The Protozoa
Class Sporozoa - Malaria
 Four species of malaria parasites infect humans,
Plasmodium vivax, P. ovale, P. malariae, and P.
falciparum. All are transmitted by female Anopheles spp.
mosquitoes.
 Geographical distribution - malaria is present worldwide
in tropical and subtropical areas.
 Transmission - naturally acquired infections are via the
bite of infected female Anopheles mosquitoes. Malaria is
also transmitted via blood transfusion, sharing of
contaminated needles among IV drug abusers, and
congenital transmission also has been documented.
The Protozoa
Class Sporozoa - Malaria
 Relapse versus Recrudesence - P. vivax is the
classic “relapsing” malaria. All can recrudesce
due to incomplete therapy. Relapse is due to
dormant stages (hypnozoites) in liver cells. Only
sporozoite induced malaria can relapse.
 Prevention - detect and treat infected people;
mosquito control.
 Immunity - incomplete immunity follows
infection. Some persons get reinfected over and
over.
The Protozoa
Class Sporozoa - Malaria
 Sickle cell trait - the malaria parasite is not
successful at utilizing “S” haemoglobin. This
trait does not confer immunity to infection, but
does offer resistance to disease.
 Duffy factor - represents the “portal of entry”
antigen for P. vivax. Persons without this factor
are immune to infection with this species, but
not the others.
The Protozoa
Class Sporozoa - Malaria
Pathology/Pathogenesis:
 Prodromal stage - time period which can include
premonitory symptoms such as headache,
myalgia, anorexia & nausea prior to the first
paroxysm.
 Paroxysm - period of chills & fever followed by
profuse sweating.
 Blackwater Fever - a complication of P. falciparum
malaria. Hemolysis and hematuria are due to a
severe immune reaction.
The Protozoa
Class Sporozoa - Malaria
Treatment: (Often complicated by an increasing
resistance of the parasite to drugs)
 Prophylaxis - administration of drug(s) prior to
entering a malarious region.
 Therapeutic - administration of drug(s) to cure
an infection.
 Drug resistance - only P. falciparum, although
strains of P. vivax on Papua, New Guinea have
been reported to be developing resistance.
The Protozoa
Class Sporozoa - Malaria
Collection of Blood for Malaria Examination:
 Finger stick - the preferred specimen. Wipe off
first drop of blood in order to avoid “tissue
juices”.
 Venous - acceptable, but a “red-top” tube is
best. Smears should be made as close to the
time of collection as possible.
 Midway between fever peaks is the best time to
collect blood.
The Protozoa
Class Sporozoa - Malaria
Mixed Infections: Possible, but are rare.
 Dominant infection - one species will usually be
dominant.
 Confirmation of other species - based upon
identifying a stage uniquely different from the
same stage of the dominant species present.
The Protozoa
Class Sporozoa - Malaria
Terms:
 Ring stage - a young trophozoite, it still
contains a vacuole in the cytoplasm.
 Developing trophozoite - the vacuole fills
in as the organism feeds, adding to its
bulk; pigment begins to appear.
 Pigment - product of the digestion of
haemoglobin to hematin.
The Protozoa
Malaria Terms: (continued)
 Schizont - the stage in which asexual
reproduction takes place with the production of
merozoites.
 Gametocyte - the stage picked up by the
mosquito vector; initiates sexual reproduction in
the mosquito.
 Sporozoite - the infective stage, a product of
sexual reproduction; is present in the salivary
gland of the vector mosquito.
The Protozoa
Malaria Terms: (continued)
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Schuffner’s stippling - a fine, granular eosinophilic
stippling seen on the infected red blood cell. Seen only
in P. vivax and P. ovale infections.
Maurer’s clefts - heavy, clefts of eosinophilic stippling
rarely seen on infected red blood cells in P. falciparum
infections. Usually sparse in number.
Prepatent period - time from infection until first
discovery of parasites in a blood film.
Incubation period - time from infection until first
symptoms appear.
The Protozoa
Components of the Malaria Parasite:
 Cytoplasm - light blue staining component of
parasite.
 Chromatin - reddish to purplish red staining,
nuclear material.
 Pigment - does not stain. Product of digestion
of haemoglobin to hematin. Color varies with
species present, generally brown to black.
The Protozoa
Malaria:
Features in Thin Blood Films:
Appearance of the infected
Red Blood Cell:
 Size - normal or enlarged.
 Stippling - present or absent.
The Protozoa
Malaria:
Appearance of the Parasite:
 Outline of the developing trophozoite smooth and rounded or irregular.
 Density of cytoplasm - compact (dark
staining), or diffuse (light staining).
 Amount & color of pigment - black,
brown, etc.; heavy, light.
 Stages present - is one stage
dominant, or are a variety of stages
present.
 Number of merozoites in the mature
schizont (a species-specific number).
The Protozoa
Malaria:
Diagnostic Features seen in Thick Blood Films:
Appearance of the Parasite: (RBC’s have been lysed)
 Stages present - rings, trophozoites, schizonts,
gametocytes.
 Outline of the developing trophozoite - smooth and
round or irregular.
 Density of cytoplasm - diffuse or compact.
 Amount & color of pigment - dense, sparse; black,
brown.
 Number of merozoites in the mature schizont - 9, 16, 24.
 Shape of the gametocyte - round or banana shaped.
The Protozoa
Plasmodium vivax - benign tertian
malaria
 Stages present in blood films - all
can be present.
 Size of infected red blood cells usually enlarged.
 Stippling - usually present if
stained at a pH of 7.0 - 7.2.
 Density of cytoplasm - diffuse,
light staining.
The Protozoa
Plasmodium vivax - benign tertian
malaria (continued)
 Pigment - present in older
organisms, brownish-black to
yellowish-black.
 Number of merozoites in the
mature schizont - average of 16.
 Length of asexual cycle - 48 hours.
 Prepatent period - 8 to 17 days.
 Incubation period - 14 days.
The Protozoa
Plasmodium ovale - benign tertian
malaria (‘ovale’ tertian)
 Stages present in peripheral
blood films - all can be present,
but one is dominant.
 Size of infected red blood cells usually enlarged, often oval with
fimbrated edges.
 Stippling - usually present if
stained at pH 7.0 - 7.2.
The Protozoa
Plasmodium ovale - benign tertian
malaria (continued)
 Density of cytoplasm - rounded
and compact, therefore dark
staining.
 Number of merozoites in the
mature schizont - average of 9.
 Length of asexual cycle - 48 hrs.
 Prepatent period - 8 to 17 days.
 Incubation period - 14 days.
The Protozoa
Plasmodium malariae quartan malaria
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Stages present in peripheral blood
films - all can be present, but one
stage usually is dominant.
Size of infected red blood cells normal or slightly smaller.
Stippling - none.
Density of cytoplasm - rounded and
compact, therefore dark staining.
The Protozoa
Plasmodium malariae - quartan
malaria (continued)
 Pigment - usually present in older
organisms, dark black.
 Number of merozoites in the
mature schizont - average of 9.
 Length of asexual cycle - 72 hrs.
 Prepatent period - 14 to 30 days.
 Incubation period - 30 days.
The Protozoa
Plasmodium falciparum malignant tertian malaria
 Stages present in peripheral
blood films - usually only rings
and gametocytes; rarely other
stages.
 Size of infected red blood cells normal.
 Stippling - rarely, Maurer’s clefts
can be seen.
The Protozoa
Plasmodium falciparum - malignant
tertian malaria (continued)
 Density of cytoplasm - compact.
 Pigment - black.
 Number of merozoites in the mature
schizont - average of 24.
 Shape of the gametocyte - banana
or sausage shaped.
 Length of asexual cycle - 48 hrs.
 Prepatent period - 5 to 15 days.
 Incubation period - 12 days.
The Protozoa