What Types Of Diseases Does The Common Cold Cause
  Having a full understanding of influenza will lead to an eventual appreciation of what types of diseases does the common cold cause. There are several reasons why Influenza A is such a terrible disease. The primary reason that the flu virus is such a formidable agent lies in the virus core, which controls the virus’s heredity and determines its characteristics and behavior. In most cold viruses, and in most living cells as well, the hereditary core is a continuous strand of compounds whose sequence never changes. Such conventional packages reproduce copies of themselves forever, with little likelihood of an accidental variation along the way; as a result, descendants of a common-cold agent such as the rhino virus are nearly always carbon copies of their ancestors in every respect: size, shape, disease-causing potential and so on.
The hereditary material of the flu virus, by contrast, consists of eight separate fragments—a less stable arrangement that allows more frequent changes in offspring, principally in the chemical composition of the two surface proteins, neuraminidase and hemagglutinin. New variants do not match antibodies that are keyed to the surface spikes of the old virus, so the new viruses tend to meet less immune resistance than the previous strain and gradually supersede it.
Because an individual’s ability to resist re-infection by a particular flu virus is highest when his antibodies already are keyed to that virus, the degree of change in the new variant will largely determine its severity in the individual and in the community.
Modest changes, known to virologists as “drifts,” cause minor epidemics, since existing antibodies react fairly well against viruses that resemble the one they originally were keyed to. But major changes, or “shifts,” produce viruses foreign to the existing store of antibodies and usually cause severe epidemics and pandemics.
Scientists believe that drift is the result of randomly produced new variations in individual flu viruses, which gradually are selected out by nature over older viruses. Unfortunately, human antibodies are not updated in the same way. A person’s encounter with each new, slightly different variant primarily triggers antibodies from his first encounter with a related strain. In subsequent encounters, antibodies aimed specifically at the drifted strain will be recalled, but in much smaller amounts. This is what types of diseases does the common cold cause, any thing that can attack your immune system.
Ordinarily this defense system works fairly well, because antibodies to one strain usually can defeat related ones. But when repeated drift gradually creates a virus quite different from the original, the old antibodies are useless and the hapless victim contracts the new strain of flu. Within the population as a whole, an accumulation of such drifts finds most people completely unprepared and causes a good-sized epidemic.
Virologists once believed that a shift was merely the product of a series of drifts, but modern analytic techniques have revealed that new virus subtypes are so radically different from their predecessors that shift and drift probably are completely different phenomena. Two major theories have been proposed to explain the dynamics of flu viruses’ shift, and the truth may combine both of them.
One major theory ascribes shifts to the recirculation of old flu subtypes that have been dormant for decades. According to this hypothesis, as more and more of the population develops antibodies to a particular flu strain, the virus may go into storage perhaps in the arctic tundra or in animals (left). Barnyard storage is a distinct possibility, because pigs, horses, ducks and chickens all suffer from influenza strains quite similar to human ones.
The virus could reside in animals either actively, as animal influenza, or in a latent state - that causes no active disease. After a time, when a generation of humans appears lacking antibodies against that virus, the stored virus presumably returns with new vigor and rapidly reemerges as the dominant flu strain.
The second theory also draws on the idea of animal storage. But in this scenario, crossbreeding may take place between two strains of the same virus type, one normally native to animals, the other to humans (page 109). Such an encounter between two flu viruses can take place in a human host, but it is most likely in a more hospitable animal, particularly wild birds, which harbor a wide variety of flu strains.
If two different flu viruses simultaneously infect same cell, their fragmented bits of hereditary material are likely to become shuffled. The progeny of this marriage may possess characteristics of both parents—the surface spikes of an avian strain, perhaps, and the ability to infect human cells. Such a radical shift would find a world of undefended individuals— and cause a pandemic.
Whatever the true explanation of drift and shift may be, they take place within a predictable time period.
Minor viral variants, or drifts, occur every two or three years on the average; their infections tend to be of a mild epidemic magnitude in the first year, milder still in the second and third. Such drift cycles rarely make newspaper headlines. Major shifts take place at irregular intervals, anywhere from 10 to 50 years apart. The flu pandemic of 1918-1919 was caused by a shift. So, presumably, were some 30 other pandemics that have been charted by medical historians from health records going back as far as 1510. We have pointed out a list below of what types of diseases does the common cold cause:
r immune system cannot do its job, the results can be serious. Disorders of the immune system include
Allergy and asthma disease - when the human immune system responds to trigger substances that actually harmless.
Immune deficiency diseases - These are disorders where resistance to disease becomes critically low.
Autoimmune diseases - Possibly the worst one this disease causes the immune system to constantly attack your own body's cells and tissues in error. |
