Transcript Prevention and Treatment of Trachoma

Prevention and Treatment of Trachoma
D. J. Gove. From University of Southampton. Now at
Sun Microsystems Inc, California, USA
J. D. Hawkins From University of Southampton. Now a
Consultant
A. K. Shahani, University of Southampton
[email protected]
[email protected]
M. E. Ward, University of Southampton
Geo Data Institute, University of Southampton
Trachoma
Bacterium
Chlamydia Trachomatis
Infectious Eye Disease
Inflamed Upper Eye Lid
Geo Data Institute, University of Southampton
Trachoma
Infection
Young children:
Reddening and irritation
Older children, Adults:
Scars on eyelids
Trichiasis: Eye lids contract.
Eye lashes turn inwards and
Damage cornea
Time
Cumulative damage to cornea results
in visual loss and blindness
Clinical Signs of Trachoma
Normal tarsal conjunctiva.
The dotted line shows
the area that should be
inspected. Notice that
the blood vessels are visible.
Trachomatous inflammation
- follicular (TF).
Clinical Signs of Trachoma
Trachomatous inflammation
- follicular and intense (TI + TF)
Trachomatous scarring
(TS).
Geo Data Institute, University of Southampton
Clinical Signs of Trachoma
Trachomatous trichiasis
(TT).
Corneal opacity
(CO).
Geo Data Institute, University of Southampton
Microbiological Information About
Chlamydial Infection
• Clinical signs appear when infection has taken hold
and the disease becomes apparent.
• Microbiological information about body’s immune
responses can detect infection well before disease
becomes apparent.
• Microbiological information is expensive.
Global Distribution of Active Trachoma
Global Distribution of Trichiasis
Trachoma
• Trachoma is the world’s major cause of preventable
blindness.
• Trachoma has been eradicated from most developed
countries. Trachoma is very common in poor countries.
• About 10% of the world’s population is at risk of
blindness from Trachoma.
• About 84 million people have active disease.
• About 8 million people are visually impaired or blind d ue
to Trachoma.
Geo Data Institute, University of Southampton
Prevention and Treatment of Trachoma
World Health Organization (WHO) SAFE strategy for
controlling Trachoma
•
•
•
•
Surgery for advanced trachoma
Antibiotics
Facial cleanliness
Environmental improvements.
Geo Data Institute, University of Southampton
Prevention and Treatment of Trachoma
Morocco has succeeded in controlling Trachoma
through using SAFE strategy
80 %
% of
active
disease
60 %
40 %
20 %
0%
Five regions of Morocco
Geo Data Institute, University of Southampton
Clinical Model
Microbiological Model
Infection Dynamics
Force of infection
Susceptible
Infected /
Diseased
Resistance
Susceptible
Duration of infection
Duration of resistance
Incubation
period
Duration of clinical signs
Point of
infection
Time
Data and Information for Models
• Data from various sources
•Demography: Life Table. Birth rate by age of woman.
• Longitudinal surveys of the population in the village of
Jali in Gambia for Clinical and Microbiological Models.
Sources: Dr Robin Bailey, Professor David Mabey,
Professor M E Ward
• Infection probabilities by age
• Duration of infection by age
• Probabilities of consequences of infection
• etc.
Data and Models: Demographics
Data and Model
Recurrence of active disease following chemotherapy
12%
9.6%
7.2%
Prevalence
4.8%
2.4%
0%
0
50
Jali data
150
Time (Weeks)
200
Model
250
Data and Models: Clinically Active Disease
Data and Models: Scarring
Data and Models: Trichiasis
Chemotherapy
Chemotherapy was modelled as an immediate
reduction in the force of infection
Geo Data Institute, University of Southampton
Chemotherapy: Single Treatment
Prevalence
of
Infection
Time in Weeks
Chemotherapy
• Treating 0 – 15 age group is almost as beneficial
as treating the whole village.
• Chemotherapy by itself will not eradicate Trachoma in
Jali and other areas with high prevalence
Repeated Chemotherapy Treatments: Age 0-15
Prevalence
of
Scarring
0
200
400
600
800
Time in Weeks
1000
Repeated Chemotherapy Treatments: Age 0-15
Prevalence
of
Trichiasis
Time in Weeks
Vaccination
• Vaccines are not available at present
• Models can provide some guidance about the “type”
of vaccine that would be effective.
• Vaccine parameters
• Duration of protection. e.g. 5 years
• Effectiveness of protection: Reduction in infection probability
e.g. Infection probability is reduced to 70% of its base value
• Vaccination is modelled as increased resistance
decreasing the number of susceptibles
Vaccination
Time to return to previous levels of infection
with various vaccines.
Vaccine
effectiveness
30%
50%
0-5 age group
2.5 year
2 years
4.5 years
0-5 age group
5 year
2 years
4.5 years
Vaccine
effectiveness
30%
0-15 age group
2.5 year
4.5 years
0-15 age group
5 year
4.5 years
50%
4.5 years
7 years
Socio-Economic Actions
• Effect of socio-economic actions is modelled as
a reduction in the force of infection
• Examples of socio-economic actions
• Actions that decrease / eliminate poverty
• Easy access to sufficient clean water
• Improved hygiene
• There is no high quality data for estimating the
effects of particular socio-economic actions
Geo Data Institute, University of Southampton
Force of Infection Reduced to 90% of Previous
Chemotherapy
Prevalence
of
Infection
Time in Weeks
Changes in Force of Infection for age 0-15
Prevalence
of
Infection
Time in Weeks
Concluding Remark
•Appropriate data + Detailed models for evaluating
treatment strategies can evolve good strategies for
eradicating Trachoma
Geo Data Institute, University of Southampton