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Infectious Diseases in the 21st Century

Infectious diseases have always caused illness and death, but in the last decade, the Institute of Medicine (IOM) has noticed a disturbing trend: The number of new infectious agents has been on the rise. These include the West Nile virus, monkey pox, and hantavirus.

In addition, diseases once thought to be nearly wiped out, such as measles, mumps, pertussis and malaria, have reappeared. The spread of sexually transmitted diseases and tuberculosis, once slowed, now appears to be accelerating again.

According to the IOM, there are several reasons for this trend, but the prime reason is a change in our way of life. Here are ways that the world in the 21st century has changed, making it easier for humans and microbes to meet:

  • Microbes by nature adapt to their environment and rapidly evolve. This makes it more difficult to create vaccines and can lead microbes to develop resistance to treatments. Careless use of antibiotics, a widespread problem in the United States, also allows microbes to develop resistance.

  • People become more susceptible to infection when their body's defense mechanisms are weakened. This can be caused by genetically inherited traits, other diseases, and malnutrition.

  • Climate and weather affect the spread of diseases. Heavy rains and consistently warmer than normal temperatures, for instance, can increase the number of mosquitoes that spread disease. Flooding can lead to the spread of water-borne diseases. Climate and weather also affect people's exposure to disease. Drought, for example, causes people to congregate in larger groups, making it easier to spread disease.

  • Economic development and changes in land use can have intentional or unintentional effects on the environment. Clearing forests, for example, can make it easier for people and rodents to come in contact with each other; this can spread disease.

  • Population growth increases the spread of infectious disease as people come in closer contact with one another.

  • Behaviors such as illegal drug use, tattooing, and body piercing increase the possible exposure to diseases.

  • Growth of medical technology, such as blood transfusions and organ transplants, has created new paths for the spread of infections. The agricultural industry's practice of giving antibiotics to animals raised for food has led to increased antibiotic resistance.

  • International travel and commerce has meant that people—as well as animals, foods and other goods—can travel quickly and nearly limitlessly to all parts of the world. This widespread travel also makes it easier for diseases and the agents that cause them to spread.

  • A breakdown of public health systems and services, such as the lack of clean water or sanitation, contributes to the spread of infectious diseases. Other weaknesses in public health that affect the spread of disease include inadequate vaccine supplies, low immunization rates, and a lack knowledge of how diseases spread or what measures control them.

  • Poverty and social inequality are closely related to death from diseases. Economic trends affect not only the people at risk for disease, but also the structure and availability of health care necessary to reduce risks.

  • War and natural disasters cause malnutrition from famine, which leads to the spread of infectious diseases. Any natural or human-made disaster that causes destruction or disruption of systems delivering public health and disease treatment allows diseases to spread.

  • Lack of political will or awareness among world leaders that we all share the same global microbial risks can lead to the spread of disease. It is not only the governments in the regions where diseases are most common that must commit themselves, but all leaders must become involved.

  • Deliberate biological attacks are a new threat in the world today. Such attacks can cause many deaths and widespread disruption. Public health systems and health care providers must be prepared to address them.

Some of the newer emerging infectious agents and disease cited by IOM are: Ebola and Marburg viruses, which cause hemorrhagic fevers; human monkey pox; West Nile virus; avian influenza (bird flu); severe acute respiratory syndrome (SARS); bovine spongiform encephalopathy ("mad cow disease"); and Semliki Forest virus. The warming of the world's climate means that diseases such as malaria that have not been common in the United States will become more frequent. The first US case of dengue hemorrhagic fever occurred in 2005 in Texas; all previous cases were in people who caught the disease in other countries.

The solution to the accidental and intentional spread of infectious agents will require global cooperation, adequate funding for public health, rapid communication of knowledge and information on diseases, and social and political commitments, the IOM says.