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 ProtozoaClass 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 ProtozoaClass Sporozoa - MalariaPathology/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 - MalariaTreatment: (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 - MalariaCollection 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 - MalariaMixed 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 ProtozoaClass Sporozoa - MalariaTerms: 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) 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 ProtozoaMalaria: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 ProtozoaMalaria: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 ProtozoaPlasmodium 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 ProtozoaPlasmodium 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 ProtozoaPlasmodium 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 ProtozoaPlasmodium 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

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 ProtozoaPlasmodium 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