Most human infectious illnesses are initially transmitted from animals, such as H1N1 influenza, Ebola virus, the SARS, MERS, and now the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes the coronavirus disease (COVID-19).
Viruses are parasitic fragments that await host cells to survive. Since they were first described, these pathogens have caused many outbreaks, epidemics, and pandemics in the past. One of the significant risk factors is human interaction with animals, and now, scientists want to determine if animals can contract these viruses from humans.
Novel Coronavirus SARS-CoV-2 Colorized scanning electron micrograph of an apoptotic cell (green) heavily infected with SARS-CoV-2 virus particles (purple), isolated from a patient sample. Image at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID
Zoonosis of SARS-CoV-2
A team of researchers in Germany aimed to investigate the susceptibility of potential animal hosts and the risk of zoonosis spill-over infections, which are illnesses transmitted to humans from animals. On the other hand, reverse zoonosis pertains to infections in humans that jump to animals.
Published in the journal The Lancet, the study underlines if certain animals can be hosts of the novel coronavirus or if they are susceptible to infection.
The team has found that pigs and chickens cannot be infected by SARS-CoV-2, while fruit bats and ferrets are susceptible to a SARS-CoV-2 infection. In particular, the susceptibility of ferrets is a valuable finding, since they could be utilized as a model animal for human infection to test treatments or vaccines.
The researchers, from the Friedrich Loeffler Institute (FLI), started infection studies in pigs, chickens, fruit bats, and ferrets by inoculating them nasally with the SARS-CoV-2 pathogen, mimicking the natural route of infection in humans.
The SARS-CoV-2 are found in the respiratory droplets when people cough, sneeze, or talk. The virus enters the body through the nose, mouth, and eyes. Once it enters, it triggers an infection that may cause symptoms such as cough, fever, and difficulty of breathing.
Egyptian fruit bats, a megabat species, were tested to determine if they are potential reservoirs for the virus. The team found that the bats became infected but did not manifest any symptoms of the disease. Further, they did not infect their fellow animals. Meanwhile, ferrets are a good model for humans in terms of respiratory infections as they can be efficiently infected with SARS-CoV-2. The virus replicates in ferrets, and they can transmit it to fellow animals.
“More efficient virus replication but no clinical signs were observed in ferrets, with transmission to all three direct contact animals. Mild rhinitis was associated with viral antigen detection in the respiratory and olfactory epithelium,” the researchers wrote in the paper.
The researchers concluded that farmed animals, such as pigs and chickens were resistant against intranasal SARS-CoV-2 inoculation under experimental conditions.
Sine ferrets resembled a mild infection in humans, they may be a useful animal model for testing vaccines and drugs against SARS-CoV-2.
To date, there is still no vaccine and treatment for COVID-19. However. there are currently 21 candidate vaccines in clinical evaluation, and 139 candidate vaccines in preclinical evaluation across the world.
Since late December 2019, when SARS-CoV-2 first emerged in Wuhan City, China, the virus has since spread to most countries across the globe, infecting more than 12.2 million people worldwide. The novel zoonotic illness has killed more than 554,000 people.
The United States is still the country with the highest number of confirmed cases, surpassing 3 million infections, and a death toll of more than 133,000.
South America is now one of the epicenters of the pandemic, with Brazil reporting a staggering 1.75 million cases and more than 69,000 deaths. Peru and Chile are also impacted by the outbreak, reporting more than 316,000 and 306,000 confirmed cases, respectively.
India and Russia also report high numbers of cases, with more than 767,000 and 706,000 cases, respectively.
Health officials still recommend observing proper preventive measures to avert infection. These include social distancing, hand washing, and regular disinfection. As many countries are easing lockdown measures, the number of cases is expected to skyrocket in the coming months. Until a vaccine is developed and administered, the novel coronavirus may still spread actively worldwide.
- Schlottau, K., Rissmann, M., Graaf, A., Schon, J., et al. (2020). SARS-CoV-2 in fruit bats, ferrets, pigs, and chickens: an experimental transmission study. The Lancet. https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(20)30089-6/fulltext#%20