Scanning Electron Microscopic Findings on Respiratory Organs of Some Naturally Infected Dromedary Camels with the Lineage-B of the Middle East Respiratory Syndrome Coronavirus (MERS-CoV) in Saudi Arabia-2018

The currently known animal reservoir for MERS-CoV is the dromedary camel. The clinical pattern of the MERS-CoV field infection in dromedary camels is not yet fully studied well. Some pathological changes and the detection of the MERS-CoV antigens by immunohistochemistry have been recently reported. However, the nature of these changes by the scanning electron microscope (SEM) was not revealed. The objective of this study was to document some changes in the respiratory organs induced by the natural MERS-CoV infection using the SEM. We previously identified three positive animals naturally infected with MERS-CoV and two other negative animals. Previous pathological studies on the positive animals showed varying degrees of alterations. MERS-CoV-S and MERS-CoV-Nc proteins were detected in the organs of positive animals. In the current study, we used the same tissues and sections for the SEM examination. We established a histopathology lesion scoring system by the SEM for the nasal turbinate and trachea. Our results showed various degrees of involvement per animal. The main observed characteristic findings are massive ciliary loss, ciliary disorientation, and goblet cell hyperplasia, especially in the respiratory organs, particularly the nasal turbinate and trachea in some animals. The lungs of some affected animals showed signs of marked interstitial pneumonia with damage to the alveolar walls. The partial MERS-CoV-S gene sequencing from the nasal swabs of some dromedary camels admitted to this slaughterhouse confirms the circulating strains belong to clade-B of MERS-CoV. These results confirm the respiratory tropism of the virus and the detection of the virus in the nasal cavity. Further studies are needed to explore the pathological alterations induced by MERS-CoV infection in various body organs of the MERS-CoV naturally infected dromedary camels.

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.