Historical record of cattle fever tick outbreaks in the United States. *Each fiscal year shows the contribution by the Permanent Quarantine and Free zones to the total number of outbreaks. The Free Zone comprises the area in the forty-eight contiguous states outside the Permanent Quarantine Zone, which is located along the Rio Grande River in southern Texas. The period shown in the graph depicts records maintained by APHIS-VS and it covers fiscal years 1960 through 2009. Data updated after .