The hunt for COVID critters

On Tuesday, a group of scholars split between New York and the University of Calgary published a new paper on COVID-19 risk in non-human primates. The topic is no joke, for just as epidemics often reach us through wildlife, the arrow can run in the other direction. Human outbreaks of the Ebola virus, in particular, are known to have led to the deaths of thousands of African western gorillas — a species whose total existing population is under 100,000. SARS-CoV-2 has made primate researchers awfully nervous: humans won't go extinct from this virus, but our cousins are much more vulnerable.

The New York/Calgary study is simple and preliminary: geneticists and anthropologists in both locations teamed up to look at primate genomes and see which species express the ACE2 target protein in more or less the same way we do. There is already research showing that rhesus monkeys, macaques and vervets can contract the virus and develop COVID-19; marmosets don't. ACE2 turns out to work similarly in most primate species, and the authors of the paper think it likely that all apes, all African and Asian monkeys, and some lemur species are susceptible to COVID-19.

What caught my attention in the study, apart from the Alberta angle, was that the team threw several other mammals into the mix of genomes under survey, including ferrets, cats, dogs, pigs, bats and pangolins. This, for me, was a throwback to the early days of the pandemic — before it even went pan-, really, when COVID-19 research was still a little more like criminal detection. SARS-CoV-2 was judged to almost certainly have descended from a bat coronavirus, but what other species may have been involved? Have pangolins been let off the hook?

You may think we are all too busy hiding and wondering about stray coughs to think about pangolins, but geneticists are still on the case. An Oct. 17 paper with the amazing title, “A Crowned Killer's Résumé,” provides a convenient update on the animal origins of SARS-CoV-2. Bats are still the only suspect when it comes to the primary reservoir of the virus, and further work has narrowed things down to a bat family, Rhinolophus — the horseshoe bats, who had also brewed up the original SARS virus among themselves before it leapt to humans through civet cats.

The suspicion that there was an intermediate species in the case of SARS-2 is strong, for a few reasons, which the (Chinese and German) authors of the “Crowned Killer” paper enumerate. There are the examples of classic SARS, and of MERS, which crossed from bat to human through camels. The COVID-19 outbreak began during the hibernation season for bats in the Wuhan area, and there were no vendors of bats at the notorious Hunan “wet market.” Known bat coronaviruses are genetically close, but not that close, to SARSCoV-2; the relationship appears to be one of common ancestry rather than direct descent.

But the search for the accessory to the crime remains incomplete. The pangolin question has geneticists divided: some find them a promising suspect, some think they're impossible. Study of codons in SARS-CoV-2 initially pointed to snakes as a host, but they don't seem to have the right flavour of ACE2; the same goes for turtles. Minks are on the list because in farm settings they have been shown to not only get COVID-19, but to pass it onto humans. In investigative parlance, we would say they definitely had the means to infect us, but not necessarily the opportunity. Domestic cats remain a possibility insofar as they can definitely transmit SARS-CoV-2 to one another.

In other words, the hunt for the intermediate species — if there is one — continues with no obvious solution yet in sight. It is, of course, astonishing that this area of research has gotten as far as it has amidst a storm of death and ruin. The natural history of SARS-CoV-2, once worked out, probably won't tell us anything that unlocks a new treatment for COVID-19. But it may help us devise regulations for animal markets and other dangerous settings, and thereby prevent us from going through this whole rigmarole again.

SARS-COV-2 HAS MADE PRIMATE RESEARCHERS

AWFULLY NERVOUS.