global health officials race good understand zika virus behind major outbreak begin brazil last year spread many countries americas follow question answer virus current outbreak people become infect zika transmit people bite infect female mosquitoes primarily aedes aegypti mosquito type spread dengue chikungunya yellow fever pan american health organization paho say aedes mosquitoes find countries americas except canada continental chile virus likely reach countries territories region aedes mosquitoes find treat zika treatment vaccine zika infection company scientists race develop safe effective vaccine zika world health organization say would take least 18 months start large-scale clinical trials potential preventative shots dangerous u.s. center disease control prevention conclude infection zika virus pregnant women cause birth defect microcephaly severe brain abnormalities baby cdc say causal relationship establish several important question must still answer study could take years accord world health organization strong scientific consensus zika cause birth defect microcephaly baby condition define unusually small head result developmental problems addition agency say could cause guillain-barre syndrome rare neurological disorder result paralysis conclusive proof damage cause zika may take months years brazil report number confirm case microcephaly 1,434 may 21 doctor brazilian health officials find suspect case microcephaly disorder suspect ones investigation decline 3,257. colombia confirm two case microcephaly link zika brazil register 91,387 likely case zika virus february april 2. current research brazil indicate great microcephaly risk associate infection first trim pregnancy health officials warn impact could see late weeks recent study show evidence zika amniotic fluid placenta fetal brain tissue symptoms zika infection people infect zika may mild fever skin rash conjunctivitis muscle joint pain fatigue last two seven days many 80 percent people infect never develop symptoms symptoms similar dengue chikungunya transmit type mosquito zika contain efforts control spread virus focus eliminate mosquito breed sit take precautions mosquito bite use insect repellent mosquito net u.s. international health officials advise pregnant women avoid travel latin american caribbean countries may expose zika case sexual transmission also report prompt health officials advise use condoms abstain sex prevent infection partner widespread outbreak active zika outbreaks report least 48 countries territories americas accord u.s. center disease control prevention cdc brazil country affect 1.usa.gov/1ovajyh africa cape verde americas 39 argentina aruba barbados belize bolivia bonaire brazil colombia costa rica cuba curaçao dominica dominican republic ecuador el salvador french guiana grenada guadeloupe guatemala guyana haiti honduras jamaica martinique mexico nicaragua panama paraguay peru puerto rico saint barthelmy saint lucia saint martin saint vincent grenadines st. maarten suriname trinidad tobago u.s. virgin islands venezuela oceania/pacific islands american samoa fiji kosrae federate state micronesia marshall islands new caledonia papua new guinea samoa tonga history zika virus zika virus find tropical locales large mosquito populations outbreaks zika record africa americas southern asia western pacific virus first identify uganda 1947 rhesus monkey first identify people 1952 uganda tanzania accord zika transmit sexual contact world health organization say sexual transmission relatively common advise pregnant women travel areas ongoing outbreaks zika virus also advise women live areas virus transmit delay get pregnant u.s. cdc investigate dozen case possible sexual transmission case involve possible transmission virus men sex partner also identify zika case argentina chile france italy new zealand likely cause sexual transmission british health officials report zika find man semen two months infect suggest virus may linger semen long infection symptoms fade paho say zika transmit blood infrequent transmission mechanism evidence zika transmit baby breast milk complications associate zika zika also associate neurological disorder include serious brain spinal cord infections long-term health consequences zika infection unclear uncertainties surround incubation period virus zika interact viruses transmit mosquitoes dengue factbox zika virus cause alarm