A county in the western part of Indiana is the site of the nation's largest current chickenpox outbreak, according to news reports.

Vigo County has seen 84 cases of the varicella-zoster virus -- marked by itchy blisters on the body, fever, stomach ache and headache -- since September, the Terra Haute Tribune-Star reported.

"Vigo County usually has less than 10 cases a year; however, since the end of September, Vigo County has reported 84 cases which would meet the definition of an unusual occurrence of disease," Dr. Joan Duwve, M.D., of the Indiana State Department of Health, told the Tribune-Star. "Prompt identification, investigation and control of chickenpox outbreaks are important. Even mild cases can be contagious."

Chickenpox is usually not dangerous for people who contract it. However, adults and older children who get chickenpox may have more serious complications as a result than younger children, according to the A.D.A.M. Medical Encyclopedia. People who are immunocompromised may also experience more severe symptoms.

Duwve also told the Star-Tribune that the chickenpox outbreak started with a child who was unvaccinated, but that even children who receive chickenpox vaccinations might be at risk since the vaccination only works 90 percent of the time. It can also occur in a less-severe form in children who have been properly vaccinated, Duwve noted.

The virus is extremely contagious -- it can be spread just by being around an infected person who coughs or sneezes, or by coming in contact with fluid from a chickenpox blister, the A.D.A.M. Medical Encyclopedia reported. The actual blisters usually don't develop until about 10 to 21 days after the first contact is made with someone with chickenpox.

Chickenpox is most common in the late winter and early spring months, according to the New York State Department of Health.

The Centers for Disease Control and Prevention notes that chickenpox vaccinations should be offered as an outbreak prevention and control measure the moment the first case is identified.

The CDC recommends that toddlers between ages 12 and 15 months should get the first dose of the chickenpox vaccine, followed by a second dose when the child is between age four and six. Older people who had never received a chickenpox vaccine before and may be at risk for catching it (if they work with children, etc.) should get two doses of the vaccine. For more information on the chickenpox vaccine, click here.