2015–16 zika virus epidemic 2015–16 zika virus epidemic an epidemic of zika fever, caused by zika virus, began in brazil and affected other countries in the americas from april 2015 to november 2016. the world health organization (who) declared the end of the epidemic in november 2016, but noted that the virus still represents "a highly significant and long term problem". it is estimated that 1.5 million people were infected by zika virus in brazil, with over 3,500 cases of infant microcephaly reported between october 2015 and january 2016. the epidemic also affected other parts of south and north america, as well as several islands in the pacific. 2015–16 zika virus epidemiccountries and territories with active transmission of the zika virus november 21, 2016dateapril 2015 – november 2016 zika virus spread to brazil from oceania in 2013 or 2014. brazil notified the who of an illness characterized by skin rash in march 2015, and zika was identified as the cause in may 2015. in february 2016, the who declared the outbreak a public health emergency of international concern as evidence grew that zika can cause birth defects as well as neurological problems. the virus can be transmitted from a pregnant woman to her fetus, and can cause microcephaly and other severe brain anomalies in the infant. zika infections in adults can result in guillain–barré syndrome. in approximately one in five cases, zika virus infections result in zika fever, a minor illness that causes symptoms such as fever and a rash. prior to the outbreak, zika was considered a mild infection, as most infections are asymptomatic, making it difficult to determine precise estimates of the number of cases. the virus is spread mainly by the aedes aegypti mosquito, which is commonly found throughout the tropical and subtropical americas. it can also be spread by the aedes albopictus ("asian tiger") mosquito, which is distributed as far north as the great lakes region in north america. people infected with zika can transmit the virus to their sexual partners. a number of countries were issued travel warnings, and the outbreak was expected to reduce tourism significantly. several countries took the unusual step of advising their citizens to delay pregnancy until more was known about the virus and its impact on fetal development. furthermore, the outbreak raised concerns regarding the safety of athletes and spectators at the 2016 summer olympics and paralympics in rio de janeiro. epidemiology number of zika cases, 2015–16 country autochthonous cases imported cases total cases deaths confirmed suspected africa angola 2 2 cape verde 27,457 7,459 guinea-bissau 10 10 madagascar 11 réunion 22 south africa 11 americasconfirmedsuspectedimportedtotaldeaths anguilla 744152 antigua and barbuda 143932409 argentina 261,821271,874 aruba 286147649 bahamas 21 324 barbados 37653 690 belize 49537 586 bermuda 55 bolivia 1297184851 bonaire 60 60 brazil 109,596200,465 310,0616 canada 374374 cayman islands 2920110240 chile 2929 colombia 8,82696,546 105,372 costa rica 1,4532,618324,103 cuba 3 3033 curaçao 820 820 dominica 791,150 1,229 dominican republic 3274,893 5,220 ecuador 8122,722153,549 el salvador 5111,353 11,404 french guiana 4839,7001010,193 grenada 108314 422 guadeloupe 37930,845 31,224 guatemala 4662,785 3,251 guyana 6 6 haiti 52,955 2,960 honduras 29831,863 32,161 jamaica 1867,052 7,238 martinique 1236,680 36,692 mexico 6,642 156,657 nicaragua 2,044 32,047 panama 5172,089422,648 paraguay 12583 595 peru 145 18163 puerto rico 34,070 12134,1915 saba 9 9 saint barthélemy 61900 961 saint kitts and nevis 26532 558 saint lucia 50822 872 saint martin 2002,825 3,025 saint vincent and the grenadines 38156 194 sint eustatius 16 16 sint maarten 62168 230 suriname 7232,755 3,4784 trinidad and tobago 643 1644 turks and caicos islands 121153130 united states 236 5,5905,826 uruguay 11 venezuela 2,38059,147 61,527 british virgin islands 3851 89 u.s. virgin islands 60380321,408 asiaconfirmedsuspectedimportedtotaldeaths china 2323 hong kong 11 israel 99 japan 77 malaysia 8 210 maldives 1 1 myanmar 11 philippines 39 645 singapore 435 1436 south korea 1414 taiwan 1313 thailand 680 6803 vietnam 141 141 europeconfirmedsuspectedimportedtotaldeaths austria 11 canary islands 33 czech republic 44 denmark 44 finland 22 france 1,0711,071 germany 5656 ireland 1515 italy 6363 madeira 22 malta 11 netherlands 9595 norway 3030 poland 22 portugal 1717 romania 33 russia 99 slovakia 11 slovenia 11 spain 297297 sweden 22 switzerland 2828 united kingdom 244244 oceaniaconfirmedsuspectedimportedtotaldeaths american samoa 547067767 australia 7676 fiji 17 17 kosrae (fsm) 1282 94 marshall islands 234 36 nauru 1 1 new caledonia 73 73 new zealand 9797 papua new guinea 6 6 samoa 10 10 solomon islands 302 302 tonga 362,010 2,046 vanuatu 1 1 totalconfirmedsuspectedimportedtotaldeaths worldwide 174,667528,1578,557711,38118 numbers shown do not include infant deaths or stillbirths. in 2015, brazil estimated a minimum of 497,593 and a maximum of 1,482,701 cases. "protocolo de vigilância e resposta à ocorrência de microcefalia" (pdf). emergência de saúde pública de importância nacional (in portuguese). ministério da saúde, secretaria de vigilância em saúde. january 22, 2016. p. 17. as early as august 2014, physicians in natal, in northeastern brazil began to investigate an outbreak of illness characterized by a flat pinkish rash, bloodshot eyes, fever, joint pain and headaches. while the symptoms resembled dengue fever, testing ruled out this and several other potential causes. by march 2015, the illness had spread to salvador, bahia and had appeared in three different states. then, in may 2015, researchers from the federal university of bahia and the evandro chagas institute determined, using the rt-pcr technique, that the illness was an outbreak of zika virus. although, the first confirmed zika virus infection in brazil were diagnosed in a returning traveller in march 2015. the uganda virus research institute conducts research near the zika forest from which the virus takes its name. the zika virus was first isolated in 1947, in a rhesus monkey in a forest near entebbe, uganda. although serologic evidence indicated additional human exposure during subsequent decades in parts of africa and asia, before the 2007 yap islands zika virus outbreak, only 14 cases of human zika virus disease had been documented. researchers generally believe the virus was brought to brazil by an infected traveler who had been exposed to the virus in french polynesia, who was then bitten by a mosquito that then infected others. phylogenetic analysis of the first brazilian infections have strongly indicated that the circulating virus is the asian, rather than african, strain of the virus, and was genetically similar to the virus found in the outbreak in french polynesia. it appears zika's route – from africa and asia to oceania and then the americas – may mirror that of chikungunya and dengue, both of which are now endemic in a large portion of the americas. the specific event that brought the virus to brazil was uncertain until march 2016. brazilian researchers had suggested that the zika virus arrived during the 2014 fifa world cup tournament. french researchers speculated the virus arrived shortly afterwards, in august 2014, when canoeing teams from french polynesia, new caledonia, easter island, and the cook islands, which had been or were experiencing zika outbreaks, attended the va'a world sprint championships in rio de janeiro. however, the outbreak in french polynesia is known to have peaked and declined precipitously by february 2014, lending doubt to the suggestion the virus arrived later that year in brazil with spectators and competitors. in march 2016, a study published in science, which developed a "molecular clock" based on the count of virus mutations in a relatively small sample, suggested zika virus arrived in the americas (most likely in brazil) from french polynesia between may and december 2013, well before the world cup and va'a championships. in the science article, faria and colleagues managed to trace the origins of the virus strain that is circulating in brazil and found that this strain has little genetic variability when compared to the strain of french polynesia; after relating the number of travellers arriving in brazil from french polynesia with the cases reported and the events happening in that year, the team was able to deduce that the virus arrived in brazil in 2013 during the confederation cup, when tahiti's team played against other teams in a few brazilian cities, which attracted many tourists from both places. zika virus usually has very mild, or no symptoms, so it took almost a year for brazil to confirm the first case of the disease. by then the outbreak was already widespread. factors associated with the rapid spread of zika virus in brazil include the non-immune population, high population density, tropical climate and inadequate control of aedes mosquitoes in the country. the zika virus epidemic also revealed structural problems of the health system, in particular in public health services and basic sanitation in brazil. the above average warm temperatures of 2015–2016 caused by a strong el nino created an environment conducive to the spread of the zika virus in brazil. the 2015 -16 el nino increased ocean and ground surface temperatures to above average . january 2016 brought about nine consecutive months with temperatures 1.04 °c above the global average. it is important to note, however, that while south america had areas experiencing 2.0 °c above average temperatures (for 1981–2010), areas including argentina, southern brazil and uruguay experienced temperatures 0.5 °c below average. precipitation is another crucial factor to consider as eastern brazil and other areas in southern south america experienced high amounts of precipitation in early 2016. the environmental conditions of increased rainfall and higher average temperatures in the south american region, lead to both a longer mosquito season and a higher mosquito density which created an environment in which the zika carrying aedes aegypti and aedes albopictus mosquitoes can thrive. looking forward, climate models suggest that regions favorable to the aedes mosquitoes will grow, widening the range of zika and other mosquito-carried diseases. the potential for epidemics will spread inland and into other regions of the world, not just in tropical environments. confirmed cases have been reported in 40 countries or territories in south america, north america, and the caribbean, as well as 16 in the western pacific and one in africa since the beginning of 2015 (see table). many countries with no cases of mosquito transmission have reported travel-related zika cases: people who moved or came home from a zika-affected region before they showed symptoms (see table). transmission