Two other common coronaviruses do not fulfill Koch’s postulates.

Last review and update: April 3, 2020.

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In the case of HCoV-NL63 and HCoV-HKU1 (other two common coronaviruses), application of all Koch’s postulates turned out to be impossible, and their role in disease therefore remains unconfirmed.

Wevers, van der Hoek, 2009 (1).

SARS-CoV-2 was discovered by Chinese scientists who isolated its RNA from Chinese patients with pneumonia that did not have other common pathogens and viruses (2). The Chinese scientists used several pieces of equipment from different manufacturers to do this.

From another article on this website:

The virus genotype used to develop a PCR test came from a single patient from Wuhan (March 18, 2020).

Wu, 2020 (2):

The patient studied was a 41-year-old man with no history of hepatitis, tuberculosis or diabetes.

The Wuhan Center for Disease Control and Prevention revealed that the patient worked at a local indoor seafood market.

Elevated levels of C-reactive protein (41.4 mg l⁻¹ of blood; reference range, 0–6 mg l⁻¹) were observed and the levels of aspartate aminotransferase, lactic dehydrogenase and creatine kinase were slightly elevated in blood chemistry tests.

Although the isolation of the virus from only a single patient is not sufficient to conclude that it caused these respiratory symptoms, our findings have been independently corroborated in further patients in a separate study.

We need to remember that isolation of RNA or DNA of an organism or of an organism itself from a patient is not sufficient to prove that it caused the disease. Koch’s Postulates should be fulfilled.

Koch’s Postulates:

The organism is consistently present in patients who have disease at a higher prevalence than in control patients.

The disease is replicated in an appropriate animal model after viral challenge, and subsequently isolated from this animal.

A specific host immune response can be demonstrated.

Wevers and van der Hoek (1) made an interesting comment on the pathogenic potential of two other common coronaviruses. It is worth to be quoted here.

Wevers, van der Hoek, 2009 (1):

Once novel viruses are identified, it is important to demonstrate their pathogenic potential and unravel a causal link with a specific disease. Proof of such a relationship ideally would imply fulfilling Koch’s postulates, which have been revisited for viral pathogens. 64 These standard criteria propose that a causal connection between a new virus and an illness may be established if:

The organism is consistently present in patients who have disease at a higher prevalence than in control patients.

The disease is replicated in an appropriate animal model after viral challenge, and subsequently isolated from this animal.

A specific host immune response can be demonstrated.

In the case of HCoV-NL63 and HCoV-HKU1, application of all Koch’s postulates turned out to be impossible, and their role in disease therefore remains unconfirmed. Currently, HCoV-HKU1 cannot be maintained in cell culture systems, and animal models are unavailable for both NL63 and HKU1 CoVs. Animal model systems susceptible for HCoV-OC43 and SARS-CoV have been developed previously, and allow present studies of coronaviral tropism, replication, recombination, and accompanying immune modulatory mechanisms. 65,66 Most recently, a very important technical achievement has been made for studying pathogenic mechanisms of HCoV-NL63, because infectious full-length cDNA clones of the HCoV-NL63 genome can be engineered. 67 Nonetheless, thus far, the only option to identify pathogenic potential of HCoV-NL63 and HCoV-HKU1 is to determine a significant association with a disease through epidemiologic studies with proper control groups. 9 An alternative strategy to gain novel insights in mechanisms of CoV pathogenesis is by extensive characterization of virus–host interactions and host cell invasion strategies. Viral receptor specificity and expression are generally important determinants of the pathogenic potential of a virus and the nature of the disease that it causes.

Selected references:

1. Brigitte A. Wevers, Lia van der Hoek. Clin Lab Med 29 (2009) 715–724.

2. Wu F, Zhao S, Yu B, et al. A new coronavirus associated with human respiratory disease in China. Nature. 2020;579(7798):265–269. doi:10.1038/s41586-020-2008-3