February 15, 2012

 

 Wildlife, trade, susceptibility amplify food risks

Food-borne illness risks cross borders, production types

 

 
fauna and flora
Photo of poultry at Chinese market (third from left) courtesy of EcoHealth Alliance

Dr. Lonnie J. King sees a "perfect microbial storm" in the increasingly global interactions of people, animals, and environments.

Speaking late last year at a meeting convened by the Institute of Medicine's Forum on Microbial Threats, Dr. King, dean of The Ohio State University College of Veterinary Medicine, said adaptation among pathogens, increased human susceptibility to disease, changing environments, intensification of the human-animal interface, human and animal movement across international borders, and antimicrobial resistance have increased the risk of food-borne diseases.

Foods ranging from peanut butter to melons have been connected with recent outbreaks in the United States, Dr. King said. Severe acute respiratory syndrome, which originated in bats in Southeast Asia and spread through civet cats, infected people through food obtained at markets containing live and slaughtered animals. Nipah virus transferred from bats to pigs in Malaysia and then to people, and infection with the virus was recently connected with consumption of raw date palm sap.

David W.K. Acheson, MD, managing director of food and import safety for the consulting organization Leavitt Partners, also spoke at the meeting. He said that although the frequency of food recalls in the U.S. is increasing, the prevalence of illnesses connected with most of the food-borne pathogens tracked by public health agencies is decreasing, indicating that the nation's food safety system is working. Improved abilities to detect pathogens and the sources of contaminated foods, along with increased consumer awareness, have helped reduce harm.

Drs. King and Acheson were among about 20 presenters at the Dec. 13-14 meeting the IOM hosted in Washington, D.C., on the topic of one-health approaches for improving food safety.

Dr. King noted that the Centers for Disease Control and Prevention estimates about 48 million food-borne illnesses occur in the U.S. annually, and a similar rate worldwide would affect more than 1 billion people yearly.

"I have no idea how many global cases there are of food-borne illnesses, but there may be more than we think," Dr. King said. He attributed the information gap to poor diagnostics and poor methods of finding and reporting illnesses, and said innovations, new techniques, and a one-health strategy will be critical for improvement.  

Finding potential outbreaks

Peter Daszak, PhD, president of the EcoHealth Alliance, said slowly evolving retroviruses have infected people in Africa through meat from wild primates. Although the viruses found in one study were latent in humans, it is possible one could trigger a pandemic and become the next HIV. 
 

"As we look to the developing world and we try to help people change behavior from hunting endangered species, what do we do?" Dr. Daszak asked.

Wildlife trade is booming in Chinese markets where SARS first emerged, he said, showing a photo of two men butchering a cat on a tile floor near chicken remains. Unhygienic facilities mix animal species near dense human populations, creating "perfect conditions for a new pathogen to emerge," he said.

Dr. William B. Karesh, executive vice president of health and policy at the EcoHealth Alliance, said conversion of wilderness for human uses such as crops, pasture, and logging camps is the biggest driver of wildlife-source zoonotic diseases. Food industry changes are the second most important.

EcoHealth Alliance is working with the CDC and U.S. Fish and Wildlife Service to test for pathogens in illegally imported wild animals and wildlife products found in packages at U.S. ports of entry. It is also working with the U.S. Agency for International Development in emerging disease hot spots as well as cataloging potentially zoonotic viruses present in rainforest primates, rodents, and bats, according to Drs. Daszak and Karesh.

Nathan Wolfe, DSc, an epidemiologist and CEO of the Global Viral Forecasting Initiative, said unprecedented global connections among world populations have led to the spread of microorganisms, from the SARS virus to fungi carried on feet. His organization is monitoring risks to those occupationally exposed to wild and domestic animals in Southeast Asia and Central Africa, where people are voluntarily collecting blood samples from butchered animals.

By finding disease emergence patterns, health authorities could detect early movements of microorganisms from animals to humans, he said. 

Interaction increasing risks

Dr. Will Hueston, executive director of the Global Initiative for Food Systems Leadership and a professor at the University of Minnesota, said feeding the world involves interdependent systems that change daily as a result of a variety of factors including consumption preferences, politics, exchange rates, and resource availability. U.S. residents seem to be increasingly selective, for example, about which parts of animals they will eat, preferring chicken breast meat and exporting dark meat and chicken feet while importing shrimp from more than 50 countries. He added that a chicken Kiev product can contain ingredients from more than 10 countries.
 

An exponential rise in global food system connections and pushes for efficiency and affordability have increased the food trade system's vulnerability to collapse, Dr. Hueston said. The concentration of ingredient production in one region or country and just-in-time supply chains are among such efficiency measures, he said.

Cultural clashes also can emerge from varied perceptions of risk, particularly when an exporting country's citizens cook a product and the importing country's citizens eat the food raw, Dr. Hueston said.

Dr. Hueston thinks food producers and processors can improve safety if they are given incentives and flexible regulations and if the public and regulators don't seek someone to blame after illnesses. He noted that risk cannot be eliminated.

Dr. King indicated that developed and developing nations alike have growing populations at increased risk of illness. As the U.S. population ages, a growing portion of that population could be immunocompromised, he said. About 90 percent of the world's growth is occurring in developing countries, and the world population living in slums is expected to double in the next 25 years. These areas are likely to be the next areas of emerging disease, he said.

Human and wildlife displacement and moving populations may introduce new diseases, and much of the food bought worldwide has some global component, he said.

"I think there's a real concern about the vulnerability of these remarkable food systems to unintentional, natural, or even intentional introduction of pathogens and contaminants," Dr. King said. "It's just too easy to do." 

Understanding pathogen behavior

Better understanding the rules governing food-borne pathogen transmission can help predict those pathogens' behavior and anticipate disease outbreaks, Dr. Daszak said. Whether a person is eating spinach produced in the U.S. or meat from wild primates, each activity has pathogen risks that need to be predicted and minimized, he said.

 

Ecologists have examined complex wildlife systems and developed computer simulations of population changes connected with climate change and deforestation. Such science can be adapted to disease systems, Dr. Daszak said.

Dr. Karesh said countries without developed diagnostic capabilities may benefit more immediately from increased disease prevention methods. Educating hunters and bush meat handlers about the risks from contaminated animals and the need to wash their hands, for example, has likely helped people in the Republic of Congo avoid contracting any known infections with Ebola since 2005.

Dr. Karesh noted that deaths of bats from white-nose syndrome in North America have let larger populations of agricultural pests survive, and declines in U.S. bat populations could cause losses estimated at billions of dollars. He said the issue presents a convincing argument for collaboration among health professions.

The 2006 U.S. outbreak involving Escherichia coli O157:H7 in spinach also demonstrates the value of considering animal-related and environmental effects on human disease, Dr. King said. The outbreak, which caused about 200 illnesses and three deaths, is believed to have connections with wild pigs, surface water, soil on the spinach farm, and nearby cattle. Surveillance of food-borne pathogens cannot be limited to monitoring of human health, he said.

Surveillance has to produce data as part of the food system and part of an integrated, holistic strategy, Dr. King said.

"That data needs to be shared as we move from being reactive and disease-focused to being proactive, preventive, and anticipatory," he said.

Preventive measures in U.S. slaughterhouses, fields

Robert V. Tauxe, MD, deputy director of the CDC Division of Foodborne, Waterborne and Environmental Diseases, expects most future food safety improvements in the U.S. will occur prior to slaughter or harvest. For example, E coli's impact on humans could be reduced by treating cattle with vaccines, probiotics, bacteriophages, or feed additives, he said.

Michael R. Taylor, deputy commissioner for foods for the Food and Drug Administration, noted that rules passed in 2009 to reduce the burden of Salmonella enteritidis connected with eggs included provisions for wildlife and pest control. The FDA announced in July 2009 the regulations were expected to prevent 79,000 illnesses and 30 deaths yearly.

Dr. Tauxe noted that Salmonella organisms have been found to cluster near stoma on fresh lettuce, and secretions from E coli O157:H7 have been shown to hold open stoma that usually close in response to bacterial flagellae. People or animals that eat the plant can become colonized.

Taylor said his agency is developing produce production standards and scrutinizing drug use in Chinese aquaculture in response to the Food Safety Modernization Act, which was signed into law in January 2011. The agency is considering standards for water contamination and animal intrusion as well as regulations on application of livestock manure on crops to ensure pathogens die before harvest.

Taylor also noted that rules for pet food production can prevent animal deaths from contaminants such as melamine and owner infection with salmonellae. Good livestock health is also needed to provide healthy food.

"The one-health perspective is just essential to preventing food-borne illness," he said.