Insect-borne diseases have tripled in the United States since 2004, and Minnesota has emerged as an epicenter of tick-related illnesses.
With 26,886 confirmed cases of tick-borne infections between 2004 and 2016, Minnesota had the seventh-highest tally in the U.S., according to the U.S. Centers for Disease Control and Prevention.
Federal officials said the findings, released in a new report Tuesday, should encourage more public health efforts to confront a growing problem — one that is at least tied to warm weather and humid streaks if not global climate change. A recent national survey found 84 percent of mosquito control agencies lacking resources for adequate monitoring.
Increased international migration of people and animals has increased threats in the U.S., which since 2004 has encountered at least nine new insect-borne germs such as chikungunya and Zika virus, according to the CDC report. Those two viruses have not been transmitted locally in Minnesota, but people traveling out of the state have been infected.
“All these diseases are basically a plane flight away,” said Dr. Lyle Petersen, director of the CDC’s vector-borne disease division.
Dr. Jennifer Halverson, an emergency department pediatrician in Minneapolis, contracted chikungunya in 2014 while providing charitable care to earthquake survivors in Haiti.
Severe joint symptoms lasted four months for her, but continue today for friends.
“They say they feel like they are 10 years older than they are,” she said.
The unofficial home of the mosquito, Minnesota has had 1,458 confirmed disease cases linked to these insects from 2004 to 2016.
Infections included West Nile virus, which didn’t exist in the U.S. until 1999. Minnesota reported 83 West Nile infections in 2016, its highest total since 2007, and five deaths due to infection-related brain swelling. The state has not yet released 2017 totals.
Higher risk state
Minnesota’s higher case total is due to the elevated risks in the state and more awareness by doctors who report cases, said state vector-borne disease epidemiologist David Neitzel.
“Our program ... is one of the most active in the country in looking for mosquito- and tick-borne diseases,” he said. “But really, while we all love our state here, it is one of the higher risk states.”
Surveying tick monitoring sites around Washington County on Tuesday, Neitzel said the severity of the upcoming season will depend on heat and humidity.
Tick numbers were healthy going into the long but mild winter.
“Spring ... finally came and now things are going to happen pretty quickly,” he said. “Ticks are out already. Mosquitoes are a few weeks behind.”
Petersen and the CDC director, Dr. Robert Redfield, sidestepped questions Tuesday about whether climate change is contributing to the rising case numbers.
However, Peterson said warmer weather in general plays a role by allowing ticks to spread to places with historically colder climates, and to stick around for longer periods of the summer.
“I can’t comment on why there is increasing temperature,” Petersen said. “That’s the job of meteorologists.”
Dr. Nicholas Watts, a global health specialist at University College London and co-author of a 2017 report on climate change and health, said warmer weather is spreading disease in many countries. In Britain, he said, tick diseases are expanding as summers lengthen, and malaria is becoming more common in northern Australia.
But Paul Reiter, a medical entomologist at the Pasteur Institute, has argued that some environmentalists exaggerate the disease threats posed by climate change.
In the Dust Bowl years of the 1930s, St. Louis encephalitis, a related virus, surged, “and it looked like climate issues were involved,” Reiter said. But the surge turned out to depend more on varying hot-cold and wet-dry spells and the interplay of two different mosquito species. St. Louis encephalitis virtually disappeared, weather notwithstanding.
Neitzel said environmental management policies play a role. Maintaining younger forests in Minnesota can support conditions for ticks, but also the deer and mice that spread them, he said.
With summer approaching, health officials encouraged people to take precautions outdoors, including wearing long-sleeve clothing, removing standing water sources that can be breeding grounds for mosquitoes, treating clothing with permethrin, and using appropriate insect repellent.
The federal report was the first to collectively tally the number of infections linked to mosquitoes, ticks and fleas.
Its total of 640,000 cases is likely an undercount. The 35,000 cases of tick-borne Lyme disease, for example, are believed to be only one-tenth of the actual number of cases.
Milder cases are probably never detected by doctors, despite the characteristic bull’s-eye rash that often accompanies an infection. Severe Lyme cases can result in joint pain, fatigue and headaches, among other symptoms.
It took 13 months, three false test results, and even an unnecessary bone biopsy before Holly Zelinsky’s Lyme disease was diagnosed two years ago.
“They thought I had cancer,” said Zelinsky, who still struggles with symptoms as well as severe nutritional deficiency from the infection.
As founder of Lyme Awareness Minnesota, she said she hopes the federal report will encourage awareness. She was recognized on the floor of the Minnesota House Monday, and talked with lawmakers about the need for more reliable testing and flexible treatment.
As a kickoff to an awareness month in May, U.S. Bank Stadium, the IDS Center and other structures featured lime green lighting Tuesday night.
The New York Times contributed to this report.