(2) Congenital influence. Diseases affecting the mother while she is
pregnant with the baby may adversely affect the offspring also. For example, some
diseases may be transmitted directly to the baby via the bloodstream, as is often seen
in the case of syphilis in the mother. Or the pregnant woman may have a disease such
as German measles (rubella), which interferes with the normal development of the child
in the uterus (in utero), even though the child does not acquire the disease. Malnutrition
in the mother could result in a poorly nourished baby and thus, possibly, an abnormally
(3) Mechanical. Purely mechanical factors are also felt to be responsible for
some abnormalities present at birth. Abnormal positioning of the baby in utero is felt to
be occasionally responsible for wryneck; torsion or twisting of the umbilical cord would
limit the blood and food supply to the baby, and dire results could occur. Any defect or
disease present at the time of birth is called a congenital disease or condition. Injuries
or effects sustained during the process of being born may be included here.
b. Parasites. Parasites are organisms that live on or within the body of man or
any other living organism, and at the expense of the one parasitized. Parasites may live
on the surface of the skin (ectoparasites), or they may enter the body through the skin,
the respiratory tract, the gastrointestinal tract, or the genitourinary tract where they may
enter the blood stream and be carried to distant parts of the body. If they live inside the
body but outside the cells, they are called extracellular endoparasites; if they enter the
body's cells, they are called intracellular endoparasites. They all cause disease by
interfering with the tissue and organ functions; they accomplish this by elaborating
toxins, or poisons; by causing inflammation, or irritation; by producing enzymes that
destroy tissue; and by causing mechanical blockage of function.
(1) Viruses. These are the smallest agents known to produce disease;
whether they are living organisms or complex chemical compounds is not known. They
are known to be intracellular endoparasites that cause such common diseases in man
as poliomyelitis, common cold, influenza, measles, mumps, chickenpox, smallpox,
hepatitis, encephalitis, warts, rabies, yellow fever, and lymphogranuloma venereum.
(2) Rickettsiae. These organisms are larger than viruses, but are still very
small, intracellular endoparasites. These organisms are transmitted to man by mites,
ticks, fleas, or lice, and they produce Rocky Mountain spotted fever, typhus (epidemic
and endemic), scrub typhus (tsutsugamushi fever), Q fever, and Rickettsialpox.
(3) Bacteria. Bacteria are minute, onecelled, organisms that may occur
alone or in large groups called colonies. Significant bacteria can be divided by their
shape into three main groups.
(a) Cocci. Cocci are round, onecelled bacteria. The primary
members of this group are staphylococci that group themselves in clusters, streptococci
that arrange themselves in chains, and diplococci that arrange themselves in pairs.