Introduction to parasites Flashcards
a) define parasite
b) examples of protozoa (5) and diseases they cause
c) examples of metazoa and diseases they cause
a) an organism that lives and feeds on or in an organism of a different species and causes harm to its host. Parasitic diseases are caused by eukaryotic protozoan and metazoan
b) Plasmodium - malaria; Trypanosomes - african sleeping sickness, Chagas disease; Babesia - babesiosis in cattle; Leishmania - leishmaniasis; Toxoplasma - toxoplasmosis
c) Parasitic worms or helminths. Helminths are further divided into roundworms (nematodes) and flatworms (cestodes and trematodes)
Define
a) direct life cycle
b) indirect life cycle
c) definitive host (+eg)
d) intermediate host (+eg)
a) when the parasite requires only a single host
b) when the parasite requires two or more hosts (can involve a vector or a predator-prey relationship
c) host in which the parasite reaches sexual maturity on or in which the parasite’s sexual reproduction occurs (Hookworm, Ancylostoma has a direct lifecycle, requiring a single vertebrate host to develop. Male and femals mate in the intestine, so the vertebrate is the definitive host)
d) host that is required for parasite development, but one in which parasite doesn’t reach sexual maturity (Plasmodium has an indirect life cycle, requiring both vertebrate and invertebrate (mosquito) host. Male and female gamates develop and fuse within the mosquito midgut. Therefore, mosquito is the definitive host and the vertebrate is the intermediate)
a) What is the main defence system of protozoans (+ example)
b) main defence of trypanosomes
a) Immune evasion. Protozoans are rapidly proliferating and small, so they can avoid detection by the immune system by hiding inside host cells and by cycling proteins that might come into contact with immune cells. Plasmodium falciparum infect erythrocytes that are missing Class I MHC, so avoid recognition and attack by cytotoxic cells
b) Live extracellularly in the bloodstream and avoid immune attack by constantly changing their variant surface glycoprotein (VSG) which forms a dense surface coat and protects the parasite from immune recognition
Helminth immunomodulation
They are large, multicellular organisms so cannot hide or transform rapidly, so have to use immunomodulation to avoid immune attack. They export a range of immunomodulatory mediators that interact with host cells and tissues, dampening Th1 and Th2 proinflammatory host responses (strong and sustained Th1 response leads to pathology, Th2-type responses result in worm expulsion, so both must be regulated by the parasite. So helminth presence is associated with overall immunosuppression). These immunomodulatory effects affect the host more systematically through bystander effects. The effects can be beneficial (if there is an overactive proinflammatory response causing pathology) or detrimental (when a pro-inflammatory response is needed to fight infections or responding to vaccines).
Helminth therapy is when a person is deliberately infected with worms to harness their immunomodulatory effects (roundworm infection shown to alleviate pathology of inflammatory bowel disease)
