Liz Szabo

USA TODAY

Texas scientists have found a genetically engineered mouse that will allow researchers to test experimental compounds against the Zika virus, a step that could speed up the development of drugs and vaccines.

Researchers need to be able to test experimental drugs on mice before trying them on humans.

But garden variety lab mice don't respond to Zika the way humans do, said Shannan Rossi, a virologist at the University of Texas Medical Branch in Galveston and lead author of a study published in the American Journal of Tropical Medicine and Hygiene.

Normal mice don't get sick after being infected with Zika, Rossi said. So testing potential drugs on them doesn't work.

But Rossi and her colleagues were able to find a type of genetically engineered mouse that does become sick when infected with Zika. These mice, which have been used in research labs for years, have been altered so that their immune systems don't mount the usual, early defense against viruses that's critical to preventing disease.

Zika Virus: Full coverage

When researchers injected young genetically altered mice with Zika, the animals became lethargic, lost weight and died within six days. Older mice became ill but didn't always develop infection, and they eventually recovered, according to the study.

Zika is a mosquito-borne virus linked to a birth defect known as microcephaly, which results in small heads and brain damage in infants. It has also been linked to infant eye abnormalities and Guillain-Barre Syndrome, a neurological disorder that can cause temporary paralysis.

Researchers around the country have been eager to test potential drugs against Zika. Doctors at the University of Texas Medical Branch are already doing preliminary testing of an antiviral drug originally developed against a related disease, called dengue.

Once drugs or vaccines are shown to be safe and effective in lab mice, their developers can apply for permission from the Food and Drug Administration to conduct to small studies in humans.

But without lab mice, experimental compounds can't move out of the test tube phase of development, said Amesh Adalja, a senior associate at the Center for Health Security at the University of Pittsburgh Medical Center. He called the new study a "major development that will open up many opportunities for research and hopefully lead to a deeper understanding of this virus and, eventually, a vaccine."

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