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2003 OMIG, Abstract 5

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Do Files Transmit Trachoma?
K. Miller1, N. Pakpour1, E. Yi1, M. Melese2, W. Alemayehu2, M. Bird1, G. Schmidt1, V. Cevallos1, L. Olinger1, J. Chidambaram1, J. Whitcher1, T. Lietman1. 1Fl Proctor Foundation, UCSF, 2Orbis International, Ethiopia.

Purpose: The common wisdom is that flies are a vector for trachoma (along with fingers and fomites), but surprisingly this teaching has not been proven. To do so we can look to four criteria which have been used to incriminate other insects suspected of transmitting disease. To date, one criterion remains unmet, the “Repeated demonstration that the suspected arthropod species, collected under natural conditions, harbors the completely identified infectious agent…” Here we report a study in which we used PCR (Polymerase Chain Reaction) to detect the presence of Chlamydia trachomatis DNA on flies in the Gurage Zone of Ethiopia.
Methods: One fly feeding on ocular secretions was collected from each of 103 children aged 1-10, among whom prevalence of chlamydial infection is close to 50%. Each fly was caught using sticky paper, avoiding any contact with the child’s face. An assistant cut out a 1cm2 segment of paper on which the fly remained trapped, and with the same scissors, cut a second equal sized piece from an arbitrary location on the same sticky paper, cleaned the scissors, and re-gloved. The second piece served as a control. Each sample and control was washed in 375ul of sterile saline. The wash was labeled with random numbers to mask if it was from a fly or a control, and then processed using Roche Amplicor PCR kits.
Results: 15/103 flies had evidence of chlamydial DNA (15%, 95% Cl 8-23%), significantly more than matched controls (0/103, McNemar probability, P=0.0001).
Conclusions: These results meet the final criterion needed to incriminate flies as a vector of trachoma. Fly control, and elements which influence fly-eye contacts such as face washing, compose a significant part of the WHO’s strategy to eliminate blinding trachoma. Although incriminating flies as a vector of trachoma is a necessary step, it is information gathered from interventional studies that will demonstrate the importance of fly control and determine how it can be most effective and cost efficient.

Supported by ITI and the Osher Foundation


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