Parasitology I - Ross University PDF

VMA 5114 Principles of Infectious Diseases Parasitology I – Basic concepts Learning Objectives 1. Comprehend host and parasite. 2. Master main characteristics of six groups of parasites.  GLOSSARY Symbiosis: An association of two organisms which can not e...

VMA 5114 Principles of Infectious Diseases Parasitology I – Basic concepts Learning Objectives 1. Comprehend host and parasite. 2. Master main characteristics of six groups of parasites.  GLOSSARY Symbiosis: An association of two organisms which can not exist independently, “living together”. Symbionts: Organisms that live in close association with each other.  GLOSSARY Symbiosis: Phoresis: An association in which two organisms merely traveling together Mutualism: An association in which both organisms are benefited Commensalism: An association in which one partner is benefited and the other is unaffected Parasitism: An association in which one partner is benefited and the other is harmed  GLOSSARY Parasitism: Host: the partner who is harmed in parasitism. Parasite: the partner who is benefited in parasitism.  HOSTS 1. Definitive host – harbors adult (sexual) stage of a parasite 2. Intermediate host – harbors larval (asexual) stage of a parasite 3. Paratenic host – harbors a parasite that does not undergo required development; a transfer host 4. Reservoir – an animal (definitive) host that serves to maintain the parasite's life cycle in nature 5. Incidental host – an unusual host, unnecessary for the maintenance of the parasite in nature  Vector An organism responsible for transmitting a parasite from one host to another – Biological Vector: A vector in which the parasite multiplies or develops – Mechanical Vector: One which transmits the parasite unchanged from host to host  Biological vector of malaria: Female Anopheles mosquito Versus Housefly: Mechanical Vector for Entamoeba histolytica. No development or growth of E. histolytica in houseflies, just passively carried.  Biological Vector Biological Vector: They may be a definitive host or an intermediate host depending upon their role in parasite’s life cycle.  DH – a mosquito for malaria parasite: sexual stage  IH – a mosquito for heart worm: Larval stage L1 – L3 (asexual stages)  PARASITES Obligate Parasite – totally physiologically dependent upon its host Temporary Parasite – parasitic for limited periods for either feeding or reproduction Facultative Parasite – organisms that are not normally parasitic but can survive for a limited period when they accidently find themselves within another organism  Parasites Ectoparasite –Lives on the host –Causes infestations Endoparasite –Lives in the host –Causes infections  ZOONOSIS Definition: any disease of animals that is transmissible to humans Examples: Trichinellosis, Chagas’ disease, Schistosomiasis, Giardiasis, Toxoplasmosis, Amebiosis, echinococcosis  PRINCIPLES 1. Protozoa Multiply in definitive host 2. Helminths Adult worms do not multiply in definitive host. Worms die over time, unless the host is re- exposed The severity of disease is proportional to worm load introduced into the host.  HOST SPECIFICITY Parasites (particularly helminths) have specificity for particular definitive and intermediate hosts. Often parasite life cycles can only be completed in a particular host. Disease manifestations of a host can differ depending whether they serve as a definitive, intermediate, or an incidental host. SURVIVAL FACTS AND FUNCTIONS Parasites adapt to every niche in host Best adapted are least pathogenic Parasite-host relationship is typically long- term/chronic/ “intimate” CONDITIONS REQUIRED FOR ENDEMIC PARASITISM Reservoir of infection Means of transmission to susceptible hosts Ability to invade and establish in new hosts Ability to reproduce  Veterinary Parasitology Three groups of eukaryotic organisms that affect health and wellbeing of animals – Protozoa (Protozoology): Single celled, nucleated – Helminths (Helminthology): Worm-like animals showing differentiation, metazoans Nematode – roundworm Cestode – tapeworm (flatworms) Trematode – fluke (flatworms) – Arthropods (Entomology): arachnids and insects; ectoparasites Parasites of veterinary importance Nematodes Cestodes Trematodes Insects Arachnids Protozoa Parasites of veterinary importance Phylum Nemathelminthes (Roundworms) Class Nematoda (Roundworms) Phylum Platyhelminthes (Flatworms) Class Cestoda (Tapeworms) Class Trematoda (Flukes) Parasites of veterinary importance Phylum Arthropoda Class Insecta Class Arachnida Kingdom Protozoa Nine phyla contain at least one genus (genera) of veterinary importance Nematodes (roundworms) Round/cylindrical Complete alimentary canal Celom, body cavity Sexes usually separate Nematodes (roundworms) Ascaris suum, adult male and female  Cestodes (tapeworms) Flat body with no colem (body cavity) No alimentary canal Hermaphroditic Scolex (head) with 4 suckers or bothria Strobila (body) with head, neck and proglottids (segments) All are parasitic with an indirect life cycle Cestodes (tapeworms) Scolex (head), neck and proglottids Cestodes (tapeworms) (Courtesy of Noah’s Archive) Cestodes (tapeworms) (RUSVM, 2013)  Trematodes (flukes) Dorso-ventrally flattened, leaf- like Incomplete alimentary canal No celom Hermaphroditic Oral and ventral suckers for attachment Fluke Internal Structure Trematodes (flukes) – Fasciola spp. Photo: Thomas Nolan  Arthropods Insects Arachnids Flies (Order Diptera) Ticks Fleas (Order Siphonaptera) Mites Lice (Order Phthiraptera) Hemiptera  Insects Identification Adults: 3 pairs of legs Head, thorax, abdomen Antenna Flies (Diptera) (Taylor et al, 2007) Fleas (Siphonaptera) Lice (Phthiraptera) RUSVM, 2006  Cimex spp. – bed bug F ENN N N N A M https://www.sgvtribune.com/2017/08/12/bed‐bugs‐make‐unwelcome‐return‐to‐southern‐california/  Arthropods Insects Arachnids Flies (Diptera) Ticks Fleas (Siphonaptera) Mites Lice (Phthiraptera) Hemiptera  Arachnids Identification Nymphs and adults: Four pairs of legs Larvae: 3 pairs of legs Body: cephalo-thorax and abdomen No antennae Palps Acari: Ticks http://www.cdc.gov/ticks/life_cycle_and_hosts.html  Acari: Mites Identification: microscopic,