Authors
L A Chapman4; L Dyson4; O Courtenay4; R ChowdhuryC BernG F Medley2; T D Hollingsworth4; 1 KalaCORE Programme, Bangladesh, Bangladesh; 2 LSHTM; 3 UCSF, United States; 4 University of Warwick Discussion
Visceral leishmaniasis (VL) has been targeted by the WHO for elimination as a public health problem (<1 new case per 10,000 people per year) in the Indian subcontinent by 2017. Progress towards this target has been made through improvements in case detection and treatment, but there is still considerable uncertainty about progression of the disease, in particular the durations of different disease stages and proportion of infected individuals that develop clinical VL. Better estimates of these parameters are required to guide control efforts, given the key role that they play in VL transmission dynamics. Using detailed epidemiological data from a high-incidence region of Bangladesh from 1999-2004, we have assessed statistically whether progression to clinical VL can be predicted from rK39 ELISA test results, and developed a Markov model of VL progression to estimate key epidemiological parameters. Our results show that individuals with high rK39 antibody titres at baseline are much more likely to progress to clinical VL than individuals with low or moderate titres, and that progression is even more likely for individuals who seroconvert to a high antibody titre over the course of a year. Although the estimated proportion of infected individuals that progress to clinical VL was higher than previous estimates, the long estimated duration of asymptomatic infection suggests that asymptomatic individuals may still contribute significantly to transmission. 
