11. Symbionts, Zoonoses And The Origin Of New Epidemics Flashcards
What are the two types of mites?
- Demodex which is a harmless commensal.
2. Sarcoptes which is an ectoparasite, an itch mite that causes scabies and burrows under the skin.
What are symbionts?
Organisms living together
What are mutualists?
Symbionts that both benefit each other
Why have parasites evolved to be less harmful?
- A parasite is not transferred if the host is killed rapidly
- The parasite benefits if the host is abundant
- Hosts react most strongly to harmful parasites
How have hosts evolved to be resistant?
Resistant hosts reproduce more
What is the role of common gut bacteria in the body?
- They are either virtually harmless parasite that use some of the food in our gut or commensals that eat what we find indigestible
- Some are mutualists
What do the mutualists common gut bacteria do?
- Partly digest food which helps us absorbs it
- Some manufacture B and K group vitamins
- Some produce other useful compounds (stimulate immune system)
- Some feed on harmful excretions of other bacteria
What is the role of Bifidus bacteria for the baby immune system?
Bifidus bacteria on the vagina and nipples of lactating women ensures the baby gets Bifidus
- Bifidus protects by decreasing other bacteria
What symptoms did the yersina pestis bacterium cause in humans?
- Fever, buboes, prostration, delirium, blackened skin, death
What was the mode of spread for the yersina pestis bacteria?
- The bacterium was passed from the rat fleas
- A ball of bacteria grows in the flea’s gut which creates a blockage
- The flea seeks a new host as it is hungry
- The flea sucks harder but fails, instead recoiling the bacteria right into the bite wound
How did the bubonic plague demonstrate zoonosis?
The fleas of wild rodents (gerbils) went to black rats and their fleas when to humans
What causes the rabies disease?
Large RNA virus that is specific to the nerves
What animals does the rabies virus come from?
There are reservoirs in resistant foxes, raccoons, bats
- It passes to dogs then humans
What three things affect the spread of disease?
- Density and movement of hosts
- Size of host population
- Nutritional and knowledge status of the host population
How does density and movement of hosts affect the spread of disease?
- High density means greater contact between individuals
- Increased movement gives more contact between individuals
How does the size of the host population affect the spread of disease?
- A disease needs an ongoing supply of susceptible individuals
(New births or immigrants)
How does the nutritional and knowledge status of the host population affect the spread of disease?
- Lack of protein can impair immune function
- Micronutrients (vit C, zinc) are essential for immune function
- Affects public understanding of how to avoid infection
What is horizontal transmission?
Between individuals, or via vector or intermediate host
What is vertical transmission?
Between generations, mother to child
What do we graph on each axis to map the rate of spread of the disease?
No infected vs time
For the graph of the rate of the spread of a disease, what is the rate of spread at a given time determined by?
The slope
Slope = r x N
What is r in the graph of the rate of spread of a disease?
R is the intrinsic rate of infection
R = p x C x D
Where P = probability of passing on the disease at each contact, C= effective average number of contacts per year and D= duration of infectiousness
How do we know there will be an epidemic?
If R > 1
What is the role of ecosystem disturbance in increasing zoonoses?
- Brings humans into contact with new hosts and parasites
- Contact between domestic and wild animals
- Increases nutritional stress in wild populations
- Greater chance of spreading native pathogens
What are some ways we can achieve bio awareness?
- Reduce biopollution by keeping exotics out with quarantine
- Increase immunisations and public health measures of ourselves and poor countries
- Address pest and disease problem relating to food production for a growing population
- Minimise the evolution of resistance
- Anticipate climate change effects
