meningococcal infection transmission and disease brian greenwood london school of hygiene &...

MENINGOCOCCAL INFECTION

Transmission and Disease

Brian Greenwood

London School of Hygiene & Tropical Medicine

THE PATHWAY OF INFECTION

Pharyngeal carrier

Respiratory droplets (meningococci)

Susceptible host

Pharyngeal carrier

CASE

Carrier

Carrier

Droplets Droplets

CASE

199

1

THE CYCLE OF INFECTION

THE PATHWAY OF INFECTION

Pharyngeal carrier

Respiratory droplets (meningococci)

Susceptible host

Pharyngeal carrier

CASE

1

2

34

THE PATHWAY OF INFECTION

Pharyngeal carrier

Respiratory droplets (meningococci)

Susceptible host

Pharyngeal carrier

CASE

1

INFECTIOUSNESS OF A CARRIER

• Density of carriage

• Duration of carriage

• Respiratory infection

Durationof carriage

% ? importance

THE PATHWAY OF INFECTION

Pharyngeal carrier

Respiratory droplets (meningococci)

Susceptible host

Pharyngeal carrier

CASE

2

SURVIVAL OF MENINGOCOCCI IN RESPIRATORY DROPLETS

• Droplet size

• Environmental temperature

• Environmental humidity

HUMIDITY AND BACTERIAL SURVIVAL

20 30 40 50 60 70 80 90 100

TownsVillages

Relative humidity (%)

Con

cen

trat

i on

of

air b

orn

e b

acte

ria

(Ghipponi et al. Bull WHO 1971; 45:95)

THE PATHWAY OF INFECTION

Pharyngeal carrier

Respiratory droplets (meningococci)

Susceptible host

Pharyngeal carrier

CASE

3

COLONISATION OF THE MUCOSA

Cilia

Epithelial cells

Numbers ofmeningococci

Integrity of the mucosa

Physicaldamage

Microbiologicaldamage

LOCAL IMMUNE DEFENSES

THE PATHWAY OF INFECTION

Pharyngeal carrier

Respiratory droplets (meningococci)

Susceptible host

Pharyngeal carrier

CASE

4

Integrity ofthe mucosa

Local immunedefenses

INVASION

Mucosa

Capillary

Carrier

Carrier

Droplets Droplets

CASE

190

10

CHANGING THE CARRIER TO CASE RATION

SURVIVAL IN THE HOST

HOST IMMUNITY

Natural exposure

Passive protection

Vaccination

Hostgenetics

Environmentalfactors

Pharyngeal carrier

Respiratory droplets (meningococci)

Susceptible host

Pharyngeal carrier

Case

IMPACT OF THE ENVIRONMENT

Survival of meningococci in droplets

Damage to mucosa facilitating colonisation

Damage to mucosa facilitating invasion

Influence on the immune response

TOPICS FOR FUTURE RESEARCH

• The impact of environmental factors on meningococcal survival in droplets.

• The impact of environmental factors on mucosal immune defences.

• The influence of the environment on the Immune response to vaccination.