Current research generally believes that the new coronavirus may be derived from bats. How the new coronavirus spreads from bats to humans also requires direct contact between humans and intermediate host animals.
However, it is unclear which animals are intermediate hosts of the new coronavirus. Recently, some scientific research teams are starting from which daily animals are susceptible to new coronaviruses to answer these questions, which is also critical to the prevention and control of the epidemic.
On April 3, local time, the research team of the State Key Laboratory of Agricultural Microbiology at Huazhong Agricultural University and the Wuhan Institute of Virology, Chinese Academy of Sciences jointly published a new study on the preprint platform bioRxiv, "SARS-CoV-2 neutralizing serum antibodies in cats: a serological investigation".
They found through cat serum survey that serum ELISA test of 102 cats collected after outbreak of new coronavirus in Wuhan area showed that serum from 15 cats (14.7%) was positive for the receptor binding domain (RBD) of new coronavirus.
Among the positive samples, 11 had a novel coronavirus neutralizing antibody. Among them, 3 cats whose patients were patients with novel coronavirus pneumonia had the highest neutralizing titers, indicating that the high neutralizing titers may be due to cats and novel coronavirus pneumonia. Caused by close contact between patients.
Corresponding authors of the study include the State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Professor of the College of Veterinary Medicine, Academician Jin Meilin, Director of the Key Laboratory of Veterinary Diagnostic Preparations of the Ministry of Agriculture, Director of the Center for Emerging Infectious Diseases, Wuhan Institute of Virology, Chinese Academy of Sciences, Chinese Academy of Sciences Researcher Shi Zhengli, Director of the Key Laboratory of Highly Pathogenic Pathogen Biology and Biosafety.
It is worth noting that within a week, the only two P4 laboratories in China (National Animal Disease Prevention and Control High-level Biosafety Laboratory, Chinese Academy of Sciences Wuhan National Biosafety Laboratory) have released information about cats and new corona. Heavy research on viruses.
This is the first research report on animals producing specific neutralizing antibodies against the new coronavirus under natural conditions. The data in the study show that the new coronavirus has infected the cat population in Wuhan during the outbreak.
The study has not been peer reviewed.
The research team said in this study that the new coronavirus infection in cats may be caused by humans passing the virus to cats. But they reminded that this still needs to be verified by investigating new coronavirus infections in large samples from cats before the outbreak.
At present, there is no evidence that the new coronavirus is transmitted from cats to humans.
However, on March 31, local time, Chen Hualan, academician of the Chinese Academy of Sciences, chief scientist of the Animal Influenza Foundation and Prevention Research and Innovation Team of the Harbin Veterinary Institute of the Chinese Academy of Agricultural Sciences, and director of the Harbin Veterinary Research Institute of the Chinese Academy of Agricultural Sciences The team led by Bu Zhigao, director of the high-level biosafety laboratory, published a study in bioRxiv.
Through a series of new coronavirus infection tests conducted in P4 (Biosafety Level 4) laboratories, they found that the new coronavirus does not replicate well in dogs, pigs, chickens and ducks, but in ferrets and cats. very effective. They also found that the virus could be transmitted from cat to cat through respiratory droplets.
Therefore, Shi Zhengli also mentioned in the study that this study pointed out the risk of cats transmitting new coronaviruses, and more research is needed to understand the transmission of new coronaviruses from humans to cats.
But it is important that "actions should be taken immediately to maintain an appropriate distance between humans and pet animals (such as cats and dogs), and strict sanitation and quarantine measures should be taken for these animals." Warnings and regulations to prevent this potential route of transmission.
Previous research by the Shi Zhengli team showed that the new coronavirus uses the same cell receptor angiotensin converting enzyme II (ACE2) as SARS-CoV to infect humans, suggesting that the new coronavirus has the same host range as SARS-CoV.
In 2003, some research teams around SARS also showed that SARS-CoV can infect ferrets and cats, which means that they may also be sensitive to new coronaviruses.
The research team pointed out that as one of the most popular pets, cats have very close contact with people.
Therefore, it is very important to investigate the prevalence of new coronaviruses in cats, especially in outbreak areas. However, so far, there is no investigation on the prevalence of new coronaviruses in cats.
Serological studies are suitable for screening antibodies against novel coronaviruses in animals. At present, several methods have been used for antibody testing of novel human coronaviruses. However, there are no available methods for detecting new cat coronavirus antibodies.
In this study, the researchers studied the serological prevalence of new coronaviruses in cats by indirect ELISA and virus neutralization tests.
The research team screened a total of 143 cat sera for antibody reactivity to the recombinant coronavirus S protein recombinant receptor binding domain (RBD) by ELISA.
The 39 serum samples collected before the outbreak had an OD value of 0.091-0.261 and a cut-off value of 0.32. Fifteen cats (14.7%) of the cat serum samples collected after the outbreak were seropositive, 5 of which were strongly positive, with an OD value greater than 0.6.
The research team also ruled out the effects of type I and type II feline infectious peritonitis virus (FIPV). Hyperimmune serum confirmed that there was no serological cross-reactivity between the two and the new coronavirus RBD protein.
In order to confirm whether there is a novel coronavirus-specific antibody in feline serum, the research team conducted a novel coronavirus neutralization test (VNT) on the above 15 ELISA positive sera.
Eleven of these cat sera have novel coronavirus neutralizing antibodies with titers ranging from 1/20 to 1/1080. Another 4 cat sera showed no neutralizing activity, including sample No. 12, which showed a strong ELISA positive and an OD value of 0.85.
Among the 5 strong ELISA positive samples, in addition to sample 12, the neutralizing activity of sample 10 was also very weak.
But the remaining three other ELISA strong positive samples No. 4, No. 14 and No. 15 were all observed to have strong neutralization, with a neutralization titer ranging from 1/360 to 1/1080.
Cats 1 and 5-9 came from the pet hospital. Cats 2 and 10-13 were initially stray cats. They were received in animal shelters after the outbreak.
It is worth noting that, consistent with high school and titer, the owners of cats No. 4, No. 14, and No. 15 were all diagnosed with new coronavirus infections.
The research team pointed out that the three cats whose owners were infected with the new coronavirus had the highest neutralizing titers (1/360, 1/360, and 1/1080, respectively). In contrast, the sera from pet hospital cats and stray cats the neutralizing activity is 1/20 to 1/80, which indicates that the high neutralizing titer may be due to the close contact between cats and patients with new coronavirus pneumonia.
Although the infection of stray cats is not fully understood, the research team believes that it is reasonable to speculate that these infections may be caused by exposure to the environment contaminated by the new coronavirus or patients with new coronavirus pneumonia fed to cats.
WB analysis of cat or human serum samples. The recovery serum of COVID-19 patients was used as a positive control, and the ELISA negative cat serum or healthy human serum was used as a negative control.
All serum samples tested were diluted 1: 100. C-N, cat seronegative. H-P, human convalescent serum. H-N, healthy human serum. Red arrow, S protein; blue arrow, N protein.
The research team also conducted a Western blot test to further verify the presence of new coronavirus-specific IgG in feline serum.
S and N proteins of purified coronavirus were detected in sera Nos. 4, 14 and 15, similar to human convalescent sera. In contrast, neither ELISA-negative cat serum nor healthy human serum detected a similar situation.
The paper points out that these results indicate that the new coronavirus infects cat populations in Wuhan, which means that this risk may also occur in other outbreaks.
A retrospective study confirmed that all ELISA-positive sera were derived from cat serum samples collected after the outbreak, which indicates that the infection of the cat may be caused by human transmission of the virus to the cat. The research team reminded that this still needs to be verified by investigating new coronavirus infections from large samples from before the outbreak.
In addition, the research team also collected nasopharyngeal and anal swabs from each cat, and performed a new coronavirus-specific qRT-PCR using a commercial kit targeting the ORF1ab and N genes. However, no double gene positive samples were detected.
The research team believes that the reason may be: first, the viral RNA load is too low to be detected; second, similar to the previous study of SARS-CoV, the cat may discharge the new coronavirus in a short time, plus no infection after infection Symptoms, the researchers did not grasp the moment of acute infection; third, the genome sequence of the cat may be mutated, causing the amplification of the cat sample to fail.
The research team mentioned that this is the first research report on animals producing specific neutralizing antibodies against new coronaviruses under natural conditions. Studies have pointed out the risks of cats transmitting new coronaviruses, and more research is needed to study the transmission of new coronaviruses from humans to cats.
"Importantly, immediate action should be taken to maintain an appropriate distance between humans and pet animals (such as cats and dogs), and strict hygiene and quarantine measures should be taken for these animals." The research team finally reminded.