Raccoon is a potential intermediate host for SARS-CoV-2

Researchers Friedrich Hofler Institute In Germany, studies have shown that raccoon dogs are potential intermediate hosts in the transmission of pathogens that cause severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-coronavirus disease 2019 (COVID-19) It was.

This study shows that animals bred on millions of farms across China are susceptible to infection, and other nearby raccoon dogs are susceptible to the virus.

Animals that were inoculated intranasally with SARS-CoV-2 were infected immediately, and animals that were exposed to the virus were infected.

“It is possible that raccoon dogs have played an unexplored role in the development of the pandemic, due to China’s significant contribution to the world’s fur production of over 50 million cats per year,” said Thomas Mettenleiter. Wrote a colleague.

The results of the study support the implementation of appropriate surveillance and risk mitigation strategies for both captive and wild raccoon dogs, they added.

A preprinted version of the paper is available on the server bioRxiv*, The article is undergoing peer review.

Study design (422 A) Outline of in vivo experiment with 28-day observation period. Animals (n = 9) were inoculated intranasally with 105 TCID50 / ml and three naive direct contacts were added at 1 dpi. At day 4 (animals #1, #2), day 8 (#3, #4), and day 12 (#5, #6), two raccoon dogs were sacrificed and necropsied. All remaining animals were euthanized 28 days post infection. Infected animals are highlighted in red. (B) Placement of individual cages for raccoon dogs in two separate rooms of the BSL 3 facility at Friedrich-Loeffler-Institut. Inoculated animals (brown), contacted animals (blue), and uninfected animals () are displayed.

Potential intermediate host

Since the first case of COVID-19 was confirmed in Wuhan at the end of last year, SARS-CoV-2 has swept the world and was declared a pandemic by the World Health Organization on March 11.^Th, 2020.

A virus closely related to SARS-CoV-2 has been confirmed in bats, but it is unknown whether it was transmitted directly to humans from bats or to intermediate hosts such as pangolins.

In the cases of SARS-CoV-1 and Middle East respiratory syndrome (MERS), it was finally found that an intermediate host was involved, but such an intermediate of SARS-CoV-2 has not yet been identified. not.

Pandemics have been caused by human-to-human transmission, but cases of contact with companion animals and human-to-animal transmission on mink farms have been reported.

“Increasing evidence supports the potential of some carnivore species to become infected with SARS-CoV-2 as a result of zoonoses, possibly leading to reinfection in humans,” Mettenleiter and the team said. ..

Natural SARS-CoV-1 infections in raccoon dogs have been reported, suggesting a potential involvement in the 2002-2003 outbreak. In addition, several studies have shown that in raccoon dogs, the host cell protein angiotensin converting enzyme 2 (ACE2) functions as an efficient receptor for both SARS-CoV-1 and SARS-CoV-2.

However, to date, there are no known studies investigating raccoon dog infection with SARS-CoV-1 or SARS-CoV-2 under controlled conditions and under serological surveillance.

What did your current research include?

Currently, Mettenleiter and colleagues susceptibility to SARS-CoV-2 in raccoon dogs by assessing virus transmission by infecting 9 animals with the virus and introducing 3 additional animals 24 hours after infection. Was tested.

Prior to the experiment, all animals were negative for virus by reverse transcription quantitative polymerase chain reaction and antibody test. Nine raccoon dogs (3 males and 6 females) were inoculated intranasally with 10 dogs.^Five TCID₅₀ SARS-CoV-2 2019_nCoV Muc-IMB-1.

Nasal, oropharyngeal and rectal swabs were taken 2, 4, 8, 12, 16, 21, and 28 days after infection, and blood samples were taken 4, 8, 12, 16, 21, 21, and 28 days after infection.

What did the research find?

Six of the first nine animals were infected with SARS-CoV-2. Animals had already begun to shed viral RNA from nasal and oropharyngeal swabs 2 days after infection, and infectious virus was isolated from individual animals by 4 days post infection.

Viral RNA was present in nasal swabs for up to 16 days after infection, with the highest amount of viral genome detected in nasal swabs, followed by oropharyngeal swabs and rectal swabs.

The virus was transmitted to two of the three contacted raccoon dogs introduced. One dog was negative because the neighbors in the cage did not shed the virus after infection.

None of the animals showed any obvious signs of infection, and no gross lesions, which may be due to SARS-CoV-2, were observed at necropsy.

However, histopathological analysis revealed mild rhinitis in 3 animals by day 4, 1 animal by day 8, and another by day 12.

“No other infection-related histopathological changes were observed, except for the mild rhinitis associated with the presence of viral antigens on the nasal mucosa,” the team said.

Serological analysis showed that by day 8 post infection, all animals had antibodies specific for SARS-CoV-2 and 2 of the inoculated animals were infected Neutralizing antibody

Testing for viral mutations

To test if viral adaptation occurred during the infection, the team performed a high-throughput sequence of SARS-CoV-2 reisolated from the nasal swabs of one inoculated dog and one infected contact dog. I ran it. The reisolated virus was identical to the inoculum and showed no mutations, suggesting that the virus was already well adapted to this potential host.

“The combination of rapid high levels of viral shedding and subtle clinical signs and histopathological changes, lack of seroconversion and viral adaptation underscores the role of raccoon dogs as potential intermediate hosts.” The team is writing.

The researchers say that the affected fur farms could function as a reservoir for SARS-CoV-2, and this risk should be mitigated by efficient and ongoing monitoring.

They also say that it may be possible to control viruses in their collections, but the spread of vulnerable wildlife species, especially free-living raccoon dogs, will be an even greater challenge for eradication. ..

“Our results support the establishment of appropriate surveillance and risk mitigation strategies for domestic and wild raccoon dogs,” the team concludes.

*Important Notices

bioRxiv It publishes preliminary, non-peer reviewed scientific reports and should not be considered conclusive and should not guide clinical practice/health-related behavior or be treated as established information.