Page 40 - parasitology for medical and clinical laboratoryprofessionals

20 CHAPTER 2

CONDITIONS LEADING TO
PARASITIC INFESTATION
Parasitic infections are more common in areas of the world
where sanitation practices are difficult due to lifestyle, avail-
ability of water, and detergents for personal cleansing and
Delmar/Cengage Learning their ova that may be on the food. Parasites may also result
for preparing food in a manner that will kill any parasites or
from an underlying larger problem such as in some areas of
the country where the patients are largely agrarian. Where
most residents of an area drink water from a well, the pos-
sibility of contracting a parasitic infection is increased. The
FIGURE 2-6 Eosinophil, a form of white blood cell
symptoms of parasitic infections depend upon what organs
present in allergic reactions and parasitic infections
of the body are most affected. Specific parasites are able to
dermatitis, rhinitis, graft rejection, pemphigus (autoim- infest every area and organ of the body, depending upon
mune skin disease), graft versus host reaction, and certain the species and the medical condition of the patient.
diseases of the lung (Figure 2-6). But there is an even more Underlying health conditions may lead to, or exacer-
dramatic elevation in the numbers of eosinophils for cer- bate, an infection by a parasite or parasites. Everyone is at
tain parasitic infections and in particular where tissue inva- risk and there are many reservoirs in which the parasite may
sion by parasites has occurred. Although a number of other safely reside for considerable periods of time until a more
conditions are known to lead to an increase in eosinophils, favorable set of conditions, such as a vulnerable victim, be-
an increase for parasitic infections may rise to level where comes available. The human bowel provides the perfect
40 to 50 percent of the white blood cells are eosinophils. environment for many of the intestinal parasites to flourish,
There are also a number of other lesser known especially if overall health is poor. They can and often do ir-
illnesses other than parasitic infections and allergies that ritate or exacerbate any other health problems already pres-
result in eosinophilia. Reactions to a variety of drugs and ent in the victim. Parasites are responsible for many health
food allergies also result in higher levels of eosinophils. problems as some species secrete toxins that affect the body
Therefore, if a significant rise in the eosinophil count is and some steal the vital nutrients from the bodies of those
found, a parasitic infection would be but one of the pos- infected. The presence of animals and the conditions they
sibilities for the increase. Substantial increases in the create also contribute to the transmission of parasites to hu-
eosinophil count must also be differentiated from ma- mans, as many different species of animals act as vectors of
lignant disorders such as myeloproliferative disorders. or are intermediate hosts for important parasites. The rela-
However, elevated levels of eosinophils are also found tionship between hosts, vectors, and humans is often quite
in a number of parasite infestations that produce an in- complex for a number of parasite species.
creased eosinophil count. Extreme cases of parasitic Other medical conditions that may promote para-
infestations may sometimes involve multiple species of sitic infections occur when excess mucus is formed, and
organisms infecting a single patient. Some of the kinds of may lead to an imbalance of normally occurring bacte-
parasites and medical conditions that may elicit a signifi- ria called normal intestinal flora. Chronic constipa-
cant increase in eosinophils include: tion where the intestines are infected will also lead to a

Trichinosis Toxocariasis Filariasis Echinococcosis
Aspergillosis* Coccidiomycosis Strongyloidiasis Ascariasis
Shistosomiasis Pneumocystis jirovecii

*Some species of Aspergillus, a fungal disease, like high temperatures with optimum
growth at a normal human temperature. It is therefore recognized as a parasite of
humans, other mammals, and birds even though it is not among the organisms commonly
considered parasites.