The West Nile virus has been detected in mosquitoes in Slidell, Covington and Mandeville, prompting St. Tammany Parish officials to step up efforts to control the two species that harbor it.

One human case of the virus has been reported in Slidell, according to the parish’s Mosquito Abatement District.

The LSU Veterinary Diagnostic Lab reported finding the virus in six pools of mosquitoes out of 60 that it tested, the district said in a news release. A pool is a group of up to 50 adult mosquitoes collected in a single location and tested as one sample.

Four of the positive samples were collected in Slidell and one each in Mandeville and Covington.

All but one of the infected pools consisted of Southern house mosquitoes, the primary species that carries the virus. It breeds in roadside ditches and is most often found in areas where homes rely on filter beds and septic tanks for wastewater treatment.

The mosquito district focuses on the Southern house mosquito, treating ditches every five to seven days to keep adults from emerging from larvae, Director Chuck Palmisano said.

As a result, the breeding level has decreased to a low of 1.7 to 1.9 larvae per sample. Left unchecked, the level can go as high as 100 to 200 larvae per sample.

The district has also targeted adult mosquitoes with ground and aerial spraying, treating 88,813 acres over the past two weeks, with a focus on the areas where mosquito pools tested positive.

The adult population has remained relatively low, according to the district.

The Asian tiger mosquito is another species that can transmit West Nile virus, and the district is placing more emphasis on it, although none of the positive tests involved that species.

The district is urging homeowners to empty containers that can hold water, such as flower pots, tires or cans. Asian tiger mosquitoes fly only about 50 yards from their breeding site, so homeowners who are having a problem with them will be able to find the source close by.

Follow Sara Pagones on Twitter, @spagonesadvocat.