A second Bergen County resident has died of West Nile virus, state health officials said Monday, amid "great concern" over what they are calling the highest number of West Nile cases seen in six years.

The death of the elderly woman this week followed that of a 62-year-old man from Lodi this month.

"The number of human West Nile virus cases is the highest we’ve seen since 2012, and the season is not over yet," New Jersey Health Commissioner Shereef Elnahal said in a press release Monday. "The pattern of hot and wet weather this summer has led to an increase in mosquito populations and associated viruses."

West Nile, primarily a bird disease, can be passed along to humans by mosquitoes that pick up the virus from infected birds, according to the federal Centers for Disease Control and Prevention. There is no vaccine and no treatment that target the virus.

As of Monday, 31 cases of West Nile virus were confirmed in New Jersey, the Department of Health reported. Six cases were reported in Bergen County, the highest number in the state, according to a Vector-borne Surveillance Report released by the department on Sept. 15.

Elnahal said the number of positive West Nile virus mosquito pools is the highest ever reported, particularly in the northwestern and central parts of the state, where levels usually are not high.

About 1,019 mosquito pools have tested positive for West Nile virus throughout the state, 118 of them in Bergen County, according to the Vector-borne Surveillance Report.

"The number of West Nile virus cases in New Jersey is of great concern," Ray Bukowski, an assistant commissioner for New Jersey’s Natural and Historic Resources, said in the release. "The warm and wet weather we have experienced increases the mosquito population."

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Bukowski said it is crucial for homeowners to eliminate "even the smallest amounts of standing water from their properties" as the weather begins to cool, to reduce the risk of exposure to mosquitoes.

That means emptying or changing flower pots, birdbaths, clogged rain gutters, plastic wading pools, wheelbarrows and trash containers that may contain standing water.

When the temperature drops below 60 degrees, mosquitoes stop being active, the New Jersey Department of Environmental Protection said. North Jersey temperatures are expected to hit lows around 60 degrees several nights this week.

West Nile virus does not cause symptoms in most people, although one in five infected may develop a fever, headache, body aches, joint pains, vomiting, diarrhea or rash, according to the CDC. People over 60 years old are at greater risk for complications.

Less than 1 percent of those infected with West Nile virus will develop severe symptoms, which include high fever, neck stiffness and swelling of the brain (encephalitis), which can lead to coma, convulsions and death, the state Health Department said.

The incubation period for West Nile virus is typically two to six days after a mosquito bite, but it can range from two to 14 days, the CDC said. For people with immune deficiencies, the incubation period can last several weeks.

Over the past five years, the Health Department has identified West Nile virus as the cause of several deaths throughout the state, including:

Two deaths in Gloucester and Morris counties in 2013

Three deaths in Cumberland, Monmouth and Passaic counties in 2015

Two deaths in Ocean and Union counties in 2016

Two deaths in Mercer and Middlesex counties in 2017

Use insect repellents and wear long-sleeved shirts and pants while outdoors to guard against West Nile. If using sunscreen, apply it before insect repellent. Babies younger than 2 months old should not be exposed to insect repellent. Instead, parents should dress babies in clothing that covers arms and legs and cover strollers and baby carriers with mosquito netting.

As of Sept. 18, there were 1,077 human West Nile cases in the United States, with North Dakota, South Dakota and Nebraska each having more than 100 cases.