Previous evidence demonstrates that camels in the Arabian Peninsula, Camelus dromedarius, are host reservoirs of the MERS-CoV virus that can efficiently transmit the virus to humans.  A new study in Dubai has found that infectiousness in camels may be highest among calves of 4-6 months of age.

Image/Maureen Metcalfe; Azaibi Tamin
Image/Maureen Metcalfe; Azaibi Tamin

This study of over 800 camels detected the presence of antibodies against MERS-CoV in a significantly higher proportion among camels that were older than 2 years versus calves under 1 year of age, 94% and 80% respectively.  However, detection of active infection by RT-PCR and cell culture isolation occurred only from nasal swab samples from young camels under the age of four years.

In 15 mother-calf pairs sampled during nine days, active infection was detected in none of the mothers, but RT-PCR testing found evidence of MERS-CoV RNA in 11 of the calves (aged 4-6 months).  The presence of viral RNA could not be detected in all but four of the calves at the end of the nine days, suggesting a short period of active shedding among camels once infected.

The population for this study included camels from three flocks across Dubai, separated by 20-40 km.  Phylogenetic analysis revealed each flock was infected with MERS-CoV virus clades differentiated from the others in lineage, but closely related to ones already circulating in the eastern Arabian Peninsula.

This team of researchers from Dubai, Hong Kong and Germany suggests that camel-to-human transmission of MERS-CoV could be significantly decreased by bolstering the natural inaccessibility of camel calves to humans.  Animal husbandry practices that separate calves from their mothers for the purposes of milk collection and herd management should be reconsidered at least until calves reach 2 years of age.

Steven Smith, M.Sc. is an Infectious diseases epidemiologist