Elizabeth Devitt notes in Nature Medicine, that unlike its cousin, the severe acute respiratory syndrome coronavirus (SARS-CoV), some important features of MERS-CoV including its transmission, incubation period, and ability to spread systemically within the host, have not been able to be defined for the MERS-CoV using non-human models, because the virus does not like to infect the same animals.
When the MERS-CoV infects a larger non-human animal, the rhesus macaque monkey, the disease it produces, while still defined as pneumonia and proving the casual link between MERS-CoV infection and disease, resolved faster and was not as severe as that in humans. These animals are also not easy to work with. I wonder if older monkeys with comorbidities have been looked at in particular? [UPDATE: The macaques above live to about 25-years]. It is this population in which MERS is most severe. Nonetheless, the monkey studies provide an excellent vehicle on which to test the usefulness of 2-drug an antiviral approach (Falzano et al, described earlier) that can clear MERS-CoV infections in vitro.
While cell/tissue culture methods using primary human airway cells have proven extremely useful for looking at cellular biology, antiviral effects, and immunobiology related to MERS-CoV infection, something with legs will be needed for future vaccines and to address the list above. We've seen many examples of how animal models massively improve our understanding of influenza virus pathogenesis, if an example is needed.
Also according to Devitt, Ian Lipkin is still wading through the data from samples collected from a range of animals that may be the natural hosts for the MERS-CoV in Saudi Arabia. Meanwhile, we recently learned of another CoV (PML/2011) found in the fecal pellets from a South African Neoromicia cf. zuluensis bat in 2011. PML/2011's nearest CoV relative was the MERS-CoV - its closest viral relative found to date (at least in the conserved RdRp region used by the authors).
This all begs the question, is there a bat animal model? CoVs, but also studies of other viruses like Hendra and Nipah, would benefit from a well-defined model based on these critters. That is, if they can be worked with and if they show any signs of these diseases - which they may not. My very quick skim of the literature found that bats used for neurological studies and for Hendra virus.