Tuesday, August 4, 2009

Meat Based Diseases: The Rise of Zoonosis

Suman Sahai

Whether swine flu originated on a pig farm in Mexico or in Asia, as is being suggested now, the fact remains that a disease that can infect both pigs and humans is circling the globe; whether it will assume epidemic proportions or not, remains to be seen. Diseases like SARS, avian flu, the ebola virus, and mad cow disease have shown us that evolutionary barriers between human and animal diseases are breaking down regularly and increasingly. Humans have become more vulnerable to cross-species illnesses today than ever before because in our globalised world, a pathogen is only a plane ride away.

International trade and the global transport of animals and animal products for food, creates easy channels for disease transfer between animals and humans. In addition, the transport of hundreds of species of wildlife, often as clandestine food, enables the transfer of the harmful bacteria, viruses, and fungi which infect both people and animals in far away places. The rapid transportation of both animal products and people has ensured that disease causing agents from infected meat do not remain confined to where they originated, but very quickly reach far away continents. Today, of the roughly 1400 documented infectious diseases, more than half are capable of infecting both animals and humans. Most of these diseases such as anthrax, bubonic plague, Lyme disease, and monkey pox are "zoonotic," that is, they originated in animals but have acquired the ability to infect people. Others, like tuberculosis, and measles are "anthropozoonotic," meaning they are typically found in humans but can infect animals as well.

Countries with Highest Incidence of Swine Flu


Swine Flu Incidence










































United Kingdom



United States of America









Source: World Health Organisation

Consuming different types of meat, some quite unconventional, has often been the cause of diseases spreading from animals to humans. Scientists now believe HIV/AIDS arose in Africa when humans ate the meat of primates that were infected with Simian Immunodeficiency Viruses. The Ebola virus has a similar history of spreading via infected bush meat. The disease first came to light in 1976, when it appeared around the Ebola River in Africa. Along with humans, the virus infects primates like gorillas, chimpanzees, and monkeys, causing severe internal and external haemorrhaging and

leading to death in up to 90 percent of its human victims. When African hunters discovered a sick or dead animal in the forest, they brought it home to feed their families or sell on the market. The Ebola virus infected all the people who handled the meat, and a chain of infections was the result. Each of the human outbreaks in central Africa during the late 1990s and after was traced to humans handling infected great apes for bush meat.

SARS (Sever Acute Respiratory Syndrome) also arose from contact with wild animals being used for food. The illness first appeared in late 2002 in China's Guangdong Province.

Human monkey pox is a rare viral zoonosis endemic to central and western Africa that has recently emerged in the USA. Patients, many of whom had been in close contact

with pet prairie dogs, started coming down with skin ulcers and fevers. It emerged that a prairie-dog dealer in Wisconsin had allowed his animals to mix with rodents imported from Ghana that were, as it turned out, carrying the monkey pox virus. An animal distributor had then sold the infected prairie dogs to pet stores in Milwaukee and Wisconsin. Within about a month, 71 human cases of monkey pox in six Midwestern states had been reported.

The SARS causing virus was traced to a small mammal called the palm civet, which is farmed in the Guangdong region and sold for human consumption. Later the virus was also found in raccoons, ferrets, and badgers being sold in Guangdong's wildlife markets.

Tens of millions of wild mammals, birds, and reptiles are traded globally every year. The number of these animals that end up as food is staggering. Experts estimate that in central Africa alone consumers eat 579 million individual wild animals a year, for a total of more than a billion kilograms of meat. People in the Amazon basin are thought to consume between 67 and 164 million kilograms of wild animal meat a year, accounting for between 6.4 million and 15.8 million individual mammals alone.

Infectious agents are also being transferred from domestic to wild animals. Tuberculosis originating from domestic cattle has now infected herds of wild bison in Canada, deer in the US, and cape buffalo and lions in South Africa. In 1999, rinderpest, a disease that came to Africa with domestic cattle imported from India, killed more wild buffalo in Kenya than had been slain by poachers in twenty years.

Is it safe to eat pork and other foods derived from pigs? You cannot get influenza by eating properly handled and cooked pork or other foods derived from pigs like bacon and sausages. However, good food hygiene helps to prevent a wide range of infections, so it is important that all food is always prepared hygienically.

• Never eat raw or poorly cooked meat.

• Keep raw meat away from cooked and ready-to-eat foods.

• Use a separate chopping board and knife to prepare raw meat.

• Wash your hands immediately after handling raw meat.

• Wash and clean surfaces and utensils thoroughly after contact with raw meat.

In addition to the more unusual bush meat in Africa and exotic wild meats in China, the growing, near insatiable demand for ‘conventional’ meat , has promoted the intensive rearing , or ‘factory farming’ of livestock and poultry in, conditions which are ideal for diseases jumping from animals to humans. The international demand for meat and poultry has given rise to an ultra intensive industry in the west, with swine, poultry, and cattle farmers now packing huge numbers of animals into limited spaces. This necessitates extensive use of antibiotics to control the spread of infections in animals confined in small cages leading to rising numbers of antibiotic resistant bacteria. When antibiotics are washed out from factory farms, they escape into water supplies and give rise to even more resistant pathogenic populations. So factory farms not only raise animals like pigs and chicken, they also raise drug resistant bacteria which are becoming a big problem in fighting infectious diseases.

The key issues of over population, population density and over consumption have created a situation in which animal-human diseases are becoming more and more prevalent. This is unfortunately accompanied by a weakening of our ability to fight these diseases because disease fighting antibiotics are becoming ineffective in the face of antibiotic resistant bacteria.

We are witnessing a sharp rise in the incidence of zoonotic diseases but we are yet to put in place an effective system to predict and control the spread of such diseases. A small start has been made by the Rockefeller Foundation which has made a grant of US $100,000 to the American Veterinary Medical Association (AVMA). This money is to help establish a National One Health Commission and a global One Health Initiative to fight zoonotic diseases like avian influenza and West Nile virus through the collaborative efforts of work being done locally, nationally, and globally. Such an initiative however will require much greater financial support if it is to make any dent in the understanding and controlling of zoonotic diseases.

Early warning system for emerging human diseases: The Canary Database. The Yale School of Medicine has launched a database containing scientific evidence about how animal disease events can be an early warning system for emerging human diseases. The

database known as the Canary Database draws its name from the practice of miners who carried canaries into coal mines as an early warning signal for carbon monoxide and other poisonous gases. The birds being more sensitive would sicken before the miners, who would then have a chance to escape or put on protective respirators.

It is known that animals succumb to environmental hazards before humans show any signs of illness. The Canary Database is a web-based collection of animal sentinel studies that have been organized in terms of their relevance to human health. The database has compiled studies on the use of animal sentinel data in human health decisionmaking

and is applying this to the interface of animal and human health. Animal health experts provide the background information on potential disease transmission between humans and wildlife for emerging diseases such as monkey pox, SARS, Avian influenza, and West Nile Virus. The information in the database should help to join the dots from incidents across the world and make predictions of looming zoonotic diseases as early as possible.