Emerging Viral Diseases

Emerging diseases are illnesses caused by new or reappearing infectious agents that typically exist in animal populations—often in isolated habitats—and can infect humans who interact with these animals. For example, some animals living in tropical forests of central Africa most likely harbor Ebola virus. Researchers think that as people clear these forests for agriculture or housing, the people become exposed to infected animals. The Ebola virus is one of many viruses known to cause hemorrhagic fever, an often fatal syndrome characterized by fever, vomiting, internal bleeding, and circulatory system collapse. Hantavirus, which is harbored by deer mice and other rodents, caused a fatal outbreak of pneumonia in the southwestern United States in 1993. The SARS virus may have transferred to humans from civet cats.

Both wild and domestic animals can harbor viruses that can be transmitted to people. Close interaction of animals with humans, as shown in Figure 24-8, can lead to the transfer of many diseases. Such diseases are of great concern to public health agencies worldwide. Vaccines are expensive to develop and often difficult to distribute, especially in underdeveloped countries. The cost of public health education to help people understand how they can prevent outbreaks of disease is also high. In addition, laws banning the sale of certain animals as pets or for food can be difficult to enforce.

figure 24-8

Avian, or bird, flu is an emerging viral disease. The close interaction of people and poultry on farms and in markets, such as this one in Hong Kong, contributes to the transfer of viruses from birds to humans.

figure 24-8

Avian, or bird, flu is an emerging viral disease. The close interaction of people and poultry on farms and in markets, such as this one in Hong Kong, contributes to the transfer of viruses from birds to humans.

figure 24-9

The smallpox virus causes painful lesions that cover the face, shoulders, and chest and, in late stages, the arms and legs. These lesions can leave disfiguring scars, can cause blindness, and may result in death due to hemorrhaging.

figure 24-9

The smallpox virus causes painful lesions that cover the face, shoulders, and chest and, in late stages, the arms and legs. These lesions can leave disfiguring scars, can cause blindness, and may result in death due to hemorrhaging.

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