Protozoal and helminth infections Flashcards
Protozoa
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)
structure of protozoal cell
food vacuole
contractile vacuole
pseudopodia
mitochondria
endoplasmic reticulum
Golgi apparatus
nucleus
Classification of protozoa
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
Malaria
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
Malaria – life cycle
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
Malaria - symptoms
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
Protozoal infections more common in
tropical areas
Malaria is caused by
Plasmodium spp. – most common and most dangerous species is P. falciparum
Helminths – general features
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
Classes of helminths
Three main classes of worms infect humans
Nematodes (roundworms)
Cestodes (tapeworms)
Trematodes (flukes)
Nematodes
(roundworms)
cylindrical body, alimentary canal
filarial
intestinal-
Intestinal nematodes
Large roundworm (Ascaris lumbricoides) Threadworm (Enterobius vermicularis) Hookworm (Necator americanus/Ancylostoma duodenale) Whipworm (Trichuris trichuria)
cestodes
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)
trematodes
(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
nematode- long roundworm
transmission- fecal-oral
symptoms- with heavy infection; slows development, shortness of breath, coughing, malnutrition, blockage of intestines
nematode- threadworm
transmission; fecal-oral
symptoms: mild-anal itching
nematode- hookworm
transmission- larvae in soil penetrate skin
symptoms: slows growth and development; anaemia
nematode- whipworm
transmission; fecal-oral
symptoms: usually asymptomatic. Heavy infection: bloody diarrhea
Ascariasis (Ascaris lumbricoides)-
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
Blood and tissue nematodes (filariae)
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
Schistosomiasis
(Bilharzia, Snail fever)
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)
Schistosomiasis - symptoms
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
Helminths - diagnosis
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
