1. 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
K. Shahani, University of Southampton
M. E. Ward, University of Southampton
Geo Data Institute, University of Southampton

2. Trachoma Bacterium Chlamydia Trachomatis Infectious Eye Disease
Inflamed Upper Eye Lid
Geo Data Institute, University of Southampton

3. Trachoma Infection Young children: Reddening and irritation
Older children, Adults:
Scars on eyelids
Trichiasis: Eye lids contract.
Eye lashes turn inwards and
Damage cornea
Cumulative damage to cornea results
in visual loss and blindness
Time

4. 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).

5. Clinical Signs of Trachoma
Trachomatous inflammation
- follicular and intense (TI + TF)
Trachomatous scarring
(TS).
Geo Data Institute, University of Southampton

6. Clinical Signs of Trachoma
Trachomatous trichiasis
(TT).
Corneal opacity
(CO).
Geo Data Institute, University of Southampton

7. 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.

8. Global Distribution of Active Trachoma

9. Global Distribution of Trichiasis

10. Trachoma blindness. Trachoma has been eradicated from most developed
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

11. 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

12. Prevention and Treatment of Trachoma
Morocco has succeeded in controlling Trachoma
through using SAFE strategy
80 %
60 %
40 %
20 %
0 %
% of
active
disease
Five regions of Morocco
Geo Data Institute, University of Southampton

13. Clinical Model

14. Microbiological Model

15. Infection Dynamics Time Force of infection Infected / Diseased
Susceptible
Resistance
Susceptible
Duration of infection
Duration of resistance
Incubation
period
Duration of clinical signs
Time
Point of
infection

16. 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.

17. Data and Models: Demographics

18. Recurrence of active disease following chemotherapy
Data and Model
Recurrence of active disease following chemotherapy
12%
9.6%
7.2%
4.8%
2.4% 0%
Prevalence
Time (Weeks)
Jali data
Model

19. Data and Models: Clinically Active Disease

20. Data and Models: Scarring

21. Data and Models: Trichiasis

22. Chemotherapy
Chemotherapy was modelled as an immediate reduction in the force of infection
Geo Data Institute, University of Southampton

23. Chemotherapy: Single Treatment
Prevalence of
Infection
Time in Weeks

24. Treating 0 – 15 age group is almost as beneficial
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

25. Repeated Chemotherapy Treatments: Age 0-15
Prevalence of
Scarring
Time in Weeks

26. Repeated Chemotherapy Treatments: Age 0-15
Prevalence of
Trichiasis
Time in Weeks

27. 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

28. Vaccination with various vaccines.
Time to return to previous levels of infection
with various vaccines.
Vaccine effectiveness
0-5 age group
2.5 year
5 year
30%
2 years
50%
4.5 years
Vaccine effectiveness
0-15 age group
2.5 year
5 year
30%
4.5 years
50%
7 years

29. 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

30. Force of Infection Reduced to 90% of Previous
Chemotherapy
Prevalence of
Infection
Time in Weeks

31. Changes in Force of Infection for age 0-15
Prevalence of
Infection
Time in Weeks

32. Concluding Remark Appropriate data + Detailed models for evaluating
treatment strategies can evolve good strategies for eradicating Trachoma
Geo Data Institute, University of Southampton