[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 6 Select Sporozoa: Plasmodium and Babesia
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serologic testing is that this methodology does
appear to help rule out malaria in patients suffering
from a fever of unknown origin, and PCR
techniques can confirm the malarial speciation,
but is usually not necessary. Representative laboratory
diagnostic methodologies are presented in
Chapter 2, as well as in each individual parasite
discussion, as appropriate.
Quick Quiz! 6-2
The best time to collect blood for Plasmodium parasites
is: (Objective 6-10)
A. Between paroxysms
B. During paroxysms
C. Morning
D. Evening
Pathogenesis and Clinical Symptoms
The typical patient remains asymptomatic following
the initial mosquito bite and exoerythrocytic
cycle of malarial infection. However, once
the erythrocytic phase is initiated and large
numbers of rupturing RBCs simultaneously
occur, the resulting merozoites and toxic waste
byproducts in the blood system produce the first
clinical symptom, a paroxysm. Considered in
part as an allergic response of the body to the
development of the schizonts and to the circulating
parasitic antigens following the release of
merozoites, a paroxysm is characterized by chills
(also known as rigor), typically lasting for 10 to
15 minutes or longer, followed by 2 to 6 hours
or more of a fever. As the fever subsides and
returns to normal, the patient experiences profuse
sweating and extreme fatigue. The periodicity of
paroxysms varies and is defined under the discussion
of each Plasmodium species; periodicity
often accounts for one of the common names
associated with each Plasmodium species as well.
Patients may experience these clinical symptoms
as a result of having a recrudescence. A recurrence,
or true relapse, occurs when patients
become reinfected with rupturing hypnozoites
months to years after the initial infection, as
is often the case with P. vivax and P. ovale
infections.
Additional malarial symptoms may include
headache, lethargy, anorexia, ischemia (insufficient
blood supply in other body tissues caused
by blockage of the capillaries and blood sinuses),
nausea, vomiting, and diarrhea. Anemia, central
nervous system (CNS) involvement, and nephrotic
syndrome may occur in all Plasmodium infections.
It is interesting to note that malaria may
mimic a number of other diseases, including
meningitis, pneumonia, gastroenteritis, encephalitis,
or hepatitis. Specific clinical symptoms are
described under the discussion of each individual
organism.
Furthermore, persons exhibiting erythrocyte
structural abnormalities such as heterozygous
(Gd A− /Gd B ) glucose-6-phosphate dehydrogenase
(G6PD) deficiency and certain hemoglobinopathies
(S, C, E, and thalassemia) tend to have a
greater resistance to malarial infections than
those who do not possess the abnormalities.
Similarly, those individuals who are Duffy blood
group–negative also tend to show a greater resistance
than those who are positive for the antigens
on their red blood cells.
Quick Quiz! 6-3
A paroxysm is: (Objective 6-1)
A. An allergic reaction
B. A periodic episode characterized by fever, chills,
sweats, and fatigue
C. Both A and B are correct.
D. None of the above
Classification
Malaria belongs to the phylum Apicomplexa,
class Aconoidasida, order Haemosporida, family
Plasmodiidae, genus Plasmodium. All five of the
Plasmodium species discussed in this chapter are
found in the blood, as indicated in Figure 6-1.