Parasitology - Lecture 3 Flashcards
What do parasites broadly require?
Require a host organism to survive/propagate
-includes viruses, bacteria, symbiotic organisms
What is a prarasite biologically?
Eukaryotic organisms which live on or in a host organism, and which utilize its resources for their own survival and propagation
What are the two classifications of parasites?
Protazoa - unicellular
Metazoa - multicellular (include helminths (internal) and ectoparasites (external))
How do parasites replicate?
Replicate extracellularly
Where do parasites largely infect?
The GI tract and blood
How are parasitic infections (GI and blood) transmitted?
Are they communicable?
- GI tract infections typically transmitted via fecal:oral route
- Blood infections typically transmitted via animal vector
- Many parasitic infections are not communicalbe
Where do parasites typically complete their life cycle?
Many complete their life cycle in TWO species:
- Definitive host - sexual stage of reproduction is complete (Primary Host)
- Intermediate host - non-sexual stages of reproduction are completed - parasite may not reproduce at this stage, or may undergo differentiation
What are the four classifications of Protozoa?
Amoeba (sacrodina)
Flagellates (mastigophora)
Ciliates (ciliophora)
Spore-forming (apicomplexa)
Describe amoebas:
nutrient
movement
human pathogen
Obtain nutrients via phagocytosis
Move via pseudopodia
- push out cytoplasm to produce ‘false feet’
- conversion of ectoplasm to endoplasm and vice versa allow amoeboid movement
Entamoeba histolytica (intesinal amoebiasis)
How are amoebas infections acquired?
Through ingestion of contaminated food and water
Describe nonivasive vs invasive ameoba infection
A noninvasive infection is the formation of a cyst that exits the host in stool
An invasive infection happens with trophozoites invade the intestinal mucousa, travel the blood stream infecting sites such as the liver, brain and lungs
Describe flagellates:
movement
human pathogen
Longe flagella that whip to facilitate movement
Organism may bear one or multiple flagella
Variety of cellular structures between flagellated protazoan parasites
Giardia lambia (giardiasis)
Trichomonas vaginalis
Trypanosoma cruzi
How are flagellate infections acquired?
Through ingestion of a mature cyst (cysts can survive weeks to months in cold water, but only cysts can survive outside host)
Describe ciliates
Cilia provide motility and aid in feeding (phagocytosis)
variety of feeding strategies and cellular sturctures
Balantidum coli - only human pathogen
Overview the general protozoan life cycle
Cyst stage - infective
- cysts are hearty, resist extreme environmental conditions
- may survive long periods of time outside a host organism
- may be the product of sexual reproduction in protazoa
Excystation
–occurs in the host organism and typically yeilds a trophozoite
Trophozoite
-feeding/proliferation stage (asexual reproductive stage)
Describe sporozoa (apicomplexa)
Have a complex subcellular strucure
- apical complex structure (may aid in entry)
- apicoplast organelle (potential functions include fatty acid synthesis, heme synthesis)
Describe the general life cycle stages of sporozoa
Sporogony yields oocysts and sporozoites
Merogony yields shizonts and merozoites
Gametogony yields gametes and zygots
Give four example of sporozoa human pathogens
Cryptosporidium
Toxoplasma gondii
Falciparum (malaria)
Babesia
List the different malaria names…
Plasmodium falciparum - most severe Plasmodium malariae Plasmodium vivax Plasmodium ovale Plasmodium knowlesi
Describe vector-borne infections
May be animate or inanimate
Inanimate vectors are mechanical - facilitate spread of pathogen
What are the animal vectors commonly?
Arthopods - mosquitoes, fleas, flies
Rodents - mice, rats
Are vector-borne infections contagious?
Not contagious IF an essential stage of the pathogen’s life cycle takes place in the vectore species
- Malaria - sexual reproduction stages occur in the mosquito
- Giardiasis - all stages of reproduction occur in humans even though the parasite infects dogs, cats, cattle, beavers
How is the pathogen controlled?
Controlled through vector control
-Epidemiology of vector-borne infections is closely related to ecology and climate, prevalence of vector
Describe helminths
Multicellular parasites
Typically infect the GI tract
How are helminths classified?
Classified by shape
- Platyhelmiths (‘flat’) - cestodes and trematodes
- Nematodes (‘threads’)
What are trematodes?
Flukes and flatworms
Describe trematodes
sexual
host
structure
Dioecious or hermaphoraditic
Require at least 1 intermediate host (mollusk)
-sexual reproduction occurs in the definitive host
-asexual stages of reproduction occur in intermediate host
Complex organismal structure
-reproductive system
-nervous system
-GI-like system
Give three examples of trematode human pathogens and where they infect
Schistosoma (blood - schistomiasis) Paragonimus westermani (lung) Fasciola hepatica (liver)
How do trematodes infect humans?
Infect human by penetrating skin
What are cestodes?
Tapeworms
Describe cestodes
structure
adult vs larval infection
Segmented, hermaphroditic (each segment), macroscopic
Adult tapeworms lead to intestinal infections
Larval infection leads to extra-intestinal cyst deposition
Give four examples of cestode human pathogens and where they come from
Taenia solium (pork) Taenia saginata (beef) Diphyllobothrium latum (fish) Echinococcus (dogs)
how do cestodes infect humans?
Infect humans by ingesting undercooked
What are nematodes?
Roundworms
Dioecious
Intestinal and extra-intestinal pathogens
Give four examples of nematode human pathogens
Enterobias vermicularis (pinworm) Necator americanus (hookworm) Trichura trichiuris (whipworm) Ascaris lumbricoides (giant roundworm)
How do nematodes infect humans?
Infect human by ingestion of embryonated eggs
