Middle East respiratory syndrome coronavirus in dromedary camels: an outbreak investigation

Abstract

Background: Middle East respiratory syndrome coronavirus (MERS-CoV) causes severe lower respiratory tract infection in people. Previous studies suggested dromedary camels were a reservoir for this virus. We tested for the presence of MERS-CoV in dromedary camels from a farm in Qatar linked to two human cases of the infection in October, 2013.

Methods: We took nose swabs, rectal swabs, and blood samples from all camels on the Qatari farm. We tested swabs with RT-PCR, with amplification targeting the E gene (upE), nucleocapsid (N) gene, and open reading frame (ORF) 1a. PCR positive samples were tested by different MERS-CoV specific PCRs and obtained sequences were used for phylogentic analysis together with sequences from the linked human cases and other human cases. We tested serum samples from the camels for IgG immunofluorescence assay, protein microarray, and virus neutralisation assay.

Findings: We obtained samples from 14 camels on Oct 17, 2013. We detected MERS-CoV in nose swabs from three camels by three independent RT-PCRs and sequencing. The nucleotide sequence of an ORF1a fragment (940 nucleotides) and a 4·2 kb concatenated fragment were very similar to the MERS-CoV from two human cases on the same farm and a MERS-CoV isolate from Hafr-Al-Batin. Eight additional camel nose swabs were positive on one or more RT-PCRs, but could not be confirmed by sequencing. All camels had MERS-CoV spike-binding antibodies that correlated well with the presence of neutralising antibodies to MERS-CoV.

Interpretation: Our study provides virological confirmation of MERS-CoV in camels and suggests a recent outbreak affecting both human beings and camels. We cannot conclude whether the people on the farm were infected by the camels or vice versa, or if a third source was responsible.

Funding: European Union projects EMPERIE (contract number 223498), ANTIGONE (contract number 278976), and the VIRGO consortium.

Figure 1

Characterisation of dromedary camel Middle East respiratory syndrome coronavirus (MERS-CoV) genome sequences (A) Nucleotide sequence fragments obtained from the nose swab of camel 5 that cover different parts of the MERS-CoV genome; purple boxes (1–6) show different fragments obtained with primers specific to MERS-CoV; red triangles show the position of the real-time TaqMan probes targeting different regions of the MERS-CoV genome. (B) Nucleotide sequences of representative MERS-CoVs' concatenated 4·2 kb sequences were analysed and a phylogenetic tree was constructed by the PhyML method; values at the branches show the result of the approximate likelihood-ratio, with values less than 0·70 not depicted.

Figure 2

Middle East respiratory syndrome coronavirus (MERS-CoV) serological response in camels from Qatar Immunofluorescence staining (green) of MERS-CoV infected and formalin fixed Huh7 cells (nuclei shown in blue) with serum samples from camel 5 (A), camel 7 (B), and camel 11 (C), negative camel control serum sample (D), a serum sample from a human case of MERS-CoV (E), and a serum sample from a healthy person (F). Fluorescent intensities (G) in relative fluorescence units (RFU) for MERS-CoV S1 antigen are shown for the 14 dromedary camels when tested at serum dilution 1/2560 versus virus neutralisation titres.