key: cord-0700433-tuzmu7p5 authors: Tilocca, Bruno; Soggiu, Alessio; Musella, Vincenzo; Britti, Domenico; Sanguinetti, Maurizio; Urbani, Andrea; Roncada, Paola title: Molecular basis of COVID-19 relationships in different species: a one health perspective date: 2020-03-17 journal: Microbes Infect DOI: 10.1016/j.micinf.2020.03.002 sha: 21472f7d3dd86085a366b5f487354824b812f12c doc_id: 700433 cord_uid: tuzmu7p5 Outside the Hubei province, China, the mild form of infection and the progressive recover of the COVID-19 patients suggest the intervention of “unconventional” biological mechanisms worthy of attention. Based on the high-homology between the Spike protein epitopes of taxonomically-related coronaviruses, we hypothesized that past contact with infected dogs shield humans against the circulating SARS-CoV-2. Elseways, the recurrent virus exposure over a short time-lapse might result in the Antibody Dependent Enhancement, triggering the violent immune reaction responsible for the severe clinical outcomes observed in the Hubei province. Nevertheless, further experimental studies are desired for a confidential evaluation of the postulated hypotheses. Since late December 2019, the world is facing a novel outbreak of an infectious disease, known as COVID-19, caused by an unidentified viral agent. Examination of patients cases reports clinical picture comparable to this observed in the SARS outbreak of 2003. This evidence is also supported by the early identification of the etiologic agent as a novel Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2) and the molecular investigations describing a high percentage of sequence homology between SARS-CoV-2 and the previous SARS-causing virus (SARS-CoV) [1, 2] . Coronaviruses are viruses with single-strand positive-sense RNA genome of approximately 30 kilobases [3] . They have been commonly found in a wide array of host spectrum including avian, camels, bats, masked palm civets, mice, dogs, and cats [2] . Since its early identification, in the very begin of 2020, several nucleotidesbased surveys and sequence homology-based alignments have been carried out with the focus to elucidate the viral origin and delineate cell-and host-tropism of the viral agent on the attempt to guide better management and control of the virus diffusion [4] . Sequence similarity alignments have reported SARS-CoV-2 being highly similar to several wildlife animals such as bats, pangolins and masked palm civets [3] . Controversial results have been reported concerning the snake coronavirus [2, 5] . Nevertheless, the sole investigation of the genetic sequences might result in a biased and/or incomplete depiction of the virus source, biology and its pathogenetic mechanism [4] . In the Hubei province, where the outbreak originated, severe cases or deaths attributed to SARS-CoV-2 infections are predominantly arising from patients suffering from one or more previous pathological conditions such as diabetes, cardiovascular and cerebrovascular disease leading to sequelae, sometimes fatal, such as cellular immune deficiency, coagulation activation, myocardia injury, hepatic and kidney injury, and secondary bacterial infection [4, 6] . Although featured by a higher fatality rate when compared with the virus of the seasonal influenza (3.4%, WHO Situation Report-37, 25/02/2020), outside the primordial outbreak site, much less warning clinical signs have been registered in the SARS CoV-2 infected patients manifesting a mild form of the disease that is not evolving into severe stages and can, in some cases, recover without medical intervention [4] . Altogether this suggests the important contribution of the biological mechanisms that cannot be explained by the sole investigation of the genetic sequences. Protein repertoire of the coronaviruses consists of four main structural and approximately 16 major non-structural proteins [3, 7] . Among the four structural proteins, the Spike protein (also known as S-protein) is involved in host tropism by means of recognition and attachment to the angiotensin-converting enzyme 2 (ACE2) receptor exposed in the outer layer of the host cell membrane [8] . A very recent amino acid sequence alignment of ACE2 from different animal species including humans, pets and the major domestic animals highlighted high protein sequence similarity between the tested animal species, suggesting a potential interaction of the viral particles with a wider array of host cells [8] . In accordance with the hypothesis of interspecies transmission of the beta coronaviruses [8] , we performed sequence homology analysis of the aminoacidic sequence of the Spike protein from SARS CoV-2 against taxonomically related coronaviruses with tropism for other animal species. Although the low homology scored while comparing the whole protein sequence (Table 1) , particular interest was dedicated to the canine respiratory coronavirus, the bovine coronavirus revealing and the human enteric coronavirus 36.93%, 38.42% and 37.68% sequence homology to SARS CoV-2 spike protein, respectively. A previous study of Hua and colleagues on the amino acid sequence of SARS CoV spike protein identified six epitopes based on the hydrophilicity, surface probability, antigenic index, and secondary structure [9] ( Table 2) . The sequence homology analysis restricted to the epitope sequences of the SARS CoV-2 revealed instead high percentage homology towards taxonomically related coronaviruses. Of these, we retain it is worth of note the high similarity occurring among 4 epitope sequences of canine respiratory coronavirus (Canine respiratory CoV BJ 232) and the circulating SARS CoV-2 (Table 3) . Highlighting the similarity at the epitope level opens new avenues in understanding the biological mechanisms undertaken during viral infection. Before the current outbreak, several studies witness the common identification of coronavirus infection in dogs [10, 11] . Previous studies performed by Szczepanski and colleagues report the possibility to grow both bovine and canine coronavirus on human cells lines such as the Human Rectal Tumor cells (HRT-18G) and Human Airway Epithelium (HAE) although featured by a strongly reduced replication efficiency [12, 13] . In this view, a previous "contact" with the canine virus might provide at least a partial/basal immunization that shields humans against the circulating SARS CoV-2. This would partially explain the mild symptoms registered among patients outside the Hubei province and without previous co-morbidities. Accordingly, high similarity percentage have also been observed between SARS CoV-2 spike proteins epitopes and bovine coronavirus, which genome and proteins appear among those included in the patented vaccinal formulation released against coronavirus. With regard to the most severe cases of infection registered both outside and within the Hubei province, it is most likely that these individuals have been primed by one or more coronavirus exposure within a narrow time window, leading to the effects of Antibody-Dependent Enhancement (ADE) [4] . Such a hypothesis is in line with the previous observations dating back to the previous SARS outcome in 2003 when human coronaviruses, known to cause mild infections, were hypothesized of priming the high mortality scored in China. Here, anti-Spike protein antibodies were indicated as potentially involved in the enhancement mechanism [14e18]. In this view, it is plausible that Hubei province patients are featured by a more severe clinical picture, since more likely to be recurrently exposed to the coronavirus. To summarize, animals have (had) a critical role in this outbreak onset and evolution. Acknowledged their pivotal role as virus reservoir, they might act in the first instance as "beneficial" source of immune-stimulating virus particles; thus, providing a shield against the circulating SARS CoV-2. However, the recurrent exposure within a narrow time-lapse might results in the detrimental triggering of violent immune responses and the evolution towards a more severe, or even fatal, clinical picture. Above hypotheses are based on the assumption that sufficient viral titer of the SARS CoV-2 is transmitted from patient to patient [19] . The previous investigation on animal betacoronavirus such as the canine coronavirus have demonstrated a high transmission efficiency through direct contact between infected animals, acknowledged the high viral titers found in the aerosols of respiratory secretions [20] . Novel investigations to assess the transmission rate of the canine respiratory coronavirus to humans are needed to better suit the above hypotheses. Also, care should be taken while evaluating the data on the sole basis of sequence homology and further studies employing purified forms of the spike proteins and/or its epitopes are desired. The authors declare no conflict of interest. Genomic characterisation and epidemiology of 2019 novel coronavirus: implications for virus origins and receptor binding First respiratory transmitted food borne outbreak? Emerging coronaviruses: genome structure, replication, and pathogenesis Is COVID-19 receiving ADE from other coronaviruses? Microb Infect 2020 Homologous recombination within the spike glycoprotein of the newly identified coronavirus may boost cross-species transmission from snake to human Cytokine responses in severe acute respiratory syndrome coronavirus-infected macrophages in vitro: possible relevance to pathogenesis Epidemiological and genetic analysis of severe acute respiratory syndrome Analysis of angiotensin-converting enzyme 2 (ACE2) from different species sheds some light on cross-species receptor usage of a novel coronavirus 2019-nCoV Identification of two antigenic epitopes on SARS-CoV spike protein Serological and molecular evidence that canine respiratory coronavirus is circulating in Italy Studies on the epizootiology of canine coronavirus Canine respiratory coronavirus employs caveolin-1-mediated pathway for internalization to HRT-18G cells Canine respiratory coronavirus, bovine coronavirus, and human coronavirus OC43: receptors and attachment factors Evasion of antibody neutralization in emerging severe acute respiratory syndrome coronaviruses Neutralizing antibody response and SARS severity Antibodydependent infection of human macrophages by severe acute respiratory syndrome coronavirus Anti-severe acute respiratory syndrome coronavirus spike antibodies trigger infection of human immune cells via a pH-and cysteine protease-independent Fc R pathway Antibodydependent SARS coronavirus infection is mediated by antibodies against spike proteins Presumed asymptomatic carrier transmission of COVID-19 Canine coronavirus highly pathogenic for dogs None.