Changes in how humans live and travel have increased the spread of diseases we get from animals, a new series of reports says. The new reports, published in the journal Lancet, focus on zoonotic infections. These are diseases that spread from other animals to humans. Infections in wildlife may be spread to humans by carriers such as mosquitoes and ticks. Sometimes they are spread by direct contact. All of these contacts have increased, the Lancet articles say. Reasons include widespread changes in land use and more world trade and travel. For example, people may be exposed to wildlife for the first time when an area opens up to logging or farming. Some infections that spread to humans from animals, such as HIV, have become pandemics. This means they affect many people across a wide area. Until now, scientists have never predicted that an infection would become a pandemic. But scientists now have tools to make such predictions possible in the future, the Lancet articles say. They say that preventing and controlling infections will require scientists and public health officials to work together. National Science Foundation News wrote about the articles November 30.

By Robert H. Shmerling, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

Have you ever heard of a "zoonosis?" It may be the most important medical condition you've never heard of.

Zoonoses are infections spread between species of animals. Usually, the term is used to describe infections spread from animals to humans. In fact, zoonoses account for about 60% of all human infections.

Examples include:

• Ebola
• Human immunodeficiency virus (HIV)
• Influenza
• Measles
• Severe acute respiratory syndrome (SARS)
• Smallpox
• West Nile virus

The most harmful zoonoses are ones that spread rapidly between humans across a large region. This is called a pandemic. Some pandemics are notorious for how deadly they are and how quickly they spread. Some notable examples include:

• Typhoid fever -- In 430 B.C., this bacterial infection killed one-fourth of the population of Athens.
• Yersinia pestis -- This bacterium causes bubonic plague. The "Plague of Justinian" killed about half of the population of Europe between 550 and 700. The same infection caused the "Black Death." This plague killed 75 million to 100 million people in Asia and Europe in the 14th century.
• Influenza -- In 1918 and 1919, the "Spanish flu" infected up to one-third of all people in the world. It killed up to 100 million people.

More recent pandemics include malaria. This disease accounts for about 650,000 deaths each year. The HIV pandemic has caused about 25 million deaths since the early 1980s.

None of the major pandemics was predicted before it emerged as a serious health threat.

For these reasons and because new infections continue to be discovered, the journal Lancet has a new series of articles about pandemics caused by zoonoses.

Here are some of the highlights:

• There are major gaps in what we know about how zoonotic infections develop and how to prevent their spread. A major challenge is figuring out which organisms are harmless and which ones are destined to cause serious illness.



• Changes in land use and agriculture, as well as more global travel and trade, increase the risk of infections spreading from animals to humans. For example, miners and loggers work now in parts of the world that were not explored in the past. They may come into contact with animals and infectious organisms that were never a problem before.



• Recent advances in technology and statistical methods may soon allow public health officials to predict future zoonotic pandemics. For instance, researchers now can collect and share enormous amounts of data. New techniques allow scientists to look closely at the genetic makeup of an organism. This may help them to identify potential pandemics much earlier than in the past.



• New policies and laws may limit the risk of these infections in the future. For example, permits for land use could take into account the animals in the area and the potential to expose people to new infections.



• Public health measures and major investments in research are needed to predict and react to future pandemics.

What Changes Can I Make Now?

Zoonotic infections represent some of the biggest health threats worldwide. Fortunately, they are also among the most preventable.

Public health measures play a big role in preventing the spread of infections. One of the most important is ensuring clean water supplies. But you also can take steps to reduce the chances that you will become sick from a zoonotic infection. For example:

• Wash your hands. Some of the best preventive measures are also the most simple. Good hand washing can help prevent the spread of many infections.
• Stay away from people who are sick. Limit close contact with someone who has a potentially contagious infection, such as the flu.
• Get vaccinated. Vaccines protect against some of the most common infections.
• Plan ahead. If you are traveling, find out what precautions are recommended to prevent infections. Travel clinics and the U.S. government are good sources of travel information.
• Follow public health advice. When a new or epidemic infection develops, public health officials may recommend precautions. For example, they may suggest avoiding travel to affected areas or wearing a mask.

What Can I Expect Looking to the Future?

These reports about zoonotic infections were published in advance of a conference to be held in Washington, D.C., next month. It is sponsored by the Forum on Microbial Threats, part of the Institute of Medicine. Look for more news from this meeting.

As outlined in this series of articles, the future should bring important progress in our ability to predict and respond to outbreaks of zoonotic infections. I hope this will happen well before the next big pandemic.