Swine Manure Application as a Source of Hepatitis E Virus and other Livestock-Related Pathogens

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The presence of indicator bacteria, hepatitis E virus (HEV), and numerous bacterial pathogen genes increased following precipitation-induced runoff events in streams draining adjacent land surfaces in Iowa where swine manure was recently applied.

USGS analyst performs DNA extractions in a laboratory

A U.S. Geological Survey analyst performs DNA extractions on enriched cultures of water from the study area. Once the DNAwas extracted it was used to detect pathogen gene markers using polymerase chain reaction (PCR). Photo Credit: Heather Johnson, USGS.

Runoff from both land application of animal manure and agricultural tile drainage are possible transport pathways for bacterial, fungal, protozoan, and viral pathogen to surface waters. Animal manure harbors not only animal-specific pathogens but also zoonotic pathogens (HEV, Campylobacter jejuni) capable of infecting humans.

This study simultaneously examined the environmental occurrence of indicator bacteria, HEV, and other livestock-related bacterial, protozoan, and viral pathogens in relation to periods of swine manure application in a basin (South Fork Iowa River) with extensive swine production (around 840,000 hogs in the 78,000-ha watershed) and in an out-of-basin control (Walnut Creek) that had similar soils and land use but no known livestock or swine manure application. Scientists determined the presence and abundance of HEV and other microbiological contaminants from water and bottom sediment collected from 6 stream sites in central Iowa during 2011 and 2012 and swine manure from two swine operations in 2011.

Increased concentrations of indicator bacteria after manure application that exceeded Iowa's State bacteria water quality standards suggest that swine manure contributes to diminished water quality and may pose a risk to human health. Additionally, the occurrence of HEV and numerous bacterial pathogen genes for Escherichia coliEnterococcus spp., Salmonella sp., and Staphylococcus aureus in both manure samples and in corresponding surface water following periods of manure application provides evidence that such swine manure applications may play an important role in the spreading of zoonotic pathogens to the surrounding environment.

Cafo hogs

A typical pen format for swine in many Iowa animal feeding operations. Photo Credit: Kent Becker, USGS.

This study detected HEV, pathogen gene markers from bacteria, and several antibiotic resistance genes that can pose mild to serious health risks to swine, humans, and wildlife. This research provides the foundational understanding required for future assessment of the risk to environmental health from livestock-related zoonotic pathogen exposures. This information could also be important for maintaining swine herd biosecurity and protecting the health of wildlife near swine facilities. Although this study focused on runoff of land-applied manure as a source of microbial pathogens to surface waters, the results could also apply to accidental manure releases due to equipment failures, manure storage overflow, severe weather events, or accidents with manure-transporting equipment.

In order to fully understand the environmental health risks and options for disease prevention, further research is needed to

  1. better understand the persistence and survival of manure-related zoonotic pathogens in water and sediment,
  2. assess the risk to animals and humans from manure-related zoonotic pathogens,
  3. ascertain manure management techniques that can reduce zoonotic pathogen load to the environment, and
  4. ascertain the scope of manure spills in the United States to better understand the risk of exposure of humans, livestock, and wildlife.

The study was funded by the U.S. Geological Survey (USGS) Environmental Health Program (Toxic Substances Hydrology and Contaminant Biology) and the U.S. Department of Agriculture Agricultural Research Service.