black11 - Parasitology Parasites include things that live...

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Parasitology Parasites include things that live internal (endoparasites) or external (ectoparasites) to the infected (or infested) host Broadly speaking, all pathogens may be classified as parasites Narrowly speaking, Parasitology is the science that studies the relatively large parasites including parasitic Protists, Worms, and, to a lesser degree, pathogenic Fungi and Arthropod ectoparasites Today we’ll consider Protists , Helminths (worms), Fungi , and the Arthropod Vectors of infectious disease
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Vectors and Hosts A Vector is a living organism that carries a disease- causing organism to new Hosts This distinction can be arbitrary, however, depending on which organism’s infection we are most concerned with Thus, the Anopheles mosquito is a vector for the parasitic disease malaria because we care more about the health of the human host than that of the mosquito However, in addition, the malaria parasite has a much greater impact on the health of the human host than it does on the health of the mosquito vector
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Biological vs. Mechanical Vector The real confusion between host and vector comes from the concept of Biological Vector Within (or upon) both a host and a Biological Vector the parasite undergoes some aspect of its life cycle Thus, in one sense, all hosts that can pass a parasite on, particularly to another species of host, is also a Biological Vector However, if the parasite does not undergo some aspect of its life cycle as it is transported by one organisms to a second, then the first organism is described as a Mechanical Vector E.g., flies can be mechanical vectos of feces-born pathogens such as Salmonella
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Types of Hosts Definitive Host : The host in which the parasite goes through its sexual cycle (I.e., fertilization & meiosis) E.g., mosquitoes serve as definitive hosts of the malaria parasite ( Plasmodium spp.) E.g., snakes (~30 species) serve as definitive hosts of Sarcocystis singaporensis , a disease of mammals
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Types of Hosts Intermediate Host : Host in which the parasite replicates but does not go through its sexual cycle E.g., mammals, including humans, serve as intermediate hosts of the malaria parasite ( Plasmodium spp.) E.g., mammals (~30 species, including humans) serve as intermediate hosts of Sarcocystis singaporensis S. singaporensis has been proposed as a biological control of rodents pests— apparently it can selectively kill them!
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Types of Hosts Reservior Hosts : The reservoir host is the population in which a parasite resides when it isn’t affecting a population that we care more about E.g., the rabies virus normally is passed back and forth among wild mammals (these serve as the reservoir hosts—the populations that we don’t much care about)
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This note was uploaded on 06/03/2011 for the course MCB 205 taught by Professor Abedon during the Spring '11 term at Ohio State.

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black11 - Parasitology Parasites include things that live...

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