(See endnotes 16, 17, 18, 19, 20)

In the last 35 years, there has been a sharp increase in the number of new diseases that have been found globally and have contributed significantly to adult morbidity and mortality. In addition, there has been a sharp increase in the prevalence of infectious diseases that had been thought to be eliminated or reduced to such low levels that they would no longer be a problem for people. Many of these diseases have now re-emerged in forms that are resistant to antibiotics, and therefore even more difficult to cure with existing medications. The community response to the outbreaks have been basically on a case-by-case basis at the local level, which is very inefficient, rather than looking at the long-range problems and instituting preventive and control programs at the global level.

Diseases spread quickly from sparsely inhabited areas of the world to highly concentrated areas of population, by means of infected people, animals, insects, rodents, food, and water, which may be distributed by modern modes of transportation. People are displaced by natural disasters or wars and may spread disease from their area to new places. These evacuees are more susceptible to outbreaks of disease in the typically overcrowded conditions where they seek sustenance and shelter. The constant threat of the use of biological weapons by terrorists adds enormous complications to the control of emerging and re-emerging infectious and zoonotic diseases. The best way to protect a given population is to try to eliminate or control the disease at its source rather than trying to control it once it has moved to other areas of the world.

Globalization has meant that food production, processing, and distribution of meat, poultry, dairy products, fish, shellfish, fruits and vegetables, etc., instead of coming from local areas, which are supervised by health departments, now come from many different nations where the amount of regulatory control and the actual conditions of processing and handling of the food source may be very inadequate. There also may be frequent sources of contamination such as water, sewage, soil, insects, rodents, and pesticides. There may be a lack of proper sanitation measures which are used to control oral fecal route infections on farms and at other agricultural facilities.

Emerging infectious diseases from different parts of the world are being introduced into vulnerable populations elsewhere, where the agents can be spread rapidly from person to person and there is little or no resistance build-up among the people who may become affected. An example of a process of spreading zoonotic diseases to humans is the consumption of bush meat (the flesh of wild animals dead or alive) by natives in primarily tropical areas where there is a shortage of protein. This allows the microorganisms that are usually found in the wild animals to cross the animal- human barrier and bring disease to people. As these individuals move to new areas, they take the disease processes with them and spread them to new vulnerable populations. An example of this would be HIV which probably spread from chimpanzees to people. Other examples of recently recognized emerging diseases include acanthamebiasis, ehrlichiosis, hepatitis C, hepatitis E, Lyme’s disease, and parvovirus B19.

Global warming is another concern for the spread of emerging infections or the re-emergence of infectious diseases. Although yellow fever and malaria have been virtually eliminated from the United States, increasing temperatures are making new areas of the country vulnerable to the growth of the mosquitoes which cause these diseases. In 2007, more than 100 residents of Ravenna, Italy, fell sick with the tropical disease chikungunya fever as the virus which typically was found in tropical regions around the Indian Ocean, had moved to northern areas because of the migration of the tiger mosquito.

The re-emergence of certain infectious diseases throughout the world is probably due to several factors including how humans live and utilize the environment; changes in technology that affect industry and the byproducts of industry; development and overuse of land; international travel and commerce; microbial adaptation and evolution; overuse of antibiotics; and a reduction in the use of public health controls. There has been a re-emergence of drug-resistant tuberculosis after more than 100 years of decline in the incidence of the disease. Staphylococcus aureus which was in decline because of the use of antibiotics has developed a highly resistant vancomycin-resistant strain of the organism. Other examples of re-emerging diseases include: anthrax, botulism, dengue fever, infection with Escherichia coli, hepatitis, shigellosis, etc.

Emerging and re-emerging infectious diseases may be delivered to unprepared areas by the use of biological weapons used by terrorists. Bioterrorism is the deliberate release of viruses and/or bacteria in order to cause sickness or death to people, animals, or plants. A variety of organisms may be utilized. See Chapter 5 on “Environmental Health Emergencies, Disasters, and Terrorism.”

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