An update from Mary Clance, MD, hospital epidemiologist: It has now been six months since the epidemic of Zika virus in South America came to the attention of U.S. public health authorities. During that time, the transmission zone has expanded northward from Brazil and now includes more than 25 countries in the Caribbean, South and Central America and Mexico. Local transmission is dependent upon two mosquito species, Aedes aegypti and albopictus, which have been established in the U.S. following importation from overseas. Both are now present in Maryland.
As of June 1, 2016, a total of 21 cases of Zika virus infection have been reported in Maryland. All were acquired in an area of known transmission outside of the U.S.
The West Nile Virus, a related Flavivirus, was imported (by humans) into the U.S. in 1999, and has since become established even though the vector mosquito (Culex) primarily feeds on birds and is less aggressive compared to the Aedes mosquitos, which are aggressive biters that prefer humans.
Considering the magnitude of international travel in this hemisphere, urban crowding, the presence of the vector mosquito adapted to both urban and suburban environments, the fact that most human infections are asymptomatic and therefore undetected, and entry into the summer mosquito season in the northern hemisphere, it is very probable that the Zika virus will become established in the U.S.
Old-fashioned public health measures regarding control of the vector are needed. This includes the removal of stagnant water sources that are mosquito breeding sites and the selective use of pesticides for both larvae and adults. Individual vigilance and tactics to avoid exposure to and bites by mosquitos are especially important this summer.