Dr. Deborah McMahan has been dealing with West Nile Virus (WNV) for most of the 14 years she's held the position of Allen County health commissioner. Much time, energy and money have been spent by McMahan and the Fort Wayne-Allen County Department of Health on surveillance, mosquito spraying and education of health-care providers and the public about the virus.
Confirmed human cases have decreased in Indiana since Allen County 2002 high of 69 cases and three deaths, with 293 cases and 11 deaths statewide that year. Still, in 2012 two of the 12 Allen County residents confirmed with WNV died. WNV is most commonly carried by the culex mosquito species, a nighttime biter.
But McMahan and health department mosquito collectors could soon be on the hunt for another species, the aedes albopictus, a daytime biter that carries chikungunya (pronounced chick-en-GUN-ya) virus. Though rarely fatal, the virus causes high fever, severe joint pain and sometimes rash, nausea and vomiting.
“We do have aedes albopictus in Indiana in the southern two-thirds of the state,” said Dr. Jennifer Brown, state public health veterinarian with the Indiana State Department of Health. Another mosquito species, aedes aegypti, also carries chikungunya (CHIKV) but the CDC reports that species has not yet been found in Indiana.
Allen County in June had the first human case of CHIKV in the state, but the person was infected when out of the country. Since then, six other Hoosiers have been confirmed by the Centers for Disease Control and Prevention, all infected when outside the U.S., most of them while visiting the Caribbean.
On Tuesday, the CDC confirmed two Floridians were the first confirmed U.S. locally-transmitted CHIKV cases, meaning they had not traveled outside the United States. Florida has had 79 confirmed cases, with 302 U.S. laboratory-confirmed cases overall as of July 22.
Indiana still has additional cases under investigation. Brown said she expects some to be positive.
With WNV, humans get it after a mosquito bites an infected bird or other animal reservoir, then the mosquito bites a person. CHIKV needs no reservoir.
“The levels in the blood are high enough of the virus that the mosquito can deposit the virus in another person,” Brown explained. This is very concerning, particularly if infected people are not going to the doctor and getting their blood tested. “In parts of the world, in localities where chikungunya is endemic, it has an 80 percent attack rate; 80 percent of people exposed are going to get sick.”
McMahan said that's why “it's such a big deal to diagnose people.” Individuals who have the virus need to remain indoors for at least a week after they become sick. “That's when you're the most viremic,” and able to pass on the disease. If the infected person is out and about, the mosquito that bites him or her can infect others.
“The thing to remember is this virus causes true joint pain … high fever and joint pain in multiple joints,” not just tenderness or muscle achiness, Brown said. Such symptoms should compel people to get a blood test right away.
The symptoms, which usually begin three to seven days after the person is bitten, also explain the history behind the name, which Brown said comes from a word in an African language meaning “that which bends,” describing the contortions it can cause the body.
“There's not much in the way of treatment except supportive care,” said McMahan, an internal medicine specialist. While most people will see symptoms subside and disappear within one to three weeks, some people can have debilitating joint pain that lasts for months, even years. At greatest risk for severe disease are newborns and older adults.
Currently, Indiana mosquito surveillance involves testing for WNV, St. Louis encephalitis and Eastern equine encephalitis but not for CHIKV. But Brown said, “If we were to start seeing evidence here of local transmission, we might change that position.”
CHIKV has also not been a mandatory reportable disease for U.S. states and territories, but Brown says the Council of State and Territorial Epidemiologists recently voted to add it to the list. In Indiana, though state code calls for reporting of all arbor-borne viruses, CHIKV is not specifically named but will also be added soon to the list.
Meanwhile, Indiana is keeping close tabs on surveillance in other states, particularly Florida.
“If we watch Florida and we don't get ongoing transmission, we will all feel much better,” Brown said. “Chikungunya is of public health significance, but we just don't know if it's going to be a problem or not. It's too early.”