Health officials in the United States say it is likely a patient there contracted the virus through sexual contact with someone who had travelled in Venezuela.
The Zika virus is usually spread by mosquitoes.
Reports it has been transmitted through sexual contact adds a new dimension to what has already been declared a global public health emergency by the World Health Organisation.
The United Nations health agency is urging people to practise safe sex.
But spokesman Christian Lindmeier says infection via mosquito remains the greatest danger.
"While it seems possible that the virus spreads through semen and is possibly transmittable through blood, these are so far only the rare cases of (sexual) transmission."
The virus is estimated to have infected 4-million people in at least 32 countries.
It has been associated with birth defects in over 4,000 babies in Brazil, though not in any other Zika-affected country yet and a causal link is yet to be proven.
Brazil is carrying out high-profile mass fumigations in a bid to protect people from the mosquito-borne virus.
But the director of the Pan American Health Organization, Carissa Etienne, says their effectiveness is limited.
"Fumigation only eliminates the adult mosquito and in the next few days you have another bunch of adult mosquitoes to deal with."
WHO spokesman Gregory Hartl has reiterated that individuals can greatly reduce their exposure to mosquitoes and the risk of contracting Zika with a few simple precautions.
"You can wear proper clothing, long sleeves, long trousers, you use insect repellent, close doors when you are inside and sleep under bed nets."
South American health ministers meeting in Uruguay have pledged to work together in the fight against Zika.
There is currently no treatment or vaccine for the virus.
Drugmakers are racing to produce a vaccine but it could take months or even years to come up with one.
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