The World Health Organization has declared the western hemisphere's outbreak of Zika virus a global health emergency. So far the virus has spread to 20 different countries in the region, but there have been no reported cases of the disease being locally transmitted on the mainland of the United States. The Aedes species of mosquito – which also spread the dengue and chikungunya viruses – have been the main vector for the disease. The Centers for Disease Control has noted there have been reports that the virus can be spread through sexual contact.
Local Texas news media are now reporting that the Dallas County Health and Human Services department has confirmed today that a patient was infected after having sexual contact with an ill individual who returned from a country where the virus is known to be present.
This first case of U.S. zika transmission is not likely to be the last. After all, the Aedes aegypti and Aedes albopictus mosquitoes are now endemic in parts of the U.S.
Despite the current alarm, it should still be recalled that while the chikungunya virus has spread via the same mosquito vectors throughout the Caribbean since 2013, there have been very few cases of the disease being locally transmitted in the mainland United States. In addition, the last reported local outbreak of dengue fever in the U.S. occurred in South Texas in 2005. It is not inevitable that there will be a major zika outbreak in the U.S.
Virulence differs. For example, the CDC reports that there were just over 2,000 cases of West Nile virus in the lower 48 states in 2015. West Nile virus has been detected in far more mosquito species than has either zika or chikungunya virus.
One final note: If the person who is trying to seduce you has just returned from a tropical trip and is experiencing joint pain and fever, maybe you both should consider putting off sex until another time.