Ticks, the small bugs that carry Lyme disease virus, have been discovered to have extensively spread across the U.S. The insects were able to invade large parts of the states in the period of 20 years.

In a press release, the Journal of Medical Entomology published the report of Centers for Disease Control and Prevention. It indicated that researchers found out that the lyme disease-carrying bugs, known as the black-legged ticks, have rapidly spread and now estimated to cover almost half of American counties.

The research was the first to be carried out since 1998 and the experts were astounded with the results. Dr. Rebecca Eisen, the lead researcher and biologist at the CDC stated in Science Mag, "Since the late 1990s, the number of counties in the northeastern United States that are considered high-risk for Lyme disease has increased by more than 320 percent."

She added, "The tick is now established in areas where it was absent 20 years ago."

Likewise, the expanded number of the black-legged ticks in U.S. is more than twice as many compared to the last survey done in 1998.

The increase presence of the bugs is connected to the rise of Lyme disease in the recent years. In 2013, the CDC revealed that the disease affects at least 300,000 Americans every year and this is 10 times higher compared to previous estimates.

The experts said that the number of people being afflicted with the disease is likely higher than what was stated because not all counties monitor ticks.

"I think the numbers could be higher. We have good confidence where it's reported or established, but low confidence in the areas with no records," said Dr. Eisen.

Ticks and Climate change

As for the cause of the spread, Eisen shared that climate change is one reason. "Where the climate is conducive we would expect to see continued expansion, but not in places like Colorado or the arid inter-mountain west because it's too dry," she explained.

It was added that climate change play a key role because the warm environmental condition is the best place for ticks to thrive.

Watch out for these symptoms:

Once a person is bitten by Lyme disease-carrying ticks, the Borrelia bacteria will spread in the body and flu-like symptoms will developed. The typical indications include headache, rash with an "eye" in the middle of the bite, fever and fatigue.

How to avoid Lyme Disease

To prevent Lyme disease, experts laid out effective advice to people living in the affected areas. Firstly, people were warned to keep away from anywhere with green space.

"To get Lyme disease, you don't have to live out in the country. There are many green belts and streams that come down into cities and those habitats support deer and ticks really well. The ticks are really everywhere unless you live in an incredible urban center where it's all asphalt and concrete," director of the Johns Hopkins Lyme Disease Clinical Research Center, Dr. John Aucott said.

On CBS News report, CDC shared these ways to prevent Lyme disease:

1. Keep away from grassy or wooded areas.
2. Apply repellents with 20 to 30 percent DEET content.
3. Treat clothes with products that have permethrin.
4. After a trip outdoors, take a bath immediately to wash off ticks that may have clung on your clothes or skin.