South Dakota health officials are watching the arrival of new mosquitoes in the state and the possible impact on West Nile Virus and other diseases.

The Aedes japonicus, or Japanese rock mosquito, has made a presence in South Dakota, said State Epidemiologist Lon Kightlinger.

“The Japanese rock mosquito can carry West Nile,” Kightlinger said. “It’s not thought to be as good a host (for West Nile) as the Culex tarsalis. But there are other diseases it can cause and be just as bad.”

The Asian species was first detected in the United States in 1998 and has worked its way across the country, according to the Centers for Disease Control (CDC).

The mosquito has now been detected in South Dakota, Kightlinger said. The insect appears to breed well in old tires, he said.

“In 2009, they found samples of it in Sioux Falls,” he said. “This mosquito is more out in the daytime, and in Sioux Falls they had day biters.”

*
Those findings fit the characteristics discovered by the CDC. Adult species of Aedes japonicus rest in wooded areas and prefer to bite during the daytime. The adult female is a medium-sized mosquito of dark- to blackish-brown appearance, with white scales on the body and legs.

Larvae are found in a wide variety of natural and artificial containers, including rock holes and used tires. Preferred sites usually are shaded and contain water rich in organic matter. Eggs can survive several weeks or months under dry conditions.

The Japanese rock mosquito came to Minnesota in recent years and shows an aggressive nature, according to media reports.

In June 2009, a Minnesota boy nearly died because of a bad mosquito bite. The 8-year-old’s mother believes the insect was the Japanese rock pool mosquito.

According to Twin Cities media reports, the mosquito bit the boy on the face. About a week later, the boy became so sick he couldn’t talk. When he tried to stand up, he had no feeling on the left side of his body. The boy slipped into a coma-like state, and doctors discovered he had contracted LaCrosse encephalitis, or inflammation of the brain.

With no cure for the virus, the boy needed to recover on his own. He needed to relearn how to read, write and talk.

The Japanese rock mosquito is not the only insect on the radar screen for officials.

Authorities are watching the northward invasion of the Asian Tiger mosquito, said Jon Lundgren, an entomologist with the U.S. Department of Agriculture (USDA) in Brookings.

“This insect originally hails from southeast Asia and has been established in the U.S. for several years down south,” he said. “It will likely invade South Dakota in the next year or two.”

Lundgren advised against focusing solely on the Asian Tiger mosquito as a new West Nile source.

“It is true that the tiger mosquito transmits diseases, but there are a lot of other mosquito species that already transmit (West Nile Virus) that are present in South Dakota,” he said.

“Again, the invasion of the tiger mosquito is certainly something to be aware of, but I am not sure that it is a game changer for South Dakota residents.”

According to the USDA, the Asian Tiger mosquito was introduced in the continental U.S. in 1985. The mosquito arrived accidentally in tires imported from Japan and can transmit viruses such as Eastern equine encephalitis and West Nile virus.

The Illinois Department of Public Health has conducted research on the Asian Tiger mosquito.

The name "tiger mosquito" comes from its white-and-black color pattern. The quarter-inch insect has a white stripe running down the center of its head and back with white bands on the legs.

The bite of the Asian tiger mosquito is not particularly irritating to most people, but the insects are persistent biters.

Male mosquitoes feed on plant juices and do not bite. Female mosquitoes seek blood to help their eggs develop. The Asian Tiger feeds during daylight hours, not at night.

Asian Tiger mosquitoes are attracted to dark clothing, perspiration, carbon dioxide and certain other odors. The mosquito will bite squirrels, dogs, deer and other animals as well as people.

In the United States, it has been found to be infected with LaCrosse encephalitis viruses and West Nile virus. However, it is unclear whether the Asian Tiger mosquito will be a significant carrier of disease in the in the United States.

South Dakota has seen a surge in mosquitoes this year, largely caused by tremendous amounts of standing water from heavy rains, Lundgren said. However, that doesn’t necessarily increase the risk for West Nile Virus, he said.

“Three components need to be in place for WNV (West Nile Virus) to take off: people, virus, and mosquitoes,” he said. “Right now, we have more than usual (numbers of) mosquitoes, but I don’t believe we have evidence for more people or virus. So certainly it is advisable to be concerned and aware of the risks associated with WNV, but I don’t think people should panic.”

Because of the rainy weather and standing water, the City of Yankton has begun its spraying operations earlier than usual. Normally, the city sprays once during the summer, just before Riverboat Days in August.

The city sprayed Fox Run Golf Course last week and, as of Monday afternoon, planned to spray the rest of the community. City officials believe the process could take about three days to complete.

Now is the time to get in the habit of using insect repellent and practicing mosquito control, Kightlinger said. He also advised staying indoors during dawn and dusk. If outdoors, he recommends wearing protective clothing and repellent.

“This will be the ninth year of West Nile in South Dakota and, while people might be used to hearing about it, they shouldn’t be complacent about prevention,” he said. “We all need to protect ourselves and our families from this virus.”

Since 2002, South Dakota has reported more than 1,700 human cases of WNV, including 26 deaths. Detections, human or animal, have been reported in every county. Peak transmission in South Dakota occurs from July through early September.

Kightlinger doesn’t have a prediction for this year’s West Nile season, but he thinks the number of cases could be higher than last year’s 21.

“I am hesitant to think we will have a low year like last year. We are 10 years into it, and we really don’t know how to predict it well,” he said. “Last year, we had 21 cases, and the year before it was 39. We had 208 (cases) in 2007, and in 2006 we had 113 cases. Within those ranges, we could have as high as 200 cases this year and as low as 20.”

One thing is for certain: West Nile has become an annual event, Kightlinger said.

“It is entrenched and part of the environment. We can expect to see more cases,” he said. “But mosquito control is important beyond just West Nile. We have 30 other diseases out there.”

Lundgren agreed that efforts shouldn’t focus strictly on West Nile.

“We often forget the Northern Great Plains were loaded with malaria even up to a few generations ago,” he said. “Lewis and Clark’s entire expedition was almost crippled by this mosquito-borne disease.”

Two major changes — prime-time television and window screens — completely changed the importance of mosquito-borne illnesses in North America during the last 50 to 100 years, Lundgren said.

“Essentially, it reduced human exposure to such low levels that a lot of these mosquito-borne illnesses don’t debilitate our society like they do in other regions around the world,” he said. “I guess we can say, ‘Thank you, Howdy Doody.’”