OMAHA — DNA tests should show within four weeks whether virulent samples of tularemia have somehow been transferred from the University of Nebraska Medical Center to a lab at the University of Nebraska-Lincoln.

The federal Centers for Disease Control and Prevention is investigating how a virulent sample ended up at the Boston University Medical Center, infecting and sickening three scientists there.

The Boston investigation has been inconclusive, but a single vial of bacteria sent by UNL was implicated, said the director of the NU Center for Biosecurity on Tuesday, Steven Hinrichs.

Hinrichs said the UNL and Boston labs use safer strains of tularemia, often called "rabbit fever," for their research.

UNMC uses virulent samples for its research, he said.

He said possible explanations for the Boston outbreak include:

* contamination of the material by blood from a Boston lab rabbit that is used to grow the bacteria.

* that the sample sent from UNL was subsequently contaminated by a virulent sample already at Boston University;

* that the UNL material was contaminated by a virulent sample obtained from UNMC.

Hinrichs said the latter scenario is unlikely, because UNMC doesn't supply UNL with its tularemia samples.

Nonetheless, the CDC is checking the DNA of med center samples to see whether it matches the Boston samples.

He also said the CDC has found no toxic contamination among the tularemia samples in Lincoln.