A recent study confirmed that cats can be infected with COVID-19, and may also transmit the virus to other cats. Still, the evidence has failed to support that cats can transmit the disease to humans. People who have contracted the disease still psoe the biggest risk of transmitting it to others.
The confirmation of infection and transmission of SARS-CoV-2 between cats was led by the University of Wisconsin-Madison, a public research university in the US. Researchers conducted tests in cats after cases of infection were reported. The results confirmed that cats could be infected and might transmit the disease to other felines. However, researchers strongly affirmed that humans with COVID-19 still pose the highest threat to other people. Results were published in the New England Journal of Medicine.
Presence of SARS-CoV-2 in Cats Possible
As a zoonotic disease, COVID-19 is caused by a virus that originated from animals. Though, scientists have not yet confirmed the true origin. In the middle of this pandemic, the largest part of the research is dedicated to the aspects of human infectivity and virology of SARS-CoV-2, the novel coronavirus. However, reports of infection in household pets have alarmed veterinarians and clinicians. Thus, research in the potential of cats and dogs to spread the disease is under investigation.
At the University of Wisconsin-Madison, a group of researchers investigated the odds of cats contracting and transmitting SARS-CoV-2. It turned out that the household feline could get infected and might spread the disease, at least, to other cats. The evidence they found in this research was not enough to support cats as a spreader of COVID-19 to people. The risk of people with COVID-19 spreading it to other individuals would be higher, compared to the assumption in cats.
"It's something for people to keep in mind. If they are quarantined in their house and are worried about passing COVID-19 to children and spouses, they should also worry about giving it to their animals," said Peter Halfmann, a lead author of the study and research professor at UW-Madison.
In the study, three cats were selected in a series of experiments to determine if the pets could be infected by COVID-19. On day one, the cats were administered with SARS-CoV-2 and observed for 24 hours. A day after the exposure, researchers retrieved nasal swab samples from the cats and tested them for viral presence. Two of the cats tested positive from the nasal swab samples, which only left one cat uninfected. For three days, the cats were simply observed by researchers.
Within three days, all cats were found to have SARS-CoV-2. This shows that a cat could get the virus and might spread it to other cats. Yet, the transmission mode is unclear. So, the next day, researchers introduced one cat to join the cages of each of the three cats, bringing the total cat models to six. Every day, they obtained nasal and rectal swab samples from six cats, in which the three newly introduced cats were not administered with SARS-CoV-2.
Two days later, one of the formerly uninfected cats was discovered shedding the virus presented in the nasal swab. Six days later, all of the cats were shedding the virus. But none of the rectal swab samples were detected with viral shedding. The shedding was limited to the nasal passages of the pets and it lasted for up to six days.
For the health condition of the cats in this study, the virus seemed to be nonlethal to the animals' health since none developed symptoms. Eventually, the cats became clear of the virus without developing obvious clinical signs of COVID-19.
"That was a major finding for us — the cats did not have symptoms," expressed Yoshihiro Kawaoka, a lead author of the study and faculty member at the University of Tokyo.
Researchers concluded that cats can become infected with SARS-CoV-2 if exposed to a person or other cats who are positive of COVID-19. Once the cats contracted the virus, they may spread to other cats and possibly other household pets without someone knowing. Because the cats are unlikely to develop symptoms, they may be considered as carriers. The angle of cats as vectors was not recognized in the study.
The implication of the study findings is this: if people are worried about spreading COVID-19 to other household members, they should worry first about passing it to their pets. Cats and dogs may not develop symptoms but they can temporarily carry the virus, which may be transferred to a preferred host. As such, the research team strongly recommends that people with COVID-19 not interact with cats and other pets. As much as possible, the patient must be isolated in a room, and pets should be prevented from entering that room to avert the unintentional spread of the disease in the household.
Severe Outcomes of Patients with COVID-19
The transmission of COVID-19 between people is the main reason why vulnerable population groups are severely affected by this pandemic. The majority of confirmed deaths worldwide is among older people, people with chronic conditions, and people with weaker immune systems. According to the Morbidity and Mortality Weekly Report by the Centers for Disease Control and Prevention, a US agency, hospitalization and mortality rates were greater in older people in the US, between February 12 and March 16, 2020.
Within that period, a total of 2,449 laboratory-confirmed cases of COVID-19 required hospital admission. In those cases, the hospitalization rate was 20.7% to 31.4%, the admission rate to the intensive care unit (ICU) was 4.9% to 11.5%, and the fatality rate was 1.8% to 3.4% across all ages. For the hospitalization, the age group with the highest rate was aged 85 years and older at 31.3% to 70.3%. For admission to ICU, the age group with the highest rate was aged 75 to 84 years at 10.5% to 31%. And for fatality, the age group with the highest rate was aged 85 years and older at 10.4% to 27.3%. This shows that the elderly would likely be more prone to COVID-19, compared to adults, teenagers, and children.
Despite the implication of the findings, the researchers say that cats do not readily spread SARS-CoV-2 to humans. Humans positive with COVID-19 have the greatest chance of transmitting the virus to people. No evidence suggests that cats can make people sick with COVID-19 and no records have proven that people have gotten ill because of their cats. As far as experts know, humans are the ones spreading the virus to household pets.