Zoonotic Diseases - Their Relationship to Rendering

By Gary G. Pearl, DVM, Veterinary Associates P/S


The emergence and re-emergence that zoonotic diseases have presented are constant challenges to most public health professions and associate industries. A zoonotic disease is one that primarily infects animals but can secondarily be transmitted to man. Zoo is used as a prefix in words such as zoonotic or zoology and is derived from the Greek word zoon meaning animal origin. Diseases possessing human health threats have particularly been important to those in medicine and agriculture. However, zoonoses has emerged as an economic, social, public health, and cultural concern for the diseases of all lower animals and the varied ways in which they cause human disease and affect human health.

Though animal agriculture has changed significantly with consolidation and fewer of the population in contact with food producing animals, the exposure to companion animals has greatly expanded. Similarly on a global basis, food animal production has not experienced the U.S. trends to the same proportion. In many countries there is still a significant percent of the population in close day-to-day contact with animals. More than 60 percent of U.S. households have at least one pet, accounting for over 140 million dogs and cats. This companion animal trend is occurring throughout the world, even in developing countries.

All of these factors, coupled with the global movement of people, animals, and animal products, provide great opportunity for the transmission of zoonotic diseases. Thus the subject of zoonoses remains an important issue for all medical professions, and all segments of animal agriculture, companion animals, and the general public. Certainly it is important to the rendering industry for its critical role in controlling zoonotic diseases and its protective benefits to human and animal health.

Rendering is a process in which both physical and chemical transformation occurs. This fact is unique when compared to other disposal options for fallen animals and non-edible tissues. The time-temperature process of rendering is effective in inactivation of microbial organisms under controlled and regulated conditions. The industry has provided an exemplary role for animal agriculture through its programs that control disease caused by bacteria, viral, parasitic, and fungal agents. A historic example is that of anthrax. Anthrax is a zoonotic disease caused by the spore-forming bacteria, Bacillus anthracis. Though it is a disease primarily of herbivores, it is a serious threat to human health.

During the past 100-plus years, rendering has provided the most effective process for inactivation of B. anthracis spores. Currently the isolated cases of anthrax are the result of animal or human contact with contaminated soil resulting from the disposal of an infected animal. Spores from the anthrax organism and other spore forming bacteria can remain in soil for many years. Most recently anthrax has brought attention to its potential as a biological warfare agent.

New infectious diseases are continually emerging. Approximately 886 of the 1,415 known human pathogens, or 61 percent, are of zoonotic origins. Further, over 75 percent of the emerging diseases that affect humans are zoonotic. Currently there are 175 diseases with increasing morbidity of which 132 are zoonotic. There is need for more research directed to the safety and biosecurity for disposing of animals or their tissues. This is especially important when addressing zoonotic diseases or a potential high-risk foreign animal disease.

Research has advanced for both rendering and incineration when compared to other disposal options. The Fats and Proteins Research Foundation has invested, directed, and published research since 1962 addressing the biosecurity properties of rendering. The Animal Protein Producers Industry has served as the biosecurity arm for the rendering industry in providing microbial and chemical residue surveillance and third-party certification programs since 1984. The Animal Co-Products Research and Education Center was established in 2005 at Clemson University with a structure and a defined research agenda for the safe utilization of disposal of inedible animal tissues. These industry investments and efforts are critically important in controlling zoonotic or potential high-risk foreign animal diseases.

The same degree of confidence for biosecurity containment is not present for those practices utilizing non-controlled time/temperature procedures or unsecured disposal sites. Practices such as burial, composting, and landfill applications have not been thoroughly researched for all infectious vectors and potential pathogen re-growth as the physical and biochemical changes in residual compost change over extended periods of time.

Zoonotic diseases are occupational hazards of concern by all personnel associated with all facets of animal exposure. Regardless of the disease, exposure to potentially infectious material that includes feces, blood, body fluids, exudates, and un-intact skin are considered hazardous. Human infection routes include oral, intraocular, intranasal, and breaks in the skin integrity.

There are numerous food animal and companion animal examples with unique environments that bring humans in close contact with a variety of animal species and their tissues or bodily excrements. Veterinary practices, animal production facilities, companion animals, and certainly rendering are all high-exposure opportunities. Human infection can be transmitted from not only those animals that are clinically ill but also apparently healthy animals that are carriers of an infectious agent or in the early stages of a disease. Further, diseased animals shed infectious agents to all of their environmental contact – bedding, cages, feed, water, soil, etc. – making them viable vector material as well.

The elimination of all risks associated with zoonotic pathogens is not possible. However, food animal producing industries as well as pet owners should definitely be aware of the hazards they present. Reasonable guidelines should be adapted for the personnel that work in potential exposure situations. These in part should adhere to the basic principles of infection control that are necessary to prevent spread of occupational zoonotic pathogens by all routes of transmission. It should be recognized that each fallen animal picked up or delivered and each rendering facility in which fallen animals or inedible tissues are delivered for processing could contain zoonotic disease organisms.

Though there are a lot of concerns regarding intentional introductions via bioterrorism, there are certainly proven events that are evident of naturally occurring zoonotic disease transmission. These real possibilities should be pri-marily addressed rather than investing disproportionate resources on biodefense programs that may be brought via our political adversaries.

It is the naturally occurring threats from thousands of tons of non-edible animal tissue and fallen animals that the rendering industry is safely processing.  That function and service are constantly being provided to the benefit of both human and animal health. Catastrophic events and potential large scale epidemics present unique challenges in which the rendering industry can certainly supplement specific emergency management programs for these events. The tenets for such catastrophic events vary but include prevention, mitigation, response plans, and recovery. Mitigation strategies are generally targeted toward defined agricultural practices but should definitely include renderers within all strategies. It’s an industry that has served as a “gatekeeper” against disease from inedible animal waste for over 150 years.

Dr. Pearl is past president of the Fats and Proteins Research Foundation, Inc.


Tech Topics – April 2009 RENDER | back