Discussion

The paper will discuss recent progress on the control of human helminth infections by mass drug administration (MDA). The main focus will be on soil transmitted helminths (STH) and the schistosome parasites, plus some reference to past LF control programmes based on community wide use of the drug albendazole . The current World Health Organization (WHO) guidelines for STH and schistosome treatment based on the concept of morbidity control in the community via the reduction of those harbouring heavy infections to less than a defined percentage level in the community based on MDA targeted at certain age groups. The definitions of high, medium and low infection status are based on eggs per gram of faeces (or urine) and are somewhat vague given a poor understanding of what levels of past or current infection induce morbidity. A multi-disciplinary approach is adopted to look at how best to calculate what type of MDA programme will work best in either reduce morbidity or interrupt transmission. The concept of transmission elimination will be discussed and proposals made on how best to measure a critical prevalence or mean intensity of infection below which transmission ceases. The papers end with a discussion of two issues. First, what are the implications arising from the use of new more sensitive diagnostic tools for the design and implementation of health policy for the control of human helminth infections? Second, at what prevalence level should MDA cease, and for how long should monitoring and evaluation programmes track events post cessation of MDA to ensure transmission interruption?