MALARIA

• Malaria


  Mal'aria - Italian for "spoiled air"
• The most important mosquito-borne parasitic disease reported in 85 countries

  
• Charles Louis Alphonse Laveran

  First to discover the presence of malarial parasites in erythrocytes

  
• Ronald Ross


  First to implicate the role of mosquitoes in the transmission of malaria parasites

  
• Bignami and Grassi


  Proved that mosquitoes transmit malaria to humans

  
• Family Plasmodiidae


  • Life cycle is similar to coccidia, but it is shared by a vertebrate and invertebrate host
  • Asexual development occurs in vertebrate hosts while sexual development occurs in blood-sucking invertebrates
  • Gamonts develop independently
  • Microgamont produces a moderate number of flagellate gametes
  • Zygote is motile
  • Sporocysts are absent. Sporozoites occur inside oocyts
  • Hemozoin (Hz) pigment may be formed from the hemoglobin of invaded erythrocytes

  
• Plasmodium spp.


  • Causative agent of malaria in humans, mammals, reptiles, and birds
  • Schizogony occurs in erythrocytes and also in various tissues (cryptozoites). Gamonts occur in erythrocytes
  • Anopheles mosquitoes are vectors of malaria in mammals while culicine mosquitoes transmit avian malaria

  
• Plasmodium spp. life cycle

  1. Inoculation of sporozoites

  2. Exoerythrocytic schizogony

  3. Erythrocytic schizogony

  4. Syngamy

  5. Sporogony

  6. Gametogony

  
• Plasmodium spp. of humans

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

  
• Plasmodium spp. of non-human primates

  • P. schwetzi
  • P. reichenowi
  • P. eylesi
  • P. coatneyi
  • P. cynomolgi
  • P. gondori
  • P. simium
  • P. inui
  • P. brasilianum
• Plasmodium spp. of rodents

  • P. berghei
  • P. vickei
  • P. chabaudi
• Plasmodium spp. of ungulates

  • P. bubalis
  • P. odocoilei
• Classification of Plasmodium spp. based on length of schizogony cycle

  • Quotidian- only 1 day; P. knowlesi
  • Tertian- 2 days; P. falciparum, P. ovale, P. vivax, P. schwetzi, P. reichenowi, P. eylesi, P. coatneyi, P. cynomolgi, P. gondori, P. simium
  • Quartan- 3 days; P. malariae, and P. inui, and P. brasilianum

  
• Plasmodium spp. of birds

  • Over 30 species are identified
  • Exoerythocytic schizonts do not occur in the liver
  • After inoculation, pre-erythrocytic schizonts are found in macrophages and fibroblasts near the inoculation site
  • Merozoites of P. gallinaceum, P. relictum and P. canthemerium enter endothelial cells, while those of P. elongatum and P. vaughani enter cells of hemopoietic system and form exoerythrocytic schizonts

  
• Plasmodium spp. of birds based on schizogony cycle

  • 24 hours: P. canthemerium, P. juxtanucleare, P. durae, P. lophurae, P. rouxi, and P. vaughani
  • 36 hours: P. gallinaceum and P. relictum
  • 48 hours: P. circumflexum

  
• Plasmodium spp. of birds based on shape of gamonts


  • Round or irregular, displaces the the nucleus: P. gallinaceum, P. canthemerium, P. juxtanucleare, P. relictum, and P. griffithsi
  • Elongate, usually does not displace the nucleus: P. circumflexum, P. durae, P. elongatum, P. rouxi, P. fallax, P. hexamerium, P. lophurae, P. polare, and P. vaughani
• Plasmodium spp. of reptiles

  • Most commonly reported in lizards, occasionally in snakes
  • At least 101 species are reported to infect reptiles
  • Three species were reportedly found in Draco volans from Palawan: Plasmodium draconis, P. vastator, and P. volans
  • One species, P. auffenbergi was found in Varanus grayi from Luzon

  
• Human malaria


  • Characterized by paroxysm, which begins with severe chill
  • P. vivax, the cause of benign tertian malaria, is the commonest and most widely distributed malarial infection in the world
  • P. falciparum, the cause of malignant tertian malaria, is the most pathogenic in humans due to its cerebral form. Another complication is blackwater fever, characterized by fever, jaundice and hemoglobinuria

  
• Avian malaria


  • Among the pathogenic Plasmodium of birds are P. canthemerium (canaries), P. gallinaceum (domestic chickens), P. relictum (pigeons), and P. juxtanucleare (chickens and turkeys)
  • Splenomegaly and anemia are common findings. Brown-tinged skin and darkening of the viscera may be observed due to pigment deposition
  • P. galinaceum and P. juxtanucleare may cause mortality as high as 90% in chickens

  
• Pathology of avian malaria

  • Experimental studies on P. gallinaceum showed that it can cause depression, fever, anorexia, reduced weight gain, poor feed conversion, anemia, and green feces. Lethargy, pale comb, diarrhea, and partial or total paralysis may be observed in acute infection. Mortality was observed between 5-10 days post-inoculation
  • Hepatomegaly and increased gall bladder volume were observed in P. gallinaceum-infected chickens. A separate study reported abnormalities in the brain, including brain edema, inflammatory infiltrates, congested capillaries
  • Plasmodium juxtanucleare can also cause CNS signs due to exoerythrocytic forms that damage the end

  
• Splenomegaly and anemia


  • Common findings in avian malaria
• Brown-tinged skin and darkening of the viscera


  • May be observed due to pigment deposition in avian malaria
• P. galinaceum and P. juxtanucleare


  May cause mortality as high as 90% in chickens
• Experimental studies on P. gallinaceum

  1. Can cause depression, fever, anorexia, reduced weight gain, poor feed conversion, anemia, and green feces

  2. Lethargy, pale comb, diarrhea, and partial or total paralysis may be observed in acute infection

  3. Mortality was observed between 5-10 days post-inoculation
• Hepatomegaly and increased gall bladder volume

  • Observed in P. gallinaceum-infected chickens
• Abnormalities in the brain

  • Including brain edema, inflammatory infiltrates, congested capillaries in P. gallinaceum infection
• Plasmodium juxtanucleare


  • Can also cause CNS signs due to exoerythrocytic forms that damage the endothelial cells of the brain
• Hepatocystis


  Infects monkeys, fruit bats, and squirrels
• Hepatocystis


  • Midges (Culicoides) are the arthropod vectors
  • Life cycle resembles that of Plasmodium, except schizogony in the liver produces visible cysts (merocyst)
  • Hemozoin pigment is deposited in the liver and spleen

  
• Hepatocystis species


  • H. kochi
  • H. semnopitheci
  • H. taiwanensis
  • H. bouillezi
  • H. cercopitheci
  • H. foleyi

  
• Haemoproteus spp.


  More than 120 species have been identified
• Haemoproteus species affecting domestic birds

  • H. columbae- pigeon
  • H. meleagridis- turkey
  • H. nettionis- duck, goose, swan
• Haemoproteus


  • Vectors are hippoboscid flies, midges (Culicoides spp.), or Chrysops spp.
  • Life cycle is similar to that of Plasmodium except that schizogony occurs in endothelial cells of blood vessels
  • Gametocytes occur in erythrocytes with a halter-shape apperance surrounding the nucleus
  • Hemozoin is also present

  
• Leucocytozoon spp.


  • Schizogony occurs in the parenchyma of liver, heart, kidney or other organs
  • Macrogametes and microgametes occur in blood cells (erythrocytes, lymphocytes, monocytes)
  • Hemozoin is not formed

  
• Leucocytozoon


  • Vectors are black flies (Simulium) or biting midges (Culicoides)
• Leucocytozoon species


  • L. simondi- young ducks and geese
  • L. caulleryi- domestic chickens
  • L. smithi- turkeys
• H. columbae


  • Considered lowly pathogenic, but heavy mortality has been noted in pigeon nestlings
  • Clinical signs are anorexia and anemia
  • Necropsy findings include enlarged and dark liver and spleen
• L. caulleryi


  • Highly pathogenic in chickens, causing anemia, hemorrhages in internal organs, splenic enlargement, and white spots in heart muscle
  • Megaloschizonts appear in the kidney, lung, and heart, not in liver
• Ducklings infected with L. simondi


  • Can be listless, anorexic, rapidly breathes, and may show nervous derangements prior to death
• Diagnosis of malaria infections

  • Microscopic examination of blood smear stained with Romanowsky stains
  • Antibody-based detection tests are available for human malaria detection, which is rapid, specific, and more sensitive
  • New-generation tests based on detection of plasmodium lactate dehydrogenase