One of the biggest employers in Ventura County faces an ownership change less than one month after it was spun off from its Chicago-area parent.

Shire Plc, a pharma company based in Dublin, Ireland, stunned the markets on Aug. 4 with a $30 billion bid for Baxalta.

Baxalta, which employs around 2,000 at two locations in Thousand Oaks, was separated from its former parent, Baxter International, just one month ago.

The Shire bid is a stock-for-stock exchange that would value Baxalta at $45.23, or 36 percent more than the closing price of Baxalta shares on Aug. 3.

Bloomberg News speculated that Shire, which benefits from low tax rates, was making the move to head off a takeover bid from another large drug maker.

For its part, Shire said that it wanted to create a global drug powerhouse focusing on rare diseases, an area where Baxalta has considerable expertise.

Its Ventura County operations focus on treatments for hemophilia and other blood-related diseases. Hemophilia treatments account for about half of Baxalta’s sales.

So-called “tax inversion” deals such as the one proposed by Shire have drawn criticism from the Obama Administration. Baxalta’s tax rate would decline from just below 25 percent to around 16 percent if the Shire takeover is completed.