Asymptomatic MERS-CoV Infection in Humans Possibly Linked to Infected Dromedaries Imported from Oman to United Arab Emirates, May 2015.

In May 2015 in United Arab Emirates, asymptomatic Middle East respiratory syndrome coronavirus infection was identified through active case finding in 2 men with exposure to infected dromedaries. Epidemiologic and virologic findings suggested zoonotic transmission. Genetic sequences for viruses from the men and camels were similar to those for viruses recently detected in other countries.

sampling were analyzed by dideoxy sequencing as previously described (13); the nucleocapsid gene sequences of all dromedary samples were found to be identical. Samples from dromedaries ADFCA-HKU1-3 were selected for further analysis, and a sequence contig encompassing the 3′ end of the ORF1AB gene through the 3′ untranslated region of the MERS-CoV genome (≈8,900 nt; sequence coverage 4) was obtained from each sample. Contigs from the 3 samples were identical, with the exception of a V221I (GTT→ATT) mutation in the ORF4b protein of the sample from dromedary ADFCA-HKU2. The viral RNA content of the 2 human samples available for analysis was too low to provide long PCR amplicons (cycle threshold 35.5 and 36.9 by upstream of E gene assay). However, partial sequences of MERS-CoV spike (466 nt, contacts 1 and 2), ORF3-4a (273 nt, contact 1), and nucleocapsid (451 nt, contacts 1 and 2) gene regions could be detected from the samples. All of these sequences were identical to those deduced from the dromedary specimens. Genomic sequences determined from this study were submitted to GenBank (accession nos. KT275306-KT275315).
The 3 sequence contigs obtained from the dromedary samples were phylogenetically closely related to those of viruses detected in humans in the Saudi Arabia, China, and South Korea in 2015 ( Figure). All sequences from this cluster, together with the partial ORF3-4a sequence detected in the sample from contact 1, shared 2 cluster-specific mutations, 79S (TCA→TCT) and P86L (CCT→CTT), in the ORF3 protein, suggesting that these viruses may share a common lineage. Apart from the unique V221I mutation, the sequences for viruses from the 3 dromedaries shared a unique ORF4a-Q102E (GAG→CAG) mutation that was not found in any published MERS-CoV genomes. Other than those mutations, All 8 dromedaries were found to be RT-PCR positive for MERS-CoV and were quarantined in a separate structure located at the same border location. Active surveillance of persons with direct or indirect contact with the infected dromedaries was initiated. A sputum sample was obtained from contact 1; it tested positive for MER-CoV by RT-PCR on 12 May, 2015. 12 A sample obtained from contact 1 on May 10 tested positive for MERS-CoV by RT-PCR; contact 1 was hospitalized in a negative-pressure room. 13 A follow-up sample was obtained from contact 1, and it tested positive for MERS by RT-PCR. † 14 A follow-up sample was obtained from contact 1, and it tested positive for MERS by RT-PCR. A nasal aspirate sample was obtained from contact 2; it tested positive for MERS by RT-PCR on May 17. † Samples were obtained from the infected dromedaries, and 5 were still MERS-CoV-positive by RT-PCR (Table 2). † 17 A sample obtained from contact 2 on May 14 tested positive for MERS-CoV by RT-PCR. 18 Contact 2 was admitted to a negative-pressure room in the same hospital as contact 1. Follow-up samples were obtained from contacts 1 and 2, and they tested negative for MERS-CoV by RT-PCR. 20 A follow-up sample was obtained from contact 2, and it tested negative for MERS-CoV by RT-PCR. 21 A follow-up sample was obtained from contact 2, and it tested negative for MERS-CoV by RT-PCR. 25 Follow-up samples from the 5 dromedaries tested negative for MERS-CoV by RT-PCR. All dromedaries were released from quarantine. End of month ‡ Contacts 1 and 2 were released uneventfully from the hospital.  all of the ORFs (nonstructural protein 13, spike, ORF3, ORF5, envelope, membrane, nucleocapsid, and ORF8b) of these virus sequences were unremarkable.

Conclusions
We report 2 cases of MERS-CoV infection in men who had direct contact with the same group of infected dromedaries. Neither man had a concurrent medical condition or a history of exposure to human MERS cases in the 14 days before their first MERS-CoV-positive test results. Genomic sequences for the viruses derived from the men and dromedaries and findings from the epidemiologic investigation suggest possible zoonotic transmission of MERS-CoV from dromedaries to humans. Although it is unlikely, we cannot exclude the possibility that the men and dromedaries were independently infected by other sources. Both infected humans were kept in the hospital for ≈2 incubation periods and were asymptomatic during this period. Clinical observations and positive RT-PCR results suggest that the men were asymptomatically infected with MERS-CoV. Asymptomatic infections have been detected previously (14). Our findings provide further evidence that asymptomatic human infections can be caused by zoonotic transmission. It is not clear whether asymptomatic infection can lead to transmission between humans. Nonetheless, our findings highlight the importance of systematic surveillance of persons who have frequent contact with dromedaries. A recent study demonstrated that persons who have frequent exposure to camels are more likely than the general population to be seropositive for MERS-CoV (4). The unique border screening program and multisectoral collaborations highlighted in this investigation serve as a model for effective MERS-CoV surveillance at the animal-human interface.
Our study had some limitations. We did not test serum samples from the human contacts; such testing would be of interest for follow-up investigation of the patients' serologic responses. We also obtained limited RNA samples from these persons, which prevented us from conducting more extensive viral sequence analyses.
MERS-CoV genomic sequences determined in this study are similar to those of viruses detected in 2015 in patients in Saudi Arabia and South Korea with hospitalacquired infections. The infected dromedaries in this study were imported from Oman, which suggests that viruses from this clade are widely circulating on the Arabian Peninsula. Sequence analyses of MERS-CoVs found in South Korea and China do not suggest that viruses from this clade are necessarily more transmissible variants (15). However, given that a single introduction of MERS-CoV from this clade caused >180 human infections in hospital settings (2) and that viruses of this clade are causing other human infections in Saudi Arabia, further phenotypic risk assessment of this particular MERS-CoV clade should be a priority.
The sequence analyses and serologic work were partly funded by a research contract from the National Institute of Allergy and Infectious Diseases, National Institutes of Health (contract no. N272201400006C), and by a grant from Area of Excellence Scheme, University Grants Committee of the Hong Kong Special Administrative Region (no. AoE/M-12/06). Nasal aspirate sample taken from Contact 2 on 14 May, 2015, was found to be RT-PCR positive for MERS-CoV. He reported no symptoms at that time. He was admitted to a negative pressure room in a hospital for close monitoring and quarantine. At the time of his admission, his temperature was 36.9C, his heart rate was 77 beats per minute, his respiratory rate was 16 breaths per minute, and his blood pressure was 132/91 mmHg. The patient did not report any history of comorbid conditions such as cardiovascular diseases, diabetes, chronic pulmonary diseases, rheumatic diseases, liver diseases, renal diseases, or malignant disorders. The patient was interviewed twice for obtaining a detailed history using two different formats. The patient did not report recent history of fever, cough, sore throat, runny nose, earache, chest pain, abdominal pain, body ache, vomiting, diarrhea, headache, or any other complaints. The patient received Tamiflu (75mg bid) starting on May 19, 2015. The patient was not given steroids at that time. The patient did not report any history of recent travel in the 10 days before testing. The patient was interviewed again on May 24, 2015, by an infectious diseases officer using a different form for obtaining additional information related to animal exposure. The patient was interviewed in Arabic. The Page 3 of 3 patient lived in a compound that is about 10 km from the camel screening center. The patient worked as a cleaner in this center for 20 months (working hours: 72 hours per week). He did not report any history of direct contact with people who had respiratory illness or fever within the 14 days prior to testing. He did not have any recent visits to a hospital. He was tested to be negative before leaving the hospital at the end of May. An official announcement was released by the corresponding health authority (http://www.haad.ae/haad/tabid/58/ctl/Details/Mid/417/ItemID/487/Default.aspx).

Information Regarding Additional Persons Screened in the Study
An additional 32 persons were tested in the study. One of these persons was confirmed to