4.1 The microbial world - infectious agents

Question 1

How small is the microbial world?

Answer 1

Question 2

What are the infectious agents of humans?

Answer 2

Question 3

What are some old diseases that have not gone away?

Answer 3

• Cholera
• Scarlet fever
• Measles

Question 4

What are some other diseases which infections are though to contribute to?

Answer 4

• Peptic ulcers: caused by Helicobacter pylori – 270,000 deaths per year.
• Heart disease
  
  • Rheumatic heart disease caused by streptococci – 376,000 deaths per year.
  • Chlamydia pneumoniae now believed to cause atherosclerosis (coronary artery disease) – 7 million deaths per year.
• Obesity and the gut microflora: Linked to a shift in gut microflora from Bacteroides spp. to Firmicutes (Bacillus, Lactobacillus, Clostridium, Mycoplasma)

Question 5

How do infections contribute to diseases such as cancer?

Answer 5

• Helicobacter also suspected of causing gastric cancers - 800,000 deaths per year.
• Hepatitis B virus causes hepatocellular carcinoma - 600,000 deaths per year.
• Papilloma virus causes cervical cancer - 237,000 deaths per year.
• Epstein-Barr virus causes lymphomas, nasopharyngeal carcinoma.

Question 6

What are emerging infectious disease (EID)?

Answer 6

• Infectious agents evolve faster than humans
• New varieties are constantly emerging due to selective pressures
• EIDs are not centred in developing countries or those in equatorial zones

Question 7

What are the three examples of emerging infectious disease categories?

Answer 7

• Newly evolved strains of existing pathogens – e.g. chloroquine resistant malaria
• Pathogens that have recently entered human population – e.g. HIV, SARS, Ebola
• Re-emerged historical pathogens – e.g. Lyme disease (Borrelia spp.)

Question 8

What is the proportion breakdown of the causative agents of emerging infections?

Answer 8

Question 9

What are the drivers of emerging infectious disease events?

Answer 9

• Microbial adaptations to new environments, host ranges
• Ecological changes
• Population growth and density
• Technology and industry
• Failures in public health measures

Question 10

How is population growth and density a driver of EID events?

Answer 10

• Human demographics and behaviour
• Sexual behaviour and attitudes around safe practices
• Illegal drug use
• Increased mobility (e.g. air travel)

Question 11

How is technology and industry a driver of emerging infectious diseases?

Answer 11

• Organ and tissue transplantation
• Medial devices and implants
• Cosmetic surgeries

Question 12

How are failures of public health measures drivers of public health measures?

Answer 12

• Inadequate or reduced preventative programs
• Inadequate vector control programs
• Misinformation and/or disinformation

Question 13

How can we control infectious diseases?

Answer 13

• Improving housing, sanitation, education
• Surveillance – monitoring patterns and emergence
• Drug therapy with Antibiotics such as Penicillin, erythromycin, mostly against bacteria and fungi
• Antiviral drugs with limited range and efficacy such as influenza, herpes, HIV
• Antiparasitic drugs such as antimalarials
• Vaccines can be highly effective but have limited range and can be costly