farm a had 70 animals ; 4 were 1 month of age , 8 were 1 year of age , and the rest were adults ( > 2 years of age ) . the herd did not go to pasture in the desert (  zero - grazing  ; type of grazing may influence types of potential exposures ) . farm b (  semi  zero - grazing  ) had 17 adults and 3 calves ; its herd was sampled in february 2014 . nasal , oral , or rectal swab samples and blood samples were collected ( table 1 ; technical appendix table ) . rt - pcr , reverse transcription pcr ; mers - cov , middle east respiratory syndrome coronavirus ; nd , not done . adults are 614 y of age ; calves are 40 d to 2 y of age . hydrolysis probe  based real - time reverse transcription pcr ( rt - pcr ) targeting mers - cov upstream of e ( upe ) and open reading frame ( orf ) 1a genes and a broad - range rt - pcr reacting across the cov family to detect other covs were used as described ( 4 ) . specimens initially positive for mers - cov were re - extracted and retested to confirm the positive results . the full genome of mers - cov was obtained directly from the clinical specimens with 34 times coverage by sequencing pcr amplicons with overlapping sequence reads and sequence assembly ( 4 ) . we constructed full - genome phylogenies using mega5 with neighbor - joining and bootstrap resampling of 500 replicates ( 6 ) . we tested serum samples for neutralizing antibody titers using a validated mers - cov spike pseudoparticle neutralization test ( 7 ) ( online technical appendix ) . at farm a , we detected mers - cov in 1 of 4 dromedaries sampled on november 30 , none of 11 sampled on december 4 , nine of 11 sampled on december 30 , and none of 9 sampled on february 14 ( table 1 ) . of the 10 dromedaries that tested positive for mers - cov , 9 had parallel nasal and fecal specimens tested , with virus detected in the nasal swab specimens from 8 and the fecal specimen from 1 . at the december 30 sampling , 7 of 8 calves and 2 of 3 adults tested positive for mers - cov , indicating that when mers - cov circulates on a farm , both calves and adults can be infected ( technical appendix table ) . because all 12 adults with serum collected before december 30 were seropositive ( titers > 320 ) , it is likely , though not certain , that the mers - cov infections in the 2 adults ( nos . 21 , 19dam ) sampled on december 30 were reinfections , as has been reported for other covs ( 8) . the seronegative 1-year - old calves , nos . 13 and 14 , had the highest nasal viral loads ( upe assay 1.3  10 to 1.78  10/ml specimen ) , and a 2-week - old calf , no . 22 , with ( presumably passively acquired ) titers of 1,280 became infected but had a much lower viral load . overall , these data suggest that prior infection or passively acquired maternal antibody might not provide complete protection from infection ( technical appendix table ) . four mers - cov  positive calves had mild respiratory signs ( cough , sneezing , respiratory discharge ) , abnormally elevated body temperature , and loss of appetite at the december 30 sampling , which resolved over a few days . 13 , 15 , 17 ) demonstrated > 4-fold rising antibody titers to mers - cov . 13 ( 1 year of age ) had a high viral load and was seronegative at the first mers - cov  positive result ( indicating that it had been recently infected ) but was mers - cov rna negative 6 weeks later , suggesting that virus shedding is not prolonged . we did not detect virus rna by rt - pcr in the 3 acute - phase serum samples from infected dromedaries ( nos . 1 , 16 , 17 ) . dromedaries from farm b were sampled once on february 11 ; all results were negative . the full genomes of mers - cov sequenced directly from a nasal swab specimen collected on november 30 were identical to those from a nasal swab specimen and a fecal specimen collected on december 30 . in addition , the complete spike gene was sequenced from 4 other mers - cov  positive nasal swab specimens , and these spike genes were genetically identical . virus isolation in vero e6 cells was attempted from 7 positive nasal swab and fecal specimens that had > 10 copies / ml in the original sample in the upe rt - pcr . 19dam ) specimens collected on december 30 ; these were the specimens with high numbers of mers - cov copies ( 9.27  10 to 1.78  10 copies / ml ) . the full - genome sequence of 1 virus culture isolate was obtained in parallel with that of the original virus in the original clinical specimen . we observed 3 nucleotide changes in orf1b , spike , and membrane protein genes in the isolates after 2 passages in vero e6 cells , of which 2 were nonsynonymous , leading to changes in spike ( s1251f ) and membrane proteins ( t8i ) . mers - covs circulating in dromedaries on farm a during a 1-month period were genetically identical over the full 30,100-nt genome in 3 viruses and the spike protein of 4 more viruses , giving a mutation rate of 0 nt substitutions per site per day ( 95% credible interval 0 to 2.7  10 ) . the estimated mutation rate for epidemiologically unlinked human mers - cov was 3.1  10 ( 95% ci 2.4  10 to 3.8  10 ) ( 9 ) . the unusual genetic stability of mers - cov in dromedaries , taken together with its high seroprevalence ( 7,1013 ) , raises the hypothesis that dromedaries might be the natural host for this virus . further longitudinal studies of mers - covs in dromedaries are needed to confirm this hypothesis . genome organization of the dromedary mers - cov detected in this study was identical to that of the virus in humans . the virus strains clustered phylogenetically within clade b ( 9 ) and were most closely related to the strain mers - cov_fra / uae and to mers - cov detected in buraidah ( saudi arabia ) and al - hasa ( figure ) . dromedaries move between al - hasa and buraidah and , more limitedly , between al - hasa and united arab emirates . phylogenetic tree of middle east respiratory syndrome coronavirus ( mers - cov ) full genomes ( 29,901 nt after trimming the ends ) or near  full genomes from humans and dromedary camels . the tree was constructed by using neighbor - joining methods with bootstrap resampling of 500 replicates . the most divergent mers - cov , egypt nrce - hku205 , was used as outgroup . genbank accession numbers of genome sequences included in this study are kj477102 , kf600652 , kf600630 , kf600651 , kf186567 , kf600627 , kf186564 , kf600634 , kf600632 , kf600644 , kf600647 , kf600645 , kf186565 , kf186566 , kf745068 , kf600620 , kf600612 , kc667074 , kc164505 , kf192507 , kf600613 , kf600628 , kf961222 , kf961221 , kc776174 , and jx869059 . the full - genome sequence of mers - cov from dromedaries in this study is 99.9% similar to genomes of human clade b mers - cov . the spike gene is the major determinant for virus host specificity . in comparison with other publically available human mers - cov sequences of these , 3 ( s457 g , l773f , and v810i ) were nonsynonymous . these amino acid changes are located outside the binding interface between mers - cov spike protein and human dpp4 receptor , suggesting these amino acid differences are unlikely to affect receptor binding . thus , these dromedary viruses may retain capacity to infect humans , as chu et al . suggested for dromedary mers - cov in egypt ( 4 ) . mers - cov may be isolated from nasal swab specimens and feces , indicating that both could be possible sources of virus transmission to humans and other animals , but virus detection rates were higher in nasal swab specimens . our preliminary data suggest that preexisting mers - cov antibody might not completely protect against re - infection ; however , this question needs more investigation . testing of dromedary camels by reverse transcription pcr and serologic testing for middle east respiratory syndrome coronavirus , al - hasa , saudi arabia ; and detailed methods used in this study
a prospective study of a dromedary camel herd during the 201314 calving season showed middle east respiratory syndrome coronavirus infection of calves and adults . 
 virus was isolated from the nose and feces but more frequently from the nose . 
 preexisting neutralizing antibody did not appear to protect against infection .