A recent study raises questions about the spread of Lyme disease after finding ticks capable of carrying the disease in counties not previously known for these ectoparasites.
Now people with Lyme disease have been found in all 50 states.
Ticks are spreading across the country
The study looking at ticks was published last month in PLOS ONE. Researchers studied submissions from citizens across the country to track where ticks were found.
Citizen-submitted tick samples were sent to researchers from Northern Arizona University and Colorado State University from January 2016 to August 2017. They were tested at no charge for four of the most common bacterial infections:
- Borrelia burgdorferi, which causes Lyme disease
- Borrelia miyamotoi, causing tick-borne relapsing fever
- Anaplasma phagocytophilum, causing human granulocytic anaplasmosis
- Babesia microti, a protozoan pathogen
The study found that ticks that can carry Lyme disease as well as other tick-borne diseases were in 83 counties across the country that hadn’t previously recorded them.
After samples were categorized and mapped, the data was sent to each citizen who submitted. Citizens from every state, except Alaska, submitted tick samples.
“There were many surprises in the results,” said Wendy Adams, research grant director of the Bay Area Lyme Foundation, which funded the study.
One surprise related to the lone star tick, an aggressive human-biting tick that can be found in the eastern half of the country. But they’re not supposed to be in California, said Adams.
However, the study found the tick in two separate locations in Northern California.
She said another surprising find by the researchers was that the Lyme disease-causing Borrelia burgdorferi was found in ticks that had just hatched from eggs — something that isn’t supposed to happen.
It’s commonly thought the bacteria is acquired from feeding on infected blood, not at birth.
Dr. John N. Aucott, associate professor of medicine at Johns Hopkins University School of Medicine and director of Johns Hopkins Lyme Disease Research Center, said the importance of this study lies in its inclusion of the West Coast, where not much data’s been recorded.
He said while Lyme disease is on the rise on the East Coast and upper Midwest, more studies are needed on the West Coast to determine if it’s spreading there.
“It’s looking at the West Coast and I think the information over time will be super valuable,” he said.
He said many of the new counties reporting ticks carrying Lyme disease were next door to counties with recorded tick activity. Not too surprising — especially in the Midwest and mid-Atlantic — which has historically been known for higher rates of tick activity and Lyme disease.
What was surprising to Aucott was the ticks found in Arizona — a state not known for ticks carrying Lyme disease.
He said there are many reasons for the spread of these ticks. This includes changing land-use patterns — mainly involving the creation of fragmented forests due to the development of suburbs. These broken up forests are the perfect habitat for deer, whose blood is a food source for ticks.
Nicole Chinnici, a molecular biologist and laboratory director at Northeast Wildlife DNA Laboratory, part of East Stroudsburg University, said an area’s mouse population also has an impact on the increase of Lyme disease because mice are the source of the bacteria.
Warmer temperatures in some areas and fewer predators of mice can also increase the Lyme disease risk.
She said as Lyme disease continues its spread in the Northeast and Midwest, other areas in the United States will most likely also be impacted.
“You’ll start to see more distribution of those cases occurring throughout California,” said Chinnici, whose laboratory offers 48-hour Lyme disease tests to the public for submitted ticks.
Rising number of Lyme disease cases
This week, Quest Diagnostics released a report finding that Lyme disease is rising in places not historically associated with the disease.
The regions with notable increases of Lyme disease include California, Arizona, and Texas.
According to a 2016 Centers for Disease Control and Prevention (CDC) map of reported cases of Lyme disease in the United States, most states have reported at least one case of the disease — however, it’s possible the disease was acquired outside the state.
“Tick-borne diseases have been reported from every state,” said CDC spokesperson Benjamin Haynes. “[The] CDC currently collaborates with partners in universities and public health agencies to continually monitor changes in tick distributions… [The] CDC urges vector control and local health departments to undertake efforts to monitor and track tick species locally to inform public health actions.”
Aucott said because the spread of Lyme disease is caused by larger patterns, such as reforestation and an increasing number of deer, it’s a challenge to fight.
He said there’s some research being done on mice vaccines to prevent the disease in those hosts in order to stop transmission.
“The best way to prevent Lyme disease is probably personal protection,” he said. Wearing long pants in high grass and treating clothes with the insecticide permethrin after hikes, for example.
“It’s very hard. That’s why it’s spreading.”