COVID-19: spreading possibilities of human – animal – human and preventive measures

Purpose – This paper reviews the possibilities of coronavirus disease 2019 (COVID-19) spreading from infected humans to pet animals and from pet animals to other animals and humans. Design/methodology/approach – A systematic literature review and meta-analysis were performed on researcharticlesfromNovember2019toAugust2020.ThisstudyexploredurgentlyneededresearchissuesonCOVID-19infectionspreadingacrossanimalsandhumansandviceversa. Findings – Essential andmuch neededprecautionary measuresand necessary preventivesteps to protectpet animals from infection were highlighted. Originality/value – Essentialinvestigationandexperimentresultswerehighlighted.Thenecessarymeasure to prevent the spread of infection among and across species and people was analyzed.


Introduction
The start of 2020 is also the beginning of the rapid spread of coronavirus (CoV) in humans . The world is struck with an epidemic of coronavirus disease 2019 (COVID-19). First, it has emerged at the end of 2019 in Wuhan, China. The rate of infection and death is very high. Such that the World Health Organization (WHO) announced the COVID-19 disease as a pandemic. The COVID-19 is the variant of the Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS) viruses, which also caused the epidemics a few years ago. The virological and genetic studies on these viruses are suggested and confirmed that the bats are the sources for these families of different viruses [1].
In order to develop the therapies and vaccines, a suitable animal model is much needed. Several kinds of research are underway on determining the intermediate animal host of SARS-CoV-2, which caused infection among humans. The animal mammals such as bats and pangolins have the worth for extensive research on whether they act as the intermediate animal host for the SARS-CoV-2 virus to humans [2].

Methodology
This paper reviews the meta-analysis on possibilities of COVID-19 spreading from animal to human (transmission across various species) based on existing research studies. The systematic literature review and meta-analysis have been done on research articles from November, 2019 to August, 2020. Figure 1 depicts the method of meta-analysis and overview of the literature review. The literature is collected from ScienceDirect, Google scholar, PubMed/Medline and other resources. The research works are identified by searching the keyword (372). The duplicate articles/research papers, draft works and grey literature are excluded (93). These articles are further filtered (41) according to the theme of this paper. From 41 research articles/papers, 20 works are referenced in this paper.

COVID-19 across companion-animals
As the COVID-19 originated from animals, it leads to the discussion on possibilities of transmission diseases with the contact of pets. During January, 2020, China's National Health Commission had raised the issue of spreading of the COVID-19 among companion animals from their owners or through the contact with the outbreak. As the COVID-19 epidemic virus spreads between the mammals, the commission suggested few necessary precautions for the pet owners and the pets. In the month March, 2020, the WHO stated the pets are safe from the infection of COVID-19 [3].
Later in the same month, the pets also got the infection from the outbreak. Then the WHO admitted that the pet could be infected and suggested that with the lack of evidence that the possibility of spreading by animals and wild animals to humans is rare and minimal. The WHO also does not have a clear idea of whether the animals (pet/wild) can be sources of the COVID-19 virus that can spread to humans and other animals. After that, the first infection in animals (tiger) by transmission from human (zookeeper) is confirmed in the Bronx zoological garden [3][4][5].

Method of metaanalysis
Further, the Ministry of Health in Singapore reported the possibilities of spreading COVID-19 from animals to humans and humans to animals. Also, they considered that the pets are not a serious reservoir for the transmission of the virus [1,2,6]. Figure 2 illustrates the possible ways of COVID-19 infection transmission among the animal-human-animal-human cycle.
Shreen et al. [7] had reported that the consumption of CoV-infected animals as the food might be the cause of the transmission of the virus from animal to human. Further, it was recommended that the utilizing and consumption of live animals and birds as the food by humans should be banned. Typically, it was suggested that the CoVs could affect the various mammal species and birds including companion animals such as dogs/cats/monkeys, cows/horses/whales, etc. Also, the nature of the CoVs is mutations, which means it can transmit the infection among other animals, including humans, and make them zoonotic pathogens [8]. Further, it was suggested that CoVs might spread among diverse animal species. However, the intermediate animal host of the SARS-CoV-2 virus is still under investigation [9].

Results on infection from companion animal to human
In medical history, animal contact is the common high-risk factor for transmitting infection from animals to humans. Sahin et al. reported that the family of CoVs is common in bats, cattle, camels and cats. It is also stated that from these animals, the CoVs can spread to infect humans. Even in recent years, the family of these viruses (MERS/SARS) was infected humans caused epidemics [10]. Further, the palm cats and dromedary camels caused the outbreaks with CoVs viruses SARS/MARS [6,11,12]. The genetic and virological studies confirm that the bats are a natural reservoir for the family of CoVs viruses. Such that SARS/MARS are found in bats before spreading to humans [13].
In July, 2020, from the mink farm, it is confirmed that the COVID-19 is spreading from the minks to humans. Extensive understanding is required on the COVID-19 virus's gene expression on different animal species and its possible transmission to other species [1].

Research concerns, challenges and preventive measures
Even the current pandemic is triggered by the human to another human by transmission (notdriven by animals), we should immediately need to concern with few necessary precautions.
(1) An extensive study and experiments are required to understand the susceptibility of COVID-19 infection transmission from animal to human and its infection dynamics across the mammals. It is essential to identify the susceptible animal species for the COVID-19 infection and transmission across animals and humans.
(2) A meta-analysis is required on the prevalence of genetic characteristics of pet animals and other animals infected by the SAR-CoV-2 virus. Most importantly, the need is to develop the vaccines or therapies; the vaccines can be developed based on the genetic structure of intermediate host animal, which spread the infection to humans. Such that significant research should be concentrated to determine the intermediate host animal as well.
(3) A few studies suggested the pigs, mice and poultry (chickens, ducks, etc.) are not susceptible to the COVID-19 infection and transmission [15,18], and a few other reports suggesting that are susceptible. But we can not assure it because later in July, 2020, the farmed mink transmitted the infection back to humans. Therefore, extensive studies and experiments are much essential in continuing them as food for humans.
(4) The findings of few experiments and investigations suggest the companion cats, ferrets and dogs are having more susceptibility to getting infected from the human. Then an extensive study and analysis are required to know the possibilities these animals cannot revert to humans or the same animal species. That is, more studies are required on the possibilities of companion animals transferring the infection to humans.
(5) Recently, the ferrets are being studied and investigated in order to evaluate the vaccines or therapeutics for the COVID-19 viruses. Then what are the other animals that can be assessed for the developments of vaccines or therapeutics? Also, the success ratio of testing vaccines on animals to humans is questionable. (14) In this ambiguous scenario, to avoid our pets getting infected from peoples or peoples getting infected from pets or pets to get infected from other animals, we should follow a few precautious measures.
(15) Until a vaccine is successfully tested or explicit knowledge on infection spreading across the animal species, we should treat our companion animals with the following cares.
We should avoid the pets to interact with other animals and humans outside of our household.
We need to keep our pets indoors more possibly to prevent from outside infection.
We should maintain social distancing while walking among dogs or cats from other outside animals, even with the people.
Do not letting our pets in public places with other dogs, for example, with street dogs or other animals to gather.
Do not let our pets even in the people-crowded places [19].

Conclusions
As the susceptibility of the animal to human transmission of the COVID-19 virus is ambiguous, we need to follow a few precautious measures. In this paper, various possibilities of animal infection among different species are studied. Regarding the human-animalhuman infection scenario, many questions may arise. Few of them are as follows: what is the reliability of the poultry or livestock animals that will not get infected by SARS-CoV-2? What is the reliability of the results with few experiments, which says animal to human transmission of infection is rare? With few results, how can one say the pigs, duck and hens cannot be the virus reservoirs for the infection in humans? What are the testing methods available for the identification of infection in poultry or other animal species?.