First Human Case of WNV In Massachusetts

The Massachusetts Department of Public Health (DPH) announced Monday that the first human case this year of West Nile Virus (WNV) was found in the state. The Plymouth County resident is in his 70s and remains hospitalized, but is recovering. He was diagnosed in late-August. WNV virus can be passed to humans through mosquito bites, and can cause fever, and in severe cases, meningitis or encephalitis.

The DPH is conducting an epidemiological investigation to pinpoint the location where the exposure occurred. “We’re still in our peak season for possible human infection with West Nile virus,” said DPH State Public Health Veterinarian Dr. Catherine Brown in a statement. “Residents need to continue to take steps to protect themselves against mosquito bites: use insect repellant, cover up, and avoid outdoor activities at dusk and after nightfall when mosquitoes are at their most active.”

According to a statement by the DPH:

In 2012, thirty-three cases of WNV were detected in Massachusetts residents. While WNV can infect people of all ages, people over the age of 50 are at higher risk for severe disease. WNV is usually transmitted to humans through the bite of an infected mosquito. Most people infected with WNV will have no symptoms. When present, WNV symptoms tend to include fever and flu-like illness. In rare cases, more severe illness can occur.

A WNV infected mosquito pool was found in the Fenway neighborhood last week, and infected pools were found earlier his summer in Jamaica Plain, Hyde Park, and Roslindale.

What’s the difference between EEE and WNV? The two diseases often get lumped together because they are both mosquito-borne illnesses, but there are significant differences between the two.

Dr. Asim Ahmed from the Division of Infectious Diseases at Boston Children’s Hospital says that early symptoms of both WNV and EEE can overlap with the flu, and include symptoms like fever, malaise, muscle aches, and sore throat. But patients with EEE will often also develop other very severe symptoms in two to three days like seizures, altered mental status, confusion, coma, and even death.

“About 80 percent of people who get WNV will have what’s called a sub-clinical infection with very mild or even no symptoms. But 20 percent of people with WNV will have mild self-limited symptoms that can mimic the flu. Most of these patients don’t see a doctor, never have a test sent, and will recover fully from the infection,” Ahmed says. “A small subset of people with WNV, about 1 in 150 to 1 in 250, will have severe disease which may result in confusion, altered mental status, polio-like flaccid paralysis [isolated weakness of a limb], seizure, and coma. One out of 10 patients with the severe form of the disease will succumb to their illness.”

The major difference between EEE and WNV, Ahmed says, is that EEE is much more severe, with a 30 to 50 percent mortality rate. Another difference is that historically within Massachusetts, EEE has mostly been found in the corridor southeast of Boston in close proximity to the wetland swamps that straddle Plymouth and Bristol counties, whereas WNV has been found throughout the state. The past two or so years, however, EEE has been found in several uncharacteristic parts of the state like Franklin, Worcester, Essex, and Middlesex counties.