Towards a quantitative risk assessment for BSE in sewage sludge

Area of Science:

• Veterinary epidemiology
• Risk assessment modeling
• Food safety science

Background:

• Bovine spongiform encephalopathy (BSE) poses a significant public health and agricultural concern.
• The potential for disease transmission through environmental pathways, such as sewage sludge application to agricultural land, requires thorough investigation.

Purpose of the Study:

• To quantify the risk of BSE transmission to humans and cattle from the use of sewage sludge on agricultural land.
• To assess the role of sewage sludge in sustaining BSE epidemics.

Main Methods:

• Development of a quantitative risk assessment model using the Source-Pathway-Receptor approach.
• Estimation of the mean concentration of the BSE agent in sewage sludge.
• Inclusion of key uncertainties: sludge treatment efficacy, BSE infection threshold in cattle, and abattoir waste management.

Main Results:

• A predicted risk of BSE transmission to cattle of 7.1 x 10^-5 per cow per year under specific assumptions of abattoir waste entering sewers.
• Acceptably low risks of BSE transmission to humans through consumption of crops grown on treated land.
• Model indicates that sewage sludge alone cannot sustain the BSE epidemic in the UK cattle herd.

Conclusions:

• The application of sewage sludge to agricultural land presents a low risk to human health.
• While risks to cattle are higher due to exposure and susceptibility, sewage sludge is unlikely to sustain BSE transmission.
• Effective containment of BSE-infected materials (brain and spinal cord) within abattoirs is crucial for disease control.