Human-animal spillover of SARS-CoV-2: Implications for public health

COVID-19 pandemic caused by the recently emerged severe acute respiratory syndrome coronavirus (SARS-CoV-2) is a significant public health catastrophe in a century. While the precise origin of SARS-CoV-2, and its mode of introduction into the human population, is not yet fully resolved, there is evidence that SARS-CoV-2 originated from bats. As zoonotic viruses infecting humans can spill back into susceptible animal hosts, SARS-CoV-2 has demonstrated the ability to infect many nonhuman animal host species. The list of animal species susceptible to SARS-CoV-2 infection continues to grow and includes domestic animals, primates, pet animals, and zoo animals. In addition, based on the ability of the spike protein to bind to the ACE-2 receptor, computational predictions have identified dozens of additional possible animal hosts for SARS-CoV-2. In addition, there are multiple reports of human infections from SARS-CoV-2 infected animals. We discovered widespread natural infection of wild white-tailed deer with SARS-CoV-2 in the USA, suggesting their role as a potential SARS-CoV-2 reservoir. Establishing an animal reservoir could facilitate the continued circulation of SARS-CoV-2 independent of circulation in humans. In addition, deer could pass on the infection to other susceptible wild animals such as rodents, foxes, and raccoons resulting in the establishment of SARS-CoV-2 enzootic transmission cycles. Such a scenario could result in virus adaptation and the emergence of novel variants that could escape the protection of current human SARS-CoV-2 vaccines. This presentation will discuss our recent findings on natural SARS-CoV-2 infection of deer and the long-term implications of human-animal-human spillover of SARS-CoV-2.

Relationship between Anti-Spike Protein Antibody Titers and SARS-CoV-2 In Vitro Virus Neutralization in Convalescent Plasma

Newly emerged pathogens such as SARS-CoV-2 highlight the urgent need for assays that detect levels of neutralizing antibodies that may be protective. We studied the relationship between anti-spike ectodomain (ECD) and anti-receptor binding domain (RBD) IgG titers, andSARS-CoV-2 virus neutralization (VN) titers generated by two different in vitro assays using convalescent plasma samples obtained from 68 COVID-19 patients, including 13 who donated plasma multiple times. Only 23% (16/68) of donors had been hospitalized. We also studied 16samples from subjects found to have anti-spike protein IgG during surveillance screening of asymptomatic individuals. We report a strong positive correlation between both plasma anti-RBD and anti-ECD IgG titers, and in vitro VN titer. Anti-RBD plasma IgG correlated slightly better than anti-ECD IgG titer with VN titer. The probability of a VN titer 160 was 80% or greater with anti-RBD or anti-ECD titers of 1:1350. Thirty-seven percent (25/68) of convalescent plasma donors lacked VN titers 160, the FDA-recommended level for convalescent plasma used for COVID-19 treatment. Dyspnea, hospitalization, and disease severity were significantly associated with higher VN titer. Frequent donation of convalescent plasma did not significantly decrease either VN or IgG titers. Analysis of 2,814 asymptomatic adults found 27 individuals with anti-RBD or anti-ECD IgG titers of 1:1350, and evidence of VN1:160. Taken together, we conclude that anti-RBD or anti-ECD IgG titers can serve as a surrogate for VN titers to identify suitable plasma donors. Plasma anti-RBD or anti-ECD titer of1:1350 may provide critical information about protection against COVID-19 disease.