Cross-sectional prevalence study of MERS-CoV in local and imported dromedary camels in Saudi Arabia, 2016-2018

The Middle East Respiratory Syndrome-Coronavirus (MERS-CoV) is an endemic virus in Middle Eastern and African dromedaries. Annually, Saudi Arabia imports thousands of camels from the Horn of Africa, yet the epidemiology of the virus in these animals is largely unknown. Here, MERS-CoV prevalence was compared in imported African camels and their local counterparts.

A total of 1399 paired sera and nasal swabs were collected between 2016 and 2018 from camels from Sudan (n = 829), Djibouti (n = 328) and Jeddah (n = 242). Imported animals were sampled on incoming ships at Jeddah Islamic seaport before unloading. Samples were screened for neutralizing antibodies (nAbs) and MERS-CoV viral RNA by RT-PCR.

The overall seroprevalence was 92.7% and RNA detection rate was 17.2 %. Imported camels had higher seroprevalence compared to resident herds (93.8% vs 87.6%, p  < 0.01) in contrast to RNA detection (13.3% vs 35.5%, p  < 0.0001). Seroprevalence significantly increased with age (p  < 0.0001) and viral RNA detection rate was ∼2-folds in camels < 2-year-old compared to older camels. RNA detection was higher in males verses females (24.3% vs 12.6%, p  < 0.0001) but seroprevalence was similar. Concurrent positivity for viral RNA and nAbs was found in > 87 % of the RNA positive animals, increased with age and was sex-dependent. Importantly, reduced viral RNA load was positively correlated with nAb titers.

Our data confirm MERS-CoV widespread in imported and domestic camels in Saudi Arabia and highlight the need for continuous active surveillance and better prevention measures. Further studies are also warranted to understand the correlates of protection in camels for proper vaccine development.