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Abstract
Zika virus (ZIKV) has recently caused a large epidemic in the Americas that is associated
with birth defects. Although ZIKV is primarily transmitted by Aedes mosquitoes, ZIKV
RNA is detectable in blood and semen of infected individuals for weeks or months,
during which sexual and other modes of transmission are possible. However, viral RNA
is usually detectable longer than infectious virus is present. We determined the frequency
of isolation of infectious virus from semen and serum samples prospectively obtained
from a cohort of patients in Puerto Rico. We confirmed isolation of infectious virus
on the basis of a tissue culture cytopathic effect, an increase in virus genome copy
equivalents (GCE), and positive results of immunofluorescence analysis; virus in infected
cells was quantitated by flow cytometry. These criteria confirmed the presence of
infectious virus in semen specimens from 8 of 97 patients for up to 38 days after
initial detection when virus loads are >1.4 × 106 genome copy equivalents/mL. Two
serum isolates were obtained from 296 patients. These findings can help guide important
prevention guidelines for persons that may potentially be infectious and transmit
ZIKV sexually.