Presentation on theme: "MEDICAL ENTOMOLOGY OVERVIEW"— Presentation transcript:
1 MEDICAL ENTOMOLOGY OVERVIEW DefinitionHistoryIntro to Arthropods and InsectsIntro to Vector-Borne Disease Concepts
2 MEDICAL ENTOMOLOGY - the study of diseases caused by arthropods public health entomology - arthropods and human healthveterinary entomology - arthropods and pets, livestock and wildlifeThese fields of study are linked by the ecology of most arthropod transmitted pathogens and parasites.
3 Arthropods affect the health and well-being of humans and animals in several ways: Direct Causes of Disease or DistressVectors or Hosts of Pathogenic OrganismsNatural Enemies of other medically harmful insects
4 Direct Causes of Disease or Distress: Ectoparasites - ticks, fleas, mitesEndoparasites - chigoe flea, myiasisEnvenomization - wasps, bees, spidersAllergic Reactions - dust mitesAnnoyance - mosquitoes, black fliesDelusory parasitosis (DP) - psychosis
5 Vectors or Hosts of Pathogenic Organisms: Arthropod serves as intermediate host and vector of pathogenic microorganismsVectors and hosts - bloodfeedingHosts only - no bloodfeeding
6 Natural Enemies of other medically harmful insects: Mites parasitic on mosquitoesFire ants consume tick eggs
7 History of Medical Entomology: References to associations between humans and arthropods – historical(Homer and Aristotle, among others, wrote about the nuisance caused by flies, mosquitoes, lice and/or bedbugs.)Important discoveries:Microscope - Leeuwenhoek 1700’sInfectious Disease - Koch et al. 1800’s
8 History of Medical Entomology - 2: Mosquitoes (Culex pipiens) and filarial worms (Wuchereria bancrofti) - Manson, 1877Tick (Boophilus annulatus) and Texas cattle fever (piroplasmosis) transmission - Smith & Kilborne, 1891Mosquito (Aedes aegypti) and yellow fever virus - Finlay, Reed, Carroll, Agramonte and Lazear, 1900Trypanosomes in cattle blood - Bruce, 1895Tsetse fly (Glossina sp.) transmission of trypanosomes - Bruce, 1896Tsetse fly transmission of trypanosomes to humans (African Sleeping Sickness) - Bruce, 1903
9 History of Medical Entomology - 3: Malaria parasites in human blood - Laveran, 1894Anopheles mosquitoes with malaria parasites - Ross, 1897Transmission of bird malaria by Culex mosquitoes - Ross, 1898Complete development of human malaria parasite in mosquitoes - Grassi, 1898Transmission of human malarial parasite by mosquitoes - Sambon and Low, 1899Only Anopheles mosquitoes transmit human malarial parasites - Watson and Christophers, 1899
10 History of Medical Entomology - 4: Mosquito transmission of dengue virus - Graham, 1902Fleas and plague - Liston, Verjbitski et al.,Triatomine bugs and trypanosomes (Chagas disease) - Chagas, 1908Black flies and onchocerciasis (river blindness) - Blalock, 1926Mosquitoes and viral encephalitides - Hammon and Reeves, early 1940’sTicks and Lyme disease - Spielman, early 1960’s
12 Taxonomy and Systematics Phylum Arthropoda:The phylum is probably monophyletic, but with 4 distinct groups.It includes lobsters, crabs, shrimp, centipedes, millipedes, daddy longlegs, insects, ticks, and mites, and spiders.There are over 1 million species of arthropods, making up the largest phylum in the animal kingdom.
13 Phylum Arthropoda - 2:Metameric - (body exhibits true segmentation - replication of muscles and nerves)Tagmatosis - (segments of the body are modified and grouped together to form mouthparts and body regions such as the thorax)Chitinous exoskeleton – nitrogenous polysaccharide
14 Phylum Arthropoda - 3:Bilaterally symmetricalJointed legsDorsal heart – open circulatory systemCNS (organized central nervous system)Striated muscle
15 Hypothetical Insect Evolution “Worm-like” ancestorMetamerism(true segmentation)Tagmatosis(segments modified and grouped together to form larger body parts)
45 Transmission efficiency: Geographic or host distribution of the parasiteIncidence of any given parasite and associated hostParasite enhancement of transmissionTransmission frequency:Shorter life cycle of parasite = more frequent and more efficient transfer to be successfulBoth transmission efficiency and frequency related to bloodfeeding frequency and efficiency of the vector. These are important factors in vector capacity.
55 Intrinsic barriers to transmission in the vector - (genetically and environmentally controlled) midgut infection, midgut escapesalivary gland infection, salivary gland escapeinsect immune response, parasite encapsulation
56 Vector competence vs. vector capacity Capacity can be measured in the field using components of number of vectors per human, number of human bloodmeals per day per vector, daily survival rate, and the extrinsic incubation rate of pathogen; vector efficiency is expressed in terms of low - high capacityCompetence can be expressed in the laboratory, but a competent lab vector is not necessarily important in disease transmission in the field.