Co-localization of Middle East respiratory syndrome coronavirus (MERS-CoV) and dipeptidyl peptidase-4 in the respiratory tract and lymphoid tissues of pigs and llamas

Distribution of aminopeptidase N coronavirus receptors in the respiratory and digestive tracts of domestic and wild artiodactyls and carnivores

Aminopeptidase N (APN) is a transmembrane protein that mediates the attachment of the spike protein of several clinically important coronaviruses (CoVs) responsible for respiratory and intestinal diseases in animals and humans. To assess the potential for APN-mediated viral tropism, we characterized APN receptor distribution in the respiratory and intestinal tissues of various artiodactyls (cervids, bovids, camelids and suids) and carnivores (canids, felids, mustelids and phocids) using immunohistochemistry. In the lungs, APN expression was limited to artiodactyls, with strong expression in the bronchiolar epithelium and weaker expression in pneumocytes. Nasal turbinate and tracheal samples, where available, showed stronger APN expression in artiodactyls over carnivores. APN was consistently detected on the microvilli of enterocytes in the small intestine across multiple taxa, while the presence in the colon was more variable. Of the animals examined, pig and alpaca consistently expressed the most abundant APN in the upper and lower respiratory tract. In silico evaluation of APN orthologue sequences from humans, artiodactyls and carnivores identified distinct evolutionary relationships. Further in silico binding predictions for alpaca alphacoronavirus and human coronavirus 229E with cognate and heterologous alpaca and human APN revealed substantial overlapping binding footprints with high conservation of amino acid residues, suggesting an evolutionary divergence and subsequent adaptation of a 229E-like or ancestral virus within a non-human animal host. This combined anatomical and in silico approach enhances understanding of host susceptibility, tissue tropism and viral transmission mechanisms in APN-dependent CoVs and has the potential to inform future strategies for disease modelling, surveillance and control.

Variable DPP4 expression in multiciliated cells of the human nasal epithelium as a determinant for MERS-CoV tropism

Transmissibility of respiratory viruses is a complex viral trait that is intricately linked to tropism. Several highly transmissible viruses, including severe acute respiratory syndrome coronavirus 2 and Influenza viruses, specifically target multiciliated cells in the upper respiratory tract to facilitate efficient human-to-human transmission. In contrast, the zoonotic Middle East respiratory syndrome coronavirus (MERS-CoV) generally transmits poorly between humans, which is largely attributed to the absence of its receptor dipeptidyl peptidase 4 (DPP4) in the upper respiratory tract. At the same time, MERS-CoV epidemiology is characterized by occasional superspreading events, suggesting that some individuals can disseminate this virus effectively. Here, we utilized well-differentiated human pulmonary and nasal airway organoid-derived cultures to further delineate the respiratory tropism of MERS-CoV. We find that MERS-CoV replicated to high titers in both pulmonary and nasal airway cultures. Using single-cell messenger-RNA sequencing, immunofluorescence, and immunohistochemistry, we show that MERS-CoV preferentially targeted multiciliated cells, leading to loss of ciliary coverage. MERS-CoV cellular tropism was dependent on the differentiation of the organoid-derived cultures, and replication efficiency varied considerably between donors. Similarly, variable and focal expression of DPP4 was revealed in human nose tissues. This study indicates that the upper respiratory tract tropism of MERS-CoV may vary between individuals due to differences in DPP4 expression, providing an explanation for the unpredictable transmission pattern of MERS-CoV.

Middle East respiratory syndrome coronavirus (MERS-CoV) internalization does not rely on DPP4 cytoplasmic tail signaling

Middle East respiratory syndrome coronavirus (MERS-CoV) infects respiratory epithelial cells in humans and camels by binding to dipeptidyl peptidase 4 (DPP4) as its entry receptor. DPP4 is a multifunctional type II membrane protein with a long ectodomain and a short six-amino-acid (aa) cytoplasmic tail. MERS-CoV is known to bind to the ectodomain of DPP4 to gain entry into the host cell. However, the role of the cytoplasmic tail in the entry process remains unclear. Here, we show that mutating or deleting individual aa residues or the entire cytoplasmic tail of DPP4 (ΔcytDPP4) does not completely prevent DPP4 from being inserted into the membrane or from allowing the binding of the MERS-CoV spike protein and pseudovirus infection. Although two mutants, ΔcytDPP4, and a single aa deleted DPP4 (ΔK6DPP4) displayed less surface presentation than wtDPP4, the spike protein could still bind and localize on different DPP4 mutants. The reduced surface expression of ΔK6DPP4 might be due to the extended transmembrane domain, which is altered by the hydrophobic tryptophan (W) residue adjacent to the deleted K6. Furthermore, HEK293T cells transiently expressing DPP4 mutants were permeable to MERS-CoV pseudovirus infection. Not only transiently expressing cells but also cells stably expressing the ΔcytDPP4 mutant were susceptible to MERS-CoV pseudoviral infection, indicating that the DPP4 cytoplasmic tail is not required for MERS-CoV entry. Overall, these data suggest that, although MERS-CoV binds to DPP4, other host factors may need to interact with DPP4 or the spike protein to trigger internalization.

Enhanced antiviral immunity and dampened inflammation in llama lymph nodes upon MERS-CoV sensing: bridging innate and adaptive cellular immune responses in camelid reservoirs

Middle East respiratory syndrome coronavirus (MERS-CoV) infection can cause fatal pulmonary inflammatory disease in humans. Contrarily, camelids and bats are the main reservoir hosts, tolerant for MERS-CoV replication without suffering clinical disease. Here, we isolated cervical lymph node (LN) cells from MERS-CoV convalescent llamas and pulsed them with two different viral strains (clades B and C). Viral replication was not supported in LN, but a cellular immune response was mounted. Reminiscent Th1 responses (IFN-γ, IL-2, IL-12) were elicited upon MERS-CoV sensing, accompanied by a marked and transient peak of antiviral responses (type I IFNs, IFN-λ3, ISGs, PRRs and TFs). Importantly, expression of inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-8) or inflammasome components (NLRP3, CASP1, PYCARD) was dampened. The role of IFN-λ3 to counterbalance inflammatory processes and bridge innate and adaptive immune responses in camelid species is discussed. Our findings shed light into key mechanisms on how reservoir species control MERS-CoV in the absence of clinical disease.

Tissue distribution of angiotensin-converting enzyme 2 (ACE2) receptor in wild animals with a focus on artiodactyls, mustelids and phocids

Natural cases of zooanthroponotic transmission of SARS-CoV-2 to animals have been reported during the COVID-19 pandemic, including to free-ranging white-tailed deer (Odocoileus virginianus) in North America and farmed American mink (Neovison vison) on multiple continents. To understand the potential for angiotensin-converting enzyme 2 (ACE2)-mediated viral tropism we characterised the distribution of ACE2 receptors in the respiratory and intestinal tissues of a selection of wild and semi-domesticated mammals including artiodactyls (cervids, bovids, camelids, suids and hippopotamus), mustelid and phocid species using immunohistochemistry. Expression of the ACE2 receptor was detected in the bronchial or bronchiolar epithelium of several European and Asiatic deer species, Bactrian camel (Camelus bactrianus), European badger (Meles meles), stoat (Mustela erminea), hippopotamus (Hippopotamus amphibious), harbor seal (Phoca vitulina), and hooded seal (Cystophora cristata). Further receptor mapping in the nasal turbinates and trachea revealed sparse ACE2 receptor expression in the mucosal epithelial cells and occasional occurrence in the submucosal glandular epithelium of Western roe deer (Capreolus capreolus), moose (Alces alces alces), and alpaca (Vicunga pacos). Only the European badger and stoat expressed high levels of ACE2 receptor in the nasal mucosal epithelium, which could suggest high susceptibility to ACE2-mediated respiratory infection. Expression of ACE2 receptor in the intestinal cells was ubiquitous across multiple taxa examined. Our results demonstrate the potential for ACE2-mediated viral infection in a selection of wild mammals and highlight the intra-taxon variability of ACE2 receptor expression, which might influence host susceptibility and infection.

Distribution of Coronavirus Receptors in the Swine Respiratory and Intestinal Tract

Coronaviruses use a broad range of host receptors for binding and cell entry, essential steps in establishing viral infections. This pilot study evaluated the overall distribution of angiotensin-converting enzyme 2 (ACE2), aminopeptidase N (APN), carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), and dipeptidyl peptidase 4 (DPP4) receptors in the pig respiratory and intestinal tract. All the receptors evaluated in this study were expressed and differentially distributed through the respiratory and intestinal tract. The presence and expression levels of these receptors could determine susceptibility to coronavirus infections. This study may have important implications for the development of research models and the assessment of the potential risk and introduction of novel coronaviruses into the swine population.

Evaluation of alpaca tracheal explants as an ex vivo model for the study of Middle East respiratory syndrome coronavirus (MERS-CoV) infection

Middle East respiratory syndrome coronavirus (MERS-CoV) poses a serious threat to public health. Here, we established an ex vivo alpaca tracheal explant (ATE) model using an air-liquid interface culture system to gain insights into MERS-CoV infection in the camelid lower respiratory tract. ATE can be infected by MERS-CoV, being 10³ TCID₅₀/mL the minimum viral dosage required to establish a productive infection. IFNs and antiviral ISGs were not induced in ATE cultures in response to MERS-CoV infection, strongly suggesting that ISGs expression observed in vivo is rather a consequence of the IFN induction occurring in the nasal mucosa of camelids.

Establishment of well-differentiated camelid airway cultures to study Middle East respiratory syndrome coronavirus

In 2012, Middle East respiratory syndrome coronavirus (MERS-CoV) emerged in Saudi Arabia and was mostly associated with severe respiratory illness in humans. Dromedary camels are the zoonotic reservoir for MERS-CoV. To investigate the biology of MERS-CoV in camelids, we developed a well-differentiated airway epithelial cell (AEC) culture model for Llama glama and Camelus bactrianus. Histological characterization revealed progressive epithelial cellular differentiation with well-resemblance to autologous ex vivo tissues. We demonstrate that MERS-CoV displays a divergent cell tropism and replication kinetics profile in both AEC models. Furthermore, we observed that in the camelid AEC models MERS-CoV replication can be inhibited by both type I and III interferons (IFNs). In conclusion, we successfully established camelid AEC cultures that recapitulate the in vivo airway epithelium and reflect MERS-CoV infection in vivo. In combination with human AEC cultures, this system allows detailed characterization of the molecular basis of MERS-CoV cross-species transmission in respiratory epithelium.

Middle East respiratory syndrome coronavirus infection in camelids

Middle East respiratory syndrome coronavirus (MERS-CoV) is the cause of a severe respiratory disease with a high case fatality rate in humans. Since its emergence in mid-2012, 2578 laboratory-confirmed cases in 27 countries have been reported by the World Health Organization, leading to 888 known deaths due to the disease and related complications. Dromedary camels are considered the major reservoir host for this virus leading to zoonotic infection in humans. Dromedary camels, llamas, and alpacas are susceptible to MERS-CoV, developing a mild-to-moderate upper respiratory tract infection characterized by epithelial hyperplasia as well as infiltration of neutrophils, lymphocytes, and some macrophages within epithelium, lamina propria, in association with abundant viral antigen. The very mild lesions in the lower respiratory tract of these camelids correlate with absence of overt illness following MERS-CoV infection. Unfortunately, there is no approved antiviral treatment or vaccine for MERS-CoV infection in humans. Thus, there is an urgent need to develop intervention strategies in camelids, such as vaccination, to minimize virus spillover to humans. Therefore, the development of camelid models of MERS-CoV infection is key not only to assess vaccine prototypes but also to understand the biologic mechanisms by which the infection can be naturally controlled in these reservoir species. This review summarizes information on virus-induced pathological changes, pathogenesis, viral epidemiology, and control strategies in camelids, as the intermediate hosts and primary source of MERS-CoV infection in humans.

Middle East Respiratory Syndrome Coronavirus

The past two decades have witnessed the emergence of three zoonotic coronaviruses which have jumped species to cause lethal disease in humans: severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1), Middle East respiratory syndrome coronavirus (MERS-CoV), and SARS-CoV-2. MERS-CoV emerged in Saudi Arabia in 2012 and the origins of MERS-CoV are not fully understood. Genomic analysis indicates it originated in bats and transmitted to camels. Human-to-human transmission occurs in varying frequency, being highest in healthcare environment and to a lesser degree in the community and among family members. Several nosocomial outbreaks of human-to-human transmission have occurred, the largest in Riyadh and Jeddah in 2014 and South Korea in 2015. MERS-CoV remains a high-threat pathogen identified by World Health Organization as a priority pathogen because it causes severe disease that has a high mortality rate, epidemic potential, and no medical countermeasures. MERS-CoV has been identified in dromedaries in several countries in the Middle East, Africa, and South Asia. MERS-CoV-2 causes a wide range of clinical presentations, although the respiratory system is predominantly affected. There are no specific antiviral treatments, although recent trials indicate that combination antivirals may be useful in severely ill patients. Diagnosing MERS-CoV early and implementation infection control measures are critical to preventing hospital-associated outbreaks. Preventing MERS relies on avoiding unpasteurized or uncooked animal products, practicing safe hygiene habits in health care settings and around dromedaries, community education and awareness training for health workers, as well as implementing effective control measures. Effective vaccines for MERS-COV are urgently needed but still under development.

Enhanced replication fitness of MERS-CoV clade B over clade A strains in camelids explains the dominance of clade B strains in the Arabian Peninsula

Middle East respiratory syndrome coronavirus (MERS-CoV) continues infecting humans and dromedary camels. While MERS-CoV strains from the Middle East region are subdivided into two clades (A and B), all the contemporary epidemic viruses belong to clade B. Thus, MERS-CoV clade B strains may display adaptive advantages over clade A in humans and/or reservoir hosts. To test this hypothesis in vivo, we compared an early epidemic clade A strain (EMC/2012) with a clade B strain (Jordan-1/2015) in an alpaca model monitoring virological and immunological parameters. Further, the Jordan-1/2015 strain has a partial amino acid (aa) deletion in the double-stranded (ds) RNA binding motif of the open reading frame ORF4a protein. Animals inoculated with the Jordan-1/2015 variant had higher MERS-CoV replicative capabilities in the respiratory tract and larger nasal viral shedding. In the nasal mucosa, the Jordan-1/2015 strain caused an early IFN response, suggesting a role for ORF4a as a moderate IFN antagonist in vivo. However, both strains elicited maximal transcription of antiviral interferon-stimulated genes (ISGs) at the peak of infection on 2 days post inoculation, correlating with subsequent decreases in tissular viral loads. Genome alignment analysis revealed several clade B-specific amino acid substitutions occurring in the replicase and the S proteins, which could explain a better adaptation of clade B strains in camelid hosts. Differences in replication and shedding reported herein indicate a better fitness and transmission capability of MERS-CoV clade B strains than their clade A counterparts.

Can cilia provide an entry gateway for SARS-CoV-2 to human ciliated cells?

A worldwide coronavirus pandemic is in full swing and, at the time of writing, there are only few treatments that have been successful in clinical trials, but no effective antiviral treatment has been approved. Because of its lethality, it is important to understand the current strain's effects and mechanisms not only in the respiratory system but also in other affected organ systems as well. Past coronavirus outbreaks caused by SARS-CoV and MERS-CoV inflicted life-threatening acute kidney injuries (AKI) on their hosts leading to significant mortality rates, which went somewhat overlooked in the face of the severe respiratory effects. Recent evidence has emphasized renal involvement in SARS-CoV-2, stressing that kidneys are damaged in patients with COVID-19. The mechanism by which this virus inflicts AKI is still unclear, but evidence from other coronavirus strains may hold some clues. Two theories exist for the proposed mechanism of AKI: 1) the AKI is a secondary effect to reduced blood and oxygen levels causing hyperinflammation and 2) the AKI is due to cytotoxic effects. Kidneys express angiotensin-converting enzyme-2 (ACE2), the confirmed SARS-CoV-2 target receptor as well as collectrin, an ACE2 homologue that localizes to the primary cilium, an organelle historically targeted by coronaviruses. Although the available literature suggests that kidney damage is leading to higher mortality rates in patients with COVID-19, especially in those with preexisting kidney and cardiovascular diseases, the pathogenesis of COVID-19 is still being investigated. Here, we present brief literature review supporting our proposed hypothesis of a possible link between SARS-CoV-2 cellular infection and cilia.

Type I and III IFNs produced by the nasal epithelia and dimmed inflammation are features of alpacas resolving MERS-CoV infection

While MERS-CoV (Middle East respiratory syndrome Coronavirus) provokes a lethal disease in humans, camelids, the main virus reservoir, are asymptomatic carriers, suggesting a crucial role for innate immune responses in controlling the infection. Experimentally infected camelids clear infectious virus within one week and mount an effective adaptive immune response. Here, transcription of immune response genes was monitored in the respiratory tract of MERS-CoV infected alpacas. Concomitant to the peak of infection, occurring at 2 days post inoculation (dpi), type I and III interferons (IFNs) were maximally transcribed only in the nasal mucosa of alpacas, while interferon stimulated genes (ISGs) were induced along the whole respiratory tract. Simultaneous to mild focal infiltration of leukocytes in nasal mucosa and submucosa, upregulation of the anti-inflammatory cytokine IL10 and dampened transcription of pro-inflammatory genes under NF-κB control were observed. In the lung, early (1 dpi) transcription of chemokines (CCL2 and CCL3) correlated with a transient accumulation of mainly mononuclear leukocytes. A tight regulation of IFNs in lungs with expression of ISGs and controlled inflammatory responses, might contribute to virus clearance without causing tissue damage. Thus, the nasal mucosa, the main target of MERS-CoV in camelids, seems central in driving an efficient innate immune response based on triggering ISGs as well as the dual anti-inflammatory effects of type III IFNs and IL10.

Middle East respiratory syndrome coronavirus (MERS-CoV) is the etiological agent of a respiratory disease causing high mortality in humans. In camelids, the main MERS-CoV reservoir host, viral infection leads to subclinical disease. Our study describes transcriptional regulations of innate immunological pathways underlying asymptomatic clinical manifestations of alpacas in response to MERS-CoV. Concomitant to the peak of infection, these animals elicited a strong transient type I and III interferon response and induction of the anti-inflammatory cytokine IL10 in the nasal mucosa. Meanwhile, a dimmed regulation of pro-inflammatory cytokines and induction of interferon stimulated genes was observed along the whole respiratory mucosa with a rapid clearance of the virus in tissues. Thus, innate immune responses occurring in the nasal mucosa might be key in controlling MERS-CoV disease by avoiding a cytokine storm. Understanding on how asymptomatic host reservoirs counteract MERS-CoV infection will aid in the development of antiviral drugs and vaccines.

Evolution, Ecology, and Zoonotic Transmission of Betacoronaviruses: A Review

Coronavirus infections have been a part of the animal kingdom for millennia. The difference emerging in the twenty-first century is that a greater number of novel coronaviruses are being discovered primarily due to more advanced technology and that a greater number can be transmitted to humans, either directly or via an intermediate host. This has a range of effects from annual infections that are mild to full-blown pandemics. This review compares the zoonotic potential and relationship between MERS, SARS-CoV, and SARS-CoV-2. The role of bats as possible host species and possible intermediate hosts including pangolins, civets, mink, birds, and other mammals are discussed with reference to mutations of the viral genome affecting zoonosis. Ecological, social, cultural, and environmental factors that may play a role in zoonotic transmission are considered with reference to SARS-CoV, MERS, and SARS-CoV-2 and possible future zoonotic events.

Induction of the Antiviral Immune Response and Its Circumvention by Coronaviruses

Some coronaviruses are zoonotic viruses of human and veterinary medical importance. The novel coronavirus, severe acute respiratory symptoms coronavirus 2 (SARS-CoV-2), associated with the current global pandemic, is characterized by pneumonia, lymphopenia, and a cytokine storm in humans that has caused catastrophic impacts on public health worldwide. Coronaviruses are known for their ability to evade innate immune surveillance exerted by the host during the early phase of infection. It is important to comprehensively investigate the interaction between highly pathogenic coronaviruses and their hosts. In this review, we summarize the existing knowledge about coronaviruses with a focus on antiviral immune responses in the respiratory and intestinal tracts to infection with severe coronaviruses that have caused epidemic diseases in humans and domestic animals. We emphasize, in particular, the strategies used by these coronaviruses to circumvent host immune surveillance, mainly including the hijack of antigen-presenting cells, shielding RNA intermediates in replication organelles, 2′-O-methylation modification for the evasion of RNA sensors, and blocking of interferon signaling cascades. We also provide information about the potential development of coronavirus vaccines and antiviral drugs.

Some pathological observations on the naturally infected dromedary camels (Camelus dromedarius) with the Middle East respiratory syndrome coronavirus (MERS-CoV) in Saudi Arabia 2018-2019

Background

The natural MERS-CoV infection in dromedary camels is understudied. Recent experimental studies showed no obvious clinical signs in the infected dromedary camels.

Aim

To study the pathological changes associated with natural MERS-CoV infection in dromedary camels.

Methods

Tissues from three MERS-CoV positive animals as well as two negative animals were collected and examined for the presence of pathological changes. The screening of the animals was carried out first by the rapid agglutination test and then confirmed by the RT-PCR. The selected animals ranged from six to twelve months in age. The sensitivity of the latter technique was much higher in the detection of MERS-CoV than the Rapid test (14 out of 75 animals positive or 18% versus 31 out of 75 positive or 41%).

Results

MERS-CoV induced marked desquamation of the respiratory epithelium accompanied by lamina propria and submucosal mononuclear cells infiltration, epithelial hyperplasia in the respiratory tract, and interstitial pneumonia. Ciliary cell loss was seen in the trachea and turbinate. In addition, degeneration of glomerular capillaries with the complete destruction of glomerular tufts that were replaced with fibrinous exudate in renal corpuscles in the renal cortex were noticed. Expression of the MERS-CoV-S1 and MERS-CoV-N proteins was revealed in respiratory tract, and kidneys.

Conclusion

To our knowledge, this is the first study describing the pathological changes of MERS-CoV infection in dromedary camels under natural conditions. In contrast to experimental infection in case of spontaneous infection interstitial pneumonea is evident at least in some affected animals.

The dipeptidyl peptidase-4 expression in some MERS-CoV naturally infected dromedary camels in Saudi Arabia 2018-2019

MERS-CoV usually causes respiratory and renal failure in some patients, which may be the underlying cause of death. Dromedary camels are the only known reservoir of the virus until now. They shed the virus in their body secretions thus potentiate a risk for human infection. MERS-CoV tropism and replication is mainly affected by the presence of certain receptor ligands on the target tissues. The dipeptidyl peptidase-4 (DPP-4) is believed to act as receptors for MERS-CoV. The main objective of this study was to determine the expression levels of the DPP-4 in various organs of some naturally infected camels. We conducted a surveillance study to identify some positive MERS-CoV infected camels. Three positive animals identified by the Real time PCR. Our results are clearly showing the high level of expression of the DPP-4 in various organs of these animals' particularly nasal turbinate, trachea, and lungs. The expression level may explain at least in part the pathogenesis of MERS-CoV in these organs. These findings confirm the pivotal roles of the DPP4 in the context of the MER-CoV infection in dromedary camels. Further studies are needed for a better understanding of the molecular pathogenesis of MER-CoV infection.

Epidemiological status of the Middle East respiratory syndrome coronavirus in 2019: an update from January 1 to March 31, 2019

Purpose

This study represents the current epidemiological status of Middle East respiratory syndrome coronavirus (MERS-CoV) worldwide in the first three months of 2019.

Patients and methods

Full details of the MERS-CoV cases available and published in the disease outbreak news on the WHO website were retrieved. Related details of laboratory-confirmed MERS-CoV were extracted and analyzed by standard statistical methods.

Results

A total of 107 cases of MERS-CoV, including 18 deaths (overall case fatality rate (CFR), 16.8%; male-specific CFR was 17.5% [14/80] and female-specific CFR was 14.8% [4/27]) were reported to WHO from the National International Health Regulation Focal Points of Saudi Arabia and Oman. The overall mean age was 50±17 years and 80 patients (74.8%) were male. The average time from the onset of the symptoms to the first hospitalization was 3±3.3 days; from the first hospitalization to laboratory confirmation was 3.6±6.5 days; from the onset of symptom to death was 17.5±11.7 days; and the mean length of hospitalization for patients with MERS-CoV was 3.5±3.9 days. Males in comparison to females had a 1.5-fold increased chance (adjusted OR =1.5 [95% CI: 1.3–1.8]) of death related to MERS-CoV infection; 1.05 [95% CI: 1.1–3.3], 1.05 [95% CI: 1.2–2.8] and 1.06 [95% CI: 1.2–2.0] for those who had exposure to camels, camel milk consumption, and close contact with MERS-CoV cases, respectively. Health care workers had 2.4 fold [95% CI: 1.2–3.1] greater odds of death compared to other people.

Conclusion

The knowledge obtained from this study can contribute to the development of a prevention program and early system warning against MERS-CoV infection.

Co-localization of Middle East respiratory syndrome coronavirus (MERS-CoV) and dipeptidyl peptidase-4 in the respiratory tract and lymphoid tissues of pigs and llamas

This study investigated the co‐localization of the Middle East respiratory syndrome coronavirus (MERS‐CoV) and its receptor dipeptidyl peptidase‐4 (DPP4) by immunohistochemistry (IHC) across respiratory and lymphoid organs of experimentally MERS‐CoV infected pigs and llamas. Also, scanning electron microscopy was performed to assess the ciliary integrity of respiratory epithelial cells in both species. In pigs, on day 2 post‐inoculation (p.i.), DPP4‐MERS‐CoV co‐localization was detected in medial turbinate epithelium. On day 4 p.i., the virus/receptor co‐localized in frontal and medial turbinate epithelial cells in pigs, and epithelial cells distributed unevenly through the whole nasal cavity and in the cervical lymph node in llamas. MERS‐CoV viral nucleocapsid was mainly detected in upper respiratory tract sites on days 2 and 4 p.i. in pigs and day 4 p.i. in llamas. No MERS‐CoV was detected on day 24 p.i. in any tissue by IHC. While pigs showed severe ciliary loss in the nasal mucosa both on days 2 and 4 p.i. and moderate loss in the trachea on days 4 and 24 p.i., ciliation of respiratory organs in llamas was not significantly affected. Obtained data confirm the role of DPP4 for MERS‐CoV entry in respiratory epithelial cells of llamas. Notably, several nasal epithelial cells in pigs were found to express viral antigen but not DPP4, suggesting the possible existence of other molecule/s facilitating virus entry or down regulation of DPP4 upon infection.