Coronaviridae, pathogenetic and clinical aspects: an update

Intestinal Tropism of a Betacoronavirus (Merbecovirus) in Nathusius's Pipistrelle Bat (Pipistrellus nathusii), Its Natural Host

The emergence of several bat coronavirus-related disease outbreaks in human and domestic animals has fueled surveillance of coronaviruses in bats worldwide. However, little is known about how these viruses interact with their natural hosts. We demonstrate a Betacoronavirus (subgenus Merbecovirus), PN-βCoV, in the intestine of its natural host, Nathusius's Pipistrelle Bat (Pipistrellus nathusii), by combining molecular and microscopy techniques. Eighty-eight P. nathusii bat carcasses were tested for PN-βCoV RNA by RT-qPCR, of which 25 bats (28%) tested positive. PN-βCoV RNA was more often detected in samples of the intestinal tract than in other sample types. In addition, viral RNA loads were higher in intestinal samples compared to other sample types, both on average and in each individual bat. In one bat, we demonstrated Merbecovirus antigen and PN-βCoV RNA expression in intestinal epithelium and the underlying connective tissue using immunohistochemistry and in situ hybridization, respectively. These results indicate that PN-βCoV has a tropism for the intestinal epithelium of its natural host, Nathusius's Pipistrelle Bat, and imply that the fecal-oral route is a possible route of transmission. IMPORTANCE Virtually all mammal species circulate coronaviruses. Most of these viruses will infect one host species; however, coronaviruses are known to include species that can infect multiple hosts, for example the well-known virus that caused a pandemic, SARS-CoV-2. Chiroptera (bats) include over 1,400 different species, which are expected to harbor a great variety of coronaviruses. However, we know very little about how any of these coronaviruses interact with their bat hosts; for example, we do not know their modes of transmissions, or which cells they infect. Thus, we have a limited understanding of coronavirus infections in this important host group. The significance of our study is that we learned that a bat coronavirus that occurs in a common bat species in Europe has a tropism for the intestines. This implies the fecal-oral route is a likely transmission route.

Swine coronaviruses (SCoVs) and their emerging threats to swine population, inter-species transmission, exploring the susceptibility of pigs for SARS-CoV-2 and zoonotic concerns

Swine coronaviruses (SCoVs) are one of the most devastating pathogens affecting the livelihoods of farmers and swine industry across the world. These include transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV), porcine respiratory coronavirus (PRCV), porcine hemagglutinating encephalomyelitis virus (PHEV), swine acute diarrhea syndrome coronavirus (SADS-CoV), and porcine delta coronavirus (PDCoV). Coronaviruses infect a wide variety of animal species and humans because these are having single stranded-RNA that accounts for high mutation rates and thus could break the species barrier. The gastrointestinal, cardiovascular, and nervous systems are the primary organ systems affected by SCoVs. Infection is very common in piglets compared to adult swine causing high mortality in the former. Bat is implicated to be the origin of all CoVs affecting animals and humans. Since pig is the only domestic animal in which CoVs cause a wide range of diseases; new coronaviruses with high zoonotic potential could likely emerge in the future as observed in the past. The recently emerged severe acute respiratory syndrome coronavirus virus-2 (SARS-CoV-2), causing COVID-19 pandemic in humans, has been implicated to have animal origin, also reported from few animal species, though its zoonotic concerns are still under investigation. This review discusses SCoVs and their epidemiology, virology, evolution, pathology, wildlife reservoirs, interspecies transmission, spill-over events and highlighting their emerging threats to swine population. The role of pigs amid ongoing SARS-CoV-2 pandemic will also be discussed. A thorough investigation should be conducted to rule out zoonotic potential of SCoVs and to design appropriate strategies for their prevention and control.

Biofilms and Coronavirus Reservoirs: a Perspective Review

Bats are a key reservoir of coronaviruses (CoVs), including the agent of the severe acute respiratory syndrome, SARS-CoV-2, responsible for the recent deadly viral pneumonia pandemic. However, understanding how bats can harbor several microorganisms without developing illnesses is still a matter under discussion. Viruses and other pathogens are often studied as stand-alone entities, despite that, in nature, they mostly live in multispecies associations called biofilms—both externally and within the host. Microorganisms in biofilms are enclosed by an extracellular matrix that confers protection and improves survival. Previous studies have shown that viruses can secondarily colonize preexisting biofilms, and viral biofilms have also been described. In this review, we raise the perspective that CoVs can persistently infect bats due to their association with biofilm structures. This phenomenon potentially provides an optimal environment for nonpathogenic and well-adapted viruses to interact with the host, as well as for viral recombination. Biofilms can also enhance virion viability in extracellular environments, such as on fomites and in aquatic sediments, allowing viral persistence and dissemination. Moreover, understanding the biofilm lifestyle of CoVs in reservoirs might contribute to explaining several burning questions as to persistence and transmissibility of highly pathogenic emerging CoVs.

Angiotensin-converting enzyme 2: The old door for new severe acute respiratory syndrome coronavirus 2 infection

Coronavirus (CoV) disease 2019 (COVID-19) is an ongoing pandemic caused by severe acute respiratory syndrome CoV 2 (SARS-CoV-2). The highly contagious SARS-CoV-2 belongs to the genus Betacoronavirus, and it is phylogenetically closely related to SARS-CoV, a human CoV that caused an outbreak back in 2002 to 2003. Both SARS-CoV-2 and SARS-CoV enter human cells via the interactions between viral crown-like spike protein and human angiotensin-converting enzyme 2 (ACE2) receptor. Here, we aim to review the involvement of ACE2 in human CoV infections by discussing the roles of ACE2 in CoV evolution, cross-species transmissibility, and COVID-19 susceptibility. We also provide our perspectives on COVID-19 treatment and prevention.

Experimental reproduction of winter dysentery in lactating cows using BCV -- comparison with BCV infection in milk-fed calves

Infection models were developed for adult cows and for young calves using the same strain of bovine coronavirus (BCV), which for the first time allows experimental reproduction of winter dysentery (WD) in seronegative lactating cows. The cattle were infected through direct contact with an experimentally inoculated calf. All experimental cattle shed faecal BCV with development of diarrhoea, being profusely watery with small amounts of blood in the most severely affected animals, including both cows and calves. The cows, in contrast to the calves, showed depressed general condition and appetite leading to a marked decrease in milk yield. Further age-associated differences were a shorter incubation period in the two youngest calves, but with milder fever and milder decrease in white blood cell counts. These findings shed light on the apparent epidemiological differences between WD and calf BCV diarrhoea suggesting that, (1) the same strains of BCV cause natural outbreaks of calf diarrhoea and WD, (2) seronegative cows are more severely affected by the infection than seronegative conventionally reared calves, and (3) unaffected general condition in diarrhoeic calves may lead to underestimation of the occurrence of calf diarrhoea in WD outbreaks.

In response to infection, all cattle produced early interferon type 1 in serum and, except for one calf, in nasal secretions. A finding not previously reported is the detection of interferon type 1 responses in bovine milk. All cattle developed high IgM antibody responses and long-lasting IgA antibody responses both systemically and locally. The serum IgM antibody responses came earlier in most of the calves than in the cows. Prolonged IgM antibody responses were detected in serum and milk, while those in nasal secretions were much shorter. BCV-specific IgA was present in nasal secretions from all cattle throughout the 6 months follow-up. The IgA antibody response in serum was detected up to 17 months post-infection and the duration showed an age-related variation indicating a more prominent IgA memory in the adult cattle and in the older calves than in the younger ones. BCV-specific IgG was detected in all cattle during the experimental period of up to 22 months.

In conclusion, WD was reproduced in seronegative lactating cows. The cows showed a more severe general diseases than seronegative calves infected concurrently. Very long-lasting IgA antibody responses were detected both systemically and locally.

Multiple receptor-dependent steps determine the species specificity of HCV-229E infection

Human coronavirus (HCV)-229E causes disease only in humans and grows in human cells and in cells of other species that express recombinant human aminopeptidase N (hAPN), the receptor for HCV-229E. We compared the species specificity of HCV-229E infection with the species specificity of virus binding using immunofluorescence, assay of virus yields, fluorescence activated cell sorting and a monoclonal antibody directed against hAPN that blocks infection. We found that HCV-229E binds to intestinal brush border membranes (BBM) and to membranes of cell lines from cats, dogs, pigs, and humans, however the virus only infects two of these species. HCV-229E will not bind to BBM or to membranes from cell lines derived from hamster or mice. Animal coronaviruses related to HCV-229E, including FIPV, CCV, and TGEV bind to cell membranes from cats, dogs, cows, pigs and humans (but not mice), while each virus infects cells from only a subset of these species. Infectious genomic HCV-229E RNA, can infect cells of all of these species. These data suggest that the species-specificity of infection for this serogroup of coronaviruses is determined at the levels of virus binding and penetration. Since binding of viral spike glycoprotein to cellular receptors is not the only limiting factor, we suggest that one or more steps associated with virus penetration may determine the species specificity of infection with the HCV-229E serogroup of coronaviruses.

Coronavirus immunogens

Coronaviruses (CV) infect a variety of livestock, poultry and companion animals. They belong to at least five antigenic groups. CV cause localized infections of the respiratory and/or intestinal tracts, with the exception of feline infectious peritonitis virus (FIPV) and hemagglutinating encephalomyelitis (HEV) which cause systemic infections. The enteropathogenic CV infect the villous enterocytes resulting in villous atrophy leading to malabsorptive diarrhea. Several CV (bovine CV-BCV, porcine respiratory CV-PRCV, infectious bronchitis virus-IBV) cause respiratory disease. Current evidence indicates that protection against enteric and respiratory CV infections is mediated by passive or active immunity at the primary site of CV replication. Maternal vaccination approaches to induce passive immunity include the use of inactivated and modified live viral vaccines. Modified live viruses and a Ts mutant CV (FIPV) are also used as oral or intranasal vaccines to induce active mucosal immunity. The success of these vaccines in the field is often compromised by a number of potential problems. Coronaviruses are spherical, enveloped viruses, ranging from 80-160 nm in diameter and containing a positive-stranded RNA genome. They possess prominent surface spikes and some species display a fringe of smaller surface projections believed to be the hemagglutinin (HE). Coronaviruses possess 3 to 4 structural proteins: the spike (S) glycoprotein (150-200 kDa), the integral membrane glycoprotein (M; 20-30 kDa) and the nucleocapsid phosphoprotein (N; 43-50 kDa). A subset of CV (BCV, HEV, turkey CV) possess a third glycoprotein on the virion surface, the HE (60-65 kDa). These proteins can be quantitated using pooled monoclonal antibodies (mAb) to distinct epitopes of each protein in ELISA. Most research has focused on the S protein as a candidate antigen for CV vaccines since it induces virus neutralizing (VN) antibodies. However the HE protein stimulates the production of VN and HE inhibiting antibodies and the M protein induces antibodies that neutralize virus in the presence of complement. Attempts to correlate in vitro VN antibody activity with in vivo protection have shown that the passive transfer of VN mAb to the S or HE protein conferred passive protection against CV challenge in some studies, but not others. Additional research has implicated a possible role for other CV proteins in immunity. Studies of mAb to the M protein of transmissible gastroenteritis (TGEV) have provided evidence for a direct role of the M protein in the induction of alpha IFN by porcine blood leukocytes. The potential significance of this phenomenon to immunity to TGEV is unclear.(ABSTRACT TRUNCATED AT 400 WORDS)