The first new mouse model in which the Zika virus can be tested was described in a medical journal on Monday.

Research into drugs or vaccines that might work against Zika has been hampered because there have been no approved animal models in which to test them. Testing is normally done first in cell lines, then in mice and finally in monkeys before human testing can ethically begin.

In The American Journal of Tropical Medicine and Hygiene, virologists at the University of Texas Medical Branch in Galveston announced that they had found a type of immune-deficient mice that lost weight, became lethargic and died when infected. Normal laboratory mice do not.

The work was done in January, and other researchers may have found other mice in which to do testing, said Shannan Rossi, the study’s lead author. But this was the first mouse model to be published in a peer-reviewed journal.