Germ Warfare

Question 1

What is an infection?

Answer 1

A disease caused by a pathogen

Question 2

Define the term pathogenicity.

Answer 2

The ability to cause disease

Question 3

What is a pathogen?

Answer 3

A micro-organism that can invade the body and cause disease

Question 4

Define the term virulence.

Answer 4

A pathogen’s power to cause severe disease

Question 5

What is an endogenous infection?

Answer 5

A disease arising from a pathogen already present in the body but previously asymptomatic.

Question 6

What is an exogenous infection?

Answer 6

A disease arising from a pathogen not normally present in the body which came from the environment.

Question 7

What is zoonosis?

Answer 7

An animal disease that can spread to humans

Question 8

Describe the properties of bacillus anthracis.

Answer 8

• Gram positive bacterium
• Causative agent of anthrax
• Infects wild and domestic animals
• Produces spores tht can survive in the soil for long periods of time
• Category 3 pathogen

Question 9

What are the characteristics of a category 3 pathogen?

Answer 9

• Humans are rarely infected
• There are multiple forms of th disease
• High mortality in some forms of the disease

Question 10

What are the types of anthrax?

Answer 10

• Cutaneous anthrax
• Inhalation anthrax
• Gastrointestinal anthrax
• Injection anthrax

Question 11

Describe the characteristics of cutaneous anthrax.

Answer 11

• >95% of cases
• Usually acquired by direct contact with infected animals or animal products.
• Incubation period is 1-12 days.
• The initial puritic papule gradually becomes a vesicular or bullous lesion, surrounded by extensive non-pitting oedema.
• The central part becomes necrotic and haemorrhagic.
• Finally there is classic black eschar - falls off in 1-2 weeks.

Question 12

Describe the characteristics of inhalation anthrax.

Answer 12

• Very rare.
• Occurs after inhalation of spores.
• Incubation period is less than one week.
• It presents as flu-like illness with non-productive cough, leading to pneumonia bacteraemia.
• High mortality rates (45-85%).

Question 13

What are the options for treatment of anthrax?

Answer 13

• Antibiotics
  
  • Cutaneous anthrax
    
    • Ciprofloxacin or doxycycline
    • 7-10 days
  • Systemic anthrax
    
    • Ciprifloxacin with either linezolid or dindamycin
• Monoclonal antibody preparations (antitoxin)
• Vaccination

Question 14

What is the relationship between pathogenicity and virulence?

Answer 14

• The capacity of an organism or agent to cause disease reflects its relative pathogenicity.
• Virulence is the measure of the pathogenicity of an organism or agent to cause disease despite host resistance mechanisms.
• It is affected by numerous variables:
  
  • Number of infecting organisms or agents (infectivity)
  • Route of entry into the body
  • Specific and non-specific host defence mechanisms
  • Intracellular growth replication
  • Virulence factors of the organism or agent

Question 15

What is an obligate pathogen?

Answer 15

• Almost always associated with disease
• Examples:
  
  • Bacillus anthracis
  • HIV

Question 16

What is a conditional pathogen?

Answer 16

• May cause disease if certain conditions are met
• Example:
  
  • Staphylococcus aureus

Question 17

What is an opportunistic pathogen?

Answer 17

• Usually only infects immuno-compromised host
• Example
  
  • Cryptococcus neoformans

Question 18

What are the characteristics of successful pathogens?

Answer 18

• Survival and transmission in the environment
• Attachment to the surface of the host
• Overcoming the body defences against infection
• Ability to damage the host, e.g. by toxin production

Question 19

What are the steps of infection?

Answer 19

• Recognition
• Attachment and entry
• Multiplication
• Evasion of host defence
• Shedding
• Damage

Question 20

What are the virulence factors of a pathogen?

Answer 20

• Toxin secretion (toxigenesis)
• Pilus formation
• Capsule
• Iron transport systems
• Adhesion factors (adhesins)
• Enzymes
• Antibiotic resistance

Question 21

Describe the properties of Staphylococcus aureus.

Answer 21

• Widespread gram positive bacteria
  
  • Natural microbiota of the skin
  • ~40% carriage
• Versatile pathogen associated with wide range of diseases
  
  • Minor skin infections
  • Food poisoning
  • Toxic shock syndrome
  • Endocarditis
  • Haemolytic pneumonia
• Complex pathology

Question 22

Describe the properties of a virus.

Answer 22

• Virus architecture is unique and bears no resemblance to any other living cell.
• Only contains the parts needed to enter and control a host cell.
• Essentially a nucleic acid (DNA or RNA) enclosed in a protein shell.
• Small (nm).

Question 23

What are protozoa?

Answer 23

Single celled eukaryotes

Question 24

What are the classifications of protozoa?

Answer 24

• Sporozoa - intracellular parasites
• Flagellates - possess tail-like structures for motility
• Amoeba - use temporary cell body projections (pseudopods)
• Ciliates - move by beating multiple hair-like structures (cilia)

Question 25

Describe the characteristics of fungi.

Answer 25

• Eukaryotic
• Multinucleate or multicellular organisms
• Yeasts are single-celled
• Thick carbohydrate wall containing chitin and glucans
• Part of normal microbiota as well as being pathogens
• Fungal infections = ‘mycoses’

Question 26

Describe the common fungal infection, cryptococcosis.

Answer 26

• Cryptococcus neoformans
• Encapsulated yeast
• Lab diagnosed by india ink
• Mainly treated with amphotericin B
• Affects lungs or meninges

Question 27

What is the term used for all parasitic worms?

Answer 27

Helminths

Question 28

What are the 3 main groups of helminths important in humans?

Answer 28

• Cestoda - tapeworms
• Trematoda - flukes
• Nematoda - roundworms
• Infections are most common in tropical/subtropical climates

Question 29

What kind of infections are caused by flukes?

Answer 29

• Urinary
• Intestinal