Here a tick,there a tick,到处都是滴答声，蜱虫：携带莱姆病的动物现在在美国更为普遍。比以往任何时候，according to new research.
In the study,专家绘制了携带莱姆病的蜱虫的分布图，发现这些蜱虫的分布范围比以前更远。现在居住在美国近50%的地方。counties.
There are two tick species that can carry theBorrelia burgdorferi引起莱姆病的细菌：黑腿蜱，又称鹿虱（Ixodes scapularis),and the western blacklegged tick (太平洋Ixodes Pacificus）The bacteria can only be transmitted to people throughthe ticks' bites.一。scapularisis the primary carrier in the eastern U.S.,and一。pacificus是西部各州的主要运输工具。
Researchers previously surveyed these ticks' distribution in 1998 and mapped the tick populations in the continental U.S.Those results showed that the ticks were present in 34 percent of U.S.counties,在41个州。
In the new study,他们研究了国家卫生部门的研究和数据，并联系了公共卫生官员，莱姆病研究人员和其他科学家。[视频：一个滴答声]
对于每一个美国county,the researchers evaluated whether tick populations for一。scapularisand一。pacificuswere "established" or "reported.""Established" meant that there was evidence that a population of ticks was alive and well,在县里繁殖，whereas "reported" meant that a few ticks had been spotted at some point,虽然不一定是最近，科学家们说。
After evaluating data for the 3,110 counties in the continental U.S.,the researchers found recorded evidence that the eastern tick,一。scapularis,is now reported or established in 1,420 counties and the western tick一。pacificus 报告或建立于111 counties.一起，the two tick species span 49 percent of U.S.counties across 43 states.
"What we saw was a prettysubstantial expansionin the northeastern U.S.在中北部各州，“Rebecca J.Eisen,lead author of the study and a research biologist at the Centers for Disease Control and Prevention,told vwin电子竞技Live Science.The ticks are also expanding farther west and east,she said.
And莱姆病病例也在上升。1991，about 10,000 Lyme disease cases were reported in the U.S.,but in 2014,more than 33,000 Lyme cases were tallied,据疾控中心称。然而，some of this increase may be due to more awareness of the disease and more cases being reported.早期莱姆病症状包括发烧，寒冷，joint pain and a distinctive "bull's-eye" rash at the site of the tick bite.如果不治疗，这种病会引起关节炎，心悸，大脑炎症，面部肌肉无力，the CDC says.
滴答声最近的一个原因距离扩展may be climate change,said Ralph M.Garruto宾厄姆顿大学生物医学人类学教授，State University of New York.
"Ticks would be able to move farther north with warmer temperatures,由于严重的寒冷和干燥条件会影响虱子的生存，”加鲁托说，who was not involved in the study.
Eisen agreed,adding that climate plays a significant role in defining the western limit of the range of theblacklegged tick."For example,在科罗拉多州，这只虱子太干了，无法存活。vwin电子竞技
Garruto also said that human activity could be creating more hospitable environments for ticks.“东北部可能会有更多的森林碎片，in part,to built environments — an aspect of research we are currently looking at," he said."Perhaps the increasing deer populations in many areas are responsible for moving [the ticks] around," as well as giving the ticks more opportunity to breed,he added.
And established tick populations can readily travel between neighboring counties,Eisen said."A county is more likely to be colonized if its neighbor has ticks,因此，附近有虱子，森林里有鹿，这很好地表明虱子可能会来到一个新的地区，”她说。[The 10 Most Diabolical and Disgusting Parasites]
She noted that many ticks do not carry the bacteria that cause Lyme disease.
The new study offers "a nice summary of the distribution oftick species有可能携带莱姆，but their distribution alone does not equate with Lyme disease," Garruto told vwin电子竞技Live Science.Researchers would need to know the percentage of ticks that are infected in order to speculate on whether the expansion of the ticks' range could lead to an increase in Lyme disease cases,他说。
“我们真的希望人们意识到风险会发生变化，and it's important to know what ticks andtick-borne disease在你住的地方和你参观的地方都很常见，”艾森说。
The findings were published online Jan.18 in the Journal of Medical Entomology.