Widespread circulation of West Nile virus, but not Zika virus in southern Iran

Abstract

West Nile virus (WNV) and Zika virus (ZIKV) are mosquito-borne viral infections. Over the past few decades, WNV has been associated with several outbreaks involving high numbers of neuroinvasive diseases among humans. The recent re-emergence of ZIKV has been associated with congenital malformation and also with Guillain–Barre syndrome in adults. The geographic range of arthropod-borne viruses has been rapidly increasing in recent years. The objectives of this study were to determine the presence of IgG specific antibodies and the genome of WNV and ZIKV in human samples, as well as WNV and ZIKV genomes in wild-caught mosquitoes in urban and rural areas of the Hormozgan province, in southern Iran. A total of 494 serum samples were tested for the presence of WNV and ZIKV IgG antibodies using ELISA assays. One hundred and two (20.6%) samples were reactive for WNV IgG antibodies. All serum samples were negative for ZIKV IgG antibodies. Using the multivariable logistic analysis, age (45+ vs. 1–25; OR = 3.4, 95% C.I.: 1.8–6.3), occupation (mostly outdoor vs. mostly indoor; OR = 2.4, 95% C.I.: 1.1–5.2), and skin type(type I/II vs. type III/IV and type V/VI; OR = 4.3, 95% C.I.: 1.7–10.8 and OR = 2.7, 95% C.I.: 1.3–5.5 respectively, skin types based on Fitzpatrick scale) showed significant association with WNV seroreactivity. We collected 2,015 mosquitoes in 136 pools belonging to 5 genera and 14 species. Three pools of Culex pipiens complex were positive for WNV RNA using real-time reverse transcription polymerase chain reaction (rtRT-PCR). ZIKV RNA was not detected in any of the pools. All WNV ELISA reactive serum samples were negative for WNV RNA. In conclusion, we provided evidence of the establishment of WNV in southern Iran and no proof of ZIKV in serum samples or in mosquito vectors. The establishment of an organized arbovirus surveillance system and active case finding strategies seems to be necessary.

Author summary

In recent decades mosquito-borne viruses have reached and adapted to new habitats, and now they can be found in nearly all continents. Facilitated goods transportation, live stock exchange, people travelling more easily, and most importantly world climate alterations, might be some of the reasons for this mosquito habitat spreading. Emergence of WNV in North America, Europe, and most Mediterranean countries like Turkey, Greece and Israel is evidence of this spreading. Furthermore, emergence and re-emergence of some of these mosquito borne viruses in new areas may be accompanied with changes in their pre-known pathogenesis. Re-emergence of ZIKV in the South Pacific and America from 2007 to 2016 was accompanied with an increase in neurovirulent diseases and congenital malformations. In this study, we evaluated the presence of WNV and ZIKV via serological and genome detection in human samples and mosquitoes (viral genome analysis) from southern Iran. This region is on the coast with a warm and tropical climate suitable for inhabitation and expansion of the vectors harboring these two viruses. We caught a large spectrum of mosquitoes from these areas. After classification, we analyzed the mosquitoes’ pools for WNV and ZIKV genomic RNA. Our results showed that 20.6% of the studied human samples were IgG reactive to WNV while no antibodies against ZIKV were detected. We found WNV RNA genome in three mosquitoes’ pools. The genomic analysis was negative for ZIKV in both human and mosquito samples. Based on the results WNV is notably circulating in southern Iran; while no evidence of ZIKV infection in people or circulation in any of the vectors was observed.