Lec 9 Malaria

8/6/2019 Lec 9 Malaria

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Learning objectives

By the end of this Unit you should:

� recognize the importance of malaria as a disease

� be able to recognize the common clinical signs and

symptoms of malaria� know that some people can have malaria without

clinical symptoms

� know that malaria is caused by the presence of

parasites in a patient¶s blood

� know that a female anopheline mosquito can

transmit malaria to people

, you must be able to find and identify parasites in a

stained blood film examined under the microscope



Malaria is caused by protozoa of the Plasmodium species.

There are 4 species which infect both humans and animals

Plasmodium malariae (quartian malaria),

Plasmodium vivax (benign tertian malaria),

Plasmodium falciparum (malignant tertian malaria, subtertianmalaria)

Plasmodium ovale (ovale tertian malaria).

Malarial Parasites



Diagram of Malaria InfectionDiagram of Malaria Infection

Infection is by mosquito bite

Infects liver, then

blood cells



� How Plasmodium

protozoa infect a human

host:

1. The bite of a femaleAnopholes mosquito injects

Plasmodium protozoa into a

human host.

2. Plasmodium travel through

the bloodstream to the liver .



3. In the liver,

Plasmodium multiply

asexually.

4. Plasmodium reenter the

bloodstream, multiply

in red blood cells, and

then burst out, infecting

new cells and

producing malaria

symptoms.

� The released

parasites (yellow),

which go on to

infect new cells or

are ingested by

another mosquito.

� Blood cells with

the malaria

parasite within the

cells.

� R ed blood cells

that have ruptured





Life CycleLife Cycle::



� The malaria parasite life cycle involves two hosts. During ablood meal, a malaria-infected female Anopheles mosquitoinoculates sporozoites into the human host .

� Sporozoites infect liver cells and mature into schizonts ,which rupture and release merozoites . (Of note, in P. vivax and P. ovale a dormant stage [hypnozoites] can persist inthe liver and cause relapses by invading the bloodstreamweeks, or even years later.)

� After this initial replication in the liver (exo-erythrocyticschizogony ), the parasites undergo asexual multiplication inthe erythrocytes (erythrocytic schizogony ).

� Merozoites infect red blood cells . The ring stagetrophozoites mature into schizonts, which rupture releasingmerozoites .

� Some parasites differentiate into sexual erythrocytic stages(gametocytes) . Blood stage parasites are responsible for the clinical manifestations of the disease.



Life cycle contLife cycle cont

� The gametocytes, male (microgametocytes) and female(macrogametocytes), are ingested by an Anophelesmosquito during a blood meal .

� The parasites¶ multiplication in the mosquito is known as

the sporogonic cycle . While in the mosquito's stomach,the microgametes penetrate the macrogametesgenerating zygotes .

� The zygotes in turn become motile and elongated(ookinetes) which invade the midgut wall of themosquito where they develop into oocysts .

� The oocysts grow, rupture, and release sporozoites ,which make their way to the mosquito's salivaryglands. Inoculation of the sporozoites into a new humanhost perpetuates the malaria life cycle



By light microscopic observations of parasites

in circulating red blood cells.



Chills

Fever

Sweating

Headaches

Nausea

Vomiting

Flu-like symptoms

Diarrhea

Jaundice (yellow fever)

Myalgia (muscle pain)





Malarial Parasites



Malarial Parasites



Shock, liver or kidney

failures*

Coma*

Seizures*

*May occur depending on

type of plasmodium

Symptoms may develop

later.



Diagnosis of malariaDiagnosis of malaria

Peripheral smear study

serological assay

Antibody DetectionIndirect Fluorescent Antibody

Enzyme immunoassays

Antigen Detection

ImmunochromatographicPCR



DiagnosisDiagnosis



Antigen Detection Antigen DetectionMalaria ImmunochromatographicMalaria Immunochromatographic

DipstickDipstickOptiMAL Assay

P. falciparum

specific

monoclonalantibody



Antigen Detection Antigen Detection

Malaria Immunochromatographic DipstickMalaria Immunochromatographic Dipstick

ProblemsProblems

� Low sensitivity with parasites density <100/ml

� Currently only useful for detection of P.

falciparum infections



Antibody Detection Antibody Detection

*-labeled antibody to

human antibody

+

Antigen-antibody-

*antibodycomplex

=

Antigen-

antibody

complex



Indirect Fluorescent AntibodyIndirect Fluorescent Antibody

(IFA)(IFA)

Microscope slide



Malaria IFA TestMalaria IFA Test

Initial detection of antibodiesInitial detection of antibodies

�Parasitemia precedes antibody ± P. vivax 2-6 days

± P. falciparum and P. malariae 4-6

days� If parasitemia is suppressed by

treatment, may develop

detectable antibody



Enzyme ImmunoassayEnzyme Immunoassay

(EIA/ELISA)(EIA/ELISA)

_

+enzyme substrate



ELISA



Antigen Detection Antigen Detection

Monoclonal

antibody

=

Antigen-antibody

complex

+

Antigen in

patient¶s serum



Sensitivity of Tools for Sensitivity of Tools for

Diagnosis of MalarialDiagnosis of MalarialInfectionInfection

1. Most sensitive:

Antibody detection

2. PCR

3. Blood filmexamination



Diagnosis of Diagnosis of UntreatedUntreated Acute Acute MalariaMalaria

� Blood film examination

� PCR



Diagnosis of Diagnosis of TreatedTreated RecentRecent MalariaMalaria

� Serology

� Blood film

examination� PCR



Diagnosis of Diagnosis of

ChronicChronic MalariaMalaria

�Screen with serology

If IFA positive:

� May do blood film

examination

� May do PCR



Malaria review: multiple formsMalaria review: multiple forms� Trophozoites (=ring forms): most numerous form to

see in peripheral blood, ring like structure (<1/2

diameter of cell), progressively enlarge and mature

to«

� Schizont: multinuclear structure, appear asintraerythrocytic collection of merozoites (each with

its own nucleus)

� Gametocyte: mononuclear structure occupying >1/2

the red cell, usually amoeboid in shape and nearly fillsentire RBC



P. falciparumP. falciparum

� Malignant tertian fever because potentially lethal

� Must be identified

� Usually only early ring forms and gametocytes

seen ± Ring forms: may have double chromatin dots, may be

multiply infected; accole or applique forms present;less than 1/5 size of RBC

± Gametocytes: banana shaped

� Infected red cells NOT enlarged, infects RBCs of all stages of maturation




� Acute intravascular hemolysis with

hemoglobinuria (³blackwater fever´)

� Infected RBCs have ³sticky knobs´ leadingto sludging, infarcts of brain, kidneys

� With no treatment, patients either die or

spontaneously resolve within one year






P. vivax and P. ovaleP. vivax and P. ovale

� Benign tertian fever

� Morphologically very similar

� P. ovale very rare, confined to Western Africa

� Both infect young RBCs and appear enlarged and pale

� All stages seen (early and developingrings, schizonts, gametocytes)



P. vivax and P. ovaleP. vivax and P. ovale

� Schuffner¶s dots may be present

� Gametocytes are amoeboid shaped, not

banana� Schizonts have 12-14 merozoites



P. malariaeP. malariae

� Associated with nephrotic syndrome

� Infects older erythrocytes, normal to small sizedRBCs

� No Schuffner¶s dots� All stages seen

� Schizonts have 6-12 merozoites, rosette pattern

� Coarse pigment may be present

� Occasional band forms (trophozoite form) seen

� Low grade cryptic infections can occur up to 40 y



P. malariaeP. malariae





Plasmodium falciparumPlasmodium falciparum



PFPF



SummarySummary

� Mosquito-borne infectious disease

� Tropics, subtropics

� P. falciparum, vivax, ovale, malariae

� Incubation period nearly two weeks� Cyclic paroxysms

� Fever

� Thick and think blood smears for diagnosis

� Drug resistance is increasing

� Chemoprophylaxis can prevent infection

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Lec 9 Malaria