Parasitology-2

Question 1

What strategy does trichromonas vaginalis use to maximise its transmission?

Answer 1

The transmission does not use cysts relying exclusively on sexual transmission, as a result men are often asymptomatic

Question 2

What are the strategies used by Leishmania to maximise transmission?

Answer 2

It lives in macrophages and monocytes which are ingested by the fly in its blood meal

Question 3

What strategy does wuchereria Bancroft use to maximise transmission?

Answer 3

This filarial nematode resides in lymphatic ducts under the skin allowing the larvae to circulate in the lymph and blood and be ingested by mosquitos

Question 4

What strategy does Plasmodium falciparum use to maximise transmission?

Answer 4

Infected red blood cells remain deep in the tissues and when gametocytes are produced they are released to the blood periphery to be ingested by mosquito

Question 5

What strategy does toxoplasma gondii use to maximise transmission?

Answer 5

Different hosts are used for different purposes, with the sexual cycle and spore production only occurring in cats intestines while other animals form tissue cysts which are infective products of the asexual cycle

Question 6

What strategy does cryptosporidium parvum use to maximise transmission?

Answer 6

Has its entire life cycle in one host, where it is restricted to intestinal epithelial cells which releases spores

Question 7

What are the different environmentally resistant infective forms produced by parasites?

Answer 7

Tissue cysts or pseudocysts produced by intracellular protozoans
Cysts and spores produced by extracellular protozoans
Larval cysts and eggs produced by worms

Question 8

What are the features of cyst formation by parasites?

Answer 8

A low metabolic condition known as hyobiosis or anabiosis is entered
A tight, thick layer of crosslinked proteins protects the parasite from harsh environmental conditions such as dessication, temperature and chemicals
Biological condition is adapted to the external environment they expect to face or the host they expect to invade
Adaptation is host specific at the level of species
Parasites will only hatch, excystate and migrate properly if they find their very specific host

Question 9

What is the importance of hypo/anabiosis?

Answer 9

There is economical loss due to animal infection, soil and water contamination
There is resistance to disinectants and chemicals
Resistance to drug treatment in the host
Reccurance of the acute disease state
Development of a chronic disease state potentially leading to cisticercosis and hidatiosis
There is the bypassfrom an asmptomatic stage to a severe form of the disease

Question 10

What occurs to cysts etc if they do not find their correct host?

Answer 10

They will not hatch or excystate but this can help in dissemination it may survive ingestion in a another species and be excreted to spread the cysts
Alternatively it may hatch or excystate but lacking the correct host environment it will die quickly

Question 11

What are examples of cysts hatching in the incorrect species?

Answer 11

Canine nematodes may infect humans, however they undergo erratic migration producing disease such as Larva migrans cutaneous (caused by ancylostoma caninum) or larva migrans visceral (caused by toxocara canis)

Question 12

What are the specific environmental conditions that cause G. Lamblia to encystate?

Answer 12

Final habitat is the duodenum-jejuni
An increase in pH
Decrease in bile salts and cholesterol
Decrease of water

Question 13

What occurs to giardia when it encysts?

Answer 13

The trophozoite form is binucleated motile flagellate cell which strongly attaches to the attachment disk
When it becomes a cyst attachment is lost and the flagella is internalized
Metabolism decreases
Vesicles (relics of the golgi) which contain cyst wall proteins are secreted and fuse to the membrane forming disulphide crosslinks and isopeptide bonds
There may also be deposit of polymers of N-acetyl glucosamine
Nuclei divide once

Question 14

What are the conditions of G. Lamblia excystation?

Answer 14

37 degrees celcius

Acidic pH

Question 15

What are the signals for encystation of entamoeba histolytica?

Answer 15

This is an intestinal extracellular parasite which has its final habitat as the cecum
The encystation signals are unknown but could be a decrease in water or the presence of bacteria

Question 16

What are the signals for excystation of entamoeba histolytica?

Answer 16

37 degrees and the presence of bile salts

Question 17

What are pseudocysts?

Answer 17

These are tissue cysts where the parasite survives intracellularly inside a membrane bound vacuole known as a parasitophosphorus vacuole

Question 18

What parasites form pseudocysts?

Answer 18

Toxoplasma gondii can form them in any tissue
Trypanosoma cruzi amastigotes can form them in the muscle of the heart and intestine
Plasmodium vivax can form them in hepatocytes

Question 19

How are the vitelline proteins of the worm egg modified upon fecundation?

Answer 19

The tyrosines are converted to DOPA

Protein crosslinking is done through phenol oxidase system

Question 20

What occurs upon fecundation of nematode eggs such as ascaris lumbricoides?

Answer 20

The eggs are produced with two additional layers a middle chitin layer and an inner lipid layer this makes them the most environmental resistant parasite in nature and the infective L3 larvae hatch out of the egg by actively digesting it

Question 21

How to cestode eggs hatch T. solium and T. saginata?

Answer 21

The shell of the eggs is very thick and can only break up by host specific degradation

Question 22

How do trematoda eggs such as those of schistosoma and fasciola hepatica?

Answer 22

The shell is very thin and water permeable with the larvae developing in an aquatic environment

Question 23

What triggers excystation pf skin infective larvae?

Answer 23

An increase in temperature
An increase in PCO2
A pH fluctuation

Question 24

How does Plasmodium Falciparum use circadian rhythms to maximise transmission?

Answer 24

Enterocytes infected with trophocytes and schizonts of plasmodium falciparum stay in the microcirculation however the gametes circulate in the blood periphery at the time at which mosquitos (vector) are most likely to be active and feed on the host

Question 25

How do Filarial Larvae use circadian rhythm to maximise transmission?

Answer 25

Filarial Larvae accumulate in the pulmonary circulation at the junctions of arterioles and venules, when there is a drop of PCO2 due to a lower level of activity there is release of microfilarie which co-incides with the nocturnal feeding behaviour of the mosquito vector
Enterobius vermicularis migrate at night to the cecum-rectum where they stick to the perianal skin where they stick and die releasing eggs containing L3 infectious larvae this causes itching during sleep allowing inadvertent hand to mouth transmission

Question 26

How do flukes exhibit circadian rhythms to maximise transmission?

Answer 26

The larvae of .S.mansoni have physical sensor organs detecting temperature, pressure and gravitation, Miracidia migrate to the depth of the snails habitat while cercariae from s.mansoni are released during the light nd are more acive with an increase in water temperature
The adults mature in the liver with males using lipid based pheromones to attract the females
Females are not sexually mature until they mate
A male will hug a female and together they migrate to their final habitat the veins of the intestinal mesentery