COVID-19: A “Beastly” Virus

When Humans and Animals Share the Challenge

It will take long time till people could super pass the terrifying nightmare they had started in 2019 and lasted for some years, and still inducing clinical affections that become milder than before. In this period the entire world looked as if living in a science fiction film, with a microscopic protagonist demonstrating its power and bringing humanity to its knees: COVID-19. This virus, also known as SARS-CoV-2, highlighted the fragility of our healthcare system. Being originated from Asian wild animals then spilled over, though the intermediate hosts transmitted infection to humans have not yet been exactly identified. The state of panic and dread that struck everyone raised concern toward unravelling/discovery surrounding potential reservoirs of the COVID-19 that could spread and transmit the virus to human and other animals and threaten the public health. Current dynamics of COVID-19 pandemic necessitates further detailed investigations concerning the transmission ability of this virus from humans to animals and vice versa and enhancing implementation of one health approach. Identification of susceptible animal species is necessary, as they may act as bridge hosts or virus reservoirs and transmit the infection to human beings. With this article, we will try to illustrate the exerted efforts to identify the possibility of circulating the virus within other categories of animal species, of which are companion animals that we frequently contact.

Starting with companion animals; the raised question was “If I am positive for COVID-19, can I infect my dog or cat? And if this happens, can pet animals circulate infection to other hosts?”. Scientists tried to answer it through data collection and analysis regarding examination of animals for COVID-19 infection either through detection of the virus, by molecular diagnosis, or detection of developed antibodies. For instance, in Italy, the most affected European country by this contagion, scientists collected data about dogs and cats from different regions, particularly from Lombardy, the epicentre of human cases. Samples have been collected from household dogs and cats living with COVID-19 positive owners, as well as from stray colonies or shelters. The analyses conducted on the collected material involved different methodologies, ranging from a simple blood test to advanced diagnostic techniques. Results revealed positive infection in significant number of tested animals; all positive samples were for antibodies diagnosis and no positivity for virus diagnosis with the advanced molecular methods in any sample. There was one case of an Italian pet cat that exhibited clear clinical signs of pneumonia was diagnosed with SARS-CoV-2 infection as confirmed by quantitative RT–qPCR using deep pharyngeal swab. Compared to dogs, cats were much more susceptible to infection. Felines showed respiratory symptoms, ranging from moderate to severe, and could transmit the virus to other individuals of their species. On the other hand, canids did not exhibit any clinical symptoms, and so far, no cases of virus transmission from one individual to another have been recorded. The only explanation of this results was the transient shedding nature of this virus and the short viraemia. Another recorded challenge for diagnosis of virus was variation in time duration of viraemia between different species, and even among individuals of the same species which might be attributed to variation in immune response in individual animals. All these variations highlight the difficulty of a comprehensive understanding of the behavior of SARS-CoV-2. Further studies were carried out in other countries as United states of America (USA), France, China, Hong Kong, Spain and Brazil. These studies confirmed positivity of dogs and cats living in the same household with owners infected with COVID-19. The clinical manifestations were not specified and represented by mild and reversible, with mainly respiratory and gastrointestinal manifestations. These studies, the frequencies of SARS-CoV-2 infection confirmed by molecular methods. Where, 17.6% in cats, 1.7% in dogs, and 10.3% of households in USA; 4% in cats and all dogs negative in France; 12% in cats and 13% in dogs in China; 12% in cats and all dogs negative in Spain; and finally, 40% in cats, 28% in dogs, and 47.6% households in Brazil. There was evidence of SARS-CoV-2 RNA persistence in some animals. The majority of samples were detected by RT-PCR in samples collected during the second and third visits. These findings reinforce the importance of longitudinal studies to investigate SARS-CoV-2 infection in pets. Animal samples should be collected close to the human onset of symptoms, and followed by serial sample collections of animals in a period of nearly 30 days. This could explain the negativity of collected samples in Italy, which were represented by single animal sample. These data suggest that close contact with human COVID-19 cases is a major risk factor for SARS-CoV-2 infection in companion animals.

A recent report from EFSA “European Food Safety Authority” in 2023 concluded that cats, ferrets and hamsters are the companion animals at highest risk of SARS CoV-2 infection, which most likely originates from an infected human, and which has no or very low impact on virus circulation in the human population.

Broadening our perspective beyond companion animals, and go toward the wildlife. There are two categories of animals in this session; wildlife (refer to free-ranging wildlife, excluding captive wild animals such as in zoo), and animals kept in zoos (referred to as captive wild animals or zoo animals). These two categories are different in their connections and interactions with humans. Globally, the number of reported wildlife species to be naturally infected by SARS-CoV-2 grows steadily, also due to the active research in this field, which should be promoted.

Regarding captive wild animals “zoo animals”, these animals are in daily close contact with humans (caretakers and technicians). Thus, susceptible species can acquire the infection mainly from in-contact infected zoo workers. There are reports of both experimental and natural infection with SARS CoV-2, mainly felids and non-human great apes. According a recent report of WOAH (World Organisation of Animal Health), natural infections of SARS-CoV-2 have been reported only in tigers, lions, snow leopards, pumas, and gorillas at zoos. However, this is still at very high risk and there is no report of spillback transmission from animals to humans. Transmission between susceptible animals in the same enclosure could occur at moderate probability but it is difficult to prove. Overall, animals kept in zoos do not represent a major public health risk in relation to SARS-CoV-2.

The virus has demonstrated that it doesn’t spare even the inhabitants of forests and meadows, revealing that wild animals are not immune to it. Of the free-ranging wildlife, infection was reported in several wild carnivores, white-tailed deer in North America, lemurs, and minks. There are numerous factors, mostly “human,” that facilitate not only the potential spread of a virus but also the exchange of viruses between different species. Of these factors are; illegal trade of wild species, cultural practices, and popular beliefs that involve the use of these animals in human consumption and their sale in markets without adequate health measures.

Among farmed animals, American mink for fur production have the highest likelihood to become infected from humans or animals and further transmit SARS-CoV-2 within animal populations and to in-contact humans. Introduction of SARS-CoV-2 into mink farms is usually via infected humans.

It is imperative to recognize that the intermingling of species and the transmission of viruses between animals and humans are phenomena that, now more than ever, require serious attention. Finally, preventive measures should be applied to reduce the risks of SARS-CoV-2 spillover to wildlife. Such as, humans dealing with wildlife should follow biosecurity measures to minimize direct contact with wild animals, especially sick and dead animals. Furthermore, safe disposal of garbage and waste from human communities in both urban and rural settings.

In conclusion, Coronaviruses are known for their capacity to jump the so-called “species barrier” that facilitates the transmission of pathogens between different species. the COVID-19 pandemic has undoubtedly been a devastating event that has shaken the world in unimaginable ways.Even though human-to-animal spillover has been reported at several instances, SARS-CoV-2 transmission from animals-to-humans has only been reported from mink-to-humans in mink farms. Non-domestic animal has played a significant role in the transmission of the SARS-CoV-2 virus between animals and humans. The present situation also warrants the need for more research and investigations with regards to the SARS-CoV-2 circulation in animals and its animal-human interface implications along with targeted surveillance and dynamic risk assessments to get an insight on the infectivity of SARS-CoV-2 under natural conditions. This would aid to design and implement effective preventive strategies to limit the transmission of this pandemic virus. Only through a profound understanding and a collective commitment to collective well-being can we hope to aim for a future where the balance between humans, animals, and nature is the cornerstone of harmonious coexistence.


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