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MICROBIOLOGY 2 NOTES PARASITOLOGY A branch of microbiology that studies parasitism and parasitic organisms( eucaryotic cells). Importance of parasitology: Parasites and their diseases have been known since ancient time but the science of parasitology is relatively young field. W.H.O. Reports: 1. The most prevalent tropical diseases 7 out of 8 are parasite. 2. Most harmful infective diseases afflicting human 5 out of 6 are parasite. 3. More than 1,000,000 people are afflicted with parasites. 4. Human play host to dozen of different parasites. 5. Parasite can also infect animals and plant DISTRIBUTION OF PARASITIC DISEASE The following factors influenced distribution of parasitic diseases. 1. Rapid travel 2. Immigration 3. Increased number of immuncompromised patients Scientific terms in parasitology Infestation: Parasitic organisms or arthropods that live on the surface of a host without multiplication Infection: Invasion and multiplication of a pathogenic parasite in the body, with accompanying reaction by the host Disease: Any damage of host tissues or organs that leads to malfunction of an organ that caused by a parasite. Vector: Any arthropod or other living organism that transports a pathogenic microorganism from an infected to a non-infected host.( e.g ..... malaria ) Definitive or Final Host: The host organism in which a parasite passes its adult and/or sexual reproduction phase (e.g. trophozoite).
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Intermediate Host: The host organism in which a parasite passes its larval stage or asexual reproduction phase. Vector is usually an intermediate host. EXCEPTION In malaria: Anopheles mosquitoes carry plasmodium and transmit malaria from host to host. Mosquito in malaria is the final or definitive host and humans are the intermediate host. Why ? Reservoir Host: An animal that harbor a species of parasite and can serve as a source of parasitic infections for humans Reservoir host can also be the intermediate host. IMMUNE RESPONSE AND PARASITE All parasites elicit immune responses including the formation of IgM, IgG, and IgA antibodies. Host?s immune response to parasitic infection is complex and time -consuming and sometime ineffective. Why? 1. Rapid rate of reproduction 2. Large size 3. Production of slime layer, and capsule 4.Complex life Cycle (various morphological forms and antigenic conversion ). 5. Masking of their surface antigens with the host cell marker (HLA =Human Leukocyte Antigen) 6. Their by-products can prevent the function of: Antibodies, Macrophages (improper processing of antibody -antigen complex), and Lymphocytes. 7. Production of high level of IgE antibody (e.g. Helminth worm) 8. Induce T- cell delayed hypersensitivity response (e.g. protozoa) 9. Parasite larval form can be distorted by host antibody, and the presence of antibody provides resistance to reinfection by new larvae, resulting in a condition called CONCOMITANT.
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