Parasitology Flashcards
What is a parasite?
A parasite is 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 cause disease in humans?
There are three main classes of parasites that can cause disease in humans:
- Protozoa
- Helminths
- Ectoparasites
What are protozoa?
Protozoa are microscopic, single-celled organisms that can be free living or parasitic in nature
Describe the mechanism of protozoa infections
They are able to multiply in humans allowing serious infections to develop from a single organism
How does protozoa transmission occur?
- Protozoa living in blood / tissues are transmitted by an arthropod vector
- Protozoa living in human intestine can be transmitted via fecal-oral route
How are protozoa classified?
Protozoa are classified by mode of movement
Name different classifications of protozoa
- Amoeba: Entamoeba
- Flagellates: Giardia, Leishmania
- Ciliates: Balantidium
- Sporozoa: Plasmodium, Cryptosporidium
What are sporozoa?
Protozoa organisms whose adult stage is not motile
Name examples of medically important protozoa infections
Entamoeba histolytica Giardia lamblia Trichomonas vaginalis Malaria (Plasmodium spp.) Toxoplasma gondii Cryptosporidium Leishmania spp. Trypanosoma cruzi Trypansoma brucei (gambiense/rhodesiense)
What are helminths?
Helminths are large, multicellular organisms (worms) generally visible to naked eye in adult stages
In adult form, helminths cannot multiply in humans
What are the 3 groups of human parasitic helminths?
- Nematodes (roundworms)
- Trematodes (flukes)
- Cestodes (tapeworms)
Outline the clinically significant soil-transmitted helminths
- Ascaris lumbricoides
- Trichuris trichiura
- Hookworm spp.
- Enterobius vermicularis
What are the filarial helminth parasites?
- Wuchereria bancrofti
- Loa loa
- Onchocerca volvulus
- Dracunculus medinensis
Name other medically important helminth parasites
Toxocara canis/cati
Trichinella spiralis
Outline trematodes
- Schistosoma mansoni/haematobium/japonicum
- Clonorchis sinensis
- Fasciola hepatica
- Paragonimus spp.
Name some common cestodes
- Taenia saginata
- Taenia solium
- Echinococcus granulosus
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).
What are the different types of mites?
- Scabies
* Trombiculid
Describe the different types of ticks
- Hard
* Soft
Name the varying types of lice
- Pediculus humanus capitis
- Pediculus humanus humanus
- Pthirus pubis
- Flies
- Botflies
What is the significance of parasitic infections?
Parasitic infections cause tremendous burden of disease in both tropics and subtropics as well as in more temperate climates
e.g. Malaria kills ~660,000 people each year
What are NTDs?
The Neglected Tropical Diseases (NTDs) include parasitic diseases such as lymphatic filariasis, onchocerciasis, and Guinea worm disease, and affect >1 billion people, largely in rural areas of low-income countries.
What are the different types of parasitic hosts?
Intermediate – host in which larval or asexual stages develop
Definitive – host in which adult or sexual stage occurs
What are the 2 types of parasitic vectors?
Mechanical: no development of parasite in vector
Biological: some stages of life cycle occur
What is a determining factor of parasitic infection presence in humans?
Relative wealth is primary determinant of distributions of parasitic infections in humans
How does wealth effect distribution of parasitic infection?
Parasitic infections are more common in poorer countries
How does geographical location effect parasitic infection distribution?
There are fewer infections in the extreme areas (further North/South and sub-saharan Africa) as climate becomes inhabitable for both humans and parasites
What are the 6 most common NTDs?
- Guinea worm disease
- Lymphatic filariasis
- Onchocerciasis
- Schistosomiasis
- Soil-transmitted helminths
- Trachoma