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Malaria
- Disease caused by protozoa in mammals, lizards, and birds.
- a. P. falciparum
- b. P. vivax
- c. P. malariae
- d. P. ovale
- e. P. knowlesi (SE Asia)
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Transmission of Malaria
- through mosquitoes and sandflies
- Mammals: Anopheles
- Lizards: Culex mosquitoes and Lutziomyia sandflies
- Birds: Culex or Anopheles
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Increasing Problems for Malaria
- Resurgence in some areas
- Drug resistance
- Insecticide resistance in mosquito vectors
- malaria reporting in some countries is repressed due to tourism
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Symptoms of malaria
- acute malaria paroxysms
- -periodic episodes of fever alternating with symptom free periods
- manifesttions and severity depend on plasmodium species and host status
- 1. immunity, general health
- 2. nutritional state
- 3. genetics
- Sickle cell=immunity.
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Relapse of Malaria
- Relapse:
- 1)pathogen disappears from blood, goes dormant in some other tissue, disease ceases
- 2)Pathogen returns to blood, disease renews
- Recrudescence:
- pathogen remains in blood at low levels, starts massive reproducing
- P. falciparum: severe, cerebral malaria
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Malaria Paroxysm
- Paroxysms associated with synchrony of merozoite release.
- Between paroxysms, temperature is normal and patient feels well.
- P. falciparum may not exhibit paroxysms
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Life Cycle of Plasmodium species
- A. Four reproductive events in each cycle of
- Plasmodium life history
- 1. Two different repetitive asexual cycles
- (Merogony) in the vertebrate host
- 2. Gamete production in the vertebrate
- (Gametogeny) infects the arthropod host
- 3. Zygote formation leads to one asexual non-
- repetitive cycle (Sporogony)
- Human: sexual, definite phase
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Development in the Vertebrate Host
- 1. Exoerythrocytic Merogony (outside red blood
- cells) phase
- 2. Asexual reproductive cycle in non circulating
- tissues
- a. Hepatocytes in mammals (liver)
- b. Mononuclear phagocytes in reptiles and birds
- Sporozites from saliva of insect invade human cell, leading to trophozoite and thus merogony (schizont to merozoite).
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Exoerythorocytic Merogony
- cycle can continue in non circulating tissue. some merozoites form a lasting stage called hypnozoites which can last 20 odd years, hiding in liver. due to some trigger, they will restart cycle and you will get sick. (Recrudescence).
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Erythroctic Merogony and Gametogeny
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Development of Malaria in the Invertebrate Host
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Sporogony in the Anthropod Host
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Specific example: Plasmodium falciparum in Humans (Exoerythrocytic)
- A. Exoerythrocytic
- Merogony
- 1. hepatocyte invasion
- 2. Asexual replication, one cycle only
- 3. 6-15 days
- 4. 10,000 merozoites
- 5. no overt pathology
- 6. Hypnozoite forms not in P. falciparuma)some EE forms exhibit delayed replication
- b)Merozoites produced weeks to months after initial infections
- c) only P. Vivax and P. ovaled) RELAPSE = HYPNOZOITE
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Specific example: P. falciparum in humans (Erythrocytic Merogony)
- Blood invasion
- 1. Merozoite invasion of cell
- a) growing parasite places demands on host cell
- b) ultrastructural modifications of erythrocyte
- c) collect in deep vascular system
- 2. Trophozoite development
- a) intracellular parasite undergoes trophic phase
- b) young trophozoite called "ring form"
- c) ingests host hemoglobin
- -cytosome
- -food vacuole
- 2. Meront (Schizont) developmenta) nuclear division
- b) many nuclei (6-40)
- c) Erythrocyte rupture and releases merozoites
POSITIVE IF CAN ANGLE POLARIZED LIGHT
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Specific example: P. falciparum in humans (Gametogony in the human host)
- 1. Microgametes (♂) & Macrogametes (♀) produced
- 2. More common as infection progresses
- 3. Taken up by mosquito during blood meal
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Specific example: P. falciparum in human host (sporogony in the mosquito vector)
- 1. Over 400 species of mosquitoes in the genus
- Anopheles
- 2. About 40 are vectors of plasmodium to
- humans
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Specific example: P. falciparum in human host (Zygote formation in the mosquito)
- 1. Occurs in mosquito gut- gametes exit blood
- cells- ♂ locates ♀, fuse
- 2. Male gamete ‘exflagellation’ most obvious
- a. 3X nuclearreplication
- b. 8 microgametesformed
3. Female gamete-no division
- 4. Zygote formation
- a. Zygote becomes motileookinete (~24 hr)
- b. Ookinete transverses gut epithelium
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Specific example: P. falciparum in human host (Oocyst formation and sporogony)
- 1. Ookinete becomes oocyst
- a. Between epithelium and basal lamina
- b. Asexual replication sporozoites
- c. Sporozoites released
- d. Penetrate salivary glands
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Controlling malaria
- A. Drugs that kill the parasite
- 1. Example: chloroquine
- 2. Problems: resistance, price, side effects,
- logistics
- B. Insecticides that kill the mosquito vector
- 1. Example: DDT
- 2. Problems: resistance, logistics, environmental impacts
C. Vaccines ????
D. Genetically Modified Mosquitoes (GMM)
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