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Table of Contents
Year : 2019  |  Volume : 56  |  Issue : 3  |  Page : 263-267

Seroprevalence of West Nile virus in Khuzestan province, southwestern Iran, 2016–2017

1 Biology Department, Payame Noor University, Tehran, Iran
2 Research Center for Emerging and Reemerging Infectious Diseases; Department of Arboviruses and Viral Hemorrhagic Fevers (National Reference Laboratory), Pasteur Institute of Iran, Tehran, Iran
3 Department of Arboviruses and Viral Hemorrhagic Fevers (National Reference Laboratory), Pasteur Institute of Iran, Tehran, Iran
4 Health Research Institute, Infectious and Tropical Diseases Research Center, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
5 Health Research Institute, Laboratory Health Center, Faculty of Medicine, Ahvaz, Iran

Date of Submission14-Jul-2018
Date of Acceptance14-Jun-2019
Date of Web Publication09-Jul-2020

Correspondence Address:
Dr Mehdi Fazlalipour
Department of Arboviruses and Viral Hemorrhagic Fevers (National Reference Laboratory), Pasteur Institute of Iran, 69 Pasteur Ave, Postcode: 1316943551, Tehran
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-9062.289391

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Background & objectives: West Nile virus (WNV) is a neurotropic Flavivirus transmitted to humans through mosquito bites. As there is no specific antiviral treatment or approved vaccine against WNV, control and prevention of the infection is the best strategy to reduce the burden of WNV-related diseases. The circulation of WNV has been indicated in several regions of Iran including the Khuzestan province. Considering the complex ecology of WNV, the latest data are necessary for the implementation of preventive measures. Therefore, the present study was designed to provide updated information on the seroepidemiology of WNV in Khuzestan province.
Methods: A total of 408 sera were taken from volunteers living in Khuzestan. The presence of specific immunoglobulin G (IgG) antibody against WNV was tested by the enzyme-linked immunosorbent assay (ELISA) method. All the data and participants’ demographic information were analyzed by SPSS and Esri’s ArcMap GIS software programs.
Results: Anti-WNV IgG antibody was detected in 97 (23.8%) out of the 408 tested sera. The highest seropositivity rate was observed in cases aged between 20–29 yr and the lowest seropositivity rate was seen in those <19 yr of age (p = 0.001). There was no statistically significant association between WNV infection and gender, occupation, and educational level. The majority of positive cases were from the city of Ahvaz (47 cases, 48.4%) and Andimeshk (32 cases, 33%).
Interpretation & conclusion: This study supports the earlier findings suggesting the circulation of WNV in Khuzestan province. Therefore, the implementation of an integrated surveillance system and training of health care workers and general population regarding the infection would be valuable to reduce the burden of possible outbreaks.

How to cite this article:
Kalantari M, Salehi-Vaziri M, Pouriayevali MH, Baniasadi V, Salmanzadeh S, Kharat M, Fazlalipour M. Seroprevalence of West Nile virus in Khuzestan province, southwestern Iran, 2016–2017. J Vector Borne Dis 2019;56:263-7

How to cite this URL:
Kalantari M, Salehi-Vaziri M, Pouriayevali MH, Baniasadi V, Salmanzadeh S, Kharat M, Fazlalipour M. Seroprevalence of West Nile virus in Khuzestan province, southwestern Iran, 2016–2017. J Vector Borne Dis [serial online] 2019 [cited 2023 Mar 31];56:263-7. Available from: http://www.jvbd.org//text.asp?2019/56/3/263/289391

  Introduction Top

West Nile virus (WNV) is an enveloped single-stranded RNA virus belonging to the genus Flavivirus, and family Flaviviridae. Since the first identification of WNV in Uganda in the late 1940s, its outbreaks and epidemics have been documented throughout the world[1]. In nature, WNV is maintained in an enzootic transmission cycle between birds and mosquitoes, mainly of the genus Culeχ2. Mammals such as humans and horses can get infected as well; however, they do not develop high titres of virus and are considered as ‘dead-end’ hosts.

Besides mosquito bites, WNV can be transmitted to humans through close contact with blood and tissues of viraemic animals, organ transplantation, breast milk, and blood transfusion[1]. In addition, vertical transmission (mother-to-child) has been indicated in one study[3]. Most human infections with WNV are asymptomatic and only 20% of infected cases develop a mild flu-like syndrome called West Nile fever. However, the severe form of the disease or WNV neuroinvasive disease (WNND) is observed in about 1 out of 150 infected individuals[4].

Since there is no specific antiviral treatment or approved vaccine against WNV infection, the implementation of continuous monitoring and surveillance studies is of great importance for the control and prevention of the infection[5]. Several lines of evidence indicate that WNV infection is endemic in Iran. Khuzestan province, in the southwest of Iran, has been reported as one of the areas where a high prevalence of antiviral antibodies has been detected in humans and horses[6],[7],[8]. Regarding the complex ecology of WNV and the fact that several factors including environmental changes can affect the epidemiology of the virus, up-to-date data are necessary for the implementation of preventive and control measures. Therefore, the present study was designed to provide updated information on the seroepidemiology of WNV in Khuzestan province.

  Material & Methods Top

This cross-sectional study was conducted between May 2016 and May 2017. A total of 408 volunteers from the general population of different cities in Khuzestan province including Ahvaz (capital city), Abadan, Ban-dar-e Emam, Behbahan, Khorramshahr, Izeh, Mahshahr, Dezful, Baq-e-Malek, Ramhormoz, and Shadegan were included in the present investigation.

Khuzestan province with an area of 63,238 km2 is located in the southwest of Iran, bordering with Iraq and some Persian Gulf countries. The climate of Khuzestan is generally hot, humid, and dry and in summer the temperature routinely exceeds 45 °C. Large and permanent rivers flow over the entire territory of the land and horse breeding centres in this province make Khuzestan a great potential area for WNV transmission among humans, birds, horses, and mosquitoes.

For the study, informed consent was obtained from all the participants visiting public health centres or laboratories for a routine checkup. Demographic data, clinical history, epidemiological data, and vaccination history were obtained by a questionnaire. Then, 10 ml whole blood was obtained by venipuncture in plain tubes (containing no coagulant), and the sera were prepared by centrifugation. The isolated sera were kept at –20 °C and then were sent to the Department of Arboviruses and Viral Hemorrhagic Fevers, Pasteur Institute of Iran, Tehran (National Reference Laboratory) in compliance with the cold chain for further analysis.

Detection of anti-WNV IgG antibody was performed using Euroimmun WNV IgG ELISA kit (Euroimmun, LuÈbeck, Schleswig-Holstein, Germany) according to the manufacturer’s instructions. The sensitivity and specificity of the kit are 99.5 and 96.9%, respectively. Positive and negative controls provided by the kit were used along with the samples. Index values >1.1 were considered positive for the WNV IgG antibody, index values between 0.8 and 1.1 were considered as equivocal results, and index values <0.8 were considered negative for anti-WNV IgG antibody.

The statistical package for social science (SPSS) software program, ver. 16.0 (SPSS Inc., Chicago, USA) was used for data analysis (using chi-square test). A two-sided p-value of <0.05 was considered statistically significant. The Esri’s ArcMap GIS ver. 10.1 was used to create the maps that outline the study area and geographic distribution of positive cases.

Ethical statement

This study was approved by the Ethics Committee of Pasteur Institute of Iran, Tehran (Ethical registry no. IR.PII.REC.1394.32), and written informed consent was obtained from all the subjects.

  Results Top

Demographic characteristics

Of the 408 enrolled subjects (mean age: 29.81 ± 8.88 yr, age range, 12–67 yr), 261 (64%) were male and 147 (36%) were female. None of the participants had a history of vaccination against yellow fever, tick-borne encephalitis, or Japanese encephalitis viruses.

Enzyme-linked immunosorbent assay

The results of ELISA revealed the presence of anti- WNV IgG antibody in 97 (23.8%) out of the 408 tested sera, of which 64 (66%) were male and the remaining 33 (34%) were female. No significant association between seropositivity and gender was observed in this study (p = 0.6, chi-squared test). [Figure 1] shows the age-specific prevalence of seropositivity. The highest seropositivity rate was observed in cases aged between 20–29 yr and the lowest seropositivity rate was seen in those <19 yr of age. This difference was statistically significant (p = 0.001, chi-square test).
Figure 1: West Nile virus (WNV) positive individuals in this study, stratified according to age group (p-value = 0.001).

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There was no significant association between occupation and seropositivity (p = 0.749). Additionally, no significant association between educational level and seropositivity was found (p = 0.445, chi-squared test). However, the majority of positive sera were among the cases having a diploma and under diploma degrees (40 and 36 cases, respectively).

Geographical distribution and clinical history

Sera were collected from 33 different locations in Khuzestan province. [Figure 2] depicts the geographical distribution of seropositive cases within the Khuzestan province. The majority of positive cases were from the city of Ahvaz (47 cases, 48.4%) followed by Andimeshk (32 cases, 33%). The geographical distribution of positive samples was statistically significant (p = 0.001).
Figure 2: D istribution of West Nile virus seropositivity in Khuzestan province, Iran 2016–2017.

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There was no statistically significant relationship between seropositivity and epidemiological history. Analysis of epidemiological data indicated that among positive samples, 10 (10.3%) had a mosquito bite, 6 (6.2%) had horse contact, 9 (9.3%) had bird contact, 22 (22.7%) had gone to riversides, 8 (8.2%) had received a blood transfusion or organ transplantation and 5 (5.2%) cases had a history of traveling abroad. Additionally, no statistically significant association was observed between the clinical symptoms and seropositivity. History of any clinical symptoms based on questionnaire indicated that the most frequent clinical symptoms in positive samples were headache (40.2%), fatigue (36.1%), myalgia (22.7%), fever >38 °C (21.6%), diarrhoea (18.6%), nausea (15.5%), vomiting (12.4%) and neck stiffness (12.4%). The least frequent history of clinical symptoms were chills (11.3%) and rash (9.3%) [Table 1].
Table 1: Clinical self-reported symptoms and epidemiological background in anti-West Nile virus (WNV) IgG positive cases

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  Discussion Top

In this study, which was conducted to provide up-to-date information on the epidemiology of WNV infection in Khuzestan province, a seropositivity rate of 23.8% was observed. Although most positive cases were males, there was no significant relationship between gender and WNV infection. Similar findings were observed in studies from Iran and Greek[9],[10]. However, in two studies conducted in north and southeast of Iran[11],[12], all the IgG-positive samples belonged to the male gender.

In the present study, there was a significant association between age and WNV seropositivity as nearly 76% of seropositive individuals were aged 20–39 yr. Since most cases of infection were observed in the working-age group, the result suggests a possible relationship between work activity and infection. It has been indicated that spending time outdoors is associated with WNV infection[13]. In 2015, Hadjichristodoulou et al[10] indicated that seroprevalence was associated with age in the Greek population. They observed that people older than 65 yr were more likely to be detected positive for anti-WNV IgG. In addition, in a study conducted in Zambia[14], participants aged 35– 44 yr were more likely to have the infection. Contrarily, a higher risk of WNV infection was observed among children in Ohio, USA[15]. This discrepancy could be due to differences in behaviours among populations that could affect the rate of exposure to WNV vectors.

The results of this study showed that occupation and social education cannot be considered as risk factors for WNV infection in Khuzestan province. In the present survey, 33 districts of Khuzestan province were studied, but the prevalence of infection in Ahvaz and Andimeshk was significantly higher than in other areas. This could be due to the fact that the majority of the samples were taken from these cities.

Several studies demonstrated the circulation of WNV in different parts of Iran[6],[7],[9],[11],[12],[16],[17], of which two studies had investigated the prevalence of WNV infection at the national level[6],[7]. Between 1971 and 1975, Saidi et al[7] evaluated WNV antibodies in human sera from 13 communities in seven provinces. From 2008 to 2009, Ahmadnejad et al[6] investigated WNV antibodies in equine sera from 260 communities in 27 provinces. Both aforementioned studies showed significant seropositivity in Khuzestan province.

Khuzestan province with huge wetlands can be a crossroads for migratory birds coming from endemic regions and a suitable region for mosquitos’ reproduction. Therefore, compatible areas for viral transmission may have more influence on the epidemiology of WNV in the region. Other studies, such as those of Ergunay et al[18] during 2011–2013 in Turkey (Mediterranean-Aegean regions as well as southeastern and northeastern Anatolia), Malkinson et al[19] in 1998 in southern Israel and Khoshdel Nezamiha et al[20] in 2012 in northwestern Iran[20], have reported WNV-infected mosquitoes, migratory birds, humans and other animals in geographical locations such as wetlands and humid tropics where the climatic condition provides a suitable environment for the establishment of viral transmission and existence of vectors.

In a study, Saidi et al[7] detected WNV antibodies in 65.1% (140/215) of participants from Khuzestan province, which is much higher than the rate observed in the present study (23.8%). It may be noted that Saidi et al[7] studied samples from Deiqi, Dezful, Khorousi, and Abadan, while in the present study, most samples were from Ahvaz and Andimeshk cities, two samples were from Dezful and Abadan; however, there were no sero-positive samples from Deiqi and Khorousi. Therefore, region-to-region comparison of the seroprevalence rates between these two studies is not possible.

It is noteworthy that the present study for the first time provides information on the prevalence of WNV in Ahvaz, the capital city of Khuzestan province, and Andimeshk and Bavi cities. The results of this study support the previous observations indicating the circulation of WNV in Iran. However, in comparison with other ar-boviral diseases which are endemic in the Middle–East, suspected samples for WNV infection referred to the National Reference Laboratory of Arboviruses and Viral Hemorrhagic Fevers, Pasteur Institute of Iran, are far few. This may be explained by the fact that physicians are still not well-acquainted with the disease and its circulation in the country. On the other hand, being a mild pathogen causing a self-limiting outbreak may lead to the under-diagnosis of WNV. However, some newly identified isolates of WNV appear to be especially virulent and an elevated incidence of WNND with a higher case fatality rate has been correlated with the studied isolates[12],[21].

The results of the present study may be limited because the positive results based on the ELISA test have not been confirmed by the plaque reduction neutralization test (PRNT), and this fact can increase unreal seropositivity results due to possible cross-reactivation among flaviviruses.

  Conclusion Top

The seropositivity results from the study area suggest the circulation of WNV in Khuzestan province of Iran. Since no specific antiviral treatment or licensed vaccine is currently available against WNV, the implementation of preventive measures is essential to control possible outbreaks of the disease. For this purpose, regular monitoring and surveillance investigations seem to be necessary. Physicians should also be vigilant to different aspects of WNV infection.

Conflict of interest

There is no any conflict of interest among the authors.

  References Top

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  [Figure 1], [Figure 2]

  [Table 1]

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