It will take several years before the CDC knows whether cases of babesiosis are increasing. "We don't know the trend," she added.
The more well-known West Nile virus is an arbovirus, which are viruses carried by mosquitoes and ticks. Of nearly 900 cases of arboviral disease cases reported to the CDC in 2011, more than 700 were West Nile virus.
"West Nile continues to be the leading cause of arboviral disease in the United States, however, other [arboviruses] do continue to cause sporadic outbreaks," said CDC's Dr. Stephanie Yendell. "We see West Nile throughout the United States."
Another such disease, called La Crosse virus, was the most common cause of arboviral disease in children, according to the CDC.
Reported cases are, however, just the tip of the iceberg, experts say. Because many people contract these arboviruses but have no symptoms or only mild symptoms, most cases are never reported, Yendell noted.
"We estimate there could have been as many as 13,000 to 34,000 cases of West Nile," she said. This estimate is pretty constant from 2008 to 2010.
"There are a number of people who never show symptoms and for many who do get sick, many will have mild symptoms like fever, rash and body ache. Fewer of these cases get reported," Yendell said.
Severe symptoms can include high fever, neck stiffness and even coma. "The mortality rate is about 6 percent for West Nile," she said.
Most cases occur in the late spring, summer and early fall, when ticks and mosquitoes are active, she added.
Because there is no treatment for these viruses, the key is prevention. These measures include repellents, protective clothing, repairing or installing screens, eliminating tall grass and standing water near homes, and community insect-contr
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