Coronaviruses are a large family of viruses that can infect both animals and humans. They are a respiratory virus named for the crown-like spikes on their surface. These viruses are culprits in several outbreaks across the globe.
Usually, coronaviruses spread in animals but can jump to humans. There are seven known types of human coronaviruses, wherein four types, namely KHU1, OC43, NL63, and 229E, cause mild to moderate respiratory infections, such as the common cold.
Three types, however, cause severe respiratory infections – the severe acute respiratory syndrome coronavirus (SARS-CoV) and the Middle East Respiratory Syndrome coronavirus (MERS-CoV).
The seventh coronavirus type is the novel SARS-CoV-2 that has spread from China across the world, causing the ongoing COVID-19 pandemic.
“The World Organization for Animal Health (OIE) has reported the natural infection of SARS-CoV-2 in at least ten animal species across continents including the Americas, Europe, Africa and Asia: domestic cats and dogs, tigers, lions, cougar, snow leopard, puma, mink, ferrets, gorilla, and otter”, says the team.
Determination of susceptible host is important in understanding the ecology of the SARS-CoV-2 virus and also potential reservoirs that can lead to animal-to-human transmission.
The SARS-CoV-2 virus has been shown to infect a wide range of animals naturally and experimentally, and prior studies indicate deer are susceptible to infection. White-tailed deer (Odocoileus virginianus) fawns have been found to be susceptible to SARS-CoV-2.
White-tailed deer are among the most abundant and geographically widespread wild ruminants in the U.S. Historically, deer contact with humans has resulted in diseases being spread to human populations.
Studying SARS-CoV-2 susceptibility and transmission in adult white-tailed deer was the objective of a new study posted to the bioRxiv* pre-print server.
This study also assessed competition between the two SARS-CoV-2 isolates, the ancestral strain, and the alpha variant.
“Additionally, the emergence and sustained transmission of SARS-CoV-2 variants of concern (VOC) has important implications in virus evolution and pathogenesis”, says the team.
What did the study involve?
The study involved a Vero6 cell line for virus propagation and transmission. Six female white-tailed deer, of which five were pregnant, approximately two years of age, were involved in the study. Four deer were infected with the ancestral strain and alpha variant and two uninfected deer were allowed to mingle with the infected ones one day post-infection.
Any signs of clinical symptoms were studied, and nasal, oropharyngeal, and rectal swabs were collected on specific days post-infection. Tissues were also collected from the upper respiratory tract (URT) and lower respiratory tract (LRT), gastrointestinal tract (GIT), central nervous system as well as accessory organs.
This was followed by RNA extraction and reverse transcription-quantitative PCR (RT-qPCR), Next-Generation Sequencing, detection of neutralizing antibodies against SARS-CoV-2, and histopathology studies of the tissue samples.
What did the study find?
Research showed high copy numbers of viral RNA in the clinical samples and tissues from the infected deer. It was also found that infection with the alpha variant leads to abundant production of the viral nucleocapsid N protein.
Tissues collected 4 days post-challenge (DPC) and 18 DPC demonstrated presences of SARS-CoV-2 in the lymphatic tissue and the upper respiratory tissues.
“Histological evaluations in the upper and lower respiratory tract tissues collected at 4 DPC revealed pathological changes described as rhinitis, marked attenuation of the respiratory epithelium of the trachea, bronchitis, and in some cases bronchiolitis”, says the team.
Next-Generation Sequencing reveals a competitive advantage of the alpha variant over the ancestral strain. This advantage is associated with Asp to Gly substitution at the amino acid position 614 of the S protein, leading to an enhanced affinity for the ACE2 receptor.
“Interestingly, we only detected viral RNA in the uterus of the deer which was not pregnant, but also had higher viral RNA levels detected systemically in tissues compared to the pregnant doe necropsied at the same time point 4 DP”, says the team.
However, it is difficult to draw any conclusion due to the small number of animals and the short study duration.
What did the authors conclude?
“Recent large-scale SARS-CoV-2 surveillance efforts in animal and humans have found evidence of reverse zoonosis (human-animal) resulting in natural infections in companion animals, farmed mink, primates, and large cat species in several countries”, says the team.
The source of these infections is mostly infected animal care workers and pet owners. However, SARS-CoV-2 was also found to mutate and cross back into the human population by giving rise to different variants that make it crucial to identify host species capable of acting as reservoirs, leading to secondary zoonotic infections in the future.
“Furthermore, this work demonstrates the need for more intensive, focused surveillance efforts on high-risk animal populations, such as farmed and wild white-tailed deer and mule deer populations, as well as farm, wildlife and zoo workers, in order to identify new animal-derived SARS-CoV-2 variants which may evade current mitigation strategies”, adds the team.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.