It's been 14 years since West Nile Virus disease arrived in the United States. A new study says the disease has cost about 780-million dollars in health care costs and lost productivity.
Before 1999, West Nile Virus had not been detected outside the Eastern Hemisphere. That changed following reports in the U.S. of serious infections and deaths.
Dr. Erin Staples is a medical epidemiologist at the Centers for Disease Control and Prevention - and the lead author of the study, which appears in the American Journal of Tropical Medicine and Hygiene. She said the virus is carried by infected mosquitoes.
"Once people get bitten and infected by the virus a fair proportion will actually not develop any symptoms. But a proportion will go on to develop either a febrile illness with muscle aches and feeling generally unwell. And in a small proportion of people that get infected - they'll go on to develop kind of a more severe presentation or clinical manifestations, which include what we call neuro-invasive disease. That means infections of the nervous system," she said.
These include encephalitis, meningitis and acute flaccid paralysis, where part or all of the body is paralyzed.
She said, "Anybody can be infected by West Nile Virus - anybody that's going outdoors - potentially getting exposed to mosquitoes - can get infected. But we tend to see kind of the more severe manifestation in people that are older than the age of 50. Otherwise, we've seen that some people with underlying medical conditions also might be at more risk for being hospitalized if they do get West Nile Virus infection and disease - as well as they're more likely to potentially die due to the infection."
From its arrival through 2012, there have been more than 37,000 cases of West Nile Virus in the United States.
"Following its introduction into the United States in 1999, it started in the Northeast and then spread across the country. So by 2003 we had seen West Nile Virus disease occur from coast to coast. And then since that time, we are considering it - what we call - an endemic disease, meaning that it will continue to occur," said Staples.
Of the more than 37,000 cases, over 1,500 patients died. About 16,000 patients had neurologic disease and over 18,000 required hospitalization.
"However," Staples said, "we do expect that that is an underestimate of the number of people infected, as well as the number of people that might have gotten sick. And some of that is due to the fact that not everybody that gets sick will actually choose to go to the doctor and be seen for their symptoms, particularly, maybe the less severe manifestations or the fever with muscle aches."
There is a test for West Nile virus, usually using a blood sample or cerebral spinal fluid or the fluid around the brain. This may be done when patients show symptoms of neurological problems.
Dr. Staples said that besides the health concerns, it's also important to know the effects of the nearly $780-million cost of the disease.
"The reason we really wanted to do that is to allow different organizations - whether it be policymakers, public health or researchers in both academia and industry - to better assess and understand the impact West Nile Virus is having on them. Not only from the morbidity, the number of cases and the mortality, but also from the economic perspective."
Little is known about the long-term effects of West Nile Virus disease. There are no medications to treat it and no vaccines to prevent it. Medical care can be expensive -- tens of thousands of dollars, for example, for those who suffer from partial or whole body paralysis. The study said patients who were hospitalized "were absent from work or school for a median 42 days."
The CDC epidemiologist said, "National surveillance efforts are critical in determining where and when outbreaks of mosquito or tick-borne diseases occur."
That allows health officials to react quickly and empty standing water areas where mosquitoes might breed or begin community insecticide spraying. Using insect repellent can also help.
The World Health Organization says the disease was first discovered in 1937 in the West Nile District of Uganda.