Apicomplexa: crypto and malaria

Question 1

outline some general characteristics from the phyla apicomplexa

Answer 1

• no free-living forms
• all parasites have a medical/ vetinary importance
• complex life cycles with spore like forms and intracellular stages
• posses an apical complex
• no cilia or flagella instead gliding motility

Question 2

what is the difference between a definitive and intermediate host

Answer 2

1) definitive host= organism in which a parasite passes its adult existence and/or the sexual reproductive phases of its lifecycle

2) intermediate host= organisms in which a parasite passes its larval stage of asexual reproductive phase of its life cycle

Question 3

outline the definitive and intermediate hosts of the coccidian parasite toxoplasma in the phylum Apicomplexa

Answer 3

definitive = members of the cat family

intermediate= broad spectrum including rodents, cattle, sheep , goats, whales and loads of mammals

Question 4

outline the definitive and intermediate hosts of the coccidian parasite cryptosporidium in the phylum Apicomplexa

Answer 4

definitive= broad host spectrum
intermediate hosts= none known

Question 5

what is an Apical complex

Answer 5

found in the invasive (sporozoite and merozoite) stages of a parasites lifecycle where it assists entry into the host cell

made up of compnents such as polar rings, conoid, subpellicular microtubles, rhoptries and micronemes

it is used to characterise the phylum

Question 6

what are the three different morphological forms seen in the phylum apicomplexa

Answer 6

1) ookinete = motile, elongate zygote produced by plasmodium and gives rise to oocyst

2) sporozoite= fusiform, motile and the invasive stage

3) merozoite= non-motile, invasive stage and the end result of schizogony aka merogony

Question 7

define gametogony, sporogony and merogony

Answer 7

1) gamonts give rise to micro and macro gametes

2) zygote gives rise to many spores or sporozoites

3) single, large, multinucleate meron gives rise to many small merozoites that infect other host cells

Question 8

give some examples of the different parasites which can be found in the phylum Apicomplexa

Answer 8

• cryptosporidium
• plasmodium
• toxoplasma gondii
• babesia
• sarcocystis

Question 9

outline some features of the parasite cryptosporidium parvum in the phylum Apicomplexa

Answer 9

a species which is found in humans causing symptoms such as diarrhoea and is transmitted via contaminated water, person to person contact or direct animal contact

major outbreaks often occur as a result of contaminated drinking water and swimming pools

Question 10

outline the lifecycle of cryptosporidium parvum

Answer 10

1) host becomes infected by ingesting sporulated oocysts

2) motile sporozoites emerge from oocyst and attach to the intestinal epithelial cells where it fuses microvilli and becomes surrounded by host membranes and becomes a trophozoite

3)this is the feeding stage and undergoes asexual replication called merogony resulting in production of 4-8 merozoites

4)mature merozoites are released into the intestinal lumen and infect new epithelial cell
they can either undergo more merogony producing more merozoites or undergo gametogony

5) some merozoites develop into macro or microgamonts
micro= undergo several rounds of replication producing numerous microgamest released into the lumen

6) micro fuse to macrogamete resulting in zygote which undergoes meiosis and sporogony resulting in 4 sporozoites

7) infectious oocysts are excreted in the faeces

Question 11

give a case study of an outbreak of crptosporidum parvum

Answer 11

2005 North wales
Source of infection traced from Llyn Cwellyn resavoir where cases were detected by water company monitoring due to increased reports of food poisoning like symptoms
- 20,000 ppl at risk only 231 infected
had to pay £60 to 70K costs

Question 12

outline some characteristics of the parasite plasmodium

Answer 12

• the causative agent of malaria
• approx 156 named species
• at least 4 species infect humans whilst other species infcet verterbrates
• each species has own specific host range and vector

Question 13

what are the 4 species of plasmodium which can infect humans

Answer 13

1) p.falciparum
2) p.vivax
3)p.ovale
4) p.malariae

Question 14

outline the transmission of plasmodium

Answer 14

the female anopheles mosquito acts as a vector
- they aquire plasmodium from blood of infected human when feeding
- plasmodium reproduces in anopheles gut
- needs mosquito to continue lifecycle
- transmitted via salivary glands

Question 15

outline the distribution of human plasmodium species

Answer 15

1) falciparum - tropical Africa, Asia and Latin America

2) vivax- worldwide in tropical and some temperate zones

3) ovale- mainly in tropical west africa

4) malariae- worldwide but patchy distribution

Question 16

what are the symptoms of malaria

Answer 16

flu- like illness 8-30 days after infection
fever, headache, muscular aches and weakness, vomiting, diarrhoea, cough
typical cycles of fever, shaking chills and drenching sweats may then develop

faciparum malaria does not show this cyclic pattern- fatal during first fever episode is fatal

Question 17

outline the tranmission cycle of malaria

Answer 17

1) sporozoites injected with saliva and invade hepatocytes in the liver
2) sporozoites undergo asexual replication within liver cells
3)culminates in the production of merozoite which are released into blood stream
4) merozoites invade erythocytes (RBC) via the use of the apical complex
5) intracellular parasite transforms into trophozoite which has a distinct ring form
6) end of the trophic phase and undergoes multiple rounds of nuclear divsion forming multinucleate schizont
7) merozoites bud from mature schizont and are released following rupture of infected RBC
8) they e infect other RBC for more replication
9) gametocytogenesis begins sexual cycle where trophozoites can either differentiate into micro/macro gametes which dont cause pathology but begin gametogenesis once in vector
10) Microgamete is motile and forms zygote with macrogamete which develops into motile ookinete which penetrates mosquito gut epithela cells forming oocysts
11) oocysts undergo multiple rounds of asexual replication resulting production of sporozoites
12) rupture of oocyst releases sporozoites which invade salivary glands

Question 18

when does gametogenesis occur in the malarial lifecycle

Answer 18

the formation of micro and macrogametes is induced when the mosquito ingests gametocytes

Question 18

outline the production of microgametes in the malarial lifecycle

Answer 18

microgamets undergoes three rounds of nuclear division
these 8 nucelli become associated with flagella that emerge from the body of microgamete when inside the mosquito gut

Question 18

when does exflagellation occur

Answer 18

when infected blood is exposed to air induced by decreases in temp, decreases in dissolved co2, xanthurenic acid presence which is an insect metabolite

Question 19

what are the three distinct replicative stages in malaria

Answer 19

1) exo-erythrocytic schizogony- liver
2) erythrocytic schizogony - blood
3) sporogony - mosquito