Geo Data Institute, University of Southampton Prevention and Treatment of Trachoma D. J. Gove. From University of Southampton. Now at Sun Microsystems

Geo Data Institute, University of Southampton

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


Trachoma

Bacterium

Chlamydia Trachomatis

Infectious Eye Disease

Inflamed Upper Eye Lid

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 blindnessTime

Clinical Signs of Trachoma

Normal tarsal conjunctiva. The dotted line shows the area that should be inspected. Notice thatthe blood vessels are visible.

Trachomatous inflammation - follicular (TF).


Trachomatous inflammation - follicular and intense (TI + TF)

Trachomatous scarring (TS).



Trachomatous trichiasis (TT).

Corneal opacity (CO).


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.



World Health Organization (WHO) SAFE strategy for controlling Trachoma

• Surgery for advanced trachoma• Antibiotics • Facial cleanliness• Environmental improvements.



Morocco has succeeded in controlling Trachoma through using SAFE strategy

Five regions of Morocco

% ofactivedisease

80 %

60 %

40 %

20 %

0 %

Clinical Model

Microbiological Model

Infection Dynamics

Susceptible

Force of infection

Infected /Diseased

Resistance Susceptible

TimePoint ofinfection

Duration of infectionDuration of resistance

Incubationperiod

Duration of clinical signs

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

ModelJali data

Prevalence

12%

9.6%

7.2%

4.8%

2.4%

0%

0 50 150 200 250Time (Weeks)

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

Chemotherapy: Single Treatment

Time in Weeks

Prevalenceof

Infection

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

Prevalenceof

Scarring

Time in Weeks

0 200 400 600 800 1000

Repeated Chemotherapy Treatments: Age 0-15

Prevalenceof

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

0-5 age group 2.5 year

0-5 age group 5 year

30% 2 years 2 years

50% 4.5 years 4.5 years

Vaccine effectiveness

0-15 age group 2.5 year

0-15 age group 5 year

30% 4.5 years 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

Force of Infection Reduced to 90% of Previous

Prevalenceof

Infection

Chemotherapy

Time in Weeks

Changes in Force of Infection for age 0-15

Prevalenceof

Infection

Time in Weeks


Concluding Remark

•Appropriate data + Detailed models for evaluating treatment strategies can evolve good strategies for eradicating Trachoma

Documents

Geo Data Institute, University of Southampton Prevention and Treatment of Trachoma D. J. Gove. From University of Southampton. Now at Sun Microsystems