Parasites - pathogenesis and immune responses

Question 1

what is parasitism?

Answer 1

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.

Question 2

are fungi considered parasites?

Answer 2

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.

Question 3

DALYs

Answer 3

disability adjusted life years

Question 4

YLDs

Answer 4

years lived with disability

Question 5

YLLs

Answer 5

years of life lost due to premature mortality

Question 6

DALYs for intestinal nematodes

Answer 6

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.

Question 7

Eukaryotes - parasite types

Answer 7

1. protozoa
2. helminths
3. ectoparasites

Question 8

Protozoa

Answer 8

• can exist in any body compartments
• single cell organism.
• intra and extra cellular
• cause a spectrum of disease

Question 9

Helminths

Answer 9

• multicellular
• highly organised
• complex life cycles (to get from one host to next)

Question 10

Ectoparasites

Answer 10

-external to the body
-insects, arachnids
tend to be overlook
-often have a role as vectors of disease, but can also cause disease

Question 11

what are some methods of parasitic transmission?

Answer 11

1. Environmental / behavioral
2. Consumption of resistant stages with food
3. Direct invasion

Question 12

Explain the environmental/behavioural method of transmission further

Answer 12

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

Question 13

give an example of a parasite that doesn’t need a cyst and why?

Answer 13

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.

Question 14

Explain the consumption of resistant stages with food method of transmission further

Answer 14

The tissue cyst of Toxoplasma

Tissue cyst of toxoplasma - Forms within host e.g. brain of rat. Now cat eat rat – its infected.

Question 15

explain the direct invasion method of transmission further

Answer 15

Schistosomes and hookworms

Question 16

what are zoonotic infections?

Answer 16

infections that circulate primarily in wild animals but can cross over and be taken up by man potentially causing a pandemic

Question 17

what are nematodes?

Answer 17

Parasitic ringworms known as the “small intestinal roundworms”

Question 18

what are ascaris?

Answer 18

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.

Question 19

Trichomonas vaginalis

Answer 19

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.

Question 20

Malaria: Anopheles mosquito

Answer 20

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.

Question 21

Trypansomes

Answer 21

Trypanosomes are protozoa that infect a variety of hosts and cause various diseases, including these 2 groups:

1. Sleeping sickness - Trypanosoma brucei in Subsaharan Africa
2. Chagas disease - Trypanosoma cruz in S America.

Very similar – closely related. Have flagella etc.

Question 22

Trypanosoma brucei

Answer 22

Transmitted by Tsetese fly. Takes blood meal, parasite goes through several life cycle stages before going to salivary gland and being ejected.

Question 23

Trypanosoma cruz

Answer 23

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.

Question 24

Mechanisms of pathogenesis

Answer 24

1. 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.
2. Invasion of host tissues
   - Disruption of metabolism: trypanosome induced cardiac failure
   - Disruption of host immune responses
3. Physical presence
   -Plasmodium aggregation in cerebral malaria, Ascaris blockage of gut
   (Ascaris = foot long. Mere presence can be problem. Block stuff.)
4. Induction of immune responses
   - Leishmania lesions associated with protective immune response
   - Toxoplasma encephalitis associated with cyst reactivation
   - Schistosome granuloma formation

Question 25

Schistosoma?

Answer 25

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.

Question 26

Toxoplasma?

Answer 26

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)

Question 27

Leishmania

Answer 27

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.

Question 28

Intestinal nematodes

Answer 28

Ascaris lumbricoides (foot long)

Hookworms

Geo helminths

Filarial worms

Question 29

Ascaris lumbricoides

Answer 29

• 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.

Question 30

Hookworms

Answer 30

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.

Question 31

Geohelminths

Answer 31

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

Question 32

Filarial worms

Answer 32

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.

Question 33

Ectoparasites

Answer 33

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