Pathogens

Avian Influenza 

Avian influenza (Al), or bird flu, is caused by avian influenza viruses that are carried by wild waterfowl and shed in the saliva, nasal excrements and feces. Domestic poultry get the disease when they come in contact with the viruses either directly from waterfowl (drinking from contaminated water, foraging in places where waterfowl have been), or from contact with other infected domestic birds, cages, feed, feces or workers that may be carrying the virus on their clothes or vehicles. It can also be spread easily with wind currents, therefore, the less birds are moved, especially off-site, the better. Static pile composting provides a tool to manage the birds on site, reducing the risk of spreading disease.

NYS law (Ag & Markets Law, Article 5, §73) require that "every person shall immediately report to the commissioner the existence among animals of any infectious or communicable disease coming to his knowledge. Every report shall be in writing and shall include a description of the diseased animal or animals, the location thereof, the name of the disease suspected, and, if known, the name and address of the owner or person in charge of such animal or animals." HPAI (any H5 or H7) is a reportable avian disease at the Federal (Animal and Plant Health Inspection Service), State (NYS Department of Agriculture and Markets and Department of Health) and Local (Cornell University) levels.

Managing potential spread

The first step in any emergency disease planning is to gather information about the disease and its control. Avian influenza (bird flu) is caused by Al viruses that are carried by wild waterfowl and shed in the saliva, nasal excrements and feces. Domestic poultry get the disease when they come in contact with the viruses either directly from waterfowl (drinking from contaminated water, foraging in places where waterfowl have been), or from contact with other infected domestic birds, cages, feed, feces or workers that may be carrying the virus on their clothes or vehicles. Avian Influenza can be classified into two forms based on the severity of illness they cause in birds. Low pathogenic avian influenza (LPAI) may go undetected and causes only mild symptoms such as ruffled feathers and a drop in egg production. It is rarely transmitted to humans and is not life-threatening. Highly pathogenic avian influenza (HPAI) causes serious illness and death in infected birds, often within 48 hours of onset. It is easily spread through a flock by contact among birds and through litter, cages, equipment and air (particularly within poultry houses). It is a serious often deadly disease if contracted by people. It is not known to be transmitted from person-to-person.

Only certain avian influenza viruses are known to cause the highly pathogenic form. Some LPAI viruses, when allowed to circulate in poultry populations, can mutate, usually within a few months, to the highly pathogenic form. The cycle for Al (Figure 1) is transmission of LPAl from wild birds to domestic flocks that can then circulate in the flock and be transported to other flocks. LPAl may undergo mutation into HPAI that can circulate in the flock and be transported to other flocks. Control of LPAI can thus help to prevent creation of HPAI. Once a flock has contracted HPAI, preventing off-site movement of birds, litter and contaminated equipment is important. Composting of dead birds and litter can control the viruses.

Prevention of LPAI is a step in preventing HPAI from occurring and thus preventing outbreaks a pandemic. This is best done through bio-security for poultry flocks: no contact with wild birds or water sources where wild birds congregate, essential personnel only in poultry facilities, clean/disinfect clothing, equipment, tires, etc., and no contact with other poultry or live bird markets. If flocks are infected, and LPAI mutates into HPAI, disposal of dead birds and infected litter becomes an issue. Moving the birds offsite for disposal can easily spread the disease. Heat destroys the virus, but it remains viable at moderate temperatures for long periods, and indefinitely in frozen material. The virus is killed by heat (56°C for 3 hours, 60°C for 30 minutes). Since properly managed composting meets these time/temperature requirements, static pile composting provides a tool to manage infected birds on site and kill the virus, reducing the risk of spreading disease.

Research in many states indicates composting is effective in inactivating the avian influenza virus (AIV). Lu, et al, 2003 showed that mixing AIV with chicken manure that contains microorganisms or their digestive enzymes or by products has the ability to destroy the virus in less than a week at ambient or higher temperatures. Senne, et al, 1994, composted birds in bins that were inoculated with HPAI virus and were unable to isolate any virus from the tissue after 10 or 20 days of composting. Research on other poultry viruses has shown them to be inactivated through composting, not only because of temperature but also due to biological activity in the composting process (Glanville, et al, 2006). Composting has also been shown to be an effective means of disposal for all sizes of birds (Flory, et al, 2007) and thus has prompted the Virginia Department of Environmental Quality to list in-house composting as the preferred method of disposal in response to disposal of entire flocks of poultry after an outbreak of avian influenza. According to the United States Environmental Protection Agency (US EPА), on-site composting has been proven effective in deactivating avian influenza virus. On-site composting limits the risk of groundwater and air pollution contamination, the potential for farm to farm disease transmission, and transportation costs and tipping fees associated with off-site disposal. Also, there is the benefit of producing a usable product.

Reducing Pathogens through Composting

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 organisms 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. There is no evidence to show whether CWD would be killed in the composting process. Compost temperatures are not high enough to inactive prions, but it is possible that microbial and enzymatic activity could (Langeveld, et al; Kirill, et al.).  Whether or not composting inactivates prions, through the process of composting the mortalities would be collected and managed to prevent nuisances such as odor.  The compost would be much more amenable to incineration than the untreated carcasses if incineration were required.  It would also be a more esthetically acceptable material than carcasses.  Guidance materials developed for NYSDOT personnel will address CWD after consultation with the NYS Departments of Health and of Environmental Conservation.

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).

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 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.