MALARIA

BLOOD & TISSUE PROTOZOA (SPOROZOA and Coccidia)

  • Major diseases include:

    • Malaria

    • Toxoplasmosis

Subphylum Sporozoa (Phylum Apicomplexa)

  • Characteristics:

    • Tissue and blood sporozoites

    • Spore formers that do not move independently

    • Notable species: Plasmodium spp., Isospora spp., Sarcocystis spp.

  • Class: Telosporea

  • Subclass: Haemosporina

    • Family: Plasmodae (all parasitic)

    • Genus: Plasmodium spp.

      • Causes malaria

Subclass: Coccidia

  • Family: Eimeriidae

    • Genus: Isospora

  • Class: Toxoplasmea

    • Genus: Toxoplasma, Sarcocystis

  • Class: Haprosporina

    • Genus: Pneumocystis

  • Subclass Haemosporina

    • Sexual and asexual cycles in alternative hosts:

      • Arthropod as primary host, human as intermediate host

Classification of Malaria-Causing Parasites

  • Subphylum: Sporozoa

  • Class: Telosporea

  • Subclass: Haemosporina

    • Sexual and asexual reproduction in alternative hosts

  • Family: Plasmodidae

    • All parasitic

  • Genus: Plasmodium

    • Undergoes exoerythrocytic and pigment-producing erythrocytic schizogony

    • Adapted for intracellular parasitism in liver and RBC of vertebrate hosts

Distribution of Malaria

  • Malaria as a globally devastating disease:

    • Causes nearly 600 million new infections and 3 million deaths annually

    • 40% of world's population lives in endemic areas, significantly affecting children under five in sub-Saharan Africa

    • Nearly 30% of annual mortality in this population attributable to malaria (WHO)

    • Eradicated in most temperate zones but endemic in much of the tropics and subtropics

Types of Plasmodium

  • Major species causing malaria in humans:

    1. Plasmodium falciparum

    2. Plasmodium vivax

    3. Plasmodium ovale

    4. Plasmodium malariae

Overview of Plasmodium Species

  • Plasmodium ovale

    • Least common, found mainly in West Africa

  • Plasmodium malariae

    • Found in tropical Africa and Asia, associated with relapsing malaria

Specifics about Plasmodium Species

  • Plasmodium falciparum

    • Most common and virulent

    • Common in tropics/subtropics of Asia and Africa

    • Responsible for highest morbidity and mortality, affecting the CNS

  • Plasmodium vivax

    • Worldwide distribution, more common in temperate regions

Life Cycle of Plasmodium

  • Two hosts involved:

    • Definitive host: Anopheles mosquitoes (sexual reproduction)

    • Intermediate host: Humans (asexual reproduction)

  • Lifecycle stages include:

    1. In mosquitoes (sexual reproduction)

    2. In humans (asexual reproduction)

Detailed Life Cycle Stages

  • Definitive Host Cycle:

    1. Mosquito acquires parasites from infected human

    2. Gametocytes mature in gut to form gametes

    3. Fertilization forms zygote, which develops into an ookinete

    4. Ookinete forms an oocyst, multiplying to form sporozoites

    5. Sporozoites are released and travel to salivary glands for transmission

Intrinsic Cycle in Humans

  • Sporozoites injected via mosquito bite

  • Exoerythrocytic cycle:

    1. Sporozoites invade liver cells

    2. Develop into exoerythrocytic schizonts, releasing merozoites into the blood

Erythrocytic Cycle

  • Merozoites invade RBCs, developing into trophozoites

  • Trophozoites feed on hemoglobin, leading to cell rupture

  • This cycle contributes to the symptoms of malaria

Symptoms of Malaria

  • Incubation period: 10-15 days after mosquito bite

  • Prodromal symptoms: flu-like signs prior to febrile attack

    • Headache, fever, muscle pain, anorexia, nausea, lethargy

  • Febrile paroxysms:

    • Periodic bouts of fever correlating with RBC rupture

    • Fever patterns: 48 hours for P. vivax, P. ovale, P. falciparum; 72 hours for P. malariae

Pathogenesis and Severe Malaria

  • Pathological effects of malaria:

    • Rupture of infected RBCs

    • Release of malaria pigment and cellular debris

    • Splenomegaly, hepatomegaly, acute febrile illness

  • Cerebral Malaria:

    • Diffuse encephalopathy, ranging from stupor to coma

    • Associated with cytoadherence of infected RBCs to the brain endothelium

Chronic Malaria

  • Relapse or recrudescence possible due to hypnozoites in P. vivax and P. ovale

  • Recrudescence refers to reactivation after symptomatic periods

Diagnosis

  • History of exposure and clinical symptoms

  • Confirmed through microscopy (thick and thin blood smears)

    • Thick smears for detection, thin for species identification

  • Gametocytes' shapes help distinguish species

Laboratory Diagnosis

  • Serologic tests for epidemiological surveys

  • Antigen detection for preliminary diagnosis

Treatment

  • Depends on:

    • Parasite species, severity of disease, patient's age, and immune status

  • Fast-acting drugs:

    • Chloroquine, primaquine for preventing future relapses

  • Artemisinin derivatives:

    • Recommended for severe cases and first-line treatment

Prevention and Control

  • Key methods:

    1. Chemoprophylaxis

    2. Personal protection from insect bites

    3. Environmental control of mosquito breeding

Chemoprophylaxis

  • Important for travelers from non-malarious areas

  • Should begin before traveling and continue post-return

Control Strategies

  • Reduce human-mosquito contact

  • Environmental modification to eliminate breeding grounds

  • Insecticide spraying to control adult populations