9. Parasites Strategies Flashcards
What is the life cycle of a hookworm infection?
- Faeces: larvae emerge on soil
- Larvae penetrate skin into blood
- Carried to heart and lungs
- Penetrate to airway then up to throat
- Human swallows larvae
- Attach in small intestine and mature
- Adults lay embryos that pass out in faeces
What happens if humans are the intermediate host?
Usually harmless if cysts are in the meat we eat. Worms colonise our guts
What happens if humans ingest dog tapeworms?
Hyatid (big) cysts develop in liver and other organs. Treated with surgery and chemotherapy
Why do insects/ticks make great ectoparasites?
- Often highly mobile
- Actively search for new hosts
- Mouthparts adapted to penetrate skin barrier
What is the vector for sleeping sickness?
Tsetse fly
What disease does the mosquito transmit?
Malaria and many others
What disease does the sand fly transmit?
Leishmaniasis
What disease does the assassin bug transmit?
Chagas’ disease
What disease do fleas transmit?
Bubonic plague
What disease do lice transmit?
Typhus
What are the life stages of a mosquito?
Eggs, larva, pups, adult
What are the parasite strategies to survive in the human body?
- Many copies, genetically variable
- Avoid recognition
- Present a moving target
- Hide from defenders
- Attack: destroy/jam the immune system
How do schistosomes (class trematoda) avoid recognition?
- They use camouflage
- Live in the blood vessels and avoid attack by coating themselves with host antigen proteins
What temporary strategy do schistosomes use while coating themselves?
- Produce enzymes that destroy or detach complement proteins
- Complement proteins attack a parasite by attaching to foreign surface components (or bound to antibodies). They then attract phagocytes and destroy the tegument of the worm and rupture the cells.
How do trypanosomes present a moving target?
- Trypanosomes can make 1000 different surface antigens
- Majority of individuals only present 1 form but there will be variation in the parasite population
- Immune system learns to recognise and destroy a major antigenic type but variation means a few individuals with a different antigen can survive
- Increase in number until the immune system learns to recognise to recognise them again
How do parasites hide from defenders in the gut?
- Tape worms, hook worms (nematodes)
- Low risk as the immune system is not strong in the gut
- Must still have a tegument that can resist digestion
How do parasites hide from defenders inside cells?
- Plasmodium (hide in liver and blood cells)
- Nematode in muscle cells
- It then makes the cell grow and get extra blood supplies
How does HIV destroy the immune system?
- Invades and divides in various immune calls
- T helper cells (key coordinators), dendritic cells and macrophages
- Causes disruption and destruction of cellular immune response
- Leaves infected person vulnerable to other infections
What are some strategies for parasites getting to new host?
- Complex life cycle that includes inert stages (survive for a long time waiting for the host)
- Free living stages
- Using an intermediate host
- Asexual multiplication
- Sexual reproduction
What is the free living stage in water?
Where the parasites feeds and waits for the host
What is the entamoeba histolytica life cycle?
- Mature trophozoite has asexual reproduction
- Produces cysts with 4 nuclei that pass in faeces
- Cysts survive but trophozoites die
- transported by fly/cockroach
- Contamination of fingers/food/water
- Ingestion
- In small intestine 8 young emerge from the cyst
What are the Ascaris?
Human/pig roundworms of the phylum nematoda
How are the ascaris spread?
- Eggs swallowed on food, hatches in gut, penetrates gut wall
- Worm to blood, into lungs, up bronchi to throat, then swallowed to the gut
- Eggs are passed out in the faeces and get onto raw vegetables
Wha tis the life cycle of the kidney roundworms?
- Unembryonated eggs are shed in urine
- Eggs embryonate in the water
- Eggs are ingested by intermediate host (earthworms)
- Larvae encyst in the paratenic host and do not develop any further
- Carnivores (including canids and mustelids) serve as the primary definitive hosts and become infected after ingesting paratenic or intermediate hosts
- Humans become incidental hosts after eating undercooked paratenic hosts
