Parasitology Flashcards
Organisms that cause diseases in humans
- Viruses
- Bacteria
- Unicellular eukaryotes that are parasites - micro parasites (protozoan parasites)
- Multicellular eukaryotes that are parasites - macro parasites e.g. worms
Size of other organisms vs parasites
- HIV (virus) - 0.2 micrometers
- E.coli 4microM length
- S.cerevisiae (yeast) - 3.6 microm diameter
- Human red blood cell - 6-8 micrometer
- HeLa cells 15-30microm diameter
- Human fibroblasts 200 microm
Unicellular Parasites:
- Plasmodium (Malaria parasite) - 1-8microm
- Bacteria (Toxoplasmosis) - 5microm
- Trypanosoma Brucei (sleeping sickness) - 6 microm
Parasitic worms:
- Wuchereria Bancroft - 10cm
- Schistosoma Mansoni - 20cm
Genes in parasites and other organisms
there isn’t really a correlation between gene number and complexity (some plants have more genes than humans)
Trypanosoma brucei - 9000
Trypanosoma cruzi - 12,000
Leishmania - 8000
Toxoplasma - 8000
Plasmodium falciparum - 5000
Wuchereria Bancrofti - 13,000
E.coli 4,400
viruses 10-100s
S.cerevisiae - 6000
Drosophilia 18,000
Humans - 20000 - 25,000
Cellular complexity of parasites
- Bacteria - surrounded by 1-2 membranes (relatively simple)
- Unicellular parasites contain complex organelles found in all eukaryotes
- in addition many parasites also contain specialised organelles malaria has plastid (from ancestors) - from endosymbiosis event where bacteria was taken up by another cell - opens up possibly using antibiotics to treat these parasitic diseases
- e.g doxycycline used to treat malaria
multicellular parasites are even more complex
- Parasitic worms comprise of many different cell types and form specialised tissues and organs e.g. neurons, fibroblasts etc
Humans are the definitive host for Cryptosporodium - simple process
Some parasites have a single host and can be acquired from the environment
- infection begins with the ingestion of water or food containing spore like oocysts
- Cryptosporodium enters the cells of the small intestine
- crypto has a simple single host life cycle
- the oocysts pass into the colon and are released in the faeces
- crypto infects others
Some parasites have a single host and can be acquired from the environment
- Humans are the definitive host for
Cryptosporidium - Cryptosporidium lifecycle - a unicellular parasite acquired by ingestion of contaminated food or water (causes diarrhoea)
- Oocyst form of the parasite is highly resistant and can persist in the environment (resistant to many disinfectants)
- Within digestive tract parasite will go through changes in pH and temp etc, so the cyst will break open and release the parasite
- parasites invade epithelial cells once released
- they can replicate sexually or asexually
they will then release oocysts into the intestine and so if you have diarrhoea they will be washed into the environment and can survive- they are very tough and can survive chlorine - parasite is passed onto environment and takes cyst form again
Many parasites have a complex life cycle and are transmitted by specific insect vectors
- The malaria parasite is a unicellular parasite and is transmitted by Anopheles mosquitoes
- The mosquito is referred to as the vector
- many parasites can be transmitted by insect vectors include some multicellular parasites
- get infected by a bite
- mosquito inject parasites form salivary gland into our blood
- parasites go to liver and replicate
- while they are replicating there are no symptoms
- take about 1 week for them to replicate
- they then burst out into blood and invade red blood cells
- they go around and around this cycle, replicating, being released and invading red blood cells again and again
- Some malaria will differentiate into forms that can be taken up by mosquito again
- no mosquitos = no malaria
- lots of pathogens and transmitted by mosquitoes
Vector control is a key tool in reducing many parasitic infections
- Preventing people from getting bitten is very important
- graph shows malaria infections that have been averted
- ITN - low tech approach - sleep under bed net which is treated with insecticide
Refer to notes for the graph
Some parasites have sexual stages in their lifecycle
- All malaria parasites have a sexual stage in their lifecycle (happens in mosquito)
- In the case of the malaria parasite the sexual stage occurs in the mosquito. The mosquito is therefore referred to as the definitive host
- some parasites will differentiate into gametocytes - male and female - genetically the same but their gene expression id different so they are not identical
- they’re the only form of these parasites that can be taken up by a mosquito - only ones that can survive in the mosquitos and continue the lifecycle
- Definitive host - where the sexual stages of the lifecycle occur
Need to know
- Life cycle stages in both human and mosquito
- understand the complexity of the parasite lifecycle
- Understand concept of sexual and asexual stages of the parasitic lifecycle
- explain what definitive host is
- considered the lifecycle in the context of vaccine development and potential of the different stages as vaccine targets and diagnostic targets
Zoonotic parasites
Zoonoses - a disease that can transmitted from animals to humans
Multicellular parasites can also be transmitted by mosquitoes - Lymphatic filariasis
- Lymphedema caused by malfunction of the lymphatic system
- adult filarial parasite resides in lymphatic system
- lymphatic system malfunctions and fails to drain fluid correctly
- leads to swelling in the legs, arms, breasts, genitalia (often to the point of disability)
- Prevention - mass drug administration
The lifecycle of Brugia malayi
Refer to notes for the diagrams
