Infectious Diseases Rejoice in Early Spring

April 6th, 2012

By Patrick Rose and Christina Brown

This year, the National Cherry Blossom Festival in Washington, D.C. celebrates 100 years since Japan gave the U.S. the trees as a gift. But the gift many people in the Washington area are celebrating is the early spring the east coast has experienced, which has led to the buds blooming early. According to the National Park Service, this year’s bloom is tied for the third earliest on record. 2011 was tied with 2005 as being the warmest year on record since documentation began in 1880. This warmer-than-average winter and March “heat wave” should grab your attention because there is more to worry about than just an earlier allergy season. Warmer weather also has serious implications for the spread of infectious diseases.

A common species of mosquito, the Anopheles, is a primary host of a variety of infectious diseases, including the West Nile virus and malaria. Not only does warmer weather allow the Anopheles to expand its habitat into the Northern Hemisphere, the mosquitoes will begin to hatch sooner than normal, which allows for a longer reproduction period. Warm temperatures also mean the mosquitoes live longer, which increases their biting activity. The result is an increase in the likelihood pathogen transmission. West Nile virus’ common occurrence in the U.S. can be correlated back to this very specific reason.

Temperature plays a similar role in the spread of dengue fever, which has been plaguing Florida recently. While dengue fever is most commonly associated with fever, headache, or muscle pains, it can also cause hemorrhagic shock and death. There are already roughly 50 million cases of dengue infection worldwide each year. Altered transmission dynamics (i.e., changes in weather patterns, longer breeding periods, and increased exposure rates for humans) can have substantial effects on both the virus and its mosquito host, as it is able to invade new areas in the U.S. Warmer weather also enables the invasion of other infectious diseases usually found in warmer climates. Cryptococcus gattii—a rare and dangerous fungus most commonly found in climates like Africa, Australia, and extreme Southern California—has been spreading throughout the U.S. Pacific Northwest for the past decade. The warmer, milder winters, allow the fungus to survive in an atypical environment. Cryptococcus gattii infects healthy individuals as well as those that are immune-compromised. Infections can result in meningitis or pneumonia, and lead to serious complications, especially in immune-compromised individuals.

These examples highlight how warmer weather impacts the spread of infectious diseases. In recent years, interest in this relationship has grown as our weather patterns have begun to shift. Infectious diseases once characterized as tropical occurrences are increasingly becoming a concern in parts of the world not normally affected by these diseases. Both international and national public health agencies are realizing the increased burden of this phenomenon on our general well being. One of the pressing questions becomes, how do we protect ourselves from the threat of emerging infectious diseases?

The answer has to include implementing and maintaining early warning systems that allow us to recognize outbreaks of emerging infectious disease. Early detection should include rigorous systems that monitor mosquito populations, for example, which have a tendency to host and transmit many different infectious diseases. Effective early warning systems should also include better reporting mechanisms for health care workers who identify unusual symptoms or clusters of occurrences. Finally, we need to reinforce continued support for drug and vaccine development. Knowing that warmer weather can increase disease transmission these steps will allow us to improve our ability to respond with appropriate public health and clinical services, and recognize any response limitations. Collaborations between epidemiologists, disease ecologists, climatologists, and policy experts could provide the necessary knowledge and skills to protect populations from the spread of these deadly diseases.

Patrick Rose, PhD is a CHHS policy analyst.

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