Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Epidemics, viral

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flu (1968). Potential epidemics due to the emergence of new

forms of the virus in 1976 (the Swine flu) and 1977 (Russian

flu) failed to materialize.

The continuing series of influenza epidemics is due to

the ability of the various types of the influenza virus to alter

the protein composition of their outer surface. Thus, the anti-

bodies that result from an influenza epidemic in one year may

be inadequate against the immunologically distinct influenza

virus that occurs just a few years later. Advances in vaccine

design and the use of agents that lessen the spread of the virus

are contributing to a decreased scope of epidemics. Still, the

threat of large scale influenza epidemics remains.

In the twentieth century, new viral epidemics have

emerged. A number of different viruses have been grouped

together under the designation of hemorrhagic fevers. These

viruses are extremely contagious and sweep rapidly through

the affected population. A hallmark of such infections is the

copious internal bleeding that results from the viral destruc-

tion of host tissue. Death frequently occurs. The high death

rate in fact limits the scope of these epidemics. Essentially the

virus runs out of hosts to infect. The origin of hemorrhagic

viruses such as the Ebola virusis unclear. A developing con-

sensus is that the virus periodically crosses the species barrier

from its natural pool in primates.

Another viral epidemic associated with the latter half of

the twentieth century is acquired immunodeficiency syn-

drome. This debilitating and destructive disease of the immune

systemis almost certainly caused by several types of a virus

referred to as the Human Immunodeficiency Virus(HIV). The

first known death due to HIV infection was a man in the

Congo in 1959. The virus was detected in the United States

only in 1981. Subsequent examination of stored blood sample

dating back 40 years earlier revealed the presence of HIV.

HIV may have arisen in Africa, either from a previously

unknown virus, or by the mutation of a virus resident in a non-

human population (e.g., primates). The tendency of the virus to

establish a latent infection in the human host before the appear-

ance of the symptoms of an active infection make it difficult to

pinpoint the origin of the virus. Moreover, this aspect of latency,

combined with the ready ability of man to travel the globe, con-

tributes to the spread of the epidemic. Indeed, the epidemic may

now be more accurately considered to be a pandemic.

Clerks wearing cloth masks to avoid airborne contamination during an epidemic.

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