en Host-pathogen interactions and susceptibility factors Host-pathogen interactions and susceptibility factors Letter to the Editor Letter to the Editor In recent decades, some 30 new human pathogens have been identified, of which 75% were spillovers from animals. In late 2019, human infections with a new coronavirus from an unknown origin emerged in China and later spread worldwide. The zoonotic source of severe acute respiratory syndrome coronavirus 2 remains unknown, and there is only some limited information about the close association between the first human cases of COVID-19 and visiting animal markets. Now, bats and pangolins are suspected as natural hosts, and large cats, raccoon dogs, dogs, minks, ferrets, and pangolins as intermediate hosts.  There is not enough evidence to prove that animals can transmit COVID-19 infection to humans, but there are some data about the transmission of SARS-CoV-2 between humans and some animal species. Animal,Covid19,spillover 1 4 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-276-1&slc_lang=en&sid=1 Ehsan Mostafavi mostafaviehsan@gmail.com 0000-0002-1997-517X No Department of Epidemiology and Biostatics, Research Centre for Emerging and Reemerging Infectious Diseases, Pasteur Institute of Iran, Tehran, Iran Zohre Eftekhari z_eftekhari@pasteur.ac.ir 0000-0003-3502-9260 Yes Research & Production Complex, Pasteur Institute of Iran, Alborz, IranResearch Center for Zoonotic Disease, Pasteur Institute of Iran, Tehran, Iran Nazanin Jabbari nazanin.jabbari@srbiau.ac.ir 0000-0002-2926-9631 No Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran Parisa Gheibi parisa.gheybi@srbiau.ac.ir 0000-0002-0645-317X No Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran; Postal Code: 1477893855