Medical Microbiology: 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 3 main classes of parasites that can cause disease in humans?
- Protozoa
- Helminths (worms)
- Ectoparasites (fleas)
What are Protozoa?
- Microscopic, single-celled organisms that can be free-living or parasitic in nature
- Tend to live in their hosts
- They’re able to multiply in humans allowing serious infections to develop
How are protozoa able to be transmitted?
- Protozoa living in human intestine can be transmitted via faecal-oral route
- Protozoa living in blood or tissue are transmitted via an arthropod vector
What are the different types of protozoa?
- Protozoa classified by mode of movement
- Amoeba e.g. Entamoeba
- Flagellates e.g. Giardia, Leishmania
- Ciliates e.g. Balantidium
- Sporozoa – Organisms whose adult stage is not motile e.g. Plasmodium, Cryptosporidium
Name some medically important protozoa infections
- Entamoeba histolytica - Causes amoebic dysentery
- Giardia lamblia
- Trichomonas vaginalis
- Malaria (Plasmodium spp.)
- Toxoplasma gondii
- Cryptosporidium - Opportunistic infection that can cause chronic diaherra in immunosuppressed individuals
- Leishmania spp.
- Trypansoma cruzi
- Trypansoma brucei (gambiense/rhodesiense)
What are Helminths?
- Large, multicellular organisms (worms) generally visible to the naked eye in their adult stages
- Can’t multiply in humans as adults
What are the different types helminths that are human parasites?
- Nematodes (roundworms)
- Trematodes (flukes)
- Cestodes (tapeworms)
Name some medically important Nematodes
-
Soil-transmitted helminths
- Ascaris lumbricoides
- Trichuris trichiura
- Hookworm spp. - cause anaemia
- Enterobius vermicularis
-
Filarial parasites
- Wuchereria bancrofti
- Loa loa
- Onchocerca volvulus
- Dracunculus medinensis
-
Others
- Toxocara canis/cati
- Trichinella spiralis
Name some medically important Trematodes
- Schistosoma mansoni/haematobium/japonicum
- Clonorchis sinensis
- Fasciola hepatica
- Paragonimus spp.
Name some medically important Cestodes
- Taenia saginata
- Taenia solium - Can cause Cysticercosis
- Echinococcus granulosus - Can cause Hydatid disease
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
What are some medically important Ectoparasites?
-
Mites
- Sacbies
- Trombiculid
-
Ticks
- Hard
- Soft
-
Lice
- Pediculus humanus capitis (head lice)
- Pediculus humanus humanus (body lice)
- Pthirus pubis (pubic lice)
-
Flies
- Botflies
What are the different types of host that a parasite can have?
- Intermediate – Host in which larval or asexual stages of parasite develop
- Definitive – Host in which adult or sexual stage of parasite occurs
What are the different types of vector that a parasite can have?
- Mechanical - When no development of parasite occurs in the vector
- Biological - when some stages of life cycle of parasite occur in the vector
What are some determinants of the global distribution of parasitic infections in humans?
-
Relative wealth (primary determinant)
- Low income countries have a much higher incidence of neglected tropical diseases, which include parasitic infections, compared to higher income countries
-
Climate
- Parasites aren’t able to survive in cooler climates
What is chagas disease and how is it caused?
- A tropical parasitic infection caused by Trypansoma cruzi (Protozoa)
- Parasite feeds on person at night and then defecates on the person
- This causes the person to scratch the bite allowing the faeces that contain the parasite to go through the skin
- Can also rub it through your eye
- Once parasite enters body it multiplies in the nerve and muscle cells
What are some characteristics of acute chagas?
- Inflammatory illness
- Occurs within 3 weeks
- Generally mild symptoms or asymptomatic
- Symptoms include:
- Local swelling (Romaña)
- Nodule or chagoma
- Fever
- Anorexia
- Lymphadenopathy
- Symptoms last 8-10 weeks
- Very rarely may cause the following conditions:
- Hepatopsplenomegaly
- Acute myocarditis
- Meningoencephalitis
- Fatality <5% of symptomatic
What effects does chronic chagas have on the cardiovascular system?
- Damage to conduction system of heart - causes arrhythmia
- Damage to the muscle of heart wall - causes cardiomyopathy
- Can also cause following problems:
- Apical aneurysm
- Thrombus formation - causes stroke
- Can cause sudden death due to arrhythmias
How does chronic chagas megacolon present and what complications can it cause?
- Presents with constipation
- Compliactions include:
- Faecaloma
- Obstruction
- Sigmoid volvulus
- Ulceration
- Perforation
