Emerging New Zoonotic Diseases

Linda Detweiler, D.V.M. & Consultant

Recent years have seen the emergence of zoonotic diseases that can pass from animals to humans and cause serious health risks, including death. Bovine Spongiform Encephalopathy (BSE), also known as mad cow disease, is a disease of the central nervous system in cattle. It can spread to humans when they consume infectious forms of proteins, known as prions, from spinal cord tissue and other central nervous system tissue from infected animals. The disease has no known cure and destroys the brain in humans who contract it, leading to death. BSE has been more of a problem in the United Kingdom and Europe than it has been in Canada and the U.S., although a cow in the U.S. was found to have BSE.

No known cases of BSE have occurred in the U.S. as a result of consuming livestock products grown in the U.S. Changes have been made to practices in the use of livestock products in feed and the United States Department of Agriculture has in place a testing protocol to identify cattle who may have it. The Center for Disease Control considers the risk of humans contracting it in the U.S. to be low. Food and restaurant companies such as McDonalds recognize the damage that BSE would do to their brands. They have developed supply chain controls aimed at assuring that the disease does not enter the system.

A far more dangerous zoonotic disease, in terms of its threat to humans, is Avian Influenza (AI). The AI virus poses the threat of creating a worldwide flu pandemic on a scale not seen since the Spanish Flu pandemic that swept the world in 1918 and killed an estimated 40 million people. AI exists in humans and in birds. As people infected with the human strain of AI come in contact with birds with the bird strain, there is the danger that the virus will undergo what’s known as a “resortment” and jump to humans in a highly contagious form and then spread from human to human rather than from bird to human.

In countries like Thailand, Vietnam, China and Cambodia, huge numbers of people live in close proximity to chickens, ducks and other birds that have the disease. In 2003, 100 million birds died of AI and some humans contracted it from birds and died as well. At last count 55 cases have occurred in humans from the dangerous H5N1 strain of the virus. In Hong Kong, 18 human cases resulted in 6 deaths. Hong Kong depopulated its entire commercial flock of 100 million birds. At present, there is only one confirmed case of AI spreading from human to human; other suspicious cases are being investigated in Vietnam as being spread from human to human.

The introduction of better biosecurity in developing countries is critical if we are to successfully head off the worldwide spread of AI. In countries such as Vietnam, there is little veterinary infrastructure or funding to pay adequate indemnity payments to families whose birds need to be destroyed. It behooves the developing nations to invest more in this effort than they have to date. At present there is inadequate incentive for poor families in those countries to report sick birds when they occur.

Biographical Sketch

DISCLAIMER
In an effort to provide wide-ranging views and perspectives regarding the practice of and issues surrounding agriculture, the Philadelphia Society for Promoting Agriculture (PSPA) seeks speakers representing a variety of perspectives. The statements and opinions they present are strictly their own and do not necessarily represent the views of PSPA.