Cattle fever ticks were eradicated in the US in 1943, with the exception of a permanent quarantine area along the border between South Texas and Mexico. White-tailed deer and nilgai facilitated the reintroduction of the tick outside the quarantine areas and into other areas of Texas. Cattle fever ticks are a threat if they carry the cattle fever pathogens, which can kill 70 to 90 percent of infected cattle. While no ticks in the US have tested positive for the pathogens, they are present in Mexico.
By Daktaridudu (Own work) [CC BY-SA 4.0], via Wikimedia Commons