Emerging Pathogens of Concern

The presence of infective agents that can be termed as “emerging” or “re-emerging” in municipal sludge should be of particular current concern. A recent review by Woolhouse and Gowtage-Sequeira (2005) identified 1,407 recognized species of human pathogens, 58% of which are zoonotic. For these pathogens, there is still a great deal that is not known about how they will be affected by many of the processes currently used in biosolids treatment. Processes that combine chemicals, such as nitrous acid and ammonia, with heat have provided effective inactivation of helminth eggs and viruses, and have simultaneously reduced the required disinfection time to attain a Class A product by at least one order of magnitude. The presence of typical food- and water-borne pathogens such as Salmonella and Campylobacter along with the emergence of new strains of Listeria and E. coli have been linked to manure run-off in animal agriculture and contamination of poultry and dairy products. Questions have emerged specifically related to human exposure to these pathogens through land application of waste material and the adequate assessment of risk. The infective dose is one key component as to whether or not it is likely that the pathogens in biosolids may be infectious to people who come in contact with it. The infective doses for the individual pathogens can vary from one organism to 106 organisms per gram dry solids. This presentation will serve to address the emerging pathogens of concern in waste treatment and the potential impact on human health.