Parasite transmission by arthropods

Published on October 26, 2010 Reviewed on June 15, 2020   41 min

A selection of talks on Microbiology

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My name is Bill Reisen. I'm a research entomologist with the Center for Vectorborne Diseases within the School of Veterinary Medicine at the University of California, Davis. My Henry Stewart talk today is entitled Parasite Transmission by Arthropods.
The objectives of my talk will be to review problems of parasite acquisition by arthropods, compare modes of replication and transmission by different parasites, and present some of the factors affecting the efficiency of this transmission.
Before we get too far into our lecture today, I'd like to go over some basic definitions to make sure we're all on the same plane. A parasite is any organism that requires another organism or host for its requisites for life. In this definition, then, not only the microorganisms transmitted by arthropods are parasites, but also the arthropods themselves, which take nutrients and sustenance from their host. Disease is caused by the interaction of the parasite infection and the response of the host. Parasites that cause disease are pathogens. A definitive host is the host in which sexual reproduction by the parasite occurs, whereas the intermediate host is where asexual reproduction occurs. In general, most arthropod vectors serve as intermediate hosts, but there are exceptions. In arthropod-borne parasite transmission, the arthropod vector provides the mechanism of transmitting or sending the parasite from one host to another. Transmission of the parasite can be nonpropagative or mechanical, and this is usually by contaminated mouth parts of the vector. In contrast, when the injected parasite develops or reproduces or propagates within the arthropod, transmission is biological. Biological transmission between the vector and vertebrate host is termed horizontal transmission, in contrast to vertical transmission that occurs only within the arthropod species. Within the arthropod, transmission can be transstadial-- across stadia, or stages of the arthropod-- or transgenerational-- from one generation to the next. A stadium is a stage of the arthropod between molts, and there are instars, or molts within stages. Intrinsic incubation is the period within the vertebrate host between infection and disease onset. The extrinsic incubation period is within the vector, and it is the time between its infection and transmission.