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Middle East respiratory syndrome coronavirus (MERSCoV) was detected in humans in 2012. Since then, sporadic outbreaks with primary transmission through dromedary camels to humans and outbreaks in healthcare settings have shown that MERS-CoV continues to pose a threat to human health. Several serologic assays for MERS-CoV have been developed globally. We describe a collaborative study to investigate the comparability of serologic assays for MERS-CoV and assess any benefit associated with the introduction of a standard reference reagent for MERS-CoV serology. Our study findings indicate that, when possible, laboratories should use a testing algorithm including >2 tests to ensure correct diagnosis of MERS-CoV. We also demonstrate that the use of a reference reagent greatly improves the agreement between assays, enabling more consistent and therefore more meaningful comparisons between results.

Summary Background Scientific evidence suggests that dromedary camels are the intermediary host for the Middle East respiratory syndrome coronavirus (MERS-CoV). However, the actual number of infections in people who have had contact with camels is unknown and most index patients cannot recall any such contact. We aimed to do a nationwide serosurvey in Saudi Arabia to establish the prevalence of MERS-CoV antibodies, both in the general population and in populations of individuals who have maximum exposure to camels. Methods In the cross-sectional serosurvey, we tested human serum samples obtained from healthy individuals older than 15 years who attended primary health-care centres or participated in a national burden-of-disease study in all 13 provinces of Saudi Arabia. Additionally, we tested serum samples from shepherds and abattoir workers with occupational exposure to camels. Samples were screened by recombinant ELISA and MERS-CoV seropositivity was confirmed by recombinant immunofluorescence and plaque reduction neutralisation tests. We used two-tailed Mann Whitney U exact tests, χ 2 , and Fisher's exact tests to analyse the data. Findings Between Dec 1, 2012, and Dec 1, 2013, we obtained individual serum samples from 10 009 individuals. Anti-MERS-CoV antibodies were confirmed in 15 (0·15%; 95% CI 0·09–0·24) of 10 009 people in six of the 13 provinces. The mean age of seropositive individuals was significantly younger than that of patients with reported, laboratory-confirmed, primary Middle Eastern respiratory syndrome (43·5 years [SD 17·3] vs 53·8 years [17·5]; p=0·008). Men had a higher antibody prevalence than did women (11 [0·25%] of 4341 vs two [0·05%] of 4378; p=0·028) and antibody prevalence was significantly higher in central versus coastal provinces (14 [0·26%] of 5479 vs one [0·02%] of 4529; p=0·003). Compared with the general population, seroprevalence of MERS-CoV antibodies was significantly increased by 15 times in shepherds (two [2·3%] of 87, p=0·0004) and by 23 times in slaughterhouse workers (five [3·6%] of 140; p Interpretation Seroprevalence of MERS-CoV antibodies was significantly higher in camel-exposed individuals than in the general population. By simple multiplication, a projected 44 951 (95% CI 26 971–71 922) individuals older than 15 years might be seropositive for MERS-CoV in Saudi Arabia. These individuals might be the source of infection for patients with confirmed MERS who had no previous exposure to camels. Funding European Union, German Centre for Infection Research, Federal Ministry of Education and Research, German Research Council, and Ministry of Health of Saudi Arabia.

BACKGROUND: Strategies to contain the Middle East respiratory syndrome coronavirus (MERS-CoV) depend on knowledge of the rate of human-to-human transmission, including subclinical infections. A lack of serologic tools has hindered targeted studies of transmission. METHODS: We studied 26 index patients with MERS-CoV infection and their 280 household contacts. The median time from the onset of symptoms in index patients to the latest blood sampling in contact patients was 17.5 days (range, 5 to 216; mean, 34.4). Probable cases of secondary transmission were identified on the basis of reactivity in two reverse-transcriptase-polymerase-chain-reaction (RT-PCR) assays with independent RNA extraction from throat swabs or reactivity on enzyme-linked immunosorbent assay against MERS-CoV S1 antigen, supported by reactivity on recombinant S-protein immunofluorescence and demonstration of neutralization of more than 50% of the infectious virus seed dose on plaque-reduction neutralization testing. RESULTS: Among the 280 household contacts of the 26 index patients, there were 12 probable cases of secondary transmission (4%; 95% confidence interval, 2 to 7). Of these cases, 7 were identified by means of RT-PCR, all in samples obtained within 14 days after the onset of symptoms in index patients, and 5 were identified by means of serologic analysis, all in samples obtained 13 days or more after symptom onset in index patients. Probable cases of secondary transmission occurred in 6 of 26 clusters (23%). Serologic results in contacts who were sampled 13 days or more after exposure were similar to overall study results for combined RT-PCR and serologic testing. CONCLUSIONS: The rate of secondary transmission among household contacts of patients with MERS-CoV infection has been approximately 5%. Our data provide insight into the rate of subclinical transmission of MERS-CoV in the home.

We investigated a case of human infection with Middle East respiratory syndrome coronavirus (MERS-CoV) after exposure to infected camels. Analysis of the whole human-derived virus and 15% of the camel-derived virus sequence yielded nucleotide polymorphism signatures suggestive of cross-species transmission. Camels may act as a direct source of human MERS-CoV infection.

SARS-coronavirus (CoV) is a zoonotic agent derived from rhinolophid bats, in which a plethora of SARS-related, conspecific viral lineages exist. Whereas the variability of virulence among reservoir-borne viruses is unknown, it is generally assumed that the emergence of epidemic viruses from animal reservoirs requires human adaptation. To understand the influence of a viral factor in relation to interspecies spillover, we studied the papain-like protease (PLP) of SARS-CoV. This key enzyme drives the early stages of infection as it cleaves the viral polyprotein, deubiquitinates viral and cellular proteins, and antagonizes the interferon (IFN) response. We identified a bat SARS-CoV PLP, which shared 86% amino acid identity with SARS-CoV PLP, and used reverse genetics to insert it into the SARS-CoV genome. The resulting virus replicated like SARS-CoV in Vero cells but was suppressed in IFN competent MA-104 (3.7-fold), Calu-3 (2.6-fold) and human airway epithelial cells (10.3-fold). Using ectopically-expressed PLP variants as well as full SARS-CoV infectious clones chimerized for PLP, we found that a protease-independent, anti-IFN function exists in SARS-CoV, but not in a SARS-related, bat-borne virus. This PLP-mediated anti-IFN difference was seen in primate, human as well as bat cells, thus independent of the host context. The results of this study revealed that coronavirus PLP confers a variable virulence trait among members of the species SARS-CoV, and that a SARS-CoV lineage with virulent PLPs may have pre-existed in the reservoir before onset of the epidemic.