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 (below) 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, the US Centers for Disease Control and Prevention (CDC) says.
Zika, which has been linked to 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 been found only in the territories of Puerto Rico, American Samoa and the US Virgin Islands.
The mosquitoes, the scientific names of which are Aedes aegypti and Aedes albopictus, were concentrated most heavily in the US southeast and southwest, according to the CDC maps that break each state down to individual counties.
The maps use 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 3141 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 Organisation advised women living in areas where Zika was 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 1400 cases of microcephaly it considers to be related to Zika infections in mothers.