| Causative organism |
C. trachomatis serovars A, B, Ba, and C |
T. pallidum ssp. pertenue
|
| Hypothesized routes of transmission |
Mechanical transfer from infected eyes to uninfected eyes via fingers, fomites, and flies. No known animal reservoir. |
Mechanical transfer from a primary or secondary yaws lesion to broken skin of an uninfected individual via direct contact or, possibly, flies. No known animal reservoir. |
| Clinical course |
Repeated episodes of active (inflammatory) trachoma over many years cause conjunctival scarring, which in some individuals eventually draws the eyelashes inward so that they rub on and damage the cornea. |
Multiple phases of disease. Primary yaws manifests as a papilloma at the inoculation site, which then ulcerates and scars over months. Untreated patients develop cutaneous, skeletal, and constitutional features of secondary yaws and, eventually, in some cases, tertiary yaws, characterized by necrotic and/or hypertrophic lesions of soft tissue and bone. |
| Epidemiology |
Active trachoma is most common in pre-school-age children, with the prevalence of blinding consequences increasing with age; even in most hyper-intense transmission areas, trachomatous blindness is rare before adulthood. |
Primary yaws is most common in school-age children. Secondary yaws occurs 1 to 24 months after untreated primary yaws. Tertiary yaws, now rare, occurs 5 or more years after untreated secondary yaws. |
| Sub-clinical infection provides a rationale for mass treatment of endemic populations |
Yes. The proportion of individuals without clinical signs who have conjunctival C. trachomatis infection varies with the local intensity of transmission. |
Yes. For each clinical case there may be more than five infected individuals without signs. Asymptomatic latent infection may persist for years between secondary and tertiary yaws. |
| Program goal |
Elimination as a public health problem: reduction in the prevalence of trachomatous trichiasis (TT) unknown to the health system to <1 per 1,000 total population, and in the prevalence of TF in 1- to 9-year-olds to <5% in each district. |
Eradication: no serologically positive children <5 years old and no new cases of active yaws for 3 consecutive years, in all countries where yaws has ever been known. |
| Strategy name |
The “SAFE” strategy: surgery, antibiotics, facial cleanliness, and environmental improvement. |
The WHO Morges strategy. |
| Recommended antibiotic |
Azithromycin |
Azithromycin |
| Recommended antibiotic dose |
20 mg/kg, maximum 1 g |
30 mg/kg, maximum 2 g |
| Recommended antibiotic schedule |
Annual mass treatment for 3 or 5 years (depending on baseline prevalence) before re-survey. |
One round of mass treatment, then targeted treatment (of all active clinical cases and their contacts) every 3 to 6 months. |
| Unit of implementation |
District (the administrative unit for health care management, which, for purposes of clarification, consists of a population unit between 100,000 and 250,000 persons). |
Conforming to the estimated extent of the endemic focus at baseline, and village- or community-based at follow-up and during surveillance. |
| Surveillance |
Population-based surveys to estimate district-level prevalences of TT and TF, conducted two years after an impact assessment has shown that elimination goals have been reached. |
Active surveillance in all villages using village volunteers and school teachers. |
