Concerns about Misinterpretation of Recent Scientific Data Implicating Dromedary Camels in Epidemiology of Middle East Respiratory Syndrome (MERS)

Samara, Emad M.; Abdoun, Khalid A.

Regarding camel-to-camel transmission, although the identification of antibodies and viral nucleic acids of MERS-CoV in DCs is remarkable, these findings suggest only that DCs can be naturally infected with MERS-CoV and provide us with no clues as to how this transmission occurs. We recognize that these findings, together with the absence of viremia, as reported by the authors, and the lack of even a single case fatality in DCs, indicate that DCs may not only be a useful animal model for evaluating candidate vaccines and drugs against MERS but also a good reservoir of MERS-CoV. However, this form of transmission cannot yet be ascertained to implicate DCs as a significant reservoir species in the epidemiology of MERS-CoV, as noted by Nishiura et al. (9) . These authors stated that two conditions should be objectively examined to confirm that an animal species constitutes a reservoir: (i) the reservoir is sufficient to maintain the disease by frequently transmitting the virus to another host, and (ii) the presence of the reservoir is essential for the continuous transmission of infection. The results presented by Lipkin and colleagues in mBio (1, 2) do not establish either of these conditions. In fact, identification of the reservoir host requires knowledge of the incidence rate to measure the transmissibility, which can be achieved by conducting a large-scale follow-up of cohort surveys or at least serial cross-sectional surveys, not one cross-sectional seroprevalence survey. Alternatively, we may implement a simple camel-tocamel transmission experiment with uninfected camel groups and no opportunity for human-to-human transmission, which could also inform us about any potential of this form of MERS-CoV transmissibility. Thus, as the authors correctly stated "Although we speculate that DC are potential reservoirs for human transmission, we cannot prove this relationship from the current data"; it is important that they carefully fulfill the above-mentioned conditions of reservoir dynamics before making speculations.