k. Psychological Disorders. The knowledge of parasites crawling inside the
body can affect anxiety level of the host. But, the more detrimental psychological
effects are those caused by the accumulation of chemicals in the system of the host.
HOST ATTRIBUTES THAT INFLUENCE RESISTANCE TO PATHOGENIC
EFFECTS OF PARASITISM
a. Fitness of the Host. The nutritional and emotional state of the host can
effect the degree of pathogenicity caused by the parasite.
b. Host Age. Both the very young and the very old are affected to a greater
degree by a parasitic infection than are young adults.
c. Specific Factors That Influence Resistance.
(1) Immunity. Host resistance to parasitic infection is very similar to the
resistance shown against bacteria. The immune system works by the formation of
antibodies against a limitless amount of substances recognized as foreign antigens by
the B lymphocytes. These blood cells, due to constant mutation, are much different
from each other in such a manner that the system contains myriads of "coded"
lymphocytes. When a parasite meets with one of these B lymphocytes that have a
specific antibody against its antigen, the lymphocyte reproduces at a high rate to
produce plasma cells. When these second generation antibodies encounter the
antigens coating the parasites, a neutralization process takes place that kills the
invaders. Immunity against parasites can be inherited or acquired. The acquired
immunity may be natural or artificial, while the artificial can be active or passive.
(2) Complement system. This is a complex system of enzymes found in
normal serum that aids the lysis (destruction) of the parasite during an antigen-antibody
reaction. Complement is composed of nine components labeled C-1 through C-9.
Component C-1 is further subdivided into C-1g, C-1r, and C-1s. The system is activated
by the immunoglobulins IgM and IgG. Complement also participates in other biological
activities such as antibody- mediated immune lysis, phagocytosis, opsonization, and
(3) Interferon. Interferon is composed of a group of soluble small proteins
produced by infected cells that inhibit multiplication of virus. The proteins are not virus
specific, but they are cell specific in production and effects.
d. Nonspecific Factors That Influence Resistance. There are some barriers
that affect parasitism. These barriers may be chemical, physical, or biological (the
antagonistic effect of organisms already present at the site in question).