[Publication date of latest article cited: July 6, 2021]
Cats have moderate risk of COVID-19 transmission, dogs a low risk, and rodents have high to low risk, because of the degree of similarity of their angiotensin converting enzyme 2 (ACE2), the molecule on the outside of cells that SARS-CoV-2 attaches to (Damas et al.; Howard; Shojaee et al.). Household mammals could function as a vector and reservoir of SARS-CoV-2.
Experiments found that cats can be infected with SARS-CoV-2 by intranasal inoculation and by staying near an infected cat, indicating respiratory droplet transmission (Gaudreault et al.; Halfmann et al.; Kansas State University; Shi et al.). Cats living in human communities have had COVID-19 (Centers for Disease Control and Prevention “Confirmation…”; Schulz et al.). Both stray and domestic cats in Wuhan had antibodies to SARS-CoV-2 after the epidemic started, but not before, perhaps indicating infection from humans and cats (Zhang Q, Zhang H, et al.). Since stray cats typically interact minimally and indirectly with humans, this shows how transmissible this virus is. A serology survey of domestic cats in Germany in April – September 2020 found their antibody prevalence (0.69%) was similar to humans (0.85%), indicating natural transmission (Michelitsh et al.).
Cats and humans can transmit SARS-CoV-2 to each other. When infected humans lived with cats, most cats did not get infected (Barrs et al.). Infected cats had vomiting, appetite loss, cough, pnuemonia, and difficulty breathing (dyspnea) (Natale et al.) , as shown in the videos in this article: (Garigliany et al.).
Cats can also get infected with feline coronavirus (FCoV, FECOV, or FECV), which has structures and functions partly similar and partly different from SARS-CoV-2 (Acheson; Ryu). So if a cat had FECOV, that probably did not cause immunity to SARS-CoV-2.
Dogs have also been infected with SARS-CoV-2 in laboratories and households. Experiments with intranasal inoculation found dogs transmitted less efficiently than cats (Shi et al.). Several times dogs were infected, perhaps by their owners (Decaro et al.; Office International des Épizooties).
Houseflies near hospitals had SARS-CoV-2 RNA both inside and outside. This shows they hypothetically could transmit either mechanically or biologically, but does not prove they actually did transmit (Soltani, et al.). Scientists tried putting SARS-CoV-2 into stomachs and cells of several species of biting midges and mosquitoes, and none were infected. This shows they probably cannot transmit COVID-19 (Balaraman et al.).
The US CDC recommends that if people and animals live together, both animals and people should similarly take precautions and seek treatment (Centers for Disease Control and Prevention, “Confirmation” “If you have pets…”, “COVID-19.and Animals..”):
Do not let pets interact with people or other animals outside the household.
Keep cats indoors when possible to prevent them from interacting with other animals or people.
Walk dogs on a leash, maintaining at least 6 feet from other people and animals.
Avoid dog parks or public places where a large number of people and dogs gather.
If a person or animal is sick with COVID-19 (either suspected or confirmed by a test), restrict contact and stay isolated from other people and animals.
If a person or animal goes to a doctor, nurse, veterinarian, etc., tell the health professional about any exposed or sick people or animals in your home.
[Publication date of latest article cited: September 14, 2021]
Fomite surfaces are also one of the ways COVID-19 spreads (Anelich et al.; Centers for Disease Control and Prevention “Scientific Brief: SARS-CoV-2 Transmission”; Centers for Disease Control and Prevention “Scientific Brief: SARS-CoV-2 and Surface”; Lee E, Wada, et al.; Marzoli et al.; Wang C, Prather K, et al.; WHO “Coronavirus disease (COVID-19): How is it transmitted?”). Hands touching these virus-laden surfaces could transfer viruses to nose, eyes, or mouth (Brosseau “COVID-19 Transmission Messages”; Kwok). Scientists using PCR found SARS-CoV-2 RNA in many places near infected people. For example, in a laboratory study SARS-CoV-2 was on 65% of surfaces near infected people (Adenaiye et al.). In a Nebraska hospital, 65% – 82% of room surfaces, personal items, and toilets had SARS-CoV-2 RNA (Santarpia et al.). In hospitals in Wuhan, scientists found SARS-CoV-2 RNA on many surfaces in patient areas, ICUs, medical staff areas, and public areas. They suspected that when patients coughed and breathed, the virus-laden droplets and aerosols deposited on surfaces (Guo et al.; Liu Y, Ning, et al.). Patients who exhaled millions of SARS-CoV-2 viruses into the air also left SARS-CoV-2 on some, but not all of, the surfaces around them (Ma et al). In a Singapore hospital, PCR found SARS-CoV-2 on several high and low touch surfaces, even after daily cleaning of the high touch surfaces. This was associated with the first few days of the patients’ illness. PCR also found SARS-CoV-2 RNA in the air of most patients’ rooms, in particles sized >4 µm and 1–4 µm, even though none had aerosol-generating procedures or intranasal oxygen supplementation (Chia et al.). Surfaces had viral RNA even in the rooms used by a patient with only mild upper respiratory symptoms, in rooms without viral RNA in the air (Ong et al.), and rooms with asymptomatic infected people (Wei L, Lin, et al.). Even 12-47 days after symptom onset, surface samples around patients had SARS-CoV-2 RNA (Feng B, Xu K, et al.).
In London hospitals, RT-qPCR found SARS-CoV-2 RNA on most surfaces in most patients’ room, staff rooms, and a public area. They could not culture the viruses, perhaps because of low concentrations or long times since viruses were deposited (Zhou J, Otter, et al.). This might be explained by other fomite studies finding that “Although infectious virus was undetectable after 48 hours, viral RNA remained detectable for 7 days” (Matson et al.; van Doremalen et al.).
In places where COVID-19 infected people lived or visited, scientists found varying amounts of SARS-CoV-2 on surfaces. For example, on publicly-used surfaces early in the pandemic, most surfaces had SARS-CoV-2 RNA occasionally (Harvey A, Fuhrmeister, et al.). On one of the cruise ships having many infected passengers, scientists found SARS-CoV-2 RNA on many surfaces in rooms of both asymptomatic and symptomatic infected passengers 17 days after the passengers left. This shows that the viral RNA can remain there that long, maybe longer, but does not completely prove that this caused transmission (Moriarty et al.). Some public playground surfaces and water fountains had SARS-CoV-2 RNA (Kozer et al.).
Scientists also suspected that viruses moved from surfaces to the air. People could disturb virus-laden droplet deposits on surfaces, such as when taking off medical clothing (Guo et al.; Liu Y, Ning, et al.). For other examples, experiments found that guinea pig hair can transmit influenza to other guinea pigs, and rubbing tissue paper can disperse influenza viruses into the air, called “aerosolized fomites.” So, perhaps SAR-CoV-2 could be spread this way (Asadi, Gaaloul ben Hnia).
It would be difficult to prove or disprove if people could get SARS-CoV-2 from fomites. Two people were infected, perhaps via fomites or air, on air flights closely studied by the Korean Centers for Disease Control (Bae, Shin, et al.). When scientists controlled the variables in experiments, infected hamsters transmitted to other hamsters by using bedding from infected hamsters, by breathing air nearby, and by living in the same cage (Mohandas et al.).
Laboratory experiments found that SARS-CoV-2 remains viable for 28 days on smooth surfaces at 20 degrees Celsius (68 degrees Fahrenheit), but they did not test longer than 28 days. They cultured the viruses in cells to test viability, a more thorough method than using PCR to find viral RNA (Marzoli et al.; Riddell et al.). Another showed it lasting 3 hours to 7 days on different materials, but none tested them for longer than 7 days. One research team spread viable SARS-CoV-2 viruses on surfaces, took samples from the surfaces after different time lengths, found them viable. After 72 hours, the viruses were still viable on plastic and stainless steel, implying they might last longer. On cardboard, no viruses lasted longer than 24 hours, and some were not viable in even less time. On copper, no viruses lasted longer than 4 hours (Marzoli et al.; National Institutes of Allergies and Infectious Diseases; van Doremalen et al.). Another set of experiments found SARS-CoV-2 lasted up to 3 hours on tissue and printing papers, 2 days on wood and cloth, 4 days on banknotes and glass, and 7 days on surgical masks, plastic, and stainless steel (Chin AWH, Chu, et al.; Marzoli et al.). After drying these viruses and leaving them on surfaces for 48 hours, they could still infect Vero cells, showing that drying is insufficient to disinfect (Jang H, Ross). SARS-CoV-2 spread on surfaces with protein decreased little, but decreased greatly on surfaces without protein. This shows that these viruses in mucous and saliva droplets and aerosols on surfaces can last long and contribute to transmission (Pastorino et al.).
In comparison, this new coronavirus SARS-CoV-2 is about as stable on surfaces as the 2003 SARS-CoV virus (van Doremalen et al.). A review of similar betacoronaviruses (SARS and MERS) and less similar alphacoronaviruses (HCoV, a cause of the common cold) found they can last 9 days (Marzoli et al.; Kampf et al.). But the new virus is spreading to more people than SARS, probably because it creates more viruses inside infected people, and can transmit more from asymptomatic infected people to others (van Doremalen et al.).
In hospitals with many COVID-19 patients, cleaning removed viruses from surfaces. In the Nebraska hospital described above, staff used frequent cleaning, powered air purifying respirators, N95 filtering facepiece respirators, and other personal protective equipment, and no staff were infected (Santarpia et al.). In Wuhan hospitals, scientists and medical staff found SARS-CoV-2 RNA on surfaces, cleaned them and their hands, sampled the surfaces again, and found no SARS-CoV-2 RNA. This shows that hand, face, and surface hygiene could probably reduce transmission (Ong et al.).
Other experts believe that only a small portion of infected people got this virus from fomite surfaces (Ma et al.). Exposure risk from publicly contaminated surfaces is lower than from inhalation (Harvey A, Fuhrmeister, et al.). Some suggest that people should put more effort into preventing other transmission modes, especially aerosols and droplets (Centers for Disease Control “CDC Updates”; Goldman; Ives, Mandavilli; Lewis D “COVID-19 rarely spreads through surfaces”; The Lancet Respiratory Medicine; Thompson).
For more information on how to disinfect surfaces, please see the menu heading “Prevention,” section on “Cleaning and Disinfecting Surfaces.”
[Publication date of latest article cited: June 12, 2021]
No reports were found of SARS-CoV-2 transmitted by eating food (Anelich et al.; Chitrakar et al.; Desai, Aronoff “Food Safety and COVID-19”; International Commission on Microbiological Specifications for Foods; Lancombe et al.; Pressman et al.; Whitworth). Viral RNA was found in people’s intestinal systems, showing potential of oral-fecal transmission (Amirian; Gu et al.; Lamers et al.; Wong et al.; Yeo et al.). As described under the menu item “Bodily Fluids” section on “Feces,” some evidence shows that it might occur, depending on whether stomach acids prevent SARS-CoV-2 can pass through stomach acid into the intestines.
Cooking probably destroys SARS-CoV-2, but refrigeration and freezing do not (Anelich et al.). Heating it to 70 °C reduced it greatly (Chin AWH, Chu JTS, et al.). But refrigeration or freezing did not reduce it numbers or viability (Chin AWH, Chu JTS, et al.).
If SARS-CoV-2 is on food surfaces, and one touched it, it could be transmitted as on any fomite surface, but the risk is probably low (Anelich et al.; Food and Drug Administration; Pressman et al.). Some physicians asked the US Department of Agriculture to warn consumers about potential transmission via food (Physicians’ Committee). For example, inspectors found SARS-CoV-2 on one batch of chicken meat, but not on people who transported it (Wu, “You probably won’t catch coronavirus from frozen food”). Others found it on cold chain food packaging surfaces (Chi Y, Wang Q, et al.). In response, food companies increased uses of chemical and electronic technologies preventing contamination and microbial growth, monitoring spoilage, detecting SARS-CoV-2 and other pathogens, and reducing human contact with foods and between workers (Chitrakar et al.; Lancombe et al.; Mallakpour et al.). But these systems are not well developed in low income countries, so SARS-CoV-2 could transmit via vegetables and aquatic foods (Gwenzi).