Rapid spread of emerging Zika virus in the Pacific area

Zika virus (ZIKV) is an emerging arthropod-borne virus (arbovirus) belonging to the family Flaviviridae and genus Flavivirus. ZIKV was first isolated from a monkey in the Zika forest of Uganda in 1947 [1Kirya BG A yellow fever epizootic in Zika Forest, Uganda, during 1972: Part 1: virus isolation and sentinel monkeys.Trans R Soc Trop Med Hyg. 1977; 71: 254-260Abstract Full Text PDF PubMed Scopus (31) Google Scholar]. Subsequently, sporadic human infections were reported in Africa and Asia. In 2007, the first large documented ZIKV outbreak was reported from Yap State, Federated States of Micronesia [2Duffy MR Chen TH Hancock WT et al.Zika outbreak on Yap Island, Federated States of Micronesia.N Engl J Med. 2009; 360: 2536-2543Crossref PubMed Scopus (2166) Google Scholar]. No further transmission was identified in the Pacific until October 2013, when French Polynesia (FP) reported the first cases; a subsequent explosive outbreak resulted in an estimated 28 000 cases seeking medical care (approximately 11% of the population) [3Cao-Lormeau VM Roche C Teissier A et al.Zika virus, French Polynesia, South Pacific, 2013.Emerg Infect Dis. 2014; 20: 1084-1086Crossref Scopus (662) Google Scholar, 4Besnard M Lastère S Teissier A et al.Perinatal transmission of Zika virus, French Polynesia.Euro Surveill. 2014; 19 (pii: 20751)Crossref PubMed Scopus (590) Google Scholar]. Phylogenetic analyses demonstrated that the FP strain was closely related to Cambodia 2010 and Yap State 2007 strains, corroborating previous findings of the expansion of the ZIKV Asian lineage [3Cao-Lormeau VM Roche C Teissier A et al.Zika virus, French Polynesia, South Pacific, 2013.Emerg Infect Dis. 2014; 20: 1084-1086Crossref Scopus (662) Google Scholar]. During the FP outbreak, most clinical cases presented with mild disease characterized by low-grade fever, maculopapular rash, arthralgia, and conjunctivitis. In November, a patient presented with Guillain-Barre syndrome (GBS), an autoimmune disease causing acute or subacute flaccid paralysis, 1 week after a confirmed acute ZIKV infection [5Oehler E Watrin L Leparc-Goffart I et al.Zika virus infection complicated by Guillain–Barré syndrome—case report, French Polynesia, December 2013.Euro Surveill. 2014; 19 (pii: 20720)Crossref PubMed Google Scholar]. Subsequent GBS cases were identified, correlating temporally with the ZIKV outbreak. The incidence rate of GBS cases during the ZIKV outbreak was approximately 20-fold higher than expected given the size of the FP population and the established incidence rates of GBS (1-2/100 000 population per year) [6Sejvar JJ Baughman AL Wise M et al.Population incidence of Guillain–Barré syndrome: a systematic review and meta-analysis.Neuroepidemiology. 2011; 36: 123-133Crossref PubMed Scopus (499) Google Scholar]. No severe disease resulting from ZIKV infection had been reported prior to the FP outbreak, but previous clinical characterization was based on a limited number of confirmed cases. The recent temporal and spatial association between the FP ZIKV outbreak and the highly unusual GBS cluster is very suspicious, but does not confirm ZIKV as the antigenic stimulus predisposing to this autoimmune disease. ZIKV is transmitted by the bite of infected mosquitoes, and has been isolated from several Aedes mosquito species [7Grard G Caron M Mombo IM et al.Zika virus in Gabon (Central Africa)—2007: a new threat from Aedes albopictus?.PLoS Negl Trop Dis. 2014; 8: e2681Crossref PubMed Scopus (499) Google Scholar], notably Aedes aegypti, which is widespread in the tropics and subtropics, and Aedes albopictus, which is established in many parts of Europe, especially in Mediterranean countries. In FP, Aedes polynesiensis is also suspected to contribute to ZIKV transmission. Non-vector borne ZIKV transmission through sexual intercourse [8Foy BD Kobylinski KC Chilson Foy JL et al.Probable non-vector-borne transmission of Zika virus, Colorado, USA.Emerg Infect Dis. 2011; 17: 880-882Crossref PubMed Scopus (833) Google Scholar] and perinatal transmission [4Besnard M Lastère S Teissier A et al.Perinatal transmission of Zika virus, French Polynesia.Euro Surveill. 2014; 19 (pii: 20751)Crossref PubMed Scopus (590) Google Scholar] has been reported. Given that transfusion-related ZIKV transmission is a potential risk, molecular screening was implemented in FP for blood donors during the outbreak: 2.8% of blood donors, who were asymptomatic at the time of donation, tested positive for acute ZIKV infection [9Musso D Nhan T Robin E et al.Potential for Zika virus transmission through blood transfusion demonstrated during an outbreak in French Polynesia, November 2013 to February 2014.Euro Surveill. 2014; 19 (pii: 20761)Crossref Scopus (511) Google Scholar]. Following the FP outbreak in late 2013, there were subsequent outbreaks in New Caledonia, the Cook Islands, and Easter Island [10Institut de Veille Sanitaire Bulletin hebdomadaire international du 5 au 11 Mars 2014. N°142.Available at: http://www.invs.sante.fr/Publications-et-outils/Bulletin-hebdomadaire-international/Tous-les-numeros/2014/Bulletin-hebdomadaire-international-du-5-au-11-mars-2014.-N-442Google Scholar] (Fig. 1). Because of the typically mild clinical symptoms, limited ZIKV diagnostic capacity, and overlapping clinical features of ZIKV, dengue, and chikungunya, which are also circulating in the Pacific, we believe that ongoing and undetected ZIKV transmission in other Pacific island countries, and potentially beyond, is highly probable. The observation that severe clinical complications may occur highlights the need to strengthen surveillance for this emerging virus, and, in the event of a ZIKV outbreak, establish rigorous clinical monitoring to detect GBS or other unusual clinical manifestations. The authors declare no conflicts of interest.