Zoonosis: Concerns Over a Swine Coronavirus

There’s no need to reiterate the threat posed by zoonotic viruses that jump from animals to humans, particularly coronaviruses. But while a bat coronavirus recently made headlines, that won’t necessarily be the case next time. A new study shows that a porcine coronavirus is capable of infecting human cells. This is something to watch closely.   Our history has been punctuated by waves of deadly diseases, particularly those originating from animal reservoirs. Since well before ancient times, humans have had to contend with deadly viral diseases that determined the fate of entire civilizations. And with industrialization, globalization, habitat destruction, and overpopulation, these threats are all the more serious because they can spread rapidly across the globe. Coronaviruses, whose potential for interspecies transmission remains a cause for concern, are currently in the spotlight and the subject of much discussion. They represent a constant threat, particularly due to their diversity, which makes it exponentially more difficult to identify high-risk isolates—those that threaten human health. In the 21st century alone, three new human coronaviruses of animal origin and three new porcine coronaviruses (CoV) have emerged suddenly and spread worldwide over the past 20 years. And if the COVID-19 pandemic teaches us anything, it is that prevention is key. It is therefore strategically crucial for public health to identify coronaviruses with high zoonotic risk and monitor them closely. Pigs, which live in close proximity to human populations, are susceptible to numerous coronaviruses. Over the past 80 years, several new coronaviruses have caused major outbreaks in pigs, including the transmissible gastroenteritis virus (TGEV), porcine respiratory coronavirus (PRCV), porcine epidemic diarrhea coronavirus (PEDV), porcine hemagglutinating encephalomyelitis virus (PHEV), and porcine deltacoronavirus (PDCoV). More recently, a new coronavirus causing porcine acute diarrhea syndrome (SADS-CoV) has been rampant, killing nearly 90% of infected piglets younger than 5 days. The swine population is therefore a potential source of new zoonotic outbreaks, and the new, highly pathogenic swine coronavirus is of particular concern. Researchers therefore sought to assess human susceptibility to the interspecies transmission and replication of SADS-CoV. And the results are alarming. SADS-CoV can replicate efficiently in a variety of animal and primate cell lines, including primary human cells derived from the lung and intestine. This is despite the fact that the virus does not use the human coronavirus receptors ACE-2, DPP4, or CD13 to bind to and enter cells. SADS-CoV can therefore infect a wide range of hosts, including both animals and humans, and has an inherent potential for interspecies transmission. Further analysis of the study suggests that cross-immunity in humans against the porcine coronavirus is likely quite limited. However, remdesivir, a broad-spectrum nucleoside analog effective against other coronaviruses—including feline infectious peritonitis (FIP)—effectively blocks SADS-CoV replication in vitro. Other effective treatment options may emerge. The only drawback is that immunodeficient or immunocompromised mice are only very slightly susceptible to the disease. As with SARS-CoV-2, there is therefore a critical need for improved animal models to better understand and combat the disease. Although the swine coronavirus has never yet been detected in humans, the risk of SADS-CoV spillover into humans is very real—with all the global medical and economic consequences that we, unfortunately, know all too well. Now more than ever, it is crucial to monitor pig populations through a One Health approach. The more closely pig populations are monitored and kept healthy, the less prevalent the virus will be and the less likely it will be to infect humans.