#16,918Although incredibly well-adapted to humans, the SARS-CoV-2 virus is also able to infect more than 2 dozen other mammalian species, and has shown signs of increasing its host range as it evolves (see WHO/FAO/OIE Joint Statement On Monitoring SARS-CoV-2 In Wildlife & Preventing Formation of Reservoirs).
There are genuine concerns that if establishes itself in a new host, this virus may take divergent evolutionary paths - possibly even recombining with other coronaviruses (MERS-CoV, BCOV, etc.) - and produce variants or a chimera that could `spill back' into humans down the road with unpredictable results.
We've already seen evidence of this in mink and in deer, both of which are highly susceptible to COVID infection.
In late 2020, Danish authorities announced the spillover of COVID into millions of susceptible farmed mink, and the discovery of several `mink specific' mutations in the virus (see Denmark Orders Culling Of All Mink Following Discovery Of Mutated Coronavirus), which subsequently jumped back into the human population.
Danish authorities immediately expressed their concerns for public health - and ordered a full 4 week lockdown, and emergency testing of all residents in North Jutland, where the virus had emerged. For several weeks, numerous countries enacted travel bans on Denmark.
The crisis was short-lived, as this `mink variant' died out when a newer, more `biologically fit' Alpha Variant emerged in the UK, and began to spread globally.
In another example, we've seen numerous reports of SARS-COV-2 spillover into North American White-Tailed Deer (see USDA/APHIS: White-Tailed Deer Exposed To SARS-CoV-2 Detected In 4 States).
Fortunately, laboratory experiments have shown that most farmed animals (pigs, chickens, cattle, etc.) to be poor hosts for the SARS-CoV-2 virus. Dogs and cats are mildly susceptible, but since they don't have contact with hundreds of other animals, aren't as likely to generate mutations.
Last February, in Preprint: Evolutionary Trajectories of SARS-CoV-2 Alpha and Delta Variants in White-Tailed Deer in Pennsylvania, we looked at evidence of the generation of deer-derived alpha variants that "diverged significantly from those in humans".
But at the same time, as SARS-COV-2 evolves, it may further increase its host range.
We've seen evidence of this happening as well, as the original SARS-CoV-2 virus was unable to easily infect laboratory mice, but as new variants emerged, their ability to infect, and replicate, in lab mice has grown stronger (see PrePrint: The B1.351 and P.1 Variants Extend SARS-CoV-2 Host Range to Mice).
All of which brings us to a new EID Journal Research letter which reports serological evidence of limited spillover of SARS-CoV-2 to cattle in Germany. While there is no evidence that this virus spreads in cattle, it raises concerns over potential divergent evolution in a bovine host, including recombination with the Bovine Coronavirus (BCoV).
For a refresher on recombination of coronaviruses, you may wish to revisit A COVID Recombination Review.
Follow the link for the full text, and associated data. I'll have a bit more, after the break.
Volume 28, Number 9—September 2022
Antibodies against SARS-CoV-2 Suggestive of Single Events of Spillover to Cattle, Germany
Kerstin Wernike , Jens Böttcher, Silke Amelung, Kerstin Albrecht, Tanja Gärtner, Karsten Donat, and Martin Beer
Author affiliations: Friedrich-Loeffler-Institut, Greifswald–Insel Riems, Germany (K. Wernike, M. Beer); Bavarian Animal Health Service, Poing, Germany (J. Böttcher); LUFA Nord-West, Oldenburg, Germany (S. Amelung); State Institute for Consumer Protection of Saxony-Anhalt, Stendal, Germany (K. Albrecht); Thuringian Animal Diseases Fund, Animal Health Service, Jena, Germany (T. Gärtner, K. Donat)
Human infection with SARS-CoV-2 poses a risk for transmission to animals. To characterize the risk for cattle, we serologically investigated 1,000 samples collected from cattle in Germany in late 2021. Eleven antibody-positive samples indicated that cattle may be occasionally infected by contact with SARS-CoV-2–positive keepers, but we found no indication of further spread.
Since its first detection at the end of 2019, SARS-CoV-2, which induces COVID-19 in humans, very rapidly spread around the world, causing a massive global pandemic that resulted in >5 million deaths in <2 years of virus circulation (1). Since the beginning of the pandemic, researchers have discussed the role of livestock and wildlife species at the human–animal interface, with a special focus on the identification of susceptible species and potential intermediate or reservoir hosts.
Under experimental conditions, various animal species could be infected with SARS-CoV-2, including nonhuman primates, felids, canids, mustelids, white-tailed deer, and several species of Cricetidae rodents; poultry or swine were not susceptible (2).
For domestic ruminants such as cattle, sheep, or goats, susceptibility after experimental inoculation was low; only a small proportion of animals could be infected without animal-to-animal transmission (3–5).
Furthermore, 26 cattle exposed in the field to SARS-CoV-2 by contact with their infected keepers tested negative by reverse transcription PCR (6). However, given the very short time at which cattle test positive by reverse transcription PCR after experimental infection (1–2 days) (3,7), serologic screening could be more beneficial for identifying previously infected animals and estimating the rate of spillover infections in the field.
We analyzed 1,000 serum or plasma samples from cattle at 83 farms in 4 federal states in Germany (Bavaria, Lower Saxony, Saxony-Anhalt, and Thuringia). Because the samples represented superfluous material from routine diagnostic submissions by the responsible veterinarians in the context of the health monitoring of the respective cattle farm, no permissions were needed to collect these specimens. Sampling dates were autumn 2021 and early winter 2021–22, during a massive wave of infections in the human population driven by the SARS-CoV-2 Delta variant of concern.
We analyzed 2–20 randomly selected serum or plasma samples per farm (Figure). Farm 31 was sampled twice; between farm samplings, the animal owner was quarantined. We do not know whether this quarantine resulted from contact with an infected person or whether the owner himself tested SARS-CoV-2 positive. All bovine samples were tested by a receptor-binding domain (RBD)–based multispecies ELISA (diagnostic sensitivity 98.31% and specificity 100%) performed as described previously (8). Initial test validation and an experimental SARS-CoV-2 infection study in cattle have demonstrated that the ELISA does not cross-react with the bovine coronavirus (BCoV) (3,8). We investigated an additional 100 cattle control samples randomly collected across Germany in 2016, and all tested negative.
Of the cattle sampled in 2021, eleven animals from 9 farms tested positive by the RBD ELISA; among them was 1 animal on farm 31, sampled after the owner was quarantined (Figure). Positive ELISA results for all but 1 sample (farm 8) could be confirmed by an indirect immunofluorescence assay that used Vero cells infected with the SARS-CoV-2 strain 2019_nCoV Muc-IMB-1 (multiplicity of infection of 0.1) as antigen matrix (3). Titers ranged from 1:8 through 1:512, and the highest titer was from the seropositive animal on farm 31 (Table).
To further confirm the reactivity toward SARS-CoV-2, we additionally tested the 11 samples that reacted positive in the RBD-ELISA by using a surrogate virus neutralization test (cPass SARS-CoV-2 Surrogate Virus Neutralization Test [sVNT; Kit; GenScript, https://www.genscript.comExternal Link). This test enables detection of neutralizing antibodies by mimicking the interaction between SARS-CoV-2 and host cell membrane receptor protein ACE2; it is reportedly highly specific but only moderately sensitive for animal samples because it does not detect low antibody titers (9). sVNT produced positive results for 4 cattle (farms 11, 31, 47, and 74; Table).
Our findings of a low number of individual seropositive cattle on several farms demonstrate that cattle might be occasionally infected and seroconvert after contact with infected humans. However, in keeping with experimental infection studies (3), intraspecies transmission seems likewise to not occur in the field.
Nevertheless, cattle farms should be included in future monitoring programs, especially because another coronavirus (i.e., BCoV) is highly prevalent in the cattle population and a BCoV infection did not prevent a SARS-CoV-2 infection in a previous study (3). Furthermore, we do not know the susceptibility of animal hosts for the Omicron variant. Double infections of individual animals could potentially lead to recombination between both viruses, a phenomenon described for other coronaviruses (10).
Although emergence is highly unlikely because of the low susceptibility of cattle for SARS-CoV-2, a conceivable chimera between SARS-CoV-2 and BCoV could represent an additional threat. Hence, ruminants should be included in outbreak investigations, and regular screenings should be performed to exclude any spread of new variants in the livestock population.
PD Dr. Wernike is a veterinarian and senior scientist at the Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany. Her research interests include emerging viruses, host–virus interactions, and immunoprophylaxis.
Just over 4 months ago, those same authors returned with China CDC Weekly Perspective: The “Wolf” Is Indeed Coming: Recombinant “Deltacron” SARS-CoV-2 Detected, where they presented the `first solid evidence for a recombinant strain from 2 types of variants of concern (VOCs) of SARS-CoV-2 (lineage AY.4 and BA.1, belonging to Delta and Omicron, respectively).
The authors then warned that the potential for new recombinants arising from confections - particularly in wild and domesticated animals - was very high. They wrote:
Taken together, the probability of co-infection with SARS-CoV-2 and other types of CoVs or even other viruses in a single host would be high, leading to the occurrence of cross-species recombination with high probability.
Therefore, it is difficult to predict which viral species SARS-CoV-2 will recombine with, and on which genes future recombination will occur. This kind of uncertainty is doomed to increase the likelihood of generating a novel recombinant virus with unknown risk to humans.
Although the emergence of a recombinant SARS-CoV-2 isolate was expected by scientists, it still attracted great attention. In addition to the need to conduct in-depth evaluation and research on the various properties of this novel recombinant virus, and adjust prevention and control strategies based on the results, it is more important to be alert to the generation of other types of recombinant viruses produced by SARS-CoV-2 and other viruses.
Therefore, it is particularly important to implement large-scale virome study in both domesticated and wild animals.
Now that the SARS-COV-2 genie is well and truly out of the bottle, there is no telling how many species it will eventually adapt to, and in what ways it will evolve.
Admittedly, most of these `field experiments' will be evolutionary failures, but it only takes one `genetic winner' to ruin our whole day.
Hopefully we get lucky, and COVID eventually fades away. But we need to be preparing for possibility that we've only seen act one, of a multi-act play.