Parasitology Flashcards by Tooks yh

What is a parasite?

An organism that lives on or in a host organism and gets its food from or at the expense of its host

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What are the different types of hosts for parasites?

Intermediate – host in which larval or asexual stages develop
Definitive – host in which adult or sexual stage occurs

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When are vectors mechanical?

○ Mechanical when no development of parasite in vector

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When are vectors biological?

○ Biological when some stages of life cycle occur within the vector

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What are the 3 classes of parasites?

Protozoa
Helminths
Ectoparasites

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What are protozoa?

• Microscopic, single celled organisms that can be free-living or parasitic in nature

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What are protozoa able to do in humans??

• Able to multiply in humans allowing serious infection to develop from single organism
§Not all parasites can multiply in humans but protozoa can

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What are the ways protozoa can be transmitted?

○ Protozoa living in the human intestine can be transmitted by the fecal-oral route
○ Protozoa living in blood or tissues are transmitted by an arthropod vector

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What are protozoa classified by and what are they?

• Protozoa are classified by modes of movement
○ Amoeba e.g. Entamoeba
§ Has pseudopodia and moves around by pushing them out
○ Flagellates e.g. Giarda, Leishmania
○ Ciliates e.g. Balantidium
○ Sprozoa – organisms whose adult stage is not motile e.g. plasmodium, cryptosporidium

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What does entamoeba histolytica cause?

○ Causes amoebic dysentery

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What does a loss of epithelia due to entamoeba histolytica cause?

○ Loss of epithelia so causes ulcer formation

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What does giardia lamblia cause?

○ Cause diarrhoea

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What happens to the villi of the small intestine due to giardia lamblia?

○ Blunting of villi in small intestine

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What does trichomonas vaginalis cause?

causes vaginal discharge

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What is toxoplasma gondii an infection from?

○ Infection from cat faeces

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What is cryptosporidium a common cause of?

○ Common cause of epidemic diarrhoea worldwide

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What is cryptosporidium a major cause of?

○ Major cause of moderate-severe diarrhoea in developing countries

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What can cryptosporidium do to growth?

Can cause growth stunting

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What are soil transmitted helminths?

○ Ascaris lumbricoides
○ Trichuris trichiura
○ Hookworm spp
○ Enterobius vermicularis

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What are filarial parasites?

○ Wuchereria bancrofti
○ Loa loa
○ Onchocerca volvulus
○ Onchocerca volvulus 
○ Dracanculus medinensis

Medically important helminths(Trematodes)

○ Schistosoma mansoni/haematobium/japonicum
○ Clonorchis sinensis
○ Fasciola hepatica
○ Paragonimus spp.

Medically important helminths(Cestodes)

○Taenia saginata
○Taenia solium
○Echinococcus

What are ectoparasites?

• Blood-sucking arthropods such as ticks, fleas, lice and mites that attach or burrow into the skin and remain there for relatively long periods of time (e.g. weeks to months)

Medically important ectoparasites

Mites(Scabies and trombiculid)
Ticks
Lice
Flies

What does scabies cause?

§ Cause itchy rash that people may scratch off and this results in secondary infection

What do you get trombiculid from?

§ Get it from walking around in the tropics in freshly grown grass

Life cycle of parasite-Schistosomiasis

• Eggs of this parasite have been deposited in the water through human faeces so the water becomes contaminated ○ Eggs develop and infect the intermediate host – the snail § The snail becomes an amplifier □ Asexual reproduction in snail releases thousands of developed eggs which infect humans when they walk in the contaminated water

What can you measure morbidity to infection using?

• You can measure morbidity to infections using DALYs – Disease Adjusted Life Years

What do opportunities for transmission depend on?

1. Household sanitation 2. Access to clean water 3. Personal hygiene behaviours

What are determinants of parasitic infections?

1. Faeco-oral 2. Food 3. Complex life cycles

What is protozoa(Chagas disease) transmitted by?

Transmitted by kissing bug

How can you reduce the opportunity for transmission?

Simple measures such as improving construction of house, keeping animals away from house reducing opportunity for transmission

What are the 3 phases of disease?

1. Acute 2. Chronic(Intermediate) 3. Determinate chronic disease

What can be detected in blood during acute phase of disease?

○ Trypanosomes can be detected in blood

What percentage develop chronic chagas after acute disease?

○ 5-10% develop chronic Chagas immediately after acute disease

What is determinate chronic disease characterised by?

○ Characterised by cardiac and intestinal disease

What does acute chagas occur within?

• Occurs within 2-3 weeks

What are generally mild symptoms of acute chagas?

``` ○ Local swelling (Romana) ○ Nodule or chagoma – rash on hand ○ Fever ○ Anorexia ○ Lymphadenopathy ```

What are acute symptoms of acute chagas?

○ Hepatosplenomegaly | ○ Acute myocarditis – rapid heart failure

How do you develop chronic chagas(Cardiac)?

• Gradually develop chronic disease after 10-30 years

What damage happens in chronic chagas(cardiac)?

* Damage to conduction system of heart causing arrhythmias | * Damage to heart muscle causing cardiomyopathy

What are most affected in chronic chagas(Digestive)?

• Oesophagus, rectum and sigmoid colon most affected

What does chronic chagas interfere with?

• Interferes with peristalsis | § Gut becomes unable to effectively move contents on so organs start to swell

What is the presentation of chronic chagas(Megacolon)?

○ Constipation if it affects the large intestine

What are complications involved with chronic chagas(megacolon)?

``` ○ Faecaloma ○ Obstruction ○ Sigmoid volvulus ○ Ulceration ○ Perforation ```

What happens in the acute phase of chagas?

○ Tissue damage caused by inflammatory response to parasite in nests of amastigotes in cardiac, skeletal and smooth muscle ○ Parasite killing by antibodies, activated innate immune response and Th1 pro-inflammatory cytokines

What happens in the intermediate phase of chagas?

○ Regulatory immune response characterised by IL-10 and IL-17 ○ Balance between killing a parasite and protecting the host

What happens in the chronic phase of chagas?

○ Chronic inflammatory response to persistent parasites in muscle and nerve cells ○ Autoimmune mechanisms ○ Damage to nerve and muscle cells resulting in loss of tolerisation so get response against host cells ○ May vary by parasite strain and tissue tropism ○ Predominance by Th1 cytokines and CD8+ T cells