President Obama is worried about an untreatable virus that's carried by mosquitoes and infecting more Americans

President Barack Obama called for the rapid development of diagnostics, vaccines, and treatments for the Zika virus, which poses a growing threat to most of the Americas.

Obama was briefed on the topic as the virus spread to more countries and territories, including the US Virgin Islands and Puerto Rico. People with the virus have also been identified in multiple US states after traveling to infected areas.

"The president emphasized the need to accelerate research efforts to make available better diagnostic tests, to develop vaccines and therapeutics, and to ensure that all Americans have information about the Zika virus," the White House said.

The Zika virus is primarily transmitted by Aedes aegypti, the type of mosquito responsible for spreading dengue, yellow fever, and numerous other infectious tropical diseases. The mosquitoes pick up the virus from infected people, according to the US Centers for Disease Control and Prevention.

There is no vaccine or treatment for Zika, partially because it didn't become a widespread problem until about 10 years ago and people who are infected have fairly minor symptoms like fever, rash, painful joints and conjunctivitis (also known as pink eye), although some short-term neurological conditions have been connected with the disease as well. It's the troublesome connection between infected pregnant women and an increased incidence of birth defects that makes containing the Zika virus a top priority.

For example, the CDC's travel notices are especially geared toward pregnant women, because of concerns about the virus' connection to brain abnormalities in babies and other neurological conditions.

Brazil, one of the areas hit hardest by the disease, had about 20 times as many babies born with a condition called microcephaly in 2015 compared to 2014. This birth defect, in which the brain is abnormally small, was often found after the mother had Zika virus-like symptoms early in the pregnancy.

Researchers still aren't sure whether the virus causes the birth defects, but there does appear to be a link. Earlier this week, the CDC issued interim guidelines for pregnant women traveling to countries where the disease is being transmitted, while some countries have gone as far as to advise citizens not to get pregnant.

Because Zika hasn't posed a threat until very recently, there aren't many treatments or vaccines in development, though companies are jumping on board to find possible ways to fight back against a possible epidemic. Others are trying to target the mosquito itself and kill it off to keep the disease from spreading, but it might be a while before those efforts are widely spread.