Parasite

Question 1

What is the difference between parasitic symbiosis and commensal?

Answer 1

Parasitic symbiosis – one member benefits, other is harmed

Commensals - parasites that derive benefit from host without causing harm

Question 2

What are the types of parasites?

Answer 2

protozoa
helminths
arthropods

Question 3

What are the properties of protozoa?

Answer 3

most parasitic protozoa are usually <50μm
unicellular eukaryotes
nucleus has a membrane
protozoa can twist and bend

Question 4

What are the structural features of protozoa and their function?

Answer 4

macronucleus and micronucleus

cilia

• locomotory structure
• hair-like structure that cover the outside of the microbe and beat in a regular, continuous pattern = movement

pellicle

• covers the outer surface
• rigid enough to support and maintain shape but allows bending and twisting when moving

gullet
- food is pushed in to form the food vacuoles

food vacuole

• storage of food
• acts as intracellular stomach, digest food by fusing with lysosomes

contractile vacuole

• helps osmoregulation
• pumps out excess water by fusing with the membrane

anal pore
- waste is ejected

Question 5

How do protozoa get their nutrition?

Answer 5

protozoa are holozoic
- require organic material = consumption of liquid or solid food

can engulf particulate food from the gullet
many protozoa have a permanent mouth = cytostome

pinocytosis
- process of drawing in fluid via the vesicles

Question 6

What are examples of protozoa and their properties?

Answer 6

amoeba - move using pseudopods and divide by binary fission

ciliates - possess cilia, two different types of nucleus and transverse fission of organism when it divides

flagellates - move using flagella and divide by binary fission

sporozoa - complex life cycle involving alternating cycles of asexual and sexual development

entamoeba histolytica
- anaerobic parasitic protozoal commensal
- invasion of the intestinal lining causes amoebic dysentery – called Amoebiasis
transmitted by faecal-oral route
infect GIT - can pass into blood and infect liver

Question 7

What is malaria? What is it caused by?

Answer 7

malaria is a disease caused by parasite 
caused by 
- plasmodium falciparum
- plasmodium vivax 
- plasmodium malariae
- plasmodium Ovale

Life cycle

• two life cycles in human
• as an indirect life cycle

Question 8

What is the life cycle of malaria in humans?

Answer 8

malarial parasites are transmitted by infected female (only female as they have eggs) anopheline mosquitos

mosquitos injects sporozoites in their saliva into the blood of humans

1st cycle - asexual and sexual cycle
spororzoites circulate the blood then settle in the parenchymal cells of the liver and multiply
= pre-erythrocytic schizogony = asymptomatic stage

spororzoites can either

• infect parenchymal cells in the liver where they remain dormant = hypnozoites
• multiply to produce merozoites

after 12 days, the parenchymal cells rupture and release the merozoites into the blood to infect red blood cells

in the RBCs the merozoites mature into trophozoites the transform to form daughter merozoites

some merozoites transform into male and female gametocytes

2nd cycle 
RBCs rupture and release
- male and female gametocytes 
- toxins = show symptoms of malaria 
- new merozoites to infect other RBCs

gametocytes and merozoites circulate the blood and are eventually picked up by female mosquitos as they bitt he human

Question 9

What is the life cycle of malaria in mosquitoes?

Answer 9

gametocytes are picked up by female mosquitos as they bite the human

in the mosquito the female gametocytes transform into ookinete

the ookinete is fertilised and forms an oocyst which produces sporozoites

spororzoites move to the salivary gland and are ready to be injected into the next human

Question 10

What are trophozoites and oocysts?

Answer 10

trophozoite - the active feeding and multiplying stage

oocysts - the stages resulting from sexual reproduction, this stage characterised with a protective membrane or thickened wall.

Question 11

What is malaria treatment?

Answer 11

treatment is effective with various quinine derivatives
- quinine sulphate, chloroquine, mefloquinine, primaquine

drugs effective against the exoerythrocytic form - before it enters the parenchymal cells in the liver

• primaquine
• stops the parenchymal cells from rupturing

drugs effective against the erythrocytic form - within th RBC

• artemisinin
• chloroquine
• kill the trophozoites and merozoites within the RBC

drugs effective against the gametocytic form

• primaquine
• kill the gametocytes

Question 12

What are the types of helminths and their properties?

Answer 12

they are worm-like parasites

• flukes = trematodes
• tapeworms = cestodes
• roundworms = nematodes

they are invertebrates
helminths develop though egg, larval and adult stages

Question 13

What are the clinically important cestodes (tapeworms) ? What is their structure?

Answer 13

clinically important cestodes are

• tenia solium
• tenia saginata
• echinococcus granulosus

generally flattened, elongated and consists of segments, proglottids
vary in length, 2mm –10m

anatomically divided into

• scolex = head
• neck = region of segment proliferation
• strobila = chain of proglottids (segments of the tapeworm)

Question 14

What are the characteristic of cestodes (tapeworms)? What is their treatment?

Answer 14

• characteristic feature is absence of alimentary canal
• substances enter the tapeworm across the tegument
• cestodes are hermaphrodotic = each proglottid possess male and female reproductive systems
• eggs are deposited in different methods according to the type of tapeworm

treatment

• praziquantel is used to treat many tenia infections
• expulsion of the scolex (head) is a must
• must have good hygiene - especially regarding animals and children

Question 15

How do arthropods infect humans with disease? What are examples?

Answer 15

• act as vectors
• acts as parasites
• illicit allergies

examples

• lice
• fleas
• mites
• ticks

Question 16

How does lice affect the body? What are symptoms? What is the treatment?

Answer 16

affect three areas of the body

• head = pediculus humanus capitis
• body = pediculus humanus humanus
• pubic region = pediculus thirus pubis

spend all of their life on one specific host
- they only leave one host to transfer to another•Head lice
both male and female feed on blood

symptoms include itching due to sensitization to louse saliva

Treatment

• shampoo containing 1% benzene hexachloride
• mixture of pyrentins (0.2%) and pipronyl butoxide (2%)
• Brushing out