Zoonotic Diseases

A reported 75 percent of recently emerging infectious diseases are of animal origin, and approximately 60 percent of all human pathogens are zoonotic. Zoonotic diseases (zoonoses) are defined as illnesses commonly found in animals that can be transmitted to humans, and can be caused by bacteria, parasites, fungi, and viruses. To date over 200 zoonotic diseases have been identified, and though seen worldwide, zoonotic diseases are especially prevalent in areas of the developing world where humans and livestock live in close proximity. By gaining an understanding of these illnesses and tracking their spread, it may be possible to limit new infections and prevent potential epidemic outbreaks.

Outbreaks of zoonoses including influenza, ebola, tuberculosis, and severe acute respiratory syndrome (SARS) have been seen worldwide in recent years. In many developing countries, zoonoses are among the diseases that contribute significantly to an already overly burdened public health system. Approximately 700 million people in developing nations keep livestock, frequently living nearby the animals, putting them at an increased risk of contracting a zoonotic disease. Brucellosis (one of the world’s most widespread zoonoses), Q Fever, and Bovine spongiform encephalopthy (BSE or “mad cow disease”) are among the zoonoses commonly encountered in regions where large numbers of farm animals are kept.

The transmission of pathogens between the environment, wildlife, livestock, and humans is a major health concern that affects humans and domestic animals, as well as impacting the sustainability of agriculture and the conservation of wildlife. According to Dr. Martyn Jeggo, director of CSIRO’s Australian Animal Health Laboratory, the recent emergence of diseases in humans which originated animals has “heightened public awareness of the multidimensional linkages between wild animals, livestock production, the environment and global public health.” In addition to those transmitted by farm animals, recent studies suggest that at least 100 of the known zoonotic diseases are derived from domestic pets. According to Dr. Peter Rabinowitz of the Yale School of Medicine, rates may be higher than studies indicate as several million infections passed between pets and people go unreported each year in the United States. Common infections transmitted to humans after sleeping with their cat or dog, or being licked by the animal include hookworm, ringworm, roundworm, cat scratch disease, and drug-resistant staph infections.

According to experts, the key to slowing the spread of zoonotic diseases and reducing the likelihood of epidemic events is careful monitoring. Through programs like the recently launched PREDICT, a project of USAID’s Emerging Pandemic Threats Program, it may be possible to develop a global early warning system through which emerging zoonotic diseases can be detected and reduced.


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