Koch’s postulates fulfilled for 2019-nCoV-2.
Developed in the 19th century, Robert Koch’s postulates are the four criteria designed to assess whether a microorganism causes a disease. As originally stated, the four criteria are:-
(1) The microorganism must be found in diseased but not healthy individuals.
(2) The microorganism must be cultured from the diseased individual.
(3) Inoculation of a healthy individual with the cultured microorganism must recreate the disease.
(4) The microorganism must be re-isolated from the inoculated, diseased individual and matched to the original microorganism.
Numbers 1 and 2 are satisfied in a study by Kim et al (2020) identified the coronavirus from patients in Korea who were suffering from COVID-19. Samples of sputum were taken from patients and inoculated into ‘Vero cells’ where they multiplied between 10 - 70 times the original sample.
The virus replication was confirmed using RT-PCR and visualised using an electron microscope. The virus was seen to be inside many cell structures and in particular inside vesicles.
The virus “RNA was amplified with primers for full-length gene analysis” and the “acquired gene was compared with 57 human and animal coronaviruses.” It was found to have 99.94% similarity to other 2019-nCoV sequences already know, 89.1% similarity to bat-CoV, 77.5% similarity to SARS-CoV and 50% similarity to MERS-CoV.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7045880/
Again numbers 1 and 2 are satisfied in a study by Zhou et al (2020), they isolated the virus from the bronchoalveolar lavage fluid of a critically ill patients.
They identified 4 “full-length genome sequences of nCoV-2019 that were above 99.9% identical to each other.”
https://www.biorxiv.org/content/10.1101/2020.01.22.914952v2.full.pdf
Again numbers 1 and 2 are satisfied in a study by Lu et al. (2020) which investigated the genome sequence of the 2019-nCoV outbreak by culturing samples from the lungs of nine patients who were infected after visiting the Huanan seafood market in Wuhan.
They managed to gain 8 complete and 2 partial genome sequences of 2019-nCoV from the nine patients that were extremely similar, exhibiting more than 99·98% sequence identity.
https://www.sciencedirect.com/science/article/pii/S0140673620302518
Numbers 3 and 4 are satisfied in a 2020 study by Chan which found that “Syrian hamsters could be consistently infected by SARS-CoV-2” and notes that “besides satisfying the Koch’s postulates, this readily available hamster model is an important tool for studying transmission, pathogenesis, treatment, and vaccination against SARS-CoV-2.”
After infection with SARS-CoV-2 the hamsters showed signs of rapid breathing, weight loss, and lung damage with extensive cell death. They also suffered “high lung viral load, and spleen and lymphoid atrophy associated with marked cytokine activation.”
Additionally, the hamsters were found to infect other hamsters when in the same cage and they developed antibodies for SARS-CoV-2.
It was also found that hamsters given serum from recovering hamsters as a prophylaxis
had a “significant decrease in lung viral load but not in lung pathology” suggesting that although pre-exposure through vaccination helped to lighten the infection it did nothing to prevent lung damage.
https://covid-19.conacyt.mx/jspui/bitstream/1000/644/1/100761.pdf
Numbers 3 and 4 are satisfied in a 2020 study by Bao which used transgenic mice that had been given human ACE2 receptors. After experimental infection of hACE2 transgenic mice with isolates of SARS-CoV-2, the mice lost weight and showed interstitial pneumonia, which are comparable with initial clinical reports of pneumonia caused by SARS-CoV-2.
Virus replication was detected in the lung of the mice and elicited the specific antibodies against SARS-CoV-2.
In clinical autopsy, histological examination showed bilateral diffuse alveolar damage with cellular fibromyxoid exudate.
The study explains that “our results clarified the pathogenicity of SARS-CoV-2 in mice, together with the previous clinical studies, completely fulfils the Koch's postulates.”
https://www.biorxiv.org/content/biorxiv/early/2020/02/28/2020.02.07.939389.full.pdf
Using the studies listed above all of Koch’s postulates have been fulfilled for 2019-nCoV-2.
The studies identified whole genome sequences from diseased humans.
The virus was isolated and cultured.
The mouse and hamster models recreated the disease in animals.
The virus was again recovered, matched to 2019-nCoV-2 and antibody production in those animals was noted.