Assessing Pathogens in Road Kill

Jean Bonhotal, Ellen Harrison

Cornell Waste Management Institute

Dept of Crop & Soil Science

101 Rice Hall Ithaca, NY14853

Prepared for the Symposium on Composting Mortalities and Slaughterhouse Residuals

Portland, Maine

May 24-25, 2005

Over 25,000 dead deer and numerous carcasses of other animals such as raccoons, coyote and fox are managed annually by NYSDOT. DOT maintains and operates a 15,656 mile highway system of interstates, expressways and collectors which comprises about 15 percent of NYS’s total of 111,000 miles of highway. The 25,000 dead deer managed annually by NYSDOT do not account for deer killed on county and local roads that must be managed by local highway departments.

Disposal options for these carcasses are limited and appropriate disposal is expensive.  Carcasses are often left by the road or dumped into low areas. These methods are becoming less acceptable as rural areas become more populated and there is increased concern for environmental quality. Water quality can become compromised when animals decompose on or below ground. Current NYSDOT practices include contracting with service providers to pick up and dispose of the animals. This is becoming costly and inefficient and service providers do not always have a legal and environmentally sound plan for disposal.  Contractors are paid between $30 and $80 per deer for pick-up and disposal (Rick McKeon, personal communication, NYSDOT) and in FY’s 2000­2002 this totaled just over $1.1 million.  Landfills generally will not take carcasses and when they do it tends to be restricted, so the NYSDOT is left with limited and/or costly disposal options.

Over the past several years, the Cornell Waste Management Institute (CWMI) has worked with dairy farms to manage mortalities through on-site static pile composting.  Workshops and demonstrations held at these sites have generated substantial interest in the process.  The NYS Department of Environmental Conservation (NYSDEC), local and regional Departments of Health, Soil and Water committees and Natural Resources Conservation Service (NRCS) staff have attended workshops and become familiar with the process.  Regional and local DOT personnel have attended workshops and indicated interest in trying composting to manage road-killed deer. In response, composting of road-killed deer is being piloted under CWMI guidance at several DOT facilities in NYS where it seems to be working well.  These piles are easy to manage, do not generate odors, and the carcasses are transformed into compost.  However, questions remain about the hygienic quality of the process and product as well as about worker health.

Passively aerated static pile composting is proving to be a good method of managing these wastes. It is simple, takes less time than dragging a carcass out back, uses equipment and materials used in daily operations and is cost effective. This method helps protect ground and surface water by keeping the carcasses out of contact with water and by reducing pathogens in properly managed piles and it reduces nuisance and odors.

The effectiveness of inactivating pathogens through composting is generally assessed by monitoring the reduction in indicator organisms.  Salmonella and fecal coliform are the usual indicator organisms.  These are the organisms that the USEPA requires for evaluation of the hygienic quality of sewage sludges.  It is widely recognized that the sensitivity of different pathogenic organism to heat varies significantly and questions have been raised about the use of the current indicator organisms.  Evaluation of the effectiveness of static pile composting to inactivate pathogens in road-killed carcasses requires identification of the pathogens that might be present and analysis of their sensitivity to inactivation by heating.  That, combined with time/temperature data from the compost piles, will provide the information needed to assess the hygienic quality of the compost product.

Chronic Wasting Disease (CWD) is a prion disease that is of concern in wild populations. CWD has just been found in NYS, it was first found in a captive herd and with intensive sampling one wild animal (April 2005). There is no evidence to show whether CWD would be killed in the composting process. Compost temperatures are not high enough to inactivate prions, but it is possible that microbial and enzymatic activity could (Langeveld, et al; Kirill, et al.). Even if compost process does not inactivate prions, the end product (woodchips and bone) would be much more amenable to incineration than the untreated carcasses if incineration were required. Plans to manage the spread of CWD in wild deer populations are being developed up by NYS Dept of Environmental Conservation and NYS Dept of Ag and Markets (for captive herds)

Very little work has been done to assess the effectiveness of pathogen-kill in static pile mortality composting.  The reduction of pathogens through composting due to elevated temperatures and microbial competition has been documented for intensively managed (frequently turned) compost piles handling other types of wastes.  Even for turned piles, little information exists for carcass composts. Some research done in Ohio suggests regularly turned compost piles containing carcasses adequately kills common bacterial and viral pathogens (Keener et al).

Composting mortalities in turned piles requires more labor, machinery and management than static pile composting, thus increasing costs. It also provides the potential for release of odors if turned too early in the process. Static pile mortality composting is a more easily managed technique. By properly constructing the compost pile to allow for adequate natural aeration, mortality composting can be completed on intact animals with little or no turning. The process appears to be effective if the animals are enclosed in chunky carbonaceous material such as wood chips.

There is a need to evaluate the effectiveness of static pile composting of mortalities bulked with wood chips. Wood chips are an appropriate and easily available material for use in NYSDOT compost piles.  Temperatures achieved in static pile composting suggest an adequate degree and duration of high temperatures to significantly reduce the survival of many pathogenic organisms, at least in the core of the piles.  Preliminary investigations by CWMI at several piles in NYS indicate that temperatures of 140 degrees F are reached and that temperatures over 130 degrees are sustained for more than 6 weeks. However, temperature and pathogen kill in static compost piles have not been studied to the extent needed to provide confidence.

NYSDOT and local highway department staff who work with carcasses need health and safety information pertaining not only to carcass-borne pathogens, but also on tick-borne diseases such as Lyme disease, Rocky Mountain Spotted Fever, babesiosis and ehrlichisosis.  Preliminary indications based on discussion with Cornell Vet College faculty indicate that ticks on deer have a relatively low infection rate at least for Lyme disease and that handling the carcasses would thus not be a major potential source of exposure.  Ehrlichiosis is known primarily in the southern U.S. but has been reported in NYS and babesiosis is rare and is mainly coastal.  However relevant data need to be gathered and assessed in order to develop appropriate guidance.  Such guidance might address the life cycle, feeding behavior and data regarding infection coupled with advice on practices to minimize the risks of exposure and infection.  This guidance would be relevant to all workers handling carcasses and not just to those engaged in composting.

An extensive study is underway to complete in depth literature searches, seed piles with indicator pathogens and provide more education on the composting process.  Questions such as “What is the thermal stability/sensitivity of the pathogens that might be present in road-killed wildlife in NYS?”, “Are there worker health and safety issues?”, “When is the process finished?” and “Where can we use the finished product?” still need to be addressed.