Parasitology Flashcards
What is a parasite?
- An organism which lives in or on another organism (its host) and benefits by deriving nutrients at the other’s expense.
- Does not necessarily cause disease
What is symbiosis?
Living together; close, long term interaction between two different species
What is mutualism?
an association in which both species benefit from the interaction
What is parasitism?
an association in which the parasite derives benefit and the host gets nothing in return but always suffers some injury
e.g. Tick feeds on animals blood – can also pass on infections to host such as Lyme disease
What is commensalism?
An association in which the parasite only is deriving benefit without causing injury to the host
What is a ‘definitive’ host?
- Either harbours the adult stage of the parasite or where the parasite utilises the sexual method of reproduction
- In the majority of human parasitic infections, man is the definitive host
What is a ‘reservoir’ host?
An animal or species infected by a parasite which serves as a source of infection for humans or other species (e.g. cattle)
What is an intermediate host?
- Harbours the larval or asexual stages of the parasite
- Some parasites require two intermediate hosts in which to complete their life cycle
What is a paratenic host?
Host where the parasite remains viable without further development
Broad groups for classification of parasites
What parasites does the ‘protozoa’ group contain?
- Flagellates
- Amoeboids
- Sporozoans
- Trypanosomes
How are GI pathogens typically transmitted?
By faecal-oral route
How are blood parasites transmitted?
By arthropod vector
Are protozoa single or multi celled?
Single celled
What are the 2 groups of Helminths?
- Flatworms (platyhelminths)
- Round worms (nematodes)
What classification are ‘cestodes’ (tape worms)?
Helminths –> flatworms (platyhelminths)
What classification are ‘trematodes’ (flukes)?
Helminths –> flatworms
Classification of Helminths
Size of Helminths?
- Large multicellular organisms adults generally visible by eye
- Adults cannot multiply in humans
REVISE IMS –> Bacteria/Virsuses/Parasites
!
What are the three main classes of parasites that can cause disease in humans?
protozoa, helminths, and ectoparasites.
What are ectoparasites?
broadly include blood sucking arthropods and those that burrow into skin.
What are the 3 types of parasitic life cycles?
- Direct
- Simple indirect
- Complex indirect
Example of a direct parasitic life cycle
Example of an indirect parasitic life cycle
Example of complex indirect life cycle
What is ‘Ascariasis’? What parasite is it caused by?
- Ascariasis is an infection of the small intestine caused by Ascaris lumbricoides
- Macroparasite
- Helminths –> nematodes (round worms) –> intestinal nematode
Where is Ascariasis usually seen?
- Areas of poor hygiene
- Peak prevalence in 3-8 year olds
How is Ascariasis acquired?
Ingestion of eggs
Life cycle of Ascariasis?
Simple
How can Ascariasis affect the lungs?
After you swallow the tiny (microscopic) ascariasis eggs, they hatch in the small intestine and the larvae migrate through the bloodstream or lymphatic system into the lungs.
Can develop Loefflers syndrome:
- Dry cough
- Dyspnoea
- Wheeze
- Haemoptysis
- Eosinophilic pneumonitis
How can Ascariasis affect the intestines?
The larvae mature into adult worms in the small intestine, and the adult worms typically live in the intestines until they die:
- Malnutrition
- Malabsorption
- Migration – into hepatobiliary tree and pancreas
- Intestinal obstruction
- Worm burden
Treatment for Ascariasis?
Albendazole –> Anthelmintic / anti-worm medication that prevents glucose absorption by worm so worm starves
What is Schistosomiasis? What parasite is it caused by?
- Schistosomiasis, also known as snail fever and bilharzia, is a disease caused by parasitic flatworms called schistosomes.
- Helminths –> flatworms (platyhelminths) –> trematodes (flukes) –> schistosomes
What can Schistosomiasis lead to?
- Undernutrition: via the suppression of appetite and inflammation-mediated cachexia.
- Anaemia: due to the haematuria
- Hepatic fibrosis and associated increased risk of oesophageal varices
- Renal failure
- Bladder tumours
- Can increase risk of transmission/acquisition of HIV
What is the intermediate host for Schistosomiasis?
Snails
life cycle of Schistosomiasis
Signs and symptoms of Schistosomiasis?
- Often asymptomatic
- Symptomatic acute infection –> Katayama syndrome
- Rash, fever, headache, myalgia, and respiratory symptoms
- Often with eosinophilia and hepato- and/or splenomegaly.
- Swimmers itch
- Katayama fever
- Chronic Schistosomiasis (can persist for years)
- Effects of eggs in distant sites: spine, lung
Which is the only Schistosoma that can infect the urinary tract? What can this lead to?
S. haematobium:
- Haematuria
- Bladder fibrosis and dysfunction
- Squamous cell CA bladder
Which Schistosomas cause hepatic/intestinal infections? What are the signs/symptoms of this?
S. mansoni, S. intercallatum, S. japonicum, S. mekongi
- Portal Hypertension
- Liver cirrhosis
- Abdo pain
- Hepatosplenomegaly
Treatment for Schistosomiasis?
Praziquantel –> anti-worm medication used to treat infections caused by Schistosoma worms
Control of Schistosomiasis?
- Chemical treatment to kill snail intermediate hosts
- Chemoprophylaxis
- Avoidance of snail infested waters
- Community targeted treatment, education and improved sanitation
What is Hydatid disease? What parasite is it caused by (& classification)?
- A parasitic infection caused by Echinococcus sp.**
- Helminths –> Platyhelminths (flatworms) –> cestodes (tape worms)
- Human is accidental host –> usual hosts are sheep and dogs
Life cycle of Hydatid disease
Clinical effects of Hydatid disease?
- Cysts: 70% liver, 20% lungs
- May remain asymptomatic for years
- Mass effect
- Secondary bacterial infection
- Cyst rupture - hypersensitivity reaction
If you have an intact cyst, why is it important not to biopsy it?
Can lets the protozoa out –> dangerous because of complications such as anaphylactic shock or spread of hydatid daughter cysts to the peritoneum
Treatment for Hydatid disease?
Albendazole + praziqantel for daughter cysts ( E granulosus)
Structure of echinococcal cyst
Hydatid life cycle
What parasite causes Malaria? What is the classification is this?
- Caused by Plasmodium sp. (microparasite)
- Protozoa –> Sporozoans –> Plasmodium sp.
What are the 4 human species of Plasmodium? Which is the most common?
- P. falciparum (most common)
- P. vivax
- P. ovale
- P. malariae
Clinical effects of Malaria?
Parasites rupture red cells, block capillaries and cause inflammatory reaction:
- Fever & Rigors (alt. days with falciparum malaria, every 48hrs or 72hrs with benign malaria)
- Cerebral malaria (confusion, headache, coma)
- Renal failure (black water fever)
- Hypoglycaemia
- Pulmonary oedema
- Circulatory collapse
- Anaemia, Bleeding and DIC
What is an erythrocytic cycle?
To begin the asexual cycle in humans, an infected female Anopheles mosquito injects sporozoites into the new human host during a blood meal.
Upon release, the merozoites invade the red blood cells where they undergo another asexual cycle called erythrocytic schizogony. This is also known as the erythrocytic cycle.
What is the erythrocytic life cycle for:
a) P. falciparum, P. vivax & P. ovale
b) P. malariae
a) 48 hours
b) 72 hours
Returning traveller + fever
What should you suspect?
- Malaria (until proven otherwise)
- Maybe viral haemorrhagic fever
Diganosis of malaria?
PCR - detection of malarial DNA
What is normally first line of treatment in Falciparum malaria?
- Co-artem –> a combination of artemether and lumefantrine. This is an Artemisinin-based combination therapy (ACT) which is usually the first line of treatment for malaria.
- Atovaquone/Proguanil Hydrochloride
How is complicated Falciparum malaria treated?
IV artesunate – must complete a full oral course when able to stop iv
What can occur in approximately 10–15% patients following intravenous artesunate treatment?
Haemolysis - Haemoglobin concentrations should be checked approximately 14 days following treatment in those treated with IV artemisinins
What supportive therapy can be given for malaria patients?
- Management of seizures, pulmonary oedema, acute renal failure and lactic acidosis
- Exchange transfusion may be helpful in hyperparasitaemia
How is Non-Falciparum Malaria treated?
Oral chloroquine
If the patient is vomiting and unable to tolerate oral chloroquine, what should be given?
Quinine IV until the patient can swallow, then complete the FULL course of chloroquine
In malaria caused by Plasmodium Vivax and Ovale, what is important to treat? Which drug is used?
-
Primaquine
- Vivax and Ovale need Primaquine 14 days to treat liver form to prevent recurrence
During treatment with Primaquine, why is it important to check the patient’s G6PD status?
Primaquine can cause haemolysis
Methods of control of malaria?
- Insecticide spraying in homes
- Larvicidal spraying on breeding pools
- Filling in of breeding pools
- Larvivorous species introduced in to mosquito breeding areas
- Use of insecticide impregnated bed nets
- Chemoprophylaxis
- Vaccine??
What is Strongyloidiasis? What parasite is it caused by (and classification of this parasite)?
- a human parasitic disease caused by the nematode called Strongyloides stercoralis, or sometimes S. fülleborni
- Helminths –> Nematodes (round worms)
Life cycle of Strongyloidiasis?
Humans can autoinfect
Strongyloidiasis is sometimes asymptomatic but can progress to Strongyloidiasis hyper infection syndrome. What can cause this? What is the mortality result of this?
- most commonly triggered by acquired or iatrogenic immunosuppression (steroids, chemo etc)
- mortality rates up to 90%
How is Strongyloides sp transmitted?
- Direct penetration of human skin by infective larvae when in contact with soil; walking barefoot is therefore a major risk factor for acquiring the infection.
- Sexual transmission in MSM (no evidence in heterosexual couple)
- Bronchial secretions (rarer)
Why can Strongyloides hyperinfection syndrome be difficult to diagnose?
- Serology often negative in hyperinfection (immunosuppressed)
- Direct microscopy often negative
- Stool culture/ concentration methods often required
Treatment of Strongyloides?
Antihelminthic Drugs:
- Ivermectin
- Albendazole
Treatment of Strongyloides hyper infection syndrome / disseminated strongyloidiasis?
- If possible, stop or reduce immunosuppressive therapy
- Ivermectin, 200 µg/kg per day orally until stool and/or sputum negative for 2 weeks.
Methods of controlling Strongyloides?
- Wear shoes when you are walking on soil
- Avoid contact with faecal matter or sewage.
- Proper sewage disposal and faecal management
Strongyloidiasis has almost disappeared in countries where sanitation and human waste disposal have improved.
What is Cryptosporidiosis? What parasite is it caused by? Classification?
- A diarrheal disease caused by microscopic parasites that can live in the intestine of humans and animals and is passed in the stool of an infected person or animal.
- Caused by: Cryptosporidium parvum and hominis
- Protozoa –> Sporozoans –> Cryptosporidium sp.
How is Cryptosporidiosis spread?
- Human to human spread with animal reservoir (cattle, sheep, goats)
- Faecal-oral spread
- (Sporadic cases can lead to outbreaks)
Cryptosporidiosis life cycle
Clinical effects of Cryptosporidiosis?
- Incubation 2-10 days (usually 7 days)
- Watery diarrhoea with mucus (no blood)
- Bloating, cramps, fever, nausea, vomiting
- Usually self-limiting (last up to 2 weeks)
Who can Cryptosporidiosis be very severe in?
- very young
- very old
- Immuno-compromised (60% HIV patients infected go on to chronic infection- can loose up to 25 litres fluid/day)
Who is at risk of Cryptosporidiosis?
-
Human-Human Spread:
- Regular users of swimming pools (can be resistant to chlorine)
- Child care workers and parents
- Nursing Home residents/carers
- Healthcare workers
- Travellers
-
Animal-Human Spread:
- Backpackers, Campers, Hikers
- Farm workers
- Visitors to farms/petting zoos
- Consumers of infected dairy products
Treament for symptomatic Cryptosporidiosis?
- Rehydration etc
- Nitazoxanide
What is Nitazoxanide?
Nitazoxanide is a broad-spectrum antiparasitic and broad-spectrum antiviral drug that is used in medicine for the treatment of various helminthic, protozoal, and viral infections
Treatment of Cryptosporidiosis in immunocompromised patients?
- Paromomycin (to kill parasite)
- Nitazoxanide (effectiveness is unclear)
- Octreotide (reduce cramps and frequency)
- HIV patients, HAART should be quickly initiated
For severe cases may need to use combination therapy parmomycin, nitazoxanide and azithromycin
Method of controlling Cryptosporidiosis?
-
Human-Human:
- Hand hygiene
- Filter or boil drinking water
- Isolate symptomatic patients in healthcare setting
- Ensure symptomatic children are kept away from school
-
Animal-Human:
- Pasteurise milk and dairy products
- Boil or filter drinking water if camping
What is Trichomoniasis? What parasite is it caused by (and classification)?
- A common sexually transmitted infection caused by a parasite
- Caused by Trichomonas vaginalis
- Protozoa –> Flagellates –> Trichomonas vaginalis
How is Trichomonas vaginalis transmitted?
Sexually
Signs and symptoms of Trichomoniasis?
Men: usually asymptomatic
Women: smelly vaginal discharge, dyspareunia, dysuria and lower abdominal discomfort, punctuate haemorrhages on cervix (“strawberry cervix”).
Life cycle of Trichomoniasis?
Treament of Trichomoniasis?
Make sure to treat ALL partners
- Metronidazole
What is Giardiasis? What parasite is it caused by? Classification of this parasite?
- an infection in your small intestine
- Caused by microscopic parasite Giardia lamblia
- Protozoa –> Flagellates –> Giardia lamblia
How is Giardiasis transmitted?
Faecal oral transmission
Signs and symptoms of Giradiasis?
Spectrum of disease: asymptomatic carriage to severe diarrhoea and malabsorption. Can cause chronic disease
- Diarrhoea
- Abdominal pain
- Bloating
- Nausea and vomiting
Symptoms usually last 1-3 weeks
life cycle of Giardiasis?
Diagnosis of Giardiasis?
Identification of cysts or trophozoites in faeces
Treament for Giardiasis?
Metronidazole/tinidazole
Prevention of Giardiasis?
Hygiene measures
Boling water
Which parasite can cause Loefflers syndrome?
Helminths –> roundworm (nematodes) –> intestinal nematodes –> Ascaris (lumbricoides)
Ascariasis can develop into Loefflers syndrome.
Which parasite can cause Katayama syndrome?
Helminths –> flatworms –> trematodes (flukes) –> Schistoma
Schistosomiasis can develop into Katayama syndrome.
What is Katayama syndrome?
Katayama syndrome is a systemic hypersensitivity reaction against the migrating schistosomula and eggs, and can occur within 14–84 days after a primary infection.
Which parasite uses snails as the intermediate host?
Schistosoma
Which parasite causes ‘Ascariasis’?
Helminths –> roundworms (nematodes) –> intestinal nematodes –> Ascaris (lumbricoides)
What is the usual host of Echinococcus?
Sheep and dogs
Which parasitic disease leads to cysts?
Hyatid disease
Which parasite can cause hyperinfection syndrome?
Helminths –> roundworms (nematodes) –> Strongyloides stercoralis
Which parasite undergo asexual multiplication in the erythrocytes to then infect red blood cells?
Protozoa –> Sporozoans –> Plasmodium sp. (malaria)
Which classification does P. falciparum belong to?
Protozoa –> sporozoans
What is artemisinin-based combination therapy (ACT) recommended for the treatment of?
P. falciparum malaria
Which parasitic disease can be sexually transmitted only between MSM?
Helminths –> roundworms (nematodes) –> Strongyloides sterocoralis/S. fulleborni
Which parasitic disease can be sexually transmitted between men and women?
Protozoa –> flagellates –> Trichomonas vaginalis
The characteristic of which parasite is autoinfection?
Strongyloides sterocoralis/S. fulleborni
Which type of malaria is Primaquine specifically used in the treatment of?
Malaria due to Plasmodium vivax and Plasmodium ovale
