Biomedical Engineering Reference
In-Depth Information
beneficial compounds, while animals and insects are common vectors for parasites and pathogens.
An individual's genetic constitution may provide information on what is best for his or her survival,
but it may not indicate what is best for the population as a whole. For example, there are times when
individuals must suffer so that the general population can survive and thrive.
Consider the interrelatedness of public health and molecular biology. Public health officials rely on
population statistics, education levels, vaccination compliance, and other predictors of disease
prevention. For example, thanks to efforts orchestrated in part by the World Health Organization,
smallpox was eradicated from the general population in the last century through vaccination. For the
sake of protecting the entire population, the health of a subset of the population was jeopardized.
Many children were subject to side effects of the smallpox vaccine, which ranged from fever to death.
From a slightly different perspective, consider that while smoking is considered detrimental to the
health of the population as a whole, there are exceptions. For individuals at risk for developing
Parkinson's Disease, smoking can reduce the risk of developing this neurologic disorder. This
protective effect of smoking is only present with patients with a genetic profile that makes them
susceptible to developing Parkinson's. Individuals without genetic susceptibility can increase their
chances of contracting Parkinson's if they smoke. Given the relatively low incidence of Parkinson's
Disease (less than 1 person per 1,000, predominantly in their 50s), prescribing smoking for the
general population would have a negative effect on public health overall.
Another example of the need for simultaneous top-down and bottom-up approach to studying the
human organism is the interrelatedness of personal and public health. A significant issue worldwide is
the interrelatedness of sickle-cell anemia and the
Plasmodium falciparum
parasite responsible for
malaria. Sickle-cell anemia is caused by a change in the chemical composition of the hemoglobin
protein that carries the oxygen inside of the red blood cells. These chemical changes in hemoglobin
cause the molecule to elongate, distorting the shape of the whole red blood cell. These sickle-shaped
red blood cells can damage the capillaries around them and the tissues that depend on the vessels
for oxygen and nourishment, resulting in clotting, and, in some cases, death of surrounding tissues.
The homozygous form of sickle-cell disease that is associated with an anemia is universally fatal; few
individuals suffering from sickle-cell disease live beyond 20. What's more, in a population free of
Anopheline mosquitoes carrying the
Plasmodium falciparum
parasite, individuals with the sickle-cell
trait (heterozygotes) are also at a distinct disadvantage to those without the trait. However, in
malaria-infested areas of the world, the sickle-cell trait has a protective effect against the malaria
parasite. Women with the trait have more offspring, compared to women without the trait, and more
of their offspring reach maturity because they are relatively unaffected by malaria.
Although malaria can be cured by drug therapy, treatment is extensive and usually associated with
numerous side effects. However, because the DNA of the
Plasmodium falciparum
parasite was
sequenced in 2002, there is increased likelihood of an engineered drug that will free those infected
from extensive medical regimens.
The pharmaceutical industry provides additional examples of the tension between bottom-up and top-
down approaches to evaluating the human condition. Consider that when the antibiotic penicillin was
discovered by Alexander Fleming, he observed, by chance, that bacterial growth on a piece of bread
was inhibited by a contaminating mold. When it was first used as an antibiotic, penicillin was effective
against the majority of bacterial infections. To a practicing clinician, there was no need to understand
penicillin's mechanism of action. All that mattered was whether the antibiotic was effective in
inhibiting or eradicating a particular pathogen, and the potential side effects, such as allergic
reactions.
As soon as penicillin was introduced into the general patient population, bacteria developed a
resistance through mutation and the natural selection process. As a result, many patients were
unable to benefit from penicillin as an antibiotic, and the market for synthetic pharmaceuticals was
born. Since the 1950s, many synthetic derivatives of penicillin have been widely used for a variety of
diseases. For example, ampicillin is one of the most useful of these derivatives and serves as a highly
effective agent against bacterial infections. As with penicillin, the side effects are normally relatively
minor, and usually limited to minor allergic reactions.
