Researchers at the Department of Animal Health, University of Cordoba, Córdoba, Spain, speculate that bovine milk consumption – specifically from cows with resistance to bovine coronaviruses – may potentially provide at least some degree of protection from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The article is available to read in full on the Frontiers in Immunology website.
The global coronavirus disease 2019 (COVID-19) pandemic, caused by the SARS-CoV-2 pathogen, continues to evolve and spread worldwide. As new variants begin to show resistance to currently circulating vaccines, it is necessary to find alternative therapies in order to eradicate the virus or to mitigate disease severity in those it reaches.
The researchers theorize such an alternative: consumption of bovine milk.
Milk is a unique nutrient-rich food source produced by mammals. It has historically been farmed from many domesticated animal species for human consumption, providing nutrients, protein, and calcium to the consumer. Additionally, milk consumption also transfers antibodies from the parent animal to the recipient, which bolsters the immune system.
SARS-CoV-2 belongs to the subgenus Sarbecovirus within the genus Betacoronavirus. A second subgenus, Embecovirus, contains Human coronavirus OC43 (OC43) and Bovine coronavirus (BCoV), which are 96% identical. Arenas and co-authors suggest that transference of BCoV antibodies to humans, which also neutralizes OC43, may also provide sufficient cross-immunity to SARS-CoV-2.
As Betacoronaviruses, SARS-CoV-2 and BCoV share many similarities. BCoV has five structural proteins: the spike glycoprotein (S), the envelope (E) protein, the membrane (M) protein, the nucleocapsid (N) protein, and the hemagglutinin-esterase (HE) protein. SARS-CoV-2 is comprised of just four structural proteins, sharing all of these except for HE.
Cross-reactivity between OC43 and SARS-CoV antibodies has been shown, signaled by determinants at the N, M and S2 regions of both viruses. These regions are highly invariable between all Betacoronaviruses, including SARS-CoV and SARS-CoV-2, suggesting that cross-reactivity between OC43 and SARS-CoV-2 is also likely.
These antibodies usually target the receptor-binding domain (RBD) region of the S protein. However, some SARS-CoV monoclonal antibodies neutralize SARS-CoV-2 through a different, currently unknown, means. Inactivation of the virus may, therefore, take place in a variety of ways, and cross-reactivity may extend to this.
Cross-reactivity (though with limited neutralization capability) between OC43 and SARS-CoV-2 has only recently been observed, with one study finding that between 40-60% of people unexposed to COVID-19 already possessed T helper cells. Furthermore, another recent study found that immunoglobins reactive to the S2 subunit of SARS-CoV-2 were present in previously unexposed subjects, likely acquired from previous human coronavirus infection.
SARS-CoV-2 and BCoV share 83% homology of their S proteins. Cross-reactivity of antibodies across coronaviruses appears to be relatively high, especially between BCoV and OC43. This is promising, as resistance to OC43 also appears to provide individuals unexposed to SARS-CoV-2 with T helper cells sufficient in binding and neutralizing the S2 subunit of the virus.
Antibodies in bovine milk survive and remain active after gastric exposure and digestion in human stomachs, and continue on to neutralize any viral RNA remnants that may also persist through into fecal matter. The authors suggest, however, that ingested antibodies, which may only individually provide a short-lived immunity before they are flushed out of the body, may persist long enough to partially or totally inactivate SARS-CoV-2, which would allow the human body to mount its own immune response far more easily.
Due to many of the heat and pasteurization treatments milk undergoes before it ultimately ends up in supermarkets, many of the antibodies are broken down or destroyed, so would likely fail to provide sufficient passive immunity. The authors, therefore, suggest that, while study into bovine milk as a novel SARS-CoV-2 immunity provider must urgently be undertaken, these treatments should be considered. Furthermore, the encompassment of milk derivatives, egg yolk, and other animal products, which can also confer passive immunity, should also be investigated to control the spread of COVID-19.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.