There’s been a large enough number of mosquitoes found to be carrying the West Nile virus this July in East Baton Rouge Parish to raise concern that it could be just a matter of time before the first human case of the virus shows up.

“The last three weeks or so we’ve had very high numbers,” Randy Vaeth, assistant director of East Baton Rouge Parish Mosquito Abatement and Rodent Control, said of mosquitoes found with the virus.

Most of the heavy concentration of West Nile virus seems to be found in the northern parts of the heavily populated areas of Baton Rouge instead of in more rural or suburban areas, but mosquitoes don’t respect boundary lines and people are urged to take precautions.

“We’re anticipating some human cases this year based on the prevalence (of the virus),” he said.

The first human cases of West Nile virus in the state were announced July 8 by the Louisiana Department of Health and Hospitals after three individuals in Livingston Parish found out they were infected through blood donation screenings or blood tests. The three people didn’t know they were infected and didn’t have any symptoms.

West Nile virus is transmitted by mosquitoes that get the virus when they feed on infected birds. The virus is then passed on to people through a mosquito bite.

In July, there have been 51 samples out of 351 that have come back as positive for the virus, Vaeth said.

Using a formula, the office has calculated that 6.7 mosquitoes out of 1,000 are positive for the virus, he said. The threshold for seeing human cases start to show up typically occurs when that number is 5 or greater.

“We’ve exceeded our threshold so we’re a little alarmed we could have some human cases,” Vaeth said.

To battle the multiple types of mosquitoes found in the parish, the abatement program has been doing extensive aerial spraying with three flights last week alone. Each flight mission can cover 10,600 acres.

“We’ve been putting up the plane pretty frequently,” Vaeth said.

After getting the virus, most people won’t develop any symptoms but about one in five people will get a fever and symptoms that could include headaches, joint pains or vomiting, according to information from the Centers for Disease Control and Prevention. These symptoms can show up anywhere from two days to two weeks after the bite. Less than 1 percent of people develop the neuroinvasive form of the virus, which attacks nerve cells and can cause a swelling of the brain, coma or even death.

Last year was a quiet one for East Baton Rouge Parish for West Nile virus that appeared over the summer and through the fall. In all, only about three samples last year came up positive for the West Nile virus in mosquitoes and there were no human cases, Vaeth said.

In addition to the Southern house mosquito which is a good carrier for the virus, the office also is battling the nuisance mosquitoes that take advantage of the frequent thunderstorms that have showed up on an almost daily basis.

Testing also is done for Eastern Equine Encephalitis and St. Louis Encephalitis, but those haven’t shown up yet this year. The main concern for East Baton Rouge Parish is usually West Nile, Vaeth said, which is why people need to remember to wear mosquito repellent, empty containers that collect water around their homes and take other precautions against getting bitten, Vaeth said.

Follow Amy Wold on Twitter, @awold10.