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Experts warn of seasonal threat posed by disease-carrying insects

Todd Hanson, manager for mosquito control at the Grand Forks Public Health Department, examines a vial of frozen mosquitoes that are used for training purposes in species identification and testing for West Nile Virus in Grand Forks. Photo by Eric Hylden/Grand Forks Herald

As the weather warms up, people in this area should be on the lookout for, and protect themselves from, ticks and mosquitoes because the risk of contracting disease from these tiny creatures is growing, experts say.

Over the past two seasons, cases of some tick-borne illnesses have jumped in North Dakota, reflecting a nationwide upswing in the number of people sickened as a result of insect bites.

Illnesses from mosquito, tick and flea bites have tripled in the U.S., with more than 640,000 cases reported from 2004 through 2016, according to a recent report from the Centers for Disease Control and Prevention.

The number of disease cases from infected mosquitoes, ticks and fleas rose from 27,388 in 2004 to 96,075 in 2016.

Nine new germs spread by mosquitoes and ticks were discovered or introduced into the United State during this time, the CDC said.

Seven of those are transmitted by ticks and two by mosquitoes, said Todd Hanson, manager for mosquito control at the Grand Forks Public Health Department.

In North Dakota, the number of reported cases of tick-borne diseases nearly doubled in one year, according to the North Dakota Health Department.

"In 2016, there were 49 cases of tick-borne diseases," said Laura Cronquist, disease epidemiologist with the department's Division of Disease Control. "In 2017, there were 93 cases."

Several factors may explain the increase, Cronquist said.

"Testing has improved and become more accessible. And our case definitions have changed; they've become a little broader due to advances in testing," she said.

"That being said, that's a pretty drastic increase."

Some of these diseases can be life-threatening, she said.

Cronquist pointed to Rocky Mountain spotted fever which is caused by a type of bacteria spread by ticks, as an example, she said.

In North Dakota, only one case of Rocky Mountain spotted fever was reported in 2016, compared to 14 cases reported in 2017, Cronquist said.

In the same time frame, the number of cases of Lyme disease, also transmitted by ticks, jumped from 32 to 56.

The quality of the health department's surveillance program also may be contributing to the increase in reported cases, she said.

"We rely on volunteer vets and zoos throughout the state to pick ticks off animals and send them into the state," she said. "Our labs identify species and test pools of ticks for different tick-borne pathogens."

The volunteers submit ticks from April through November.

Officials are finding that "deer ticks are more widespread than we previously thought," she said.

Increases in disease cases throughout the U.S. are likely due to many factors, the CDC reported.

Mosquitoes and ticks and their germs they spread are increasing in number and moving into new areas. As a result, more people are at risk for infection.

Also, overseas travel and commerce are becoming more common and travelers may be infected with a mosquito-borne disease in one country and then unknowingly transport it home.

Cool weather advantage

The CDC's mention of a growing threat of Zika and chikungunya is not cause for worry "because the two species of mosquitoes that carry those viruses are not this far north," Hanson said.

He is most concerned about the potential impact of a type of mosquito, the Culex tarsalis, which is most responsible for spreading the West Nile virus in this region.

A delayed spring has been an advantage in the annual mosquito fight in the Grand Forks area.

"The cooler spring has been very helpful to us," said Hanson.

Cooler-than-normal conditions have slowed the egg-to-adult life cycle of mosquitoes.

His larviciding and surveillance program will start up Monday with training for a full staff of about 40 employees, he said.

Hanson and his crew will begin the work of monitoring traps, collecting and counting mosquitoes, and bringing them back to the lab for identification. They separate the Culex tarsalis from other types, Culex pipiens and Culex restuans, he said.

"There's a lot of hype about the Zika virus, but Zika is not a threat to us in this region," Hanson said. "West Nile is something we have and are going to have every year, especially in late July and early August.

"That's why we emphasize taking precautions to avoid exposure, such as wearing protective clothing, applying a repellent with DEET, and eliminating mosquito breeding spots," he said.

"If you have standing water, you can be raising mosquitoes that spread West Nile virus right in your backyard—and it doesn't take a very large amount."