Parasitic Infections Flashcards by Felyx Wong

Define parasite.

An organism living in or on a host and dependent on the host for nutrition – causing damage

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What is the difference between an endoparasite and an ectoparasite?

Endoparasite – exist INSIDE the host

Ectoparasite – exist on the host

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What are the two groups of endoparasites and what are the features of organisms within these two groups?

Protozoa 
 Unicellular  
 Eukaryotes (membrane bound nucleus)  
 Some have insect vectors  
 NO eosinophilia  
Metazoa 
 MULTIcellular
 They are helminths/worms
 Free living, intermediate hosts and vectors
 Cause eosinophilia if they invade the blood

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State the classes of organisms within the two groups of endoparasites.

Protozoa  
 Amoeba
 Coccidia
 Ciliates
 Flagellates 
Metazoa 
 Roundworms
 Flatworms
 Flukes

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Give some examples of amoeba.

Entamoeba histolytica

Entamoeba dispa

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Give some examples of coccidia.

Plasmodium species
Toxoplasma
Cryptosporidium

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Give an example of a ciliate.

Balantidium coli

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Give some examples of flagellates.

Trypanosoma
Trichomonas
Giardia
Leishmania

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What is the main difference between the two types of amoeba?

Entamoeba histolytica can cause invasive amoebiasis

Entamoeba dispar is a normal commensal of the GI tract

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What is amoeba infection caused by?

Ingestion of mature cysts in food or water contaminated by faeces

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Describe how E. histolytica infection causes disease.

The cysts enter the small intestine and release active amoebic particles (trophozoites), which invade the epithelial cells of the large intestines, causing flask-shaped ulcers
Infection can spread from the intestines to other organs e.g. liver, lungs and brain
Invasive amoebiasis may often cause amoebic liver abscesses

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How many nuclei are there in mature cysts?

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What are the treatment options for amoebiasis?

Nitroimidazole derivatives (kills trophozoites but not the cysts)  
Parmomycine or Diloxanide Furoate

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What are the five types of plasmodium that cause malaria?

Falciparum 
Malariae 
Vivax 
Ovale 
Knowlesi

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What are the two types of host for plasmodium?

Human

Female anopheles mosquito

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What are the two stages of malaria in humans?

Liver

Blood

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Describe the symptoms of malaria.

PAROXYSMAL (occurs every 4-8 hours) 
Fever  
Chills 
Headaches  
Vomiting  
Muscle pain

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State some complications of malaria.

Severe anaemia (due to intravascular haemolysis) 
Cerebral malaria 
Liver failure  
Shock  
Pulmonary oedema 
Abnormally low blood sugar 
Kidney failure  
Swelling and rupturing of the spleen

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What are the treatments for uncomplicated malaria?

Chloroquine (look at notes for the rest of the treatment options)

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What is the treatment for severe malaria?

Artemisinin-based combination therapy

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How is malaria diagnosed?

Blood film (+ Giemsa stain)

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What are the routes of infection of toxoplasma gondii?

Eating undercooked meat of animals harbouring tissue cysts
Consuming food or water contaminated with cat faeces
Blood transfusion
Organ transplantation
Transplacentally from mother to foetus

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Which group of patients are particularly vulnerable to toxoplasma infection?

Immunocompromised

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What can toxoplasma infections cause in these individuals?

CNS disease
Brain lesions
Pneumonitis
Retinochoroiditis

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What does cryptosporidium cause?

DIARRHOEA (mainly in the immunocompromised)

How is it treated?

Fluid rehydration

How are most diarrhoeal protozoal diseases diagnosed?

Stool examination

What are the reservoirs of balantidium coli?

Primates Rodents Pigs

What are the effects of balantidium coli infection in immunocompromised patients?

``` Persistent DIARRHOEA Dysentery Abdominal pain Vomiting Nausea ```

How can drinking water be cleared of ovoid giardia lamblia cysts?

Filtration | Ovoid cysts can survive standard chlorination procedures

What is the main symptom of giardiasis?

DIARRHOEA

How is giardia transmitted?

Faeco-oral

What are the acute symptoms of giardiasis?

``` Diarrhoea Greasy stools that tend to float Stomach or abdominal cramps Nausea/vomiting Dehydration ```

What is the treatment for giardia?

Metronidazole

How is trichomonas transmitted?

Sexually transmitted

Where does trichomonas infection mainly tend to reside?

Urethra

What are the symptoms of trichomoniasis?

Dysuria Vulval itching Vaginal discharge Offensive smelling urine

What effect does trichomonas infection have on HIV transmission?

It enhances HIV transmission

What is the treatment for trichomoniasis?

Metronidazole

Can adult worms multiply in man?

In which subset of the population is there a significant burden of worms?

School-aged children – this has a massive impact on their development

What are the three groups of Helminths? Give some examples of each.

``` Roundworms (nematodes)  Ascaria  Hookworms  Filaria  Strongyloides Flatworms (cestodes)  Taenia (tapeworms) Flukes (trematodes)  Schistosoma ```

Where do the adult ascaria worms live?

Small intestine

Describe the passage of ascaria larvae once they hatch in the small intestine.

Infective eggs are swallowed The larvae hatch in the small intestine and invade the intestinal mucosa They are carried via the portal and systemic circulation to the lungs The larvae mature further in the lungs, penetrate the alveolar walls, ascend the bronchial tree and are swallowed When they reach the small intestine, they mature into adult worms

How long can adult ascaria live?

1-2 years

Describe the symptoms of ascariasis.

Often asymptomatic Infections with a large number of worms can cause abdominal pain or intestinal obstruction Malnourishment (because of worms feeding on contents of small intestine) Loeffler’s pneumonia – penetration of larvae into lungs leads to pools of blood and epithelial cells clogging the airspaces in the lungs (resulting bacterial infections can be fatal)

What is the treatment for ascariasis?

Albendazole or Mebendazole

How are most helminth infections diagnosed?

Stool examination

Describe the passage of hookworm larvae across the body.

The same as ascaria

Where do adult hookworms live?

Small intestine

What is a key feature of hookworm infection and what is this caused by?

Iron deficiency anaemia – caused by localised bleeding in the small intestine

What is the treatment for hookworm infection?

Albendazole or Mebendazole

What is the biological name whipworm?

Trichuras trichiura

Where do adult whipworms live?

Caecum and ascending colon

What are the symptoms of whipworm infection?

Blood diarrhoea and anaemia (due to severe vitamin and iron loss)

What is the treatment for whipworm infections?

Albendazole or Mebendazole

What is a potential therapeutic use of whipworms?

Helminth therapy for allergies and autoimmune diseases

What are the two forms of filaria?

Brugia malayi | Wucheria bancrofti

Describe the location of microfilariae in the blood.

They are found in the peripheral blood at night | They are found in the deep veins during the day

How is lymphatic filariasis diagnosed?

Blood smear | Antigen detection with immunochromatic test (ELISA)

What is a distinguishing feature of Loiasis?

Worms can get into the eye and cross under the conjunctiva so you see something wriggling in your vision

What is the insect vector in Loiasis?

Chyrops fly

What are the three main types of flatworm for which humans arethe only definite host?

Taenia solium Taenia asiatica Taenia saginata

Describe the symptoms of flatworm infection.

``` Most people are asymptomatic Abdominal pain Weight loss Loss of appetite Upset stomach NOTE: people with T. saginata infection tend to have more symptoms ```

How is flatworm infection diagnosed?

Stool examination – tapeworm segments are found in the stool or identification of eggs in the stool

What important condition does Taenia solium cause?

Cysticercosis

What is the treatment for flatworm infections?

Praziquantel

What are the three main types of schistosoma?

Schistosoma mansoni Schistosoma haematobium Schistosoma japonicum

What is the intermediate host in schistosoma?

Freshwater snails

Where do the adult worms live in schistosomiasis?

Venule

Where do the eggs progressively move to?

``` Small intestine (mansoni and japonicum) Bladder and ureters (haematobium) ```

Describe the symptoms of schistosomiasis.

``` Possible rash or itchy skin Fever Chills Cough Muscle aches Most people have NO SYMPTOMS in early stages of infection ```

What is the treatment of schistosomiasis?

Praziquantel

Name some ectoparasites.

Sarcoptes scabiei – Scabies (causes rash) Pediculus humanis capitis (head louse) Pediculus humanis corporis (body louse) Pthirus pubis (crab louse)

How are ectoparasites transmitted?

Direct contact