6.4/6 - Antibiotic resistance & endemic diseases

What causes antibiotic resistance?

1. Within a bacterial population, there is genetic variation due to random mutations

2. Usage of an antibiotic exerts a selection pressure

3. Bacteria with genes resistant to a particular antibiotic survive & reproduce, passing on resistant genes to offspring

4. Over many generations, the frequency of resistant bacteria increases

What causes antigen variability?

1. A random genetic mutation changes the DNA base sequence, which results in a different sequence of codons on mRNA

2. Different primary structure of antigen → meaning hydrogen/ionic bonds & disulfide bridges form in different places in tertiary structure

3. Different shape of antigen

How does antigen variability affect the incidence of disease?

• When memory cells are no longer complementary to the antigen, the immune system cannot recognise the pathogen, so the individual is not immune & can be reinfected (e.g. HIV)

• Many varieties of a pathogen → difficult to develop vaccine containing all antigen types

How do hospitals minimise the spread of antibiotic resistant bacteria?

• Screening & quarantine of affected patients

• Hygiene code of practice (e.g. alcohol-based antibacterial gels & hand washing)

• Antibiotics prescribed only when necessary & course completed to minimise selection pressure

Why is it so difficult to control the spread of antibiotic-resistant bacteria?

Horizontal conjugation transfers plasmids with resistance allele from one bacterium to another rapidly

How is endemic malaria controlled?

• Spraying insecticides onto the walls of houses

• Introducing predators of mosquito larvae (e.g. fish & dragonflies)

• Releasing thousands of sterile male mosquitoes, so reproduction is unsuccessful

• Use insecticide-treated bed nets & wear long-sleeved clothes to prevent bites

• Remove stagnant water from areas around homes to reduce prevalence of mosquitoes locally

• Use anti-malarial drugs

What is the role of science in combating malaria?

• Study the biology & ecology of Plasmodium & Anopheles to understand their life cycles & so, derive new treatments to control them

• Evaluate the success of existing treatments in the lab & field

• Advise governments & local hospitals on the best treatments for each situation

• Train local health-workers in the most appropriate techniques

• Develop accurate diagnostic tools to avoid overuse of expensive drugs

What are the ethical & social implications of controlling endemic malaria?

• Treatments must be evidence-based to reduce safety concerns

• Difficulty obtaining informed consent if knowledge of medical trials is poor

• Using insecticides kills other organisms, which reduces biodiversity (e.g. crops & animals)

• Expensive to implement, especially since many affected countries have low GDP

• Opportunity cost: money could be spent on other initiatives (e.g. malnutrition)

What are the practical difficulties of controlling endemic malaria?

• Widespread endemic

• 2 hosts involved

• High antigen variability

• Parasite enters host cells, which shields it from immune response