Identifying the animal source of human infections with Middle East respiratory syndrome coronavirus (MERS-CoV) is a priority. The detection of antibodies specific for the virus in dromedary camels and of identical viral sequences in tomb bats and in patients with MERS suggests that these two animals serve as MERS-CoV reservoirs. Epidemiological data indicate that currently circulating MERS-CoV strains are unlikely to cause an epidemic by spreading between humans, as their reproduction number (the number of new cases arising from a single infected person) is 0.69, which is too low to maintain continuous, widespread transmission; in comparison, the reproduction number of severe acute respiratory syndrome (SARS) CoV is 0.89. Thus, by preventing viral transmission from animal reservoirs to humans, it is hoped that the spread of MERS-CoV can be stopped. BBC News/Lancet