenically different strains. SYN: flu, grip (1), grippe. [It. influence (of planets or stars), fr. L. influentia, fr. in-fluo, to flow in]- i. A the most common type of i.. These strains have a high propensity for antigenic change resulting in mutations, partly because they can infect various animals where dual infections can occur, giving rise to new hybrid strains. The infections occur in epidemics, which may occur every 2–3 years and which vary in size and severity; perhaps the most important of the three types of i. (A, B, and C).- Asian i. a worldwide i., apparently originating in China in the summer of 1957, which produces a milder disease than that of the pandemic of 1917–1919.- i. B i. caused by strains of i. virus type B; outbreaks are usually more limited than those due to i. virus type A, although infections by the two types are clinically indistinguishable; occasionally associated with Reye syndrome.- i. C i. caused by strains of type C i. virus; the disease is milder than that caused by types A and B and has become uncommon in recent years.- endemic i. i., usually of a less severe type, occurring with some degree of regularity during the winter season, especially in the larger cities of the world. SYN: i. nostras.- Hong Kong i. i. caused by a serotype of i. virus type A and first identified in Hong Kong in 1968.- i. nostras SYN: endemic i..- Russian i. a pandemic of a strain i. A virus thought to have originated in Russia; occurred in 1978.- Spanish i. i. that caused several waves of pandemic in 1918–1919, resulting in more than 20 million deaths worldwide; it was particularly severe in Spain (hence the name), but now is thought to have originated in the U.S. as a form of swine i..- swine i. an acute respiratory disease of swine caused by strains of i. virus type A; it is believed to have become adapted to swine in the United States during the great human pandemic in 1918; fatal cases, as in such cases of pandemic i. in humans, are commonly associated with secondary bacterial pneumonia.
* * *in·flu·en·za .in-(.)flü-'en-zə n1 a) any of several acute highly contagious respiratory diseases caused by strains of three major orthomyxoviruses now considered to comprise three species assigned to three separate genera: (1) influenza A (2) influenza B (3) influenza Cb) any human respiratory infection of undetermined cause not used technically2) any of numerous febrile usu. virus diseases of domestic animals (as shipping fever of horses) marked by respiratory symptoms, inflammation of mucous membranes, and often systemic involvementin·flu·en·zal -zəl adj
* * *n.a highly contagious virus infection that affects the respiratory system. The viruses are transmitted by coughing and sneezing. Symptoms commence after an incubation period of 1-4 days and include headache, fever, loss of appetite, weakness, and general aches and pains. They may continue for about a week. With bed rest and aspirin most patients recover, but a few may go on to develop pneumonia, either a primary influenzal viral pneumonia or a secondary bacterial pneumonia. Either of these may lead to death from haemorrhage within the lungs. The main bacterial organisms responsible for secondary infection are Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus, against which appropriate antibiotic therapy must be given. An influenzal infection provides later protection only against the specific strain of virus concerned; the same holds true for immunization.
* * *in·flu·en·za (in″floo-enґzə) [Ital., from L. influentia influence, from the belief that the stars influenced epidemics] an acute viral infection of the respiratory tract that may occur in isolated cases, in epidemics, or in pandemics; causative viruses are classified in genera Influenzavirus A, Influenzavirus B, and Influenzavirus C. Influenza usually has a 3-day incubation period and lasts for 3 to 10 days. It is marked by inflammation of the nasal mucosa, pharynx, and conjunctiva; headache; myalgia; often fever, chills, and prostration; and occasionally involvement of the myocardium or central nervous system. Necrotizing bronchitis and interstitial pneumonia may occur in severe cases, opening the way for secondary bacterial pneumonia due to Streptococcus pneumoniae, Haemophilus influenzae, or Staphylococcus aureus. Called also flu and grippe. influenzal adj
Medical dictionary. 2011.