Parasites Flashcards
Define parasitism.
Metabolic dependence on host. Requires nutrients/stimuli from the host to the detriment of the host
Define commensalism.
No metabolic dependence. One partner benefits, the other is disadvantaged/not effected
Define mutualism.
No metabolic dependence. Both partners benefit
Define parasite.
An organism which lives on or in another organism ‘host’ and benefits by deriving nutrients at the host’s expense
What defines an organism as protozoa? Name four species
Unicellular parasite.
- Amoebae
- Flagellates
- Apicomplexa
- Ciliates
What defines an organism as metazoa? Name two species and any sub-species
Multicellular parasite.
- Plathelminths (flat worms)
- Cestodes (tape worm)
- Trematodes (fluke) - Nematohelminths (round worms)
- Nematodes (round worm)
What is a direct life-cycle?
Transmission from one host to another host of the same species
What is an indirect life-cycle?
Transmission wherein the life-cycle involves 2+ hosts of different species
What is a definitive host?
The host in which the the sexual reproduction of the parasite occurs
What is an intermediate host?
The host in which only asexual reproduction occurs and the larve stage is present
What is an accidental host?
The host is considered the ‘dead-end host’ as it is not the normal host and the parasite cannot complete it’s life-cycle
What is a vector?
An organism that conveys the parasite from one host to another host
What is a biological vector?
A vector wherein the parasite undergoes further development (eg: Anopheles mosquito)
What is a mechanical vector?
A vector wherein the parasite undergoes no further development (eg: flies)
What type of life-cycle does an Amoeba have?
Direct life-cycle
Briefly describe the amoeba life-cycle.
2 stages.
- Trophozoite (motile, feeding, binary fission)
- Cyst (infective for humans)
How are amoebae transmitted?
Direct faeco-oral transmission (contaminated food/water)
What is the pathogenesis of amoebae?
- Excystation in intestine followed by multiplication
- Trophozoites adhere to large intestine epithelium (disrupts the epithelial barrier and results in invasion)
What disease do amoebae cause in humans?
- Assymptomatic
- Dysentry (inflammation of intestine = diarrhoea with blood)
- Flask-shaped ulcers
- Hepatic and lung abscesses
Which species of direct apicomplexa causes disease in humans?
Intestinal Cryptosporidium
What type of life-cycle do apicomplexa have?
Direct and indirect life-cycle
Briefly describe the direct apicomplexa life-cycle.
- Entire life-cycle can occur in 1 host
1. Low infection dose with thick-walled oocyte
2. Excystation of oocyst in duodenum releasing sporozoites (which bind and invade intestinal epithelial cells)
How are direct apicomplexa transmitted?
Direct faeco-oral transmission (contaminated food/water)
What is the pathogenesis of direct apicomplexa?
- Intestinal disease (intestinal epithelium death > villous atrophy > impaired intestinal absorption)
- Extra-intestinal disease (immunocomprimised patients develop biliary and respiratory tract infections)
What disease do direct apicomplexa cause in humans?
- Self-limiting diarrhoea
- Significant malabsorption
- Fluid and electrolyte imbalances
How is an direct apicomplexa infestation diagnosed?
Stool microscopy
How is an direct apicomplexa infestation managed?
- Supportive fluid electrolyte therapy
- HAART (HIV patients)
- Co-trimoxazole
Which species of indirect apicomplexa causes disease in humans?
Toxoplasma gondii
Briefly describe the indirect apicomplexa life-cycle.
- Definitive host = cats
- Intermediate host = humans / warm blooded animals
- Oocyst containing sporozoites
- Cresant shaped tachyzoite (motile and replicate)
- Tissue cyst containing bradyzoites (dormant)
How are indirect apicomplexa transmitted?
- Ingestion of oocyst shed in cat faeces
- Ingestion of raw meat containing cyst with bradyzoite
- Congenital transmission (transplacental)
- Organ transplant, blood transfusion or needle-stick injury
What disease do indirect apicomplexa cause in humans?
- Immunocompetent: low grade fever, flu-like symptoms
- Immunocomprimised: disseminated disease, fever, myositis, CNS involvement
How is an indirect apicomplexa infestation diagnosed?
- Serology
- Radiology
- Histopathology
- Molecular testing
How is an indirect apicomplexa infestation managed?
- Folic-acid antagonists:
- pyrimethamine-sulfadiazine
- trimethoprim-sulfamethoxazole - Prophylaxis for immunocomprimised
What aids the prevention of an intestinal nematode infection?
- Hygiene and sanitation (handwashing)
- Avoid soil pollution (faecal matter)
- Avoid use of night soil
- Mass treatment of families / school children
What is the recommended treatment for an intestinal nematode infection?
- Mebendazole / Albendazole
What life-cycle do nematodes (roundworms) have?
Direct life-cyle
What is the transmission of nematodes?
- Ingestion of embryonated ova
- In-tact skin penetration by infective (filariform) larvae
What general structure do nematodes have?
- Cylindrical body cavities
- Seperate sexes
What disease does Ascaris lumbricaides cause?
- Migration of larvae: Loeffler’s Syndrome (heart-lung migration)
- Migration of adults: mouth and anus
- Adults in small intestinal: lumen obstruction (malnutrition)
How is Ascaris lumbricoides diagnosed?
- Stool microscopy (ova)
- Identify adult worms passed
Name two hookworm species.
- Ancylostoma duodenale
2. Necator americanus
What is the pathogenesis of a hookworm infestation?
- Migration of larvae: heart-lung
- Adults attach to small intestine mucosa and feed on blood (cause anaemia)
What disease do hookworms cause in humans?
- Ground itch: larval skin penetration
- Loeffler’s Syndrome
- Intestinal worms: abdominal pain, weight-loss, anaemia, hypoproteinaemia
How is a hookworm infestation diagnosed?
- Stool microscopy (ova)
What does the parasitic life-cycle form of Strongyloides Stercoralis (nematode) entail?
Adult female > duodenal mucosa where eggs hatch
Larvae in faeces
Filariform larvae in soil
What does the free living life-cycle form of Strongyloides Stercoralis (nematode) entail?
Male and female mate
Eggs hatch and develop into larvae
What consitutes an auto-immune or hyperinfection by Strongyloides Stercoralis?
- Immunocomprimised hosts
- Accelerated development in small intestines
- Reinvasion
What disease cause Strongyloides Stercoralis in humans?
- Skin penetration
- Larval migration
- Intestinal infection
- Hyperinfection Syndrome
How is Hydatid disease diagnosed?
- History of animal contact
- CT scan
- Serology
What is the recommended treatment for Hydatid?
- Surgical: removal of accessible cysts
- Albendazole
What is the recommended treatment for Strongyloides Stercoralis?
- Ivermectin
2. Albendazole
How is Strongyloides Stercoralis diagnosed?
- Stool or duodenal aspirate for larvae
What organism causes Hydatid disease?
Echinococcus granulosus (small adult tapeworm)
What is the definitive host for Hydatid disease (Echinococcus granulosus)?
Dog, jackal, wolf (carnivores)
What is the intermediate host for Hydatid disease (Echinococcus granulosus)?
Sheep, cattle, horse (herbivores)
What is the accidental host for Hydatid disease (Echinococcus granulosus)?
Humans
Where do Hydatid disease (Echinococcus granulosus) cysts occur in humans?
Liver, bone, lungs and brain
What defines Hydatid disease?
Space occupying lesions in organs, liver and lungs
What is the general structure of cestodes (tapeworms)?
- Flattened
- No digestive tract
- Scolex with segmented hermaphroditic proglottids (auto-fertilization)
What type of life-cycle do cestodes have?
Indirect
What is the definitive host of cestodes?
Humans
What is the intermediate host of cestodes?
Pigs and cattle
How are cestodes of the Taenia solium species transmitted?
- Ingestion of contaminated food with human faeces containing ova
What is the pathogenesis of Taenia solium?
- Larvae migrate to muscle and organs (then calcify)
- Neurocysticercosis (seizures and hydrocephaly)
How is Taenia solium diagnosed?
- Stool microscopy (need scolex or gravid proglottid to differentiate species)
What is the recommended treatment for Taenia solium?
- Albensazole (7-14days)
