10 States Where Rare and Exotic

Diseases Lurk

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Bugging Out

In the mid-1900s, health experts said the U.S. had won the war on infectious diseases, thanks in part to vaccination and stepped-up sanitation.

Don't relax just yet. Climate changes, uneven vaccination, globe-trotting travelers, and other factors have contributed to a resurgence of some types of bacteria, viruses, and disease-carrying insects.

Here are 10 U.S. states that have experienced outbreaks of a rare or exotic disease. Some, like West Nile, are relative newcomers; others, like dengue fever, are old scourges making a comeback.

Arizona

Few states have escaped West Nile, a mosquito-borne virus that has infected more than 30,000 people and killed countless crows and other birds since entering the U.S. in 1999.

But lately Arizona is catching the worst of it. In 2010, it had 107 cases of an especially virulent form of the disease that can cause seizures, nerve damage, and even death.

Although the virus spreads to the brain in less than 1% of cases, people over 50 are at the highest risk. Arizona, a favorite retirement destination, is reminding residents to wear insect repellent and eliminate standing water in a "Fight the Bite" campaign.

California

Every few years, whooping cough (or pertussis) resurfaces in the U.S. In 2010, California reported 9,477 cases of this highly contagious, potentially deadly bacterial infection, the largest outbreak since the 1940s. (Health officials say a falloff in vaccines, including the Tdap booster shot for teens and adults, is to blame.)

As if that weren't enough, California also has a disproportionately high number of cases of typhoid fever, an infection spread through contaminated food and water that causes stomach pain, weakness, and a sky-high fever. In 2009, California accounted for 90 of the 400-odd cases in the U.S.

Colorado

In the early 1990s, an unusual respiratory disease struck dozens of healthy adults in Colorado, New Mexico, Arizona, and Utah, killing half of them. The "Four Corners outbreak" was eventually pinned on hantavirus, which spreads via mouse waste. (Humans can be exposed by drinking from dirty cans or inhaling dust in rodent-infested buildings.)

Although the virus was lurking in the U.S. for decades, unusually heavy rainfall in the 1990s is blamed for driving up rodent, and thus virus, numbers. Since 1993, Colorado has had 75 of the country's 568 cases of hantavirus pulmonary syndrome, a deadly respiratory complication.

Delaware

Although it takes its name from the bucolic Connecticut town where a mysterious outbreak of arthritis-like symptoms was first described in 1975, Lyme disease is now most common in Delaware. The First State reported 111 cases for every 100,000 inhabitants in 2009—a rate 42% higher than in Connecticut.

Clusters of Lyme cases can also be found as far south as Maryland and as far west as Minnesota. The ticks that shuttle the Lyme disease-causing bacteria between deer, mice, and men have a wide foothold—and thanks to warming winters that fuel the tick population, it could be getting wider.