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Medical Terminology for Understanding the Flu

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Influenza-Related Medical Terminology

Influenza-related medical terminology is terms pertaining to various aspects of the flu. Some of the terms pertain to the flu virus itself, including how it is categorized and transmitted. Others pertain to the illness, including its complications, its treatment and its prevention. Most of the terms relate to microbiology and infectious diseases in general.  But they are relevant to influenza as well.  
Medical Terms Re: Flu


Antigenic drift – Is gradual relatively minor changes in the HA and/or NA surface proteins of an influenza virus. It is thethe flu result of a point mutation that occurs as the virus replicates. This phenomenon will allow a virus to drift from an initial appearance years previously and still cause infection several years later. Much of the population has immune protection from prior strains of a virus, but not new ones with subtle changes in the HA and NA proteins resulting from the drift. The drift can also account for the recurrence of disease by a subtype of the virus which had stopped causing disease but resumed after forming a new strain as a result of this process. It is responsible for seasonal outbreaks and epidemics. Also it is the reason for the need to update the flu vaccine seasonally.

Antigenic shift – Is the sudden emergence of a new virus subtype that results from the mixing or reassortment of the antigenic shiftgenetic material between two or more different strains or subtypes of viruses infecting the same cell of a host organism. The influenza virus is a well-recognized example but it does occur with some other viruses. It only occurs with the type A influenza virus though, because it is the only type that doesn’t infect just humans. The result is a change in the structure of the surface HA and NA antigens. The new virus will be able to infect human cells because the immune system does not recognize those new antigens which it has never encountered. The result can be a pandemic as was the case with the appearance of the Asian flu more than 40 years ago.

Centers for Disease Control (CDC) – Is the agency of the U.S. government which tracks and investigates public health trends. Its stated mission is “to promote health and quality of life by preventing and controlling disease, injury and disability.”

Complication – Is a disease or injury that develops or worsens as a result of another disease or treatment of that disease. From this vantage point influenza is the other disease.

Epidemic – Is the unusually high incidence of a disease in an area or population. It differs from a pandemic in that even though the disease outbreak is greater than expected based on past experience, it is limited to a particular region. Additionally, the CDC relates it to the number of deaths per week it causes.

Flu-like symptoms – Are many of the symptoms typically seen with the flu that are present with conditions other than the flu. Some of those conditions are the result of infection caused by pathogens other than the flu virus. Others are conditions not caused by infection at all.

Hemagglutinin (HA) – Is the protein on the surface of the influenza virus that plays an important role in its attachment to and entry into a host cell. It is the main immunogen in the influenza vaccine.

Host range – Is the species that a virus will infect.

Mutation – Is a change in the genetic code of an organism. – Mutate – v. – Mutant – adj.

Neuraminidase (NA) – Is the protein on the surface of the influenza virus which contains an enzyme that cleaves newly formed viruses from the host cell.  That action promotes their release to infect other epithelial cells of the respiratory tract.

Neuraminidase inhibitor – Is an FDA approved class of antiviral drug used to prevent and treat uncomplicated influenza.

Pandemic ­– It is a global epidemic involving more than one continent.  It is the result of the emergence of a new strain of flu virus which has never infected people before.

Recombination – Is the process of shuffling or rearrangement of genetic code, resulting in new combinations of genes. Another name for it is re-assortment.

Natural reservoir – Is an organism in which a virus or other pathogen normally lives and multiplies. It does not experience infection or injury. But it is a source of infection of a different organism(s).

Self-limited – The reference to a definite and limited course of a disease not usually affected by treatment.

Species – Is a classification category of naturally existing organisms with certain similarities, usually including interbreeding only among themselves.

Strain – Is a more specific type or subtype of a virus which takes into account any mutation which has occurred since its initial identification. For the influenza A virus it is a subcategory of a subtype. It is not the same as a subtype of the influenza A virus, although some use the term that way.



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