Health experts warned that a second case of ticks, which carry diseases like mosquitoes, occurred in Washington state last month after last year, requiring attention.
The mite, which carries a bacterial pathogen called Anaplasmosis, first infected a woman in her 80s in Whatcom County in Washington State last year, before attacking a woman in her 40s in Puyallup last month.
The Whatcom County senior was discharged after receiving hospitalization.
The Puyallup woman was hospitalized for 10 days after being bitten by a tick in the nearby woods earlier last month with symptoms including fever, lethargy, muscle aches and vomiting, and is now recovering at her home, the Tacoma-Pierce County Health Department said.
Her state authorities are investigating the forests of Puyallup and Eatonville where she went. Experts said that although anaplasmosis occurs mostly in the southern regions of the United States, it tends to gradually spread to the north due to global warming.
An academic study published early last year said the disease is widespread in northern California and has likely already invaded neighbouring Oregon and Washington states.
Anaplasmosis, which is spread by black-legged ticks, is unfamiliar in Northwest America, but has been known for a long time in the Midwest and Northeast, said experts, explaining that wild animals, such as deer, which are the main hosts of these ticks, are moving around their habitats due to climate change.
Experts said it is almost certain that the elderly Whatcom County and the Puyallup woman are not the first victims of anaphylaxis in Washington State. Dogs infected with Anaplasmosis are found every year in Northwestern America, evidence that ticks already live in the region, they said.