The epidemiological dynamics of infectious trachoma may facilitate elimination

Abstract

Introduction Trachoma programs use mass distributions of oral azithromycin to treat the ocular strains of Chlamydia trachomatis that cause the disease. There is debate whether infection can be eradicated or only controlled. Mass antibiotic administrations clearly reduce the prevalence of chlamydia in endemic communities. However, perfect coverage is unattainable, and the World Health Organization's goal is to control infection to a level where resulting blindness is not a public health concern. Here, we use mathematical models to assess whether more ambitious goals such as local elimination or even global eradication are possible. Methods We fit a class of non-linear, stochastic, susceptible–infectious–susceptible (SIS) models which allow positive or negative feedback, to data from a recent community-randomized trial in Ethiopia, and make predictions using model averaging. Results The models predict that reintroduced infection may not repopulate the community, or may do so sufficiently slowly that surveillance might be effective. The preferred model exhibits positive feedback, allowing a form of stochastic hysteresis in which infection returns slowly after mass treatment, if it returns at all. Results for regions of different endemicity suggest that elimination may be more feasible than earlier models had predicted. Discussion If trachoma can be eradicated with repeated mass antibiotic distributions, it would encourage similar strategies against other bacterial diseases whose only host is humans and for which effective vaccines are not available.

Coinfection dynamics of two diseases in a single host population

“…It is a simplified version of the two-disease three-strain model in Gao et al [17] in which the first disease exhibits both drug sensitive and resistant strains. The cotransmission dynamics of two diseases modeled as a SIS process is of interest as a simplified model of, for instance, ocular chlamydia [33, 32, 34] and respiratory pneumococcal colonization [36]. In hyperendemic trachoma regions, both organisms are common and both are affected by trachoma control programs [24].…”

Modelling the Effects of Mass Drug Administration on the Molecular Epidemiology of Schistosomes

“…This has been demonstrated for the NTD trachoma (Chlamydia trachomatis) in communities where MDA of antibiotic eye ointment are used (Lietman et al, 2011). This model included estimates of transmission parameters relating to reinfection from both within or outside the community.…”

Trachoma

“…A mathematical model [66] demonstrated that large-scale elimination may be an achievable goal in hyper-endemic regions, even with incomplete coverage. Return of infection is sufficiently slow that surveillance could be effective in stopping re-emergence.…”