Blood and Tissue Parasites

Malaria Genetic Protection

Sickle Cell disease and trait - stresses parasites
G-6-PD - oxidative damage
Diffy Neg - P. vivax protection

Malaria Vector

Female Anopheles Mosquito

Malaria Life Cycle (inside human)

blood meal, injects sporozoites
to liver ~ 3o mins
ring stage in RBC, troph, schizont, gametocyte
blood meal, ingest gametocyte

Malaria Disease Manifestation

Initial - flu-like
fever cycles
high fever
joint pain
no lymphadenopathy - rules out if present

Recrudescence

Repeated attack of malaria due to survival of parasites in RBCs or liver cells

Days to weeks later

Dormancy period

Relapse

Recurrence of disease after apparent cure through treatment

Weeks to months later

May be due to insufficient treatment

Plasmodium falciparum

Tropics
"malignant tertian fever", "blackwater fever"
high levels of parasitemia
fatal in 8-10 months, severe malaria
36-48 hour cycles (3 days)
neurological manifestations
Kidney failure, metabolic acidosis, hypoglycemia
Blood bananas

Plasmodium falciparum Ring Stage

Thin, delicate, 1/5 diameter of RBC

1-2 chromatin dots per ring

Multiple rings in one RBC

Normal RBC size

Plasmodium falciparum Gametocytes

Blood bananas

1.5x diameter of RBC

coarse chromatin

crescent or sausage shaped

Severe Malaria

No previous exposure, immunocompromised, pregnant people

Cerebral malaria (neurological)

Severe anemia - intravascular hemolysis

Hemoglobinuria

Pulmonary edema or acute respiratory distress syndrome

Blood coagulation abnormalities and thrombocytopenia

Cardiovascular collapse and shock

Plasmodium vivax

Most common malarial infection

Tropics, subtropics, temperate zones

“benign tertian malaria”

moderate to severe

non-fatal, but relapses common

~48 hour life cycle (3 days cycle)

splenomegaly

Duffy Negative provides protection

Plasmodium vivax Ring form

Thick cytoplasm, single large chromatin dot

Cytoplasm becomes amoeboid

Schuffner’s dots

Larger RBCs

Sometimes multiple rings per RBC

Plasmodium vivax Troph

Amoeboid

Schuffner’s dots

Large RBCs

Fine brown pigment

Plasmodium vivax Schizont

16-24 merozoites

Large, amoeboid

Plasmodium vivax Gametocyte

Oval, fill host RBC

Large RBC

Dark blue cytoplasm with fine brown pigment

Schuffner’s dots

Plasmodium malariae

Common

Sporadic distribution

“Benign quartan malaria”

Low parasitemia levels

non-fatal, recrudescence common

life cycle: 72 hours, (4 day cycle)

associated with Kidney Disease: proteinuria, nephrotic syndrome, possibly due to Ag-Ab complex deposits

Plasmodium malariae Ring

Normal RBC size

“bird’s eye”

Usually 1 chromatin dot

Thicker cytoplasm ring

Plasmodium malariae Troph

“Band Form” or “basket form”

Elongate across host RBC

Coarse pigment

Plasmodium malariae Schizont

6-12 merozoites

Rosette or cluster

Fill most of normal sized RBC

Coarse pigment

Plasmodium malariae Gametocye

Compact

Tend to fill RBC

Normal-small RBC

Dark pigment scattered through cytoplasm

Plasmodium ovale

2nd rarest form of malarial infection

Limited to Central West Africa and Pacific Islands

Non-fatal, spontaneous recovery

48 hour life cycle

Visually similar to P. vivax

Plasmodium ovale Ring

1-2 chromatin dots

Can be multiple rings per RBC

RBCs not enlarged

Plasmodium ovale Troph

Compact

RBCs tend to become oval with fimbriation (spiked/jagged edges)

Schuffner’s dots

Pigment less-coarse, more diffused

Plasmodium ovale Schizont

4-16 merozoites

Oval shape with fibrillation (jagged edges) common

Lighter, less coarse pigment

Plasmodium ovale Gametocyte

RBC not enlarged

Fill most of RBC

Fimbriation may occur

Plasmodium knowlesi

Newest and rarest form of human malaria, previously known in monkeys

Difficult to distinguish from P. falciparum and P. malariae

24 hour cycle

must use molecular methods to diagnose

renal dysfunction and thrombocyopenia

more severe and higher parasitemia than P. malariae

Immunological responses: Naive vs Native

Naive populations: more frequent, more severe disease

Native populations: acquired innate immunity, much less severe disease state

Immunological Responses to Malarial Stages

effective in adults after uninterrupted lifelong heavy exposure

Injected sporozoites: attacked by circulating antibodies, not effective

Liver stage: Cytotoxic T cells and interferon mediate killing in liver (exoerythrocytic)

RBC stage: Antibodies inhibit growth, block merozoite invasion, block adhesion to RBC surface (erythrocytic)

Mosquito stage: human antibodies kill ingested parasites