The former finance director of the San Mateo County Mosquito and Vector Control District and her assistant have been charged with embezzling more than $450,000 from the agency, a prosecutor said Thursday.

For the former finance director, Jo Ann Seeney, 60, it's the third time she has faced such charges. The county didn't run a criminal background check when it hired her in 2009, so it was unaware she was already accused of embezzling hundreds of thousands of dollars from two previous employers.

Seeney, also known as Jo Ann Dearman, and a bookkeeper, Vika Sinipata, 35, stole from the mosquito control district from 2009 to 2011 by giving themselves extra pay and bogus time off, said San Mateo County District Attorney Steve Wagstaffe.

The two also padded their deferred compensation funds with excessive contributions, used the agency's credit cards for personal purchases and transferred county money into their accounts, Wagstaffe said. Each was charged with eight felony counts of embezzlement.

The alleged embezzlement was uncovered in January of last year when a report showed that the district's agricultural account had been overspent by $150,000. A manager disputed the finding, prompting a member of the agency's board to ask for records.

The board member took her concerns to the county counsel's office, which led to an audit showing more discrepancies, authorities said.

At the time the district hired Seeney in February 2009, officials didn't know that she had been arrested in late 2007 for allegedly embezzling $568,000 from a former employer, Foster City medical supply company ConforMIS Inc. Later, prosecutors also charged her with stealing tens of thousands of dollars from another ex-employer, Woodside general contractor Mark de Bibo & Co.

Even as those cases were winding through the courts, Seeney continued to oversee the mosquito control district's finances. She went on leave last year and, in March, she pleaded guilty to the charges and was sent to state prison to serve a two-year sentence.

The mosquito control district "was not required to perform criminal background checks" when Seeney was hired, said the agency's general manager, Robert Gay. "The district is now performing criminal background checks on all new hires."

Seeney has been returned from state prison to San Mateo County Jail, where she is being held in lieu of $250,000 bail.

Sinipata was hired five months after Seeney and handled payroll, bookkeeping and other financial duties. She is being held in lieu of $150,000 bail.