Parasitology-1

Question 1

What are the genuine parasites?

Answer 1

Protozoans and helminthes

Question 2

How is the symbiotic relationship of parasitism believed to form?

Answer 2

There is an intimate mutualistic relationship between two different specices
After a long evolutionary process this relationship will become obligatory to the parasite
The host may be harmed in the parasitic relationship however a successful parasitic relationship requires long term co-existence of host and parasite which resembles commensalism

Question 3

What are the features of the parasite host relationship?

Answer 3

Most parasites can no longer exist outside of the host environment
Parasite genomes are reduced with some genes and pathways being lost
This results in parasites becoming scavengers
There is however also innovation in parasites allowing it to adapt to its niche

Question 4

What is the most successful parasite and what is its “formula”?

Answer 4

Toxoplasma gondii which has no host restriction and a very low frequency of disease

Question 5

What are the key stages of a parasites life cycle?

Answer 5

Invasion, dissemination, transmission

Question 6

What are the different mechanisms of parasitic invasion and transmission?

Answer 6

Many protozoans produce cysts and spores and worms produce eggs which can be transmitted via ingestion
Active penetration of skin, this is limited to worms
Vectors such as insects and snails which are also functional hosts of the parasite
A combination of vectors and penetration such as schistosoma which develops to a larval stage in a snail, this can then swim through the water and penetrate the skin
Sexual transmission with only Trichomonas vaginalis through vaginal intercourse or several spores may be ingested through anilingus behaviour

Question 7

What are the cysts, spores and eggs produced by parasites?

Answer 7

Environmental resistant life forms adapted for oral infection which can be of diagnostic value

Question 8

What is the difference between monoxenic and heteroxenic parasites?

Answer 8

Monoxenic parasites have a simplified life cycle where there is only one host required for full development while heteroxenic parasites need more than one host to fully develop and are very polymorphic

Question 9

What are examples of monoxenic parasites?

Answer 9

Trichomonas vaginalis which is transmitted via sexual contact
Entamoeba Histolytica which is transmitted through the faecal oral route
Giradia Lamblia which is also transmitted through the faecal oral route but has zoonotic potential

Question 10

What is the life cycle of trypanosoma cruzi?

Answer 10

An insect takes a blood meal and injects metacyclic trypomastigotes into the human, inside human cells these transform into amastigotes and multiply via binary fission these can then transform into trypomastigotes when they enter into the bloodstream where they can be taken up by the insect transforming into epimastigotes and replicating in the insects gut
These will then progress to the hindgut and transform into metacyclic trypomastigotes to begin the cycle again
This parasite also has zoonotic potential with possums

Question 11

Why is cryptosporidium parvum unique compared to other apicomplexa?

Answer 11

While most apicomplexa are heteroxenic (such as toxoplasma and plasmodium) cryptosporidium is monoxenic which is transmitted through the faecal oral route often through contaminating swimming water and accidental ingestion

Question 12

What forms of reproduction are present in apicomplexan reproduction?

Answer 12

Sexual reproduction through the use of dimorphic gametes and fecundation with the zygote producing sporozoites which resides in the spore
Asexual reproduction in apicomplexan parasites by multiple fission by endogeny where daughter cells are formed through internal budding forming multinucleated parasites called schizonts. New parasites are released after schizogony and are called merozoites

Question 13

What is the life cycle of plasmodium?

Answer 13

The mosquito takes a blood meal and injects sporozoites into the human these migrate to the liver where they infect liver cells and form schizonts these will rupture forming merzoites which infect red blood cells as immature trophozoites from here there can be asexual reproduction in the blood cell or differentiation into gametes which can be taken up by a mosquito where they form macrogametes and go through several developmental stages to form sporozoites to begin the life cycle again

Question 14

What is unique about the toxoplasma gondii life cycle?

Answer 14

This can exhibit a monoxenic cycle in cats or a heteroxenic cycle

Question 15

What is a nematode that has larvae which need to mature in the lung?

Answer 15

Ascaris lumbricoides or strongyloides stercoralis

Question 16

What is the life cycle of ancylostoma duodenale?

Answer 16

Has a filaform larvae which can penetrate the skin allowing it to mature into adults in the small intestine allowing eggs to be excreted in faeces

Question 17

What is the lifecycle of acaris lumbricoides?

Answer 17

This nematode is transmitted via the feaecal oral route but the spores released in the faeces must first have contact with the soil to fully develop
This is also seen in strongyloides stercoralis and ancylostoma duodenale

Question 18

What nematode is transmitted through the faecal oral route and does not require contact with the soil for maturation?

Answer 18

Enterobius vermicularis

Question 19

What is the life cycle of filarial nematodes?

Answer 19

It is a heteroxenic dependant on an insect vector
The nematode infects humans with L3 larvae which mature into adults in lymphatics. The adults produce sheathed microfilariae that migrate into the lymph and blood channels
The mosquito will take another blood meal and ingest microfilariae which develop to L3 in the mosquito

Question 20

What is the typical life cycle of tapeworms?

Answer 20

These are typically heteroxenic for example taenia solium and taenia saginata which are excreted from the intestine and infect the environment where it can be uptaken by cattle which ingest oncospheres which develop into cysticerci in the muscle which can be ingested by humans in the form of undercooked meat
Echinococcus granulosus follows a similar cycle but does not require a human stage and can infect carnivorous animals

Question 21

What is the typical life cycle of trematodes?

Answer 21

Typically heteroxenic vector-borne infections with often involving water snails

Question 22

What is the life cycle of schistosoma mansoni?

Answer 22

schistosoma mansoni has gametes secreted by humans in the feces or urine, they then form an egg which hatches releasing miracidia which penetrate snail tissue where they grow for several generations until cercariae are released into the water which can penetrate human skin, this process causes them to lose their tails and circulate in the blood until they from mature adults
Paired adult worms migrate to form the shed gametes

Question 23

What is the life cycle of fasciola hepatica?

Answer 23

Unembryonated eggs are secreted by humans and livestock in the faeces these become embryonated in the water where miracida hatch and penetrate snails to develop into free swimming cercariae which encyst on water plants which can be ingested by livestock and humans