First serologic evidence of Middle East Respiratory Syndrome (MERS-CoV) infection in camels (Camelus dromedarius), Turkey

Abstract

In Turkey, camels are bred and used for various purposes such as touristic, traditional camel wrestling and transportation in the Aegean, Central Anatolia, Marmara, Mediterranean and Southeastern Anatolia regions. We examined serum samples belonging to 188 dromedary camels from 72 herds in 9 cities in Turkey for antibodies to MERS-CoV using indirect ELISA. 52.7% of the camel sera were seropositive for MERS-CoV and moderate levels of antibodies against MERS-CoV were detected (mean OD: 1.90 ± 0.97). This indicates that Turkish dromedary camels demonstrate a significantly high prevalence of MERS-CoV infection and follow-up studies should continue to monitor the epidemiological status of this infection in camels in Turkey.

Introduction

The Middle East Respiratory Syndrome Coronavirus (MERS-CoV) infection was first reported in humans in Saudi Arabia in June 2012 (Zaki et al., 2012). As of the end of 2021, 2578 confirmed cases of MERS-CoV infection and 888 deaths were reported by the World Health Organization across 27 countries, 12 of which are Eastern Mediterranean countries (WHO, 2021). The only case in our country was reported in a patient who died in 2014 after being transferred to Hatay from a hospital in Jeddah after getting sick in Saudi Arabia (Bayrakdar et al., 2015).

The virus circulates effectively in dromedary camels as its natural reservoir and causes only a mild infection (Widagdo et al., 2019). This infection could be sporadically transmitted from dromedary camels to humans and later between humans, though the latter is rare ((Widagdo et al., 2019; Killerby et al., 2020). However, research has found that the virus spreads more effectively among dromedary camels than among humans (Meyer et al., 2014; Müller et al., 2014; Widagdo et al., 2019). The prevalence of MERS-CoV antibodies in the general population in Saudi Arabia is less than 4%, but these antibodies were found in approximately half (~ 50%) of keepers in close contact with camels (Adney et al., 2020). Moreover, neutralizing antibodies and/or viruses were observed in natural infection induced in various species like cattle, sheep, goat, llama, and alpaca (David et al., 2018; Kandeil et al., 2019), but not in poultry (Suarez et al., 2020).

Camels are bred and used in most regions in Turkey for numerous purposes, including touristic purposes, traditional camel wrestling, and transportation (Atasoy and Özbaşer, 2014). The camel population in Western Anatolia is mostly used for camel wrestling, which is held in 60–70 places every year during winter. As one of the most interesting activities of tourism in these regions, thousands of people watch camel wrestling, including women and children (Yılmaz and Ertuğrul, 2014), and these individuals come into direct or indirect contact with camels. The current study aimed to serologically investigate the MERS-CoV infection in camels for the first time in Turkey and to determine the epidemiological status of the infection in Turkey.

Materials And Methods

Study population

We randomly took 188 serum samples from 72 herds of seemingly healthy native camels (Camelus dromedarius) that were likely older than 8 years between September 2019 and January 2022. These camels were sampled on the voluntary basis of owners from 9 cities (Antalya, Aydın, Balıkesir, Çanakkale, Denizli, İzmir, Muğla, Nevşehir, and Şanlıurfa) located in the Aegean, Central Anatolia, Marmara, Mediterranean, and Southeastern Anatolia regions of Turkey. Table 1 shows the distribution of the serum samples according to cities.

Ethical approval

The study protocol was approved by the Local Animal Ethics Committee of the Institute of Pendik Veterinary Control, İstanbul, Turkey (No.06/10.05.2019).

Indirect Enzyme-Linked Immunosorbent Assay (ELISA)

We used a commercial ELISA kit (Cat.no# RV-402310-1, Alpha Diagnostic International, USA) for the detection of MERS-CoV-specific antibodies in accordance with the manufacturer’s instructions. We first prepared a stock dilution of 1:10 in sample diluent and then tested all the samples in a 1:200 dilution prepared using 1:10 stock in low NSB diluent to reduce non-specific binding. We used 4 calibrators as 1U/ml, 2.5 U/ml, 5 U/ml, and 10 U/ml when performing the test. Seropositivity was calculated based on the OD₄₅₀ value of the first calibrator.

Data analysis

Descriptive statistics are given as frequency and percentage. Pearson’s chi-squared test was performed to compare the seroprevalence of MERS-CoV between different cities. The statistical significance level was accepted as p<0.05 All statistical analyses were performed using the IBM SPSS Statistics for Windows, Version 23.0 (Armonk, NY:IBM Corp.).

Results

A total of 52.7% of the camel sera (99/188) were seropositive for MERS-CoV and the remaining 47.3% were seronegative (89/188) (Figure 1). The seroprevalence was highest in Nevşehir (78.6%), followed by Balıkesir (75.0%), Şanlıurfa (66.7%), Aydın (55.7%), İzmir (52.5%), Muğla (50.0%), Antalya (45.0%), Çanakkale (25.0%), and Denizli (23.1%) (Table 1).

The differences between the cities in terms of seroprevalence rates were not statistically significant (p=118). Also, moderate levels of antibodies against MERS-CoV were detected (mean OD: 1.90±0.97).

Discussion

In the current study, we detected MERS-CoV-specific antibodies in 99 (52.7%) of 188 camels sampled from different cities in Turkey over a period of about 3 years. Seroepidemiological studies on dromedary camels have reported seroprevalence rates ranging from 0 to 100.0% (Reusken et al., 2013; Corman et al., 2014; Meyer et al., 2014; Chan et al., 2015; Crameri et al., 2015; Liu et al., 2015; Wernery et al., 2015). Some studies found no seropositivity among Bactrian camels in Mongolia, so the authors believed that this breed might not be susceptible to infection (Chan et al., 2015; Liu et al., 2015). However, Bactrian (41.0%) and hybrid breed (55.0%) camels in Dubai demonstrated MERS-CoV-specific antibodies, suggesting that Bactrian camels could be a potential source of infection (Lau et al., 2020). The present study revealed that Turkish dromedary camels had a high prevalence of MERS-CoV infection, in parallel with previous research (Corman et al., 2014; Meyer et al., 2014; Wernery et al., 2015; Sitawa et al., 2020). Moreover, numerous studies have reported that MERS-CoV seropositivity increases with age (Meyer et al., 2014; Wernery et al., 2015; Sitawa et al., 2020). It is likely that the high prevalence in our sample could be associated with the advanced age of the camels (< 8 years).

In this study, the seroprevalence rates ranged from 23.1% to 78.6% between cities (Table 1). The differences between the cities in terms of seroprevalence rates were not statistically significant (p=118). Still, these differences could have stemmed from the insufficient sample size in Balıkesir, Şanlıurfa, and Muğla, or from the different herd sizes between cities.

Aside from the high seropositivity rates among camels, we did not include any case reports from humans. Unlike SARS-CoV-2, the number of MERS-CoV cases has been very low, because the infection has shown weak transmission characteristics for humans at first contact and has not presented human-to-human transmission (Suarez et al., 2020). Besides, most of the available data on the high mortality rates of MERS-CoV originated from hospitalized patients, so only the most severe clinical manifestations might have been observed. This hypothesis was further strengthened by a 2015 cohort study on a Saudi Arabian population, where the mortality rate decreased to 10% (Petrosillo et al., 2020). Moreover, previous research has highlighted that the MERS-CoV infection alone may not be fatal in humans and that some risk factors like diabetes mellitus, heart disease, smoking, and other respiratory infection have contributed to fatal outcomes (Alraddadi et al., 2016; Alfaraj et al., 2017; Widagdo et al., 2019). However, given the high fatality rates (~36%) among humans (WHO, 2021), it should not be ignored that high seropositivity in camels could still pose a risk for individuals who are in close contact with camel populations.

Our findings indicate that MERS-CoV antibodies are quite common in dromedary camels in Turkey. Follow-up studies should continue to monitor the epidemiological status of the infection in camels in Turkey. Furthermore, planning a seroepidemiological research on individuals who are in close contact with camels would make significant contributions for displaying the epidemiology of this infection in Turkey.

Declarations

Acknowledgements

This study was supported by the General Directorate of Agricultural Research and Policies, Ministry of Agriculture and Forestry, Republic of Turkey (Project No.TAGEM/HSGYAD/Ü/21/A5/P1/3901).

Data availability

All data generated or analyzed during this study are included in this published article and its additional files.

Code availability

Not applicable

Author contributions

ZP and VSA contributed significantly to the content and design of the work. VSA prepared the original draft and writing/proofreading; ZP performed the laboratory testing, PA analysed statistically all data and, KG organised the sampling on the field. All authors have read and approved to final version of the manuscript.

Conflict of interest

The authors declare that they have no conflict of interest.

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Tables

Table 1. Distribution of seropositivity to the MERS-CoV.