Flashcards in Chapter 3 Deck (19):
Why have the main causes of death changed since 1900?
Vaccinations, hygiene, access to clean water and antibiotics
How does the generation time for bacteria and host compare?
Bacteria is an hour on average compared to 20 years by host
Where are resistance genes found?
On plasmids, which can be handed over directly (through genes) to other bacteria
What does the host-pathogen relationship depend upon?
The speed of the host's acquired immune response, the microbe's ability to multiply, spread and cause disease, the host's ability to contain and eliminate
What happens if there is a delayed response from the host's immune system?
The microbe causes disease and then sheds.
What is an example of adaptation?
The Myxoma virus that infects rabbits and is spread by mosquitoes.
Introduced into Australia to control the rabbit population. Initially 99% died but then more rabbits survived over time as a less lethal strain of the virus replaced the original and the rabbits adapted
How does the time the microbe is around affect the damage it does?
The longer the microbe is around, the less damage it will cause because it will select for the resistant population and the virus will mutate into a non-lethal strain.
Ex: HIV, CJD
What are the four types of microbial infection?
1. Microbial attachment/penetration mechanism
2. Biting arthopod
3. Skin wound/animal bite
4. Antimicrobial defences impaired
(1-3 the antimicrobial defences are still intact)
What are the 6 steps of infection?
1.Attachment and possible entry into the body
2.Local or general spread in body
4.Evasion of host defences
5.Shedding from body (exit)
6. Damage to host (not required but usually happens with shedding)
What are Koch's postulates used for?
To determine if a germ causes a disease or not
What are Koch's postulates?
1. The suspected germ much be present in every case of the disease.
2. The germ must be isolated and grown in pure culture.
3. The cultured germ must cause disease when it is inoculated into a healthy host.
4. The same germ must be reisolated from the diseased host.
How can the postulates be tested for unculturable organisms?
Use the naturally infected as your culture
Tresponema pallidum papllidum for syphillis
How can the postulates be tested during the involvement of more than one pathogen?
Ex: HDV will only infect people who are already infected with Hepatitis B.
How can the postulates be tested if the infection is only in humans?
What is the molecular evolution of Koch's postulates?
1, The virulence trait under study should be associated much more with pathogenic strains of species than with nonpathogenic strains.
2.Inactivation of genes associated with the suspected virulence trait should decrease pathogenicity.
3. Replacement of the mutated gene with a normal wild-type gene should fully restore pathogenicity.
4. The gene should be expressed at some point during the infection and disease process.
5. Antibodies or immune system cells directed against the gene products should protect the host.
What does the severity of the infection depend upon?
Dose and route of infection, age, sex, nutritional status and genetic background
What disease does not appear until many years after infection?
What causes Whipple's disease?
16 mRNAs on the uncultivatable Tropheryma whippelii