Parasitology Flashcards
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
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
When are vectors mechanical?
○ Mechanical when no development of parasite in vector
When are vectors biological?
○ Biological when some stages of life cycle occur within the vector
What are the 3 classes of parasites?
- Protozoa
- Helminths
- Ectoparasites
What are protozoa?
• Microscopic, single celled organisms that can be free-living or parasitic in nature
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
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
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
What does entamoeba histolytica cause?
○ Causes amoebic dysentery
What does a loss of epithelia due to entamoeba histolytica cause?
○ Loss of epithelia so causes ulcer formation
What does giardia lamblia cause?
○ Cause diarrhoea
What happens to the villi of the small intestine due to giardia lamblia?
○ Blunting of villi in small intestine
What does trichomonas vaginalis cause?
causes vaginal discharge
What is toxoplasma gondii an infection from?
○ Infection from cat faeces
What is cryptosporidium a common cause of?
○ Common cause of epidemic diarrhoea worldwide
What is cryptosporidium a major cause of?
○ Major cause of moderate-severe diarrhoea in developing countries
What can cryptosporidium do to growth?
Can cause growth stunting
What are soil transmitted helminths?
○ Ascaris lumbricoides
○ Trichuris trichiura
○ Hookworm spp
○ Enterobius vermicularis
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?
- Household sanitation
- Access to clean water
- Personal hygiene behaviours
What are determinants of parasitic infections?
- Faeco-oral
- Food
- 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?
- Acute
- Chronic(Intermediate)
- 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
