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1 Biology of Malaria Vectors and Parasite-Vector Relationships Dawn Wesson Tulane Department of Tropical Medicine

Dec 16, 2015

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  • Slide 1
  • 1 Biology of Malaria Vectors and Parasite-Vector Relationships Dawn Wesson Tulane Department of Tropical Medicine
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  • 2 Malaria Vector Biology Anopheline Life Cycle habitat preferences, types of habitat, unpolluted water Anopheline Life Cycle habitat preferences, types of habitat, unpolluted water Effect of human activities on habitat creation agriculture, irrigation, etc. Effect of human activities on habitat creation agriculture, irrigation, etc. Biology of Malaria Vectors General and Specific Biology of Malaria Vectors General and Specific
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  • 3 Family Culicidae > 3500 species 3 subfamilies: Anophelinae - Anopheles, Bironella and Chagasia, ~ 500 species Toxorhynchitinae - Toxorhynchites, 70+ species (all non-bloodfeeding) Culicinae - Aedes, Culex, Haemagogus, Mansonia, and all other genera, > 3000 species Anophelinae Toxorhynchitinae Culicinae time
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  • 4 Anopheles mosquito life cycle
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  • 5 eggs
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  • 6 AnophelineCulicine Adult
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  • 7 Genus Anopheles 6 subgenera: Cellia - >230 species, most important Old World malaria vectors (Africa and Asia) Anopheles - >180 sp., were the most important malaria vectors in Europe and N. America Nyssorhynchus - >40 sp., most important New World malaria vectors Kertezia - >10 sp., NW, bromeliads Lophopodomyia 6 sp., NW tropics Stethomyia 5 sp., NW tropics
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  • 8 Anopheles Habitat Preferences Effects of human activities Effects of human activities Major malaria vectors tend to be colonizing species in temporary habitats free of established predators Major malaria vectors tend to be colonizing species in temporary habitats free of established predators They have evolved with humans to take advantage of these environments They have evolved with humans to take advantage of these environments
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  • 9 LARVAL HABITAT - An. albimanus in Cuba WHO/TDR/Service, 1992
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  • 10 LARVAL HABITAT - An. bellator in Brazil from bromeliades WHO/TDR/Service, 1992
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  • 11 LARVAL HABITAT - An. pseudopunctipennis in Mexico WHO/TDR/Service, 1992
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  • 12 LARVAL HABITAT - An. stephensi from water tanks on rooftops in Dubai WHO/TDR/Service, 1992
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  • 13 LARVAL HABITAT - Standing water created by road building in Benin WHO/TDR/Olliaro, 1988 LARVAL HABITAT - Irrigation ditches provide Anopheles breeding sites in the Gambia WHO/TDR/Lindsay, 1991
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  • 14 WHO/TDR/Lindsay, 1991 WHO/TDR/Martel, 1994 LARVAL HABITAT - Rice fields and irrigated areas provide Anopheles breeding sites in Viet Nam and the Gambia
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  • 15 WHO/TDR/Service, 1992 WHO/TDR/Ragavoodoo, 1992 Roof water breeding site of An. arabiensis in Mauritius Water storage pots, breeding site of An. gambiae and other mosquitoes in Nigeria
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  • 16 WHO/TDR/HOLT Studios, 1992 Anopheles gambiae Biology of Anopheles gambiae
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  • 17 Anopheles gambiae Major malaria vector in sub-Saharan Africa Major malaria vector in sub-Saharan Africa Typical anopheline life cycle, but extreme preference for living around and feeding on humans Typical anopheline life cycle, but extreme preference for living around and feeding on humans Preferred oviposition sites small temporary pools in full sunlight Preferred oviposition sites small temporary pools in full sunlight Seasonal abundance correlates with rainfall Seasonal abundance correlates with rainfall
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  • 18 Anopheles gambiae life cycle Other sites irrigated areas (rice fields); drying streams in dry season; habitats created by humans Other sites irrigated areas (rice fields); drying streams in dry season; habitats created by humans Eggs laid on water or damp soil; hatch 48 hr. 2 weeks Eggs laid on water or damp soil; hatch 48 hr. 2 weeks Larvae can crawl across damp soil from drying pool to another with water Larvae can crawl across damp soil from drying pool to another with water Larval development -
  • 36 Peritrophic Matrix (PM) The peritrophic matrix is a layer of acellular material separating ingested food from epithelial cells The peritrophic matrix is a layer of acellular material separating ingested food from epithelial cells peritrophic comes from the Greek word peri for around; trophic is the Greek word for food. The PM surrounds the food bolus. peritrophic comes from the Greek word peri for around; trophic is the Greek word for food. The PM surrounds the food bolus. Peritrophic membrane was termed >100 years ago but membrane implies lipid bilayer. The PM is not -- it is a sheath of cheesy material of amorphous appearance. The word matrix is more suitable! Peritrophic membrane was termed >100 years ago but membrane implies lipid bilayer. The PM is not -- it is a sheath of cheesy material of amorphous appearance. The word matrix is more suitable!
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  • 37 Other important points -- PM The signal that activates PM secretion is the physical distention of the midgut epithelium; eg, ingestion of partial bm does not trigger PM formation The signal that activates PM secretion is the physical distention of the midgut epithelium; eg, ingestion of partial bm does not trigger PM formation Mosquitoes, blackflies, and sandflies secrete different type of PM during larval life Mosquitoes, blackflies, and sandflies secrete different type of PM during larval life PM is permeable to digestive enzymes PM is permeable to digestive enzymes Possible barrier to pathogen infection Possible barrier to pathogen infection
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  • 38 Structure of salivary glands Structure varies among insect phyla Structure varies among insect phyla In mosquitoes, salivary glands of both sexes are paired organs located in the thorax, and each gland consists of 3 lobes connected to a main salivary gland duct (male sgs small) In mosquitoes, salivary glands of both sexes are paired organs located in the thorax, and each gland consists of 3 lobes connected to a main salivary gland duct (male sgs small) Female sgs have two identical lateral lobes and one shorter medium lobe. Lateral lobes can be divided according to proximal and distal regions (different regions secrete different proteins) Female sgs have two identical lateral lobes and one shorter medium lobe. Lateral lobes can be divided according to proximal and distal regions (different regions secrete different proteins)
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  • 39 Function of the salivary glands Saliva contains enzymes that digest sugars Saliva contains enzymes that digest sugars Salivary gland secretions play a role in the maintenance of feeding mouthparts - saliva acts as a lubricant Salivary gland secretions play a role in the maintenance of feeding mouthparts - saliva acts as a lubricant In ticks, water in ingested blood is cycled back through the sgs where it is returned to the host In ticks, water in ingested blood is cycled back through the sgs where it is returned to the host
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  • 40 Salivary Glands and Bloodfeeding Salivary glands produce a saliva that facilitates rapid and efficient feeding (hemagglutinin, anticoagulant, antiplatelet activity, vasodilators) Salivary glands produce a saliva that facilitates rapid and efficient feeding (hemagglutinin, anticoagulant, antiplatelet activity, vasodilators) Parasites can increase the probability of their transmission by modifying arthropod salivary activities Parasites can increase the probability of their transmission by modifying arthropod salivary activities Malaria sporozoites infect the female-specific salivary gland lobes (distal-lateral and medial) Malaria sporozoites infect the female-specific salivary gland lobes (distal-lateral and medial)
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  • 41 Salivary Glands and Bloodfeeding -2 Parasite invasion causes cellular damage in the glands 4-5x reduction in apyrase activity Parasite invasion causes cellular damage in the glands 4-5x reduction in apyrase activity The salivary apyrases of blood-feeding arthropods are nucleotide hydrolysing enzymes and have been implicated in the inhibition of host platelet aggregation through the hydrolysis of extracellular ADP. The salivary apyrases of blood-feeding arthropods are nucleotide hydrolysing enzymes and have been implicated in the inhibition of host platelet aggregation through the hydrolysis of extracellular ADP. Sporozoite-infected mosquitoes take longer to probe more sporozoites released Sporozoite-infected mosquitoes take longer to probe more sporozoites released Also, more interrupted feedings bite more frequently before achieving successful bloodmeal Also, more interrupted feedings bite more frequently before achieving successful bloodmeal
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  • 42 Immune responses of vectors Arthropod immune responses are not like vertebrate antigen-antibody reactions but the internal defense mechanisms are still specific and effective in destroying pathogens and parasites. Arthropod immune responses are not like vertebrate antigen-antibody reactions but the internal defense mechanisms are still specific and effective in destroying pathogens and parasites. Much of what we know comes from immune studies of lepidopteran larvae. Much of what we know comes from immune studies of lepidopteran larvae.
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  • 43 Cuticular and gut barriers The arthropods pos
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