Uptick in lab-confirmed seroprevalence of MERS infections 

A large study tracing levels of the MERS-CoV virus in the blood serum of a population in western Saudi Arabia over five years has revealed that asymptomatic or mild infections are still lurking and possibly being silently exported. 

Middle East Respiratory Syndrome Coronavirus (MERS-CoV), the virus behind MERS, was first identified in a pneumonic patient in Saudi Arabia in 2012. In 2015, the kingdom experienced a major MERS outbreak of 2,077 infections and 773 deaths, a toll that was reported by the World Health Organisation to be the worst worldwide. 

The outbreak resulted in hospital shutdowns and an eventual increase in research into the then-novel coronavirus and its only proven reservoir animal, the dromedary camel, to trace its epidemiology and explore therapeutic paths. Since then, scientists have been trying to get to the root of how sporadic community cases crop up and spread. 

In this new study, researchers at KAIMRC sifted through thousands of archived human blood sera collected between 2011 and 2016 from healthy adult donors of 50 nationalities inhabiting the Western part of Saudi Arabia. 

Their goal was to “search for traces of positivity,” according to Mohammad Bosaeed, a coronavirus researcher at KAIMRC and an infectious diseases consultant at the Ministry of National Guard Health Affairs, who was not involved in the study. “The researchers tried to see if there are camel handlers, for instance, who had zero positivity, comparing them with other people in the population who didn’t have any camel exposure,” he explains. 

The scientists examined the blood samples for MERS-CoV S1-specific antibodies, using ELISA, an immunological assay designed to detect and quantify antibody content in response to an antigen. They also confirmed the results by testing for neutralizing antibodies using neutralization tests on both live viruses and pseudotypes, which are clinical surrogates of the live virus.

The ELISA test was positive in about 2.3% of the 7,461 samples, spanning 18 nationalities, while neutralizing antibodies were confirmed in 17 samples. Seroprevalence—the level of the virus as detected in blood samples—was greatest in people aged 15 – 44 from Saudi Arabia, Egypt, Yemen, Pakistan, Palestine, Sudan, and India without significant preference.

Seroprevalence was greater  in males than females, despite slightly increasing prevalence in both sexes over time. “There’s a big difference between males and females, which is related to exposure and contact with proxies, like husbands who might be camel handlers and deal with the animals,” says Bosaeed. “Risks increase when the person is dealing with the meat of the animals as well.” 

Bosaeed says the slight increase in serum positives, including in females, is not a cause for worry. “After 2016, we’re doing well in terms of knowing how to deal with the virus and taking measures against it,” he adds. 

Nevertheless, the study authors recommend “enhanced and continuous surveillance” to monitor the transfer of potentially positive MERS-CoV cases inside and outside the kingdom through general travel or camel trade.

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