Protozoal and helminth infections

Question 1

Protozoa

Answer 1

Diverse group of single celled “animal-like” eukaryotes, 2-100 µm
Part of the “protists” (=protozoa, slime molds, unicellular algae)
Most free-living, some are pathogens
Prevalent in (sub)tropical regions
Can infect tissues/organs
intracellular parasites in cells
extracellular parasites in blood, intestine, urogenital system
Transmission by vector (e.g. malaria, sleeping sickness) or contaminated water/soil/food (e.g. amoeba, toxoplasmosis)

Question 2

structure of protozoal cell

Answer 2

food vacuole
contractile vacuole
pseudopodia
mitochondria
endoplasmic reticulum
Golgi apparatus
nucleus

Question 3

Classification of protozoa

Answer 3

Amoeba - move by pseudopodia
e.g. Entamoeba histolytica
Flagellates - have flagella
trypanosomes, Leishmania
Ciliates - have cilia
most are not pathogenic
Apicomplexa (sporozoa) - have apical complex
all are parasitic, e.g. Plasmodium, Toxoplasma

Question 4

Malaria

Answer 4

Malaria - mala aria = bad air; in past also called marsh fever
Found in >100 countries, but mainly tropical areas of Africa, Asia and South America
40% of world population at risk, but 90% of deaths are in Africa
Number of deaths has been decreasing over the last 5-10 years, thanks to better prevention strategies and new drugs such as artemisinin

most common of the diseases- plasmodium falciparum

least common- plasmodium malariae

Question 5

Malaria – life cycle

Answer 5

Parasites injected with saliva of blood-feeding female mosquitos (Anopheles sp.)
Multiply in liver (~2 weeks)
Released from liver – then infect RBCs repeatedly (days)
Mosquitoes ingest parasites with blood meal
Parasites go through reproductive phase inside mosquito

sporozoites- capillaries- liver cell entry- liver - liver cell rupture- RBC penetration asexual reproduction- development into gametocytes- uptake during blood mean

Question 6

Malaria - symptoms

Answer 6

Uncomplicated
Classical malaria attack: 6-10 hours of
cold stage - shivering
hot stage - fever
sweating stage
Other: headache, body aches, nausea, vomiting, weakness, enlarged spleen

Severe (complicated)
Cerebral malaria - abnormal behaviour, seizures, coma, other neurological abnormalities (25-50% mortality rate)

Shock (sudden drop in blood flow)

Severe anaemia due to haemolysis

Pulmonary oedema - breathing problems

Liver failure, jaundice

Swelling, rupturing of spleen

Question 7

Protozoal infections more common in

Answer 7

tropical areas

Question 8

Malaria is caused by

Answer 8

Plasmodium spp. – most common and most dangerous species is P. falciparum

Question 9

Helminths – general features

Answer 9

Multicellular, with differentiated organs; no circulatory tract
Vary greatly in length < 1 mm to >10 m
At anterior end some have suckers, hooks, or plates that are used for attachment

Most worms do not have full life cycle in humans
Replicate free, in another host, or only part of life cycle is in humans
Weight of infection proportional to number of infecting organisms

Tough cuticle; difficult for immune system to eradicate

Some (e.g. blood flukes) camouflaged by coating with host molecules

Parasitic helminths feed on body fluids or intestinal contents

Question 10

Classes of helminths

Answer 10

Three main classes of worms infect humans

Nematodes (roundworms)

Cestodes (tapeworms)

Trematodes (flukes)

Question 11

Nematodes

Answer 11

(roundworms)
cylindrical body, alimentary canal
filarial
intestinal-
Intestinal nematodes

Large roundworm (Ascaris lumbricoides)

Threadworm (Enterobius vermicularis)

Hookworm (Necator americanus/Ancylostoma duodenale)

Whipworm (Trichuris trichuria)

Question 12

cestodes

Answer 12

tapeworms)
flat, ribbon shaped; no digestive tract – nutrients absorbed through cuticle

Adult tapeworms that infect humans can > 10 m, and live for decades

Humans usually primary host: ingestion of cyst (=resting/dormant stage) from undercooked meat/fish - worm in lumen of the gut, and symptoms are minor

Humans rarely are secondary host: ingestion of egg, and larval stages will invade tissue (muscle, brain)

Question 13

trematodes

Answer 13

(flukes)
leaf-shaped, blind-branched alimentary tract in
the blood
lungs-from eating infected crab andd crayfish
intestinal
liver-from eating freshwater fish
Live for decades in tissue or blood vessels

Cause progressive damage to vital organs

Use snail as intermediate host – some use secondary host

Question 14

nematode- long roundworm

Answer 14

transmission- fecal-oral
symptoms- with heavy infection; slows development, shortness of breath, coughing, malnutrition, blockage of intestines

Question 15

nematode- threadworm

Answer 15

transmission; fecal-oral
symptoms: mild-anal itching

Question 16

nematode- hookworm

Answer 16

transmission- larvae in soil penetrate skin
symptoms: slows growth and development; anaemia

Question 17

nematode- whipworm

Answer 17

transmission; fecal-oral
symptoms: usually asymptomatic. Heavy infection: bloody diarrhea

Question 18

Ascariasis (Ascaris lumbricoides)-

Answer 18

long roundworm
Adult worms 10-30 cm, may escape from anus, mouth, nose, or ears
Max intensity infection in children at 5-10 yr
Migration of larvae - to the lungs - causes most of the damage
Heavy infection: abdominal pain, malnutrition
Severe infection: blockage of intestines
Adult parasites can migrate to other organs

Question 19

Blood and tissue nematodes (filariae)

Answer 19

Live in subcutaneous tissues and lymphatic vessels

Adults discharge larvae (microfilariae)

Microfilariae circulate in blood, ingested by insects

In insect develops into infective larvae

Can be asymptomatic for many years

Question 20

Schistosomiasis
(Bilharzia, Snail fever)

Answer 20

After malaria. 2nd greatest economic impact of parasitic diseases (~200,000 deaths annually)

• Caused by Schistosoma spp. (blood-flukes); mainly S. mansoni, S. haematobium, and S. japonicum
• Worms 0.6-2.6 cm
• Main route of contamination through infected water (eggs excreted in faeces or urine)

Question 21

Schistosomiasis - symptoms

Answer 21

Within days: develop of rash or itchy skin (“swimmers itch”)

After 1-2 months: fever, chills, cough, muscle aches

Main damage by eggs stuck in tissues and subsequent response of immune system

Organ damage because of inflammation and scarring - e.g. liver, intestines, lungs, bladder; can lead to bladder cancer

Question 22

Helminths - diagnosis

Answer 22

Intestinal nematodes/cestodes:
Eggs or larvae can be detected in faecal sample

Sometimes incidental diagnosis; e.g. coughing up or vomiting ascarids

Schistosomas:
Eggs in faecal sample or urine

Tissue nematodes:
Adults in tissue (difficult); microfilaria in blood