COVID-19 Crisis in the Light of Veterinary Science
Dr.UTPAL DAS
Supdtg. Veterinary Officer
Deptt. of Health, Kolkata Municipal Corporation
COVID-19 is certainly a newly emerged zoonosis; though it is not yet understood properly. A big uncertainty envelops the world since December, 2019. COVID-19 (SARS-CoV-2) is the latest addition to the seven corona viruses found in humans and experts said that all the viruses came either from bats or mice or turkey or cow or pig or cats or dogs. However, pneumonitis with unknown etiology were detected in Wuhan, China in December 2019, and shortly after, a novel coronavirus (sever acute respiratory syndrome coronavirus 2[SARS-CoV-2]) was identified as the causative agent. The virus spread rapidly to other parts of China and many other countries. Despite tremendous efforts to contain the disease, the World Health Organization declared the spread as a global pandemic, referred to as coronavirus disease 2019 (COVID-19).
As Veterinarian, we have been succeeding the development of COVID-19 and hence, the present popular article provides a knowledge update on these points:-
- Zoonotic transmission from animal to human
- Potential risks to animals
- Intra and inter species transmission between animals
- Possible reverse zoonotic dissemination from human to animal
- Development of suitable animal models necessary for the evolution of vaccine and anti viral drugs or drug regimen.
The possible mechanisms of transmission of SARS-CoV-2 include droplet inhalation; direct contact with the person infected by the disease, direct contact with the persons exposed to the virus (animal/meat handlers), infected animals, and indirect (fomites) contact transmission. SARS-CoV-2 may have evolved from pangolin-CoV and adapted to humans via natural selection. Further studies are needed to substantiate that pangolins are an intermediate host. According to another school of thought, the potential reservoirs for SARS-CoV-2 are bats. Protein sequences alignment and phylogenetic analysis showed that turtles, pangolin, and snakes have been identified as alternative intermediate hosts for SARS-CoV-2.
With wide host adaptability, and the ability to undergo mutations and genetic recombination, CoVs may continue to pose a potential threat to public health. The microbes, with their ability to undergo genetic variations, and survive inside different hosts may evolve into a novel species as evidenced from our previous experience with the Influenza virus. The novel CoV may have evolved in a similar fashion. Studies so far have noted that there may be two types of SARS-CoV-2 strains (L, and S type) circulating throughout the world. But the good news is that the SARS-CoV-2 is comparatively stable than its predecessor SARS-CoV in terms of the mutations and the genetic variations. SARS-CoV-2 has wide host adaptability that includes humans, birds, livestock, masked palm civets, mice, dogs, cats, camels, pigs, chickens, and bats, wherein they typically cause respiratory illness. Companion animals like Cats and Dogs are often in close contact with humans, and thus, it is important to determine their suspectibility to SARS-CoV-2. COVID-19 has been reported in two dogs in Hong Kong that live with COVID-19 human patients have become infected and tested positive. One of the dogs developed specific antibodies against SARS-CoV-2 and scroconverted, indicating an active infection. Canine cases of COVID-19 were also reported in the Netherlands and US. A family in North Carolina U.S.A. experienced mild COVID-19 symptoms, and their pug also showed mild symptoms with inappetence. All three family members tested SARS-CoV-2 positive, and the virus was detected in the dog. The family owned two dogs and a cat, but only one dog tested positive. In Netherlands, a COVID-19 patient owned a dog and three cats, and the dog was suffering severe breathing problems. This bulldog tested SARS-CoV-2 positive and was euthanized due to the illness. The three cats also developed specific antibodies for SARS-CoV-2. All four animals appeared to have contracted the virus from their COVID-19 owner. In contrast to dogs, cats appear to be highly susceptible to the virus. In Belgium, a cat living with its COVID-19 owner became clinically ill, exhibiting respiratory problems accompanied by diarrhea and vomiting. The specific viral sequence of SARS-CoV-2 was detected in the feces and gastric vomitus of the cat, and that sequence was identical to that of the cat owner, indicating the occurrence of reverse zoonotic transmission of SARS-CoV-2 from human to animal. In Wuhan, 102 cats were tested, and 15% of them were scroconverted, indicating SARS-CoV-2 exposure of cats from either people or other cats. An additional case of COVID-19 in cat was reported in Hong-Kong. This cat did not show any clinical signs, but oral, nasal, and fecal samples tested were found to be positive. In the US, SARS-CoV-2 positive cats have been reported in two separate areas in the state of New York. A veterinarian tested one cat after it exhibited mild respiratory symptoms. The cat was SARS-CoV-2 positive, but no one in the household was found as positive. This cat may have contracted the coronavirus outside of the house-hold from a person with COVID-19. In another case, a cat with respiratory symptoms and living with a COVID-19 patient tested positive. These data clearly show that cats are susceptible to SARS-CoV-2 and may contract COVID-19. A controlled experiment was conducted to support the observation showing that cats are susceptible to COVID-19. The results of that experiment showed that cats are highly susceptible to SARS-CoV-2, with the viral sequence detected in the nasal turbinates, soft palate, tonsils, and small intestine. The infections led to massive lesions in their nasal passages; adolescent cats were especially vulnerable to COVID-19. Notably, the coronavirus spread from infected cats to uninfected cats via respiratory droplets. Feline cases of COVID-19 have additionally been reported in Spain, France, and Germany
So, these companion animals are the victims of the reverse zoonosis, though rarely infected; but not infectious. Among farm animals, minks at two breeding farms in the Netherlands showed various symptoms including respiratory illness and were found to have been infected with SARS-CoV-2. The minks were likely to have contracted the virus from farm staff, and mink farms were subsequently placed under quarantine. A subsequent study suggested that an infection took place from minks to humans, and cats played a role in the spread of the virus between farms, implicating possible occurrence of interspecies transmission (cat to mink) and secondary zoonotic transmission (mink to human) of SARS-CoV-2. In experimental infections, pigs, chickens, and ducks remained SARS-CoV-2 negative and did not develop any clinical signs. Viral sequences were not detected in any swabs collected from virus-inoculated animals, and the animals remained sero-negative for two weeks post-infection. Therefore, pigs, chickens, and ducks seem not to be susceptible to SARS-CoV-2. Regardless, a wider range of farm animal species needs to be examined to assess the risks of SARS-CoV-2 infection and to identify possible impacts of COVID-19 on the agricultural and food supply industries.
It is logical to speculate that secondary transmission may occur from COVID-19 animals to humans, despite no direct evidence showing whether transmission from cats to humans can occur. Among wildlife, lions and tigers are susceptible to SARS-CoV-2. Four tigers and two lions at the Bronx Zoo in New York City, developed clinical symptoms associated with respiratory illness, and testing confirmed as SARS-CoV-2 positive. The big cats had been exposed to a zookeeper who was COVID-19 positive and actively shedding the virus, indicating occurrence of reverse-zoonotic transmission.
Susceptibility to COVID-19 has been evaluated in laboratory animals, companion animals, and farm animals in attempts to identify animal models of SARS-CoV-2 infection. Upon infection, susceptible animals may not show symptoms, or even if they do exhibit clinical signs, their symptoms may not match those of COVID-19 in humans. Thus, the establishment of an appropriate animal model is crucial. Among laboratory animals, ferrets, golden Syrian hamsters, and monkeys have been shown to be susceptible to SARS-CoV-2, and they develop clinical symptoms. Ferrets are a good model for human influenza, particularly as they can sneeze, spreading the virus in the air. SARS-CoV-2 infects ferrets, but fatalities have not been observed. The virus was detected in ferret nasal washes, saliva, urine, and faces, and airborne transmission was observed. A monkey-based study was conducted using four rhesus macaques. These monkeys were successfully infected, and viral replication occurred in the nose, pharynx, lung, and gut. Using this monkey model, the efficacy of remdesivir, a polymerase inhibitor, was examined. Recovery in remdesivir-treated animals was significantly better than that in control animals. Only one of six treated animals had mild breathing difficulty, whereas all animals in the control group showed breathing difficulty. In treated monkeys, the viral load in the lungs was significantly lower, and lung damage was significantly milder than those in the control animals.
The high susceptibility of the Felidae family (lions, tigers, jaguars, leopards, cougars, and cheetahs) and, in particular, monkeys to COVID-19 implies a potential for outbreaks in great apes (chimpanzees, gorillas, orangutans) in zoos, animals-holding facilities, primate research centers, and national wildlife parks. Risk assessments are needed to prepare for the conservation and protection of such animals.
A combination of ecological disturbance, deforestation like landscape changes, human behaviors, and public health factors contributes to the frequency of contacts between humans and wildlife, and such contacts pose a risk of exposure to transboundary animal viruses. Moreover, it is alarming that 75% of the 132 emerging human infections over the past 12 years have been caused by pathogens originating from animals and have the potential to create global problems. As, we are living in the “Era of Zoonoses”, the application of knowledge of ‘Clinical Veterinary Public Health’ is of immense importance. In this period within the COVID-19 pandemic, societies and human behaviors are quickly changing, and to accommodate these changes, the customary roles of public health Veterinarians should unfold accordingly. This pandemic is like a world war between the virus and the science; except in this case, the whole world is on the same side and this war can be won by complete global collaboration collectively. COVID-19 pandemic perhaps acts as a catalyst to initiate One Health Surveillance (OHS) in many countries. Public Health Veterinarians should have significant roles in maintaining healthy ecosystems and protecting animals and humans from emerging and transboundary infections. Such roles should be based on the One Health framework, the application of which can reduce economic impacts on the livestock industry and food supply.
