Mosquitoes that can transmit the Zika virus have been found to live in nearly all US states, according to maps released this week by authorities trying to assess the public health threat.
The maps show the two breeds of virus-carrying mosquitoes, the yellow fever and the Asian tiger mosquito, can live in the nation's northernmost states of Michigan, New Hampshire, Washington state and Minnesota, according to the US Centers for Disease Control and Prevention (CDC).
Zika, which has been linked to numerous cases of the birth defect microcephaly in Brazil, has spread rapidly in Latin America and the Caribbean. Microcephaly is marked by small head size that can lead to severe developmental problems in babies.
In the United States, Zika has only been found in the territories of Puerto Rico, American Samoa and the US Virgin Islands.
The mosquitoes, whose scientific names are Aedes aegypti and Aedes albopictus, were concentrated most heavily in the U.S. Southeast and Southwest, according to the CDC maps that break each state down to its individual counties.
The maps (http://tmsnrt.rs/1U5njHx and http://tmsnrt.rs/1U5nP8t) utilised data back to 1995, including information from the CDC, university researchers and local health departments.
The Asian tiger mosquito, which lives in semi-rural settings, was captured at least once in 40 states, while the yellow fever mosquito, which prefers urban areas, was found in 26 states, the CDC said.
Overall, they were found in roughly a third of the 3,141 counties in the United States, it said.
"Accurate and up-to-date information for the geographical ranges of Ae. aegypti and Ae. albopictus in the United States is urgently needed," authors of a paper containing the maps wrote this week in the Journal of Medical Entomology.
On Thursday, the World Health Organization advised women living in areas where Zika is being transmitted to delay getting pregnant, advice already given by several countries where the virus is in widespread transmission.
The connection between Zika and microcephaly came to light last fall in Brazil, which has confirmed more than 1,400 cases of microcephaly it considers to be related to Zika infections in mothers.