Disease

Question 1

‘Old’ diseases

Answer 1

Plague – Yersinia pestis

Anthrax – Bacillus anthracis

Botulism and tetanus – Clostridium species

Scarlet fever – Streptococcus pyogenes

Diphtheria –Corynebacterium diphtheria

Whooping cough – Bordetella pertussis

(Cholera – Vibrio cholerae)

(TB – Mycobacterium tuberculosis)

(Syphilis – Treponema pallidum)

Question 2

Plague

Answer 2

: Yersinia pestis, Enterobacteriaceae

most feared bacterial disease, killed 1/3rd Europe middle ages, Surat -Indian outbreak 1994 (50 deaths), panic and huge economic impact

Bubonic (transmitted via flea bite - zoonosis), pneumonic (direct respiratory).

Infects lymphatic, blood, lungs

Rapid antibiotic treatment, or close to 100 % mortality

Question 3

Diphtheria

Answer 3

: Corynebacterium diphtheriae

disease of young

characteristically shaped bacteria, grows in throat, swelling in neck

Potent toxin, spread throughout body – inhibits synthesis of proteins and kills cells. Spread by airborne route.

Toxoid, early, highly effective vaccine.

Question 4

Scarlet fever

Answer 4

: Streptococus pyogenes

scarlet fever late 19th early 20th century – red rash, fatal, puerperal fever and death post child birth

streptococcal gangrene, necrotising fasciitis

airborne and foodborne transmission – spread rapidly within families, could loose ¾ of one family.

Strep A are generally sensitive to antibiotics.

Question 5

Whooping cough

Answer 5

: Bordetella pertussis

Highly contagious infection of respiratory system

Dry cough, severe bouts, whoop

Complications, seizure, brain damage, pneumonia - young infants/ babies (affects all ages)

Vaccine effective, but short lived protection, last few years reappearance of disease

Question 6

‘Over the next hour alone, ____people will die from an infectious disease - ______ children under five. Of the rest, most will be working-age adults

Answer 6

1 500 die from an infectious disease

over half of them children under five

Question 7

1998 worldwide, % of children die of infectious disease; % of adults die of infectious disease

Answer 7

63% children

48% adults

Question 8

Emerging and re-emerging bacterial diseases

Change of lifestyle

Answer 8

Tuberculosis – Mycobacterium tuberculosis (re-emerging) (HIV, drug resistance)

Legionnaire’s disease – Legionella pneumophila, (air conditioning and conference centre)

Food poisoning – Salmonella, Campylobacter (fast food)

Question 9

Emerging and re-emerging bacterial diseases

Recognition

Answer 9

Flesh eating bacterium’ – Streptococcus pyogenes (apparent new disease)

Ulcers – Helicobacter pylori (association proven)

[Meningococcal meningitis – Neisseria meningitidis (more significant due to greatly decreased incidence of infectious disease in young adult)]

Question 10

Emerging and re-emerging bacterial diseases

Newly evolved bacteria

Answer 10

Killer E. coli’ – E. coli O157:H7; E. coli O104:H4 (new toxin) – 50 deaths within a couple of months- acquired Shiga-like toxin, similar to that produced by Shigella dysenteriae

O157 is enteropathogenic causes damage to intestinal epithelial walls and produces toxin, goes into blood, kidney damage, leads to death.
O104 is enteroaggregative, produces very high levels of same toxin & antibiotic resistant strains

Cholera – Vibrio cholerae 0139 (new strain, new coat)- acquired new ‘O antigen’ – a lipopolysaccharide covering surface – hide better from immune response

Antibiotic resistant strains eg MRSA - resistance to many penicilllin based antibiotics.

Question 11

Emerging and re-emerging bacterial diseases

Misuse

Answer 11

Bioterrorism
– Bacillus anthracis (anthrax)
- Yersinia pestis (plague)
- Clostridium botulinum (botulinum toxin)

Question 12

Evolution of a bacterial pathogen

Answer 12

• genome reduction due to deletion events
• gene acquisition by HGT
• mutations, rearrangements

Intracellular bacteria downsize the genome, to get rid of genes where product is provided by host

Many free- living bactaria and facultative pathogens acquire new genes that help them survive in a new environment.

All bacteria undergo mutations that enhance survival.

Question 13

pathogen

Answer 13

Organism capable of inducing damage

Commensal (non-pathogenic) -> parasitic (pathogenic) association with the host

Question 14

Virulence of a bacterium depends on

Answer 14

(i) infectivity
(ii) invasiveness
(iii) pathogenic potential

Question 15

Opportunistic pathogens

Answer 15

Escherichia coli (post-op/ cancer septicaemia) Staphylococcal aureus (older patients)

Question 16

Disease is a balance between virulence of pathogen and resistance of host

Answer 16

commensalism Parasitism

Virulence of pathogen ->

Question 17

Stages in pathogenesis

Answer 17

1. Reservoir and Transmission
2. Adhere to and colonise host
3. Evasion of host immune system
4. Growth and multiplication in select environment (niche)
5. Damage
6. Dissemination

Question 18

Reservoir and Transmission

Answer 18

Microbes adapted to mode of transmission and infection.

Human respiratory system – airborne, inanimate objects, hands etc
Oral – GI tract, generally local eg most Salmonella but may become systemic eg typhoid
Water/ food- faecal/oral route

Animals (zoonoses) – insect vector often injected into blood, by passes skin

Humans; soil – direct contact; sexually transmitted; wound puncture eg rusty nail

Question 19

Vibrio cholerae

Answer 19

infected via faecal-oral route

Vibrio cholerae is an aquatic, Gram –ve curved rod
some strains cause cholera, 60% fatal if untreated
water-borne transmission ; epidemics in disaster zones

It has pili and flagella:
Flagella required for motility, follows chemical gradient to mucosal surface / TCP pili required for attachment, bacteria also interact with each other to form a colony (biofilm) of bacteria at intestinal epithelium (required for disease)

~does not invade, localised in intestine (IgA).
~ responds to low pH and change in temperature from 20 C to 37 C
~Cholera toxin is an enzyme:ADP ribosylase acts on adenylate cyclase complex and result in Loss of Na+ and Cl- / Massive loss of water / Profuse diarrhoea, salt imbalance

Question 20

Adhere to and colonise host

Answer 20

via pili (fimbriae) - long thin structures extending from cell surface,

• terminal adhesins, bind specifically to host cell carbohydrate
• Colonisation - establishment of a site of bacterial reproduction on or within host
• may initiate invasion of host tissue

via other surface molecules

Question 21

Evasion of host immune system

Answer 21

Capsule - Carbohydrate, anti-phagocytic ; may mimic host molecules

Enzymes - destroy components of immune system
Modify surface molecules to mimic host antigens

Invade host cells, hide from immune system

Question 22

Growth and multiplication in select environment (niche)

Answer 22

adapt to environment (temperature, pH, redox potential, osmolarity, nutrients, iron)

differential gene expression

Question 23

Damage

Answer 23

responsible for symptoms of disease

degradative enzymes, aid spread of bacterium, and toxins interfering with normal physiological process eg cholera toxin

Induce inappropriate immune response, results in disease

Question 24

Effects of some bacterial toxins

Answer 24

Cholera toxin - salt imbalance in intestine and fluid secretion (diarrhoea)

Diphtheria toxin – inhibits protein synthesis

Botulinum toxin – a highly potent neurotoxin

Tetanus toxin – a neurotoxin, lockjaw

Endotoxin, (LPS) Gram –ve bacteria, overstimulation of immune response

Question 25

Dissemination

Answer 25

Leave host, return to reservoir, find new host :
~ Sneezing, coughing
~ Diarrhoea
~ Decomposition dead body
~ Lesion, contact

Question 26

Foodborne Infectious disease

Answer 26

• Bacteria colonize the gastrointestinal tract
• invade the tissue or secrete a toxin which leads to symptoms of gastroenteritis.
• e.g. E. coli O157, Salmonella, Shigella, Vibrio cholerae, Campylobacter

Question 27

Foodborne Intoxication

Answer 27

bacteria multiply in the food, produce the toxin in the food; toxin is ingested, gastroenteritis.

• presence of living bacteria in the food is not essential.
• Clostridium botulinum (botulism), staphylococcal food poisoning)
• Characterised by a rapid onset (6h) of illness

Question 28

commensal

Answer 28

association where only bacterium benefits, host gains no benefit

Question 29

epidemiology

Answer 29

study of occurrence, agents, distribution and control of disease in a defined population

Question 30

carrier

Answer 30

an infected host and potential source of infection

Question 31

host

Answer 31

organism in/on which micro-organism is growing

Question 32

virulence

Answer 32

relative pathogenicity, determined by infectivity, invasiveness and pathogenic potential (often between different strains)