ClinPara

• Sporozoa (Apicomplexa)


  Phylum distinguished morphologically by the presence of a specialized complex of apical organelles (micronemes, rhoptries, polar ring, conoids and dense granules) which help in invasion into the host cell
• Orders in Class Coccidea

  • Eimeriida
  • Haemosporida
  • Piroplasmida
• Order Haemosporida and Order Piroplasmida include the blood parasites belonging to genus Plasmodium (the causative agent of malaria) and Babesia (rare parasites infecting humans) respectively
• Malaria is one of the oldest documented diseases of mankind
• The name "Malaria" ("Mal" means bad and "aria" means air) was derived from the ancient false belief that "disease is spread by air pollution through stagnant water and marshy lands"
• Alphonse Laveran (1880) was the first to discover the causative agent Plasmodium, in the red blood cell (RBC) of a patient in Algeria
• Sir Ronald Ross, in 1897 had described the sexual cycle of the parasite in female Anopheles mosquito in Secunderabad, India
• More than 125 species of Plasmodium exist infecting wide range of birds, reptiles and mammals
• Human infection is mainly caused by five species

  • P. vivax
  • P. falciparum
  • P. malariae
  • P. ovale
  • P. knowlesi
• Definitive host


  Female Anopheles (Anopheline) mosquito where the sexual cycle (sporogony) takes place
• Intermediate host


  Man where the asexual cycle (schizogony) takes place
• Male Anopheles doesn't feed on man and feeds exclusively on fruit juices, i.e. why male Anopheles doesn't transmit the disease
• Anopheline mosquitoes of primary importance in India

  • Anopheline culicifacies in rural areas
  • A. stephensi in urban areas
  • A. fluviatilis in hilly areas
  • A. minimus
  • A. philippinensis
  • A. sundaicus
  • A. maculatus
• Sporozoites


  The infective form of the parasite present in the salivary gland of female Anopheles mosquito
• When Plasmodium species is transmitted by blood transfusion or through placenta, merozoites act as infective form
• Mode of transmission


  1. Man gets infection by the bite of female Anopheles mosquito

  2. Sporozoites from the salivary gland of the mosquito are directly introduced into the blood circulation
• Rare modes of transmission

  • Blood transfusion
  • Transplacental transmission
• Human Cycle


  1. Pre-erythrocytic schizogony

  2. Erythrocytic schizogony

  3. Gametogony
• Pre-erythrocytic schizogony


  Occurs in liver, sporozoites enter hepatocytes and transform into trophozoites which undergo nuclear divisions to form pre-erythrocytic schizonts containing merozoites
• As only few hepatocytes are infected by Plasmodium, so hepatic damage doesn't occur in malaria
• Hypnozoites


  Some sporozoites of P. vivax and P. ovale don't develop further and may remain in liver, causing relapse of malaria after many years
• Relapse


  Reappearance of malaria symptoms due to reactivation of hypnozoites in liver
• Recrudescence


  Reappearance of malaria symptoms due to persistence of asexual blood stages
• Erythrocytic schizogony


  Merozoites enter RBCs, transform into trophozoites, schizonts and undergo nuclear divisions to produce new merozoites which are released to infect more RBCs
• Prepatent period


  Time interval between entry of parasite into man and demonstration of parasite in peripheral blood
• Prepatent period for different Plasmodium species

  • P. vivax - 8 days
  • P. falciparum - 5 days
  • P. malariae - 13 days
  • P. ovale - 9 days
• Malarial pigment


  Undigested product of hemoglobin metabolism like hematin, excess protein and iron porphyrin
• Appearance of malarial pigment varies, mostly it is brown black in color and numerous (except in P. vivax it is yellowish brown in color and in P. falciparum, it is few in number)
• Number of merozoites per mature schizont


  • P. vivax - 12-24 (average 16)
  • P. falciparum - 18-24 (average 20)
  • P. malariae - 6-12 (average 8)
  • P. ovale - 8-12 (average 8)
• Incubation period


  Time interval between entry of parasite to the body and appearance of first clinical feature
• Incubation period for different Plasmodium species

  • P. vivax - 14 days (ranges 8-17 days)
  • P. falciparum - 12 days (ranges 9-14 days)
  • P. malariae - 28 days (ranges 18-40 days)
  • P. ovale - 17 days (ranges 16-18 days)
• In P. falciparum infection, the later stages of erythrocytic cycle occur in the capillaries of brain and internal organs, hence only the ring forms are found in the peripheral blood by microscopic examination but not late trophozoites and schizonts
• Gametocytes


  Sexual forms of the parasite that develop after a series of erythrocytic cycles
• Time of appearance of gametocytes in the circulation from first appearance of asexual forms


  • P. vivax - 4-5 days
  • P. falciparum - 10-12 days
  • P. malariae - 11-14 days
  • P. ovale - 5-6 days
• Individuals harboring gametocytes are considered as carriers or reservoirs of infection and play an important role in the transmission of the disease
• Exflagellation


  Process where the nucleus of the male gametocytes divides into eight flagellated actively motile bodies (microgametes) which protrude out and break free
• Mosquito Cycle


  1. Zygote formation

  2. Ookinete formation

  3. Oocyst formation

  4. Sporozoite formation
• Extrinsic incubation period


  Time required to complete the life cycle of parasite in mosquito
• Extrinsic incubation period for different Plasmodium species at 25°C


  • P. vivax - 8-10 days
  • P. falciparum - 9-10 days
  • P. malariae - 25-28 days
  • P. ovale - 14-16 days
• Mixed infection with different Plasmodium species can occur in the same mosquito and same human host