3- Parasitology- Pt 1.docx

- **Parasitology: General Info** - Symbiosis is the association of 2 organisms that cannot exist independently, and therefore are living together. - Phoresis is an association in which 2 organisms merely travel together. - Mutualism is an associatio...

- **Parasitology: General Info** - Symbiosis is the association of 2 organisms that cannot exist independently, and therefore are living together. - Phoresis is an association in which 2 organisms merely travel together. - Mutualism is an association in which both organisms are benefited. - Commensalism is an association in which 1 partner is benefited and the other is unaffected. - Parasitism is an association in which 1 partner (parasite) is benefited and the other (host) is harmed. - Symbionts are organisms that live close in association with each other. - Zoonosis is any disease of animals that is transmissible to humans. - Ex: Trichinellosis, Chaga's disease, Schistosomiasis, Giardiasis, Toxoplasmosis, Amebiosis, and echinococcosis - Protozoa will multiply within a definitive hosts. - Helminths are adult worms that do not multiply within a DH, so the worms will die over time, unless the host is re-exposed to the parasite. - In helminth infections, the severity of the disease is proportional to the worm load introduced into the host. - Parasites adapt to every niche in the host. - They are best adapted are the least pathogenic, as parasite-host relationships are typically long-term/chronic/ "intimate". - Conditions required for endemic parasitism include: - Reservoir of infection - Means of transmission to susceptible hosts - Ability to invade and establish in new hosts - Ability to reproduce - **Hosts** - Host **types** include: - The definitive host (DH) harbors the adult (sexual) stage of a parasite. - Ex: A dog is a definitive host for Toxocara canis and Echinococcus species - The intermediate hosts (IH) harbors the larval (asexual) stage of a parasite. - The paratenic hosts (PH) harbors a parasite that does not undergo any required development, and is solely used for transportation. - A reservoir is an animal (definitive) host that serves to maintain the parasites life cycle in nature. - Ex: A dog is a reservoir host for leishmania - An incidental host is an unusual host, unnecessary for the maintenance of the parasite in nature. - Ex: Humans are incidental hosts for Trichinella spiralis which migrate to the human muscle. - Host **specificity** means that parasites (particularly helminths) have specificity for particular DH and IH. - Often the parasites' life cycle can only be completed in a particular host. - Disease manifestations of a host can differ depending whether they serve as a DH, IH, or incidental host. - **Vectors** - Vectors are an organisms responsible for transmitting a parasite from 1 host to another. - Vectors can be biological or mechanical. - Biological vectors are ones in which the parasite multiples or develops. - Biological vectors can be a definitive host or intermediate hosts depending on their role in the parasite's life cycle. - Ex: Female Anopheles mosquitos transmitting malaria act as a DH - Ex: Mosquitos transmitting heart worms act as an IH, as the parasite goes through asexual stages (larval stages L1-L3) within the mosquito. - Mechanical vectors are ones which transmits the parasite unchanged from 1 host to another. - Ex: Housefly transmitting Entamoeba histolytica (which is passively carried) - **Parasite: Types** - Obligate parasites fully physiologically depend on a host (to complete its life cycle) - Temporary parasites are parasitic for limited period for either feeding or reproduction. - Facultative parasites are organisms that are not normally parasitic but can survive for a limited period when they accidentally find themselves within another organism. - Ectoparasites live on the host, typically causing infestations. - Ex: Human body louse (Pediculus humanus) - Endoparasites live inside of the host, typically causing infections. - Ex: Ascaris suum - **Veterinary Parasitology** - 3 groups of eukaryotic organisms that affect the health and wellbeing of animals includes: - Protozoa (protozoology) which are single celled and nucleated - Helminths (helminthology) which are worm-like animals showing differentiation, metazoans - Examples include: - Nematodes which are round worms - Cestodes which are tapeworms (flatworms) - Trematodes which are flukes (flatworms) - Arthropods (entomology) which are arachnids and insects; ectoparasites - Parasites of veterinary importance include: - Phylum nemathelminthes (roundworms) - Class Nematoda (roundworms) - Phylum Platyhelminthes (flatworms) - Class Cestoda (tapeworms) - Class Trematoda (flukes) - **Parasites: Specific Info** - Cestodes have a flat body with no colem (body cavity), no alimentary canal, and are hermaphroditic. - They have a scolex (head) with 4 suckers or bothria. - They have a strobila (body) with a head, neck, and proglottids (segments). - All cestodes are parasitic with an indirect life cycle. - Trematodes have a dorso-ventrally flattened, leaflike body with an incomplete alimentary canal, and they lack a celom. - They are hermaphroditic and use a ventral and oral suckers for attachment. - Arthropods can be differentiated into insects and arachnids. - Insects include: flies (order Diptera), fleas (order Siphonaptera), lice (order phthirapteran), and Hemiptera. - Insect adults have 3 pairs of legs, a head, thorax, abdomen, and antenna. - Arachnids include: ticks, and mites. - Arachnida as nymphs or adults have 4 pairs of legs, while their larvae have 3 pairs of legs. - The arachnid body has a cephalon-thorax, abdomen, palps, and lack antennae. - Acari (mites) are microscopic (less that 1mm long), and their body has scales, spines, setae (hairs), and their legs may have claws or sucks used to attach to hosts. - Protozoa are unicellular, prokaryotic organisms that can be classified based on their mode of locomotion. - They can accomplish locomotion by: pseudopodia, flagella, gliding movement (no locomotion organelle), or cilia. - Trophozoites are 50-150micrometers in size, are ciliated, and have a kidney-bean shaped nucleus. - Cysts are up to 60micrometers in size, and their cilia is sometimes evident inside.