Parasites - pathogenesis and immune responses Flashcards
what is parasitism?
the activity of an organism that spends any portion it its life in direct contact with a host species, at the expense of the host
e.g. tapeworm, helminths.
Parasites – co evolved with man (they don’t want to kill host as they survive in hosts). Thrive, reproduce, and move to next host.
These parasites = impact on communities rather than high mortality / killing.
are fungi considered parasites?
Fungi (which is the plural form of fungus) are not considered as parasites
-parasite usually restricted to organisms belonging either to the protozoan parasite or the helminth groups.
DALYs
disability adjusted life years
YLDs
years lived with disability
YLLs
years of life lost due to premature mortality
DALYs for intestinal nematodes
5.19 million DALY’s
2700 deaths
by comparison, malaria is 82 DALYs, or TB / HIV. Hence in neglected category. That’s why often overlooked compared to other larger disease.
Eukaryotes - parasite types
- protozoa
- helminths
- ectoparasites
Protozoa
- can exist in any body compartments
- single cell organism.
- intra and extra cellular
- cause a spectrum of disease
Helminths
- multicellular
- highly organised
- complex life cycles (to get from one host to next)
Ectoparasites
-external to the body
-insects, arachnids
tend to be overlook
-often have a role as vectors of disease, but can also cause disease
what are some methods of parasitic transmission?
- Environmental / behavioral
- Consumption of resistant stages with food
- Direct invasion
Explain the environmental/behavioural method of transmission further
This method is associated with a resistant cyst or ova to protect from the environment. This cyst/ova communicates with the environment, allowing molecules in and out. Signals trigger the next stage in the life cycle, for example pH or temp.
Contaminated water supply, food supply– transmision. Ie in Giardia – linked to diarrhea
give an example of a parasite that doesn’t need a cyst and why?
Trichomonas vaginalis (STI) - no need for cyst formation due to the directness of contact -transmitted sexually, from one mucosal surface to next. No need for protection from outside world.
Explain the consumption of resistant stages with food method of transmission further
The tissue cyst of Toxoplasma
Tissue cyst of toxoplasma - Forms within host e.g. brain of rat. Now cat eat rat – its infected.
explain the direct invasion method of transmission further
Schistosomes and hookworms
what are zoonotic infections?
infections that circulate primarily in wild animals but can cross over and be taken up by man potentially causing a pandemic
what are nematodes?
Parasitic ringworms known as the “small intestinal roundworms”
what are ascaris?
Take up egg, hatches in gut, released in larvae stage.
From gut migrates to lungs, then back to gut, matures to female. But egg can survive in environment for weeks to months.
Peak infection in 16-20yr old community rather than 5 yr old.
Trichomonas vaginalis
This is a close relative of guardian. Giardia has a cyst to help it survive, but trichomonans vaginalis is sexually transmitted from one mucosal surface to next, so it doesn’t need a cyst. This means it saves energy.
Adult stage = eukaryotic cell. Has some flagella. Large cytoplasm.
If put into water = burst.
In cervix = infection, discharge and inflammation. Because of trichomonas but also secondary bacterial infect.
Malaria: Anopheles mosquito
Transmitted by Aedes arthropods, Leishmania, filarial worms
Aedes arthropods fill their gut with blood. Excess liquid squeezed out into egg (That droplet)
Mouth parts – allows to take blood meal and secrete saliva to digest blood and stop clotting.
Malaria parasite uses this to survive. Taken up into salivary gland, go through life cycle stages within mosquito, then injected back into host.
Aedes mosquito transmits leishmania and filarial worms. Essentially same process though.
continuous infection – Uninfected Human bitten by infected Arthropod, becomes infected human. Infected human then bitten by uninfected arthropod, becomes infected arthropod.
Trypansomes
Trypanosomes are protozoa that infect a variety of hosts and cause various diseases, including these 2 groups:
- Sleeping sickness - Trypanosoma brucei in Subsaharan Africa
- Chagas disease - Trypanosoma cruz in S America.
Very similar – closely related. Have flagella etc.
Trypanosoma brucei
Transmitted by Tsetese fly. Takes blood meal, parasite goes through several life cycle stages before going to salivary gland and being ejected.
Trypanosoma cruz
Transmitted by bugs, infects muscle tissue of heart.
Reproducing, disrupting physiology of nerve fibres as well as structure. Loses ability to pump (lays down more muscle, thickens)
Also see this in nerve fibres of gut associated with trypanasoma cruzi.
Also have trypomastigote (T) stages.
Mechanisms of pathogenesis
- Disruption of normal physiological function
- Giardia: uptake and metabolism of bile induces malabsorption
- Disrupts uptake and metabolism of fats, as competes for bile salts. Upsets fat metabolism. - Invasion of host tissues
- Disruption of metabolism: trypanosome induced cardiac failure
- Disruption of host immune responses - Physical presence
-Plasmodium aggregation in cerebral malaria, Ascaris blockage of gut
(Ascaris = foot long. Mere presence can be problem. Block stuff.) - Induction of immune responses
- Leishmania lesions associated with protective immune response
- Toxoplasma encephalitis associated with cyst reactivation
- Schistosome granuloma formation
Schistosoma?
Worm - male and female permanently bound together. Sit in blood vessel, take nutrients and pump eggs with hooks on it.
Disrupts liver – liver creates granuloma. Lays down fibrotic, and immune cells. To encapsulate egg.
Egg works way through wall of blood vessel.
Schistosoma mansoni – in hepatic portal vein. Eggs work way through liver to bile ducts, to outside world.
Toxoplasma?
A protozoa parasite with a close relation to malaria.
Toxoplasma tachyzoites are found in blood stream and infect macrophages. Lipases and proteases secreted
Illness reflects life cycle stage. When in lymph, macrophages, blood , get flu like symptoms.
Lay down latent = tissue cyst. Bradyzoites get energy supply from lipid. Cyst wall made of host and parasite proteins (immunological. Silent - hardly recognised)
Cerebral abscess - cysts can also form in brain. (infectious if eat brain, muscle that has this = trasmision)
CT scan shows ring enhanced lesions. Reflects presence of multiple cysts being reactivated. Immune response seen as result.
Life cycle: sexual cycle in cats, any vertebrates can have asexual cycle.
Rats and mice get them. Presence of tissue cysts in brain affects behaviour – take more risks (mouse infected more likely to run than hid, further transmission)
Leishmania
Transmitted by a fly - cutaneous lesion is the damage from where the fly has injected parasite into the skin
Leishmania infect macrophages. Site of infection recruits immune response. Surface of epidermis becomes fragile.
Ulceration = damage done by presence of infection. Then secondary bacterial infection = ulcer.
Amastigotes within macrophages in bone marrow biopsy. Reproduce in that stage.
Can cause visceral, mucocutaneous and cutaneous disease
Diff stages, infection of spleen (in child) leading to oedema. Muco-cutaneous disease (breakdown and reabsorption of bone). Skin ulceration.
Vaccination in past – take lesion and inoculate themselves.
Intestinal nematodes
Ascaris lumbricoides (foot long)
Hookworms
Geo helminths
Filarial worms
Ascaris lumbricoides
- transmitted by eggs in human faeces
- larvae migrate around body, pathogenesis is associated with their migration
- migrate around = raised IgE, results in allergic pneumonia
- migrate up trachea, down into gut and turn to adult females.
- gut pathology associated with vast numbers of worms in gut.
- single worm not too bad. Increased number of worms has a significant effect.
- gut pathology associated with numbers of parasites and nutrient competition
- asvaris competes for B12, anemia associated with it
treatment:
-anti worm tablet.
benzimidazoles = anti parasitic. Has 2 effects – stop respiration and affects action of worms. Cant fight peristalis.
-If obstruction = surgery.
Hookworms
Ancyclostoma duodenale / Necator americanus
Hookworms don’t have eggs
Skin penetrating larve
Stylets in buccal cavity to facilitate blood feeding
Then tracheal osesahpgeal migration like ascaris. (same symptoms here)
Skin invasion; cutaneous larva migrans
At skin get cutaneous larva migrants (allergic response to antigens left)
Lung migration; haemorrhage & pneumonia
Gut, anaemia & protein loss (200 mL/day)
A lot of them = substantial blood meal. See anaemia and protein loss associated.
Geohelminths
Transmitted primarily through contaminated soil, contaminate environment then infect man.
Called geohelminths bc have a direct life cycle that requires no intermediate hosts or vectors
parasytic infection occurs through faecal
Contamination of soil, foodstuff of water
adult geohelminths cause soil transmitted helminthiasis geohelminths
juvenile geohelminths are the infective forms and undergo tissue migratory stages whereby they infect vital organs such as lungs and liver
Filarial worms
Long lived
Require larval passage through insect vector
Complex life/ cycles, inoculated through skin.
Large adult worms, live within tissues of body (not in gut) live in lymph nodes and lymph vessels.
Immune response is associated with presence of worms
4 major species
Lymphatic disease:
- Wucheria bancrofti,
- Brugia malayi
Blindness:
- Onchocerca volvulus
- Loa loa
Worms blocked lymph glands.
Oedema associated with presence of worms, but also blockage of lymph vessels. Stops liquid draining out
Hanging scrotom, tissue loses elasticity.
Skin can seem coarse and granular (elephantiasis). Lays down think tissue, loses elasticity.
Presence of worms drive this.
Treat patient and kill worms in one swoop = huge reaction, as they are suppressing immune response (and no longer suppressed)
mazzotti reaction – like anaphylactics shock.
Onchocerca volvulus - Cornea being thickened – can = blindness.
Black fly transmites this inection.
Ectoparasites
Fleas. Can trasmit infection, drive immune response.
Also have ticks.
Transmits: Rickettsia rickettsii, bacterial infection.
Louse, highly evovled to diff parts of body. Head lose don’t survive in pubic region.
Rosacea = inflammation of skin. They are unsure what drives it (e.g. during pregnancy, person in 50s drink too much)
Likely multifactorial. Everyone has skin mites, tail in hair follicule, ppl with rosacea have increased count of skin mites
(don’t know if cause or effect, may be inflammed skin = more food.) more correlational
