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Information about Plasmodium

Published on February 25, 2014

Author: PakRose1



Plasmodium • • > 100 species Both animals and humans 1. P. vivax  Benign Tertian Malaria (humans) 2. P. ovale  Benign Tertian Malaria (humans) 3. P. malariae  Benign Quartan Malaria (humans/chimpanzees) 4. P. falciparum  Malignant Tertian Malaria (humans)


Geographical Distribution • P. vivax and P. falciparum  more common P. ovale  rarest of the 4 species • > 200 million people worldwide > 1 million deaths per year Most common lethal infectious disease

Geographical Distribution • Tropical & subtropical areas esp. Asia, Africa, Central and South America Certain regions in SE Asia, S. America, E. Africa  Chloroquine Resistant strains of P. falciparum

HABITAT • Female Anopheles  sexual cycle • Liver & RBCs of man  asexual cycle RBC Age Variable:  P. vivax  youngest erythrocytes  P. malariae  oldest erythrocytes  P. falciparum  RBCs of every age

Anopheles, Culex and Aedes aegyptii

MORPHOLOGY • Peripheral blood stained with Leishman’s stain 1. Small Trophozoites (Ring forms): Infected RBC  at first ring form a) b) c) Dot/rod shaped nucleus (red) Peripheral rim of cytoplasm (blue) Central clear vacuole like area (not stained) Different species have different rings

MORPHOLOGY 2. Large Trophozoite: • • Ring form  Large trophozoite Fine grains of pigment Hematin 3. Schizont: Large trophozoite  schizont  N/C fragments merozoites 4. Gametocytes: • • • Male and female distinguishable Fully grown  rounded  occupies most of RBC P. falciparum  sausage shaped  crescent in RBC

Plasmodia in RBCs

LIFE CYCLE • HOST: Definitive Host  Female anopheles (sexual cycle) Intermediate Host  Man (asexual cycle) • VECTOR: Female Anopheles

LIFE CYCLE • Sexual cycle initiated in Humans  Gametocytes (gametogony in RBCs)  mosquitoes  fusion of M/F gametes  oocyst  many sporozoites (sporogony) • Sexual cycle  Sporogony (sporozoites) • Asexual cycle  Schizogony (schizonts)

Detailed Life Cycle

Oocysts in Mosquito

PATHOGENESIS • Usual Incubation periods: Vivax : 14 days Malariae: 28 days Falciparum: 11 days • Transmission: Mosquito bite I/V drug abuse Blood transfusion Transplacental (congenital) FEVER, ANEMIA, SPLENOMEGALY

PATHOGENESIS • Malarial Relapses: • P. vivax  2 years • Para-erythrocytic stage  liver parenchyma  dormant but viable • Resistance lowered  released and activated  complete erythrocytic cycle • Not in P. falciparum as no para-erythrocytic stage • Transmission other than mosquito bites no relapses

Natural Protection • Sickle cell trait (heterozygous) • Duffy blood group antigen –ve (homozygous recessive) (P.vivax) • G6PD deficiency • Premunition: • Partial immunity • Humoral antibodies  block merozoites from invading RBCs • Low level of parasitemia low grade symptoms

PATHOGENESIS • Commonly Involved Organs: 1. 2. 3. 4. Changes in Blood Spleen Liver Bone Marrow

Signs and Symptoms • • • • • • • • • • • Abrupt fever, chills and rigors Headache Initially may be continuous then periodic Upto 41ºC or 106 ºF Nausea, vomiting, abdominal pain, anorexia, distaste of mouth Drenching sweats afterwards Well between febrile episodes Splenomegaly 1/3 hepatomegaly Anemia Falciparum fatal bcz of brain and kidney damage

Laboratory Diagnosis 1. Blood Exam: a. Microscopic Exam: • • • • • Take blood during pyrexia Not after even single dose of anti-malarials Thick and thin smears made, dried and stained Thick smear  presence of organisms Thin smear  identification of species

Laboratory Diagnosis • Thin Smear: • • • • • • Single drop of blood Spread to allow single cell layer Leishman’s stain Oil immersion lens Ring shaped trophozoites in RBCs P. falciparum gametocyte banana, sausage or crescent shaped • Other species gametocytes are spherical • > 5 % RBCs infected  Dx of P. falciparum

Laboratory Diagnosis • Thick Smear: • • • • • 3-5 drops on slide allowed to dry Several cell layers thick Field’s stain or Giemsa stain Oil immersion lens Stain removes Hb from RBCs

Thin and Thick Smear

Laboratory Diagnosis 1. Blood Exam: b. TLC and DLC: • • TLC low  leucopenia In fever may be high Monocytosis containing pigments

Laboratory Diagnosis 2. Biopsy: • BM and liver biopsies in difficult cases 3. Therapeutic Test: • Anti-malarials given  if fever subsides  Dx made 4. Serological Tests: • • • • Fluorescent antibody testing Complement fixation test Flocculation test Hemagglutination test

Treatment  Falciparum easily treated before complications as no relapses and no paraerythrocytic stage  Chloroquine is treatment of choice for sensitive strains of plasmodia (merozoites)  Primaquine (Hypnozoites)  Mefloquine or quinine and doxycycline (chloroquine resistant strains of falciparum)  Atovaquone and proguanil (Malarone) (CR falciparum)

Prevention Chemoprophylaxis Mosquito netting Window screens Mosquito repellants Protective clothing Special care during night time DDT or kerosene oil spray over pools of water  Drainage of stagnant water  No vaccine presently available       

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