Scientists in the United States may have discovered an important piece of the puzzle in the battle against Zika virus. They have identified a genetically modified strain of mice that develop Zika that can be used to test vaccines and drugs against the mosquito-borne illness.

The number of babies born with smaller heads increased since last year, and its link to the spreading Zika virus has spurred worldwide health scare. Health agencies struggle to contain the spread of the virus but one valuable tool that could stem the outbreak is the development of a successful vaccine.

Scientific research for vaccines and drugs that can work against the dreaded virus, has been hampered and delayed due to lack of approved animal models for testing. Before human trials could be started, animals like mice and then in monkeys should be tested first.

The new mouse model could be used for testing drugs and vaccines to battle Zika virus. Aside from that, the genetically engineered mice provided valuable information of the virus's pathogenesis and this could help in developing potent treatments.

Published in the American Journal of Tropical Medicine and Hygiene (AJTMH), virologists from the University of Texas Medical Branch (UTMB) in Galveston found a type of immune-deficient mice that became lethargic, lost weight and died when infected with the virus.

In 2010, the team injected several lab mice with an Asian strain of virus. This is the same type that has caused an outbreak in Latin America and the Caribbean. Laboratory mice don't usually get sick after infection with Zika virus but they found that those with impaired immune response developed the disease.

The team also found that aside from the mice being sick with the virus and the viral particles found in several organs, the highest concentrations were found in the brain, testes and spleen.

"This research team's dedication and previous research on dengue and other arboviruses enabled them to quickly develop this model for Zika virus, an important first step to enable testing of candidate vaccine and therapeutics," said Stephen Higgs, president of the American Society of Tropical Medicine and Hygiene (ASTMH).

The mouse model is already available for antiviral testing. Initial testing is already on its way with an antiviral developed by a member of the UTMB team, Pei-Yong Shi, to treat dengue fever, another mosquito-borne disease.