After comparing how infections from SARS-CoV-2 (which causes COVID-19) and two other human coronaviruses develop in cynomolgus macaques, researchers report that SARS-CoV-2 gives the animals a mild COVID-19-like disease. The results - based on a combination of experimental and historical infection data - suggest these animals are a promising model for testing COVID-19 therapeutics. Treatments for COVID-19 are urgently needed, as are animal models to test them. Which animal(s) can be used most precisely to model the efficacy of control measures in humans remains a question. To better understand key pathways in the pathogenesis of SARS-CoV-2, Barry Rockx et al. infected young and old cynomolgus macaques with SARS-CoV-2 (from a strain from a German traveler returning from China), as well as with MERS-CoV, comparing their results with historical reports of infections by SARS-CoV. All experiments were performed under Biosafety Level-3 conditions. SARS-CoV-2 leads to mild infection with little to no symptoms, the authors report, even as animals infected were shedding the virus; this is similar to how asymptomatic humans shed the SARS-CoV-2 virus. Viral RNA was detected at higher levels and for longer duration in older macaques, the authors report, though none showed the severe symptoms that older humans do. Also, like influenza, the animals shed the virus from the respiratory tract very early during infection as compared to with SARS-CoV; this could explain the explosive global spread of COVID-19 and why case detection and isolation may not be as effective as it was for controlling SARS-CoV. The macaques infected with MERS-CoV did not develop notable symptoms during study period. "This study provides a novel infection model which will be critical in the evaluation and licensure of preventive and therapeutic strategies against SARS-CoV-2 infection for use in humans," write the authors.