Parasitology lecture 1 Flashcards
define parasite
an organism living in or on another organism, the host, and benefiting at the expense of the host.
the majority of animals are parasitic, 4,000 animal species but 5,000 tapeworm species, 200,000 parasitic wasp species etc
define endoparasite
a parasite that invades the host, including the gut.
define ectoparasite
a parasite generally external to the host e.g. ticks
define definitive host
a host in which the parasite reaches sexual maturity or sexually reproduces.
define intermediate host
a host required for parasite development but doesnt reach sexual maturity in it.
what are the major endoparasitic groups?
1 - Protozoa (reproduce directly in the host)
a - trypanosomes - sleeping sickness
b - leishmania spps - leishaniasis
c - plasmodium spps - malaria
d - babesia spps - tick bourne disease of cattle
2 - Metazoa (generally no direct replication in the host).
Helminths
a - Nematodes - ascaris, hookworms, filarial worms
b - trematodes - schistosomes
c - cestodes - tapeworms
parasite life cycle classifications and why important to understand.
1 - direct life cycle - sinlg ehost species
2 - indirectly life cycle - 2 or more host species eg involve vector (mosquito) or predator-prey relationship
3 - zoonosis - found mainly in animals but may pass to humans. animal reservoir.
imp to understand as their complexities cause different disease manifestations, make them susceptible to different control measures, and give them different mechanisms of immune evasion.
Ascaris lumbricoides
- description, lifecycle, establishing infection, survival in host, host damage
1 - suum is close relative
2 - parasitic nematode. direct cycle. 15-35cm long adult. 1 year lifespan. adult female = 200,000 eggs a day
3 - eggs embryonate in soil, infective stage is v resilient and can survive over 10 years but sensitive to UV light.
4 - male and female adult in small intestine - eggs in faeces - ebryogenesis to infective larvae in eggshell - ingestion - larvae hatch, enter villus of SI enter portal circulation - lungs, penetrate alveoli, migrate to pharynx - swallowed - repeat.
5 - about 1.3million infected.
6 - establish infection - orofaecal, many resilient eggs, easy to be infected (hygiene, night soil fertiliser)
7 - survivial in host - feed on liquid in intestinal lumen, large so problem for immune system, location in lumen makes it difficult for immune system to reach
8 - damage to host
- heavy infection fatally block gut (hundereds of worms)
- damage lungs (pneumonitis) when migrating
- allergic response to worm metabolites, strong Th2, rashes, eye pain, asthma
- other clinical: abdominal pain, nausea, vomiting, impaired vit A absorption, lactose intolerance, decreased protein and fat utilisation.
- 1.5million kids never recover from the physical and cognitive development issues.
Necator americanis
1 - hookworms. direct cycle. much smaller than ascaris at around 1cm.
2 - adult in small intestine feed on blood - egg in faeces - egg hatches to release infective larvae - attach to skin and penetrate - migrate to lungs, coughed up , swallowed - repeat.
4 - active invasion, may live 15 years, adult female around 10,000 eggs a day, infections flourish if soil contaminated by the faeces, juveniles dont develope below 17degrees C.
5 - host damage - messy feedeing on blood in SI. heavy infections may lose up to 200ml blodd per day. anaemia. moderate infection causes slight intermittent abdominal pain and loss of appetite. heavy infections can cause catastrophic malnutrition impairing child physical and cognitive development.
6 - survival in host - produce anti-coagulants, antiinflammatory AChE, superoxide dismutase to inactivate ROS intermediates, proteinases to digest host chemokines etc, pro-apoptotic factor.
7 - hookworm elicits the immune response but causes recruited T cell apopotosis hence fairly asympotomatic, probably contributing to longevity of infection.
Filarial Nematodes - wucheria bancrofti
1 - Wucheria bancroft - causes filariasis (elephanitiasis)
2 - indirect cycle, blood feeding vector (mosquito). complex immune response is a major contributor to disease. 4-10cm long.
3 - adult worm in lymph node - microfilaria released into blood - injested by mosquito, develope into infective larvae - ifective larvae enters feeding wound - repeat.
4 - infection in a broad equatorial belt, inflammatory response due to adult worm antigen and bacterial infections (enter with worm or endosymbiotic).
- lymph return blocked, accumilation and duct dilation, progressive infiltration of fibrous connective tissue.
- most commonly affects scrotum, legs and arms.
5 - ? - wolfbachia bacterial recently found in mutualistic association, kill with antibiotics causes germline tissue apoptosis of worm so output drops and lifespan from 10 to 2 years.
define microfilaria
The microfilaria is an early stage in the life cycle of certain parasitic nematodes in the family Onchocercidae.
Filarial Nematodes - onchocerca volvulus
1 - indriect life cycle, transmitted by blood feeding blackfly.
2 - complex immune response a major factor in disease
3 - 20-50cm in length. adult worm in subcutaneous nodules - microfilaria released into skin - microfilaria ingested by blackfly and develope into larvae - infective larvae enter wound during feeding - repeat.
4 - microfilaria not adult causes pathology
5 - adult worm nodules can sometimes cause elephantiasis, degenerating microfilaria in skin cause dermatitis called sowda - profound psychological burden.
6 - microfilaria that leave skin may invade eye, cause inflammation and sclerosing keratisis of the cornea (build up of fibrous tissue causing blindness).
7 - may be 1,500 blind per 100,000 where endemic
8 - ? - wolfbachia bacterial recently found in mutualistic association, kill with antibiotics causes germline tissue apoptosis of worm so output drops and lifespan from 10 to 2 years.
Toxoplasma gondii
1 - intracellular parasitic protozoa with direct and indirect lifecycle.
2 - cat is the definitive host.in gut epithelial cells - oocysts in faeces - oocyst can reenter another cat or ingested by intermediate vertebrate ie mouse, rat, cow ,man. - parasite develope and produce cyst in tissues, can cross placenta to foetus. - tissues eaten with cyst to infect cat or intermediate causing tissue cysts.
3 - in humans a major cause of birth defects. spontaneous abortion in sheep. can affet all birds and mammals.
4 - cell invasion - many parasitic protozoa are intracellular and many are cell type specific but t.gondii invades many cell types. enter via phagocytosis or active parasite driven entry. generally via receptor interaction with parasite ligand (cell specificity). invasion is active and mediated by the parasite cytoskeleton in contrast to bacterial and viral entry. ends up in a parasitophorous vacuole where it replicates then bursts out.
5 - survival in macrophages - as it actively invades then the normal lysosome fusion, acidification and ROS formation don’t occur.
- the parasitophorous vacuole excludes host TM proteins to stop these processes. also interferes with translocation of NF-kB to cell nucleus.
6 - pathogenesis - about 13% of world pop infected. high where raw meat is consumed. most human infections are asymptomatic or mild. cysts can persist for years asymptomatically. if immunosuppressed then may disseminate leading to ocular toxoplasmosis and fatal CNS disorders. an example of a serious opportunistic infection in AIDS patients.
- congenital may cause death or disability of newborn.
How are parasitic diseases controlled?
1 - public health - correct sewage disposal - water supplies clean - food produciton and inspection - education 2 - vector control - vital to know mechanisms/cycle - drainage schemes (china?) - spraying - bite avoidance
