Not to make anyone feel uneasy after this whole pandemic thing, but a new study says there’s another viral threat looming on the horizon.

An international team of researchers is drawing attention to the fact that the Middle East respiratory syndrome (MERS-CoV), could mutate to become a global problem quite easily. While MERS has caused issues in the past and was highly lethal, it didn’t seem to be able to jump from one human to another, which limited its impact.

However, such an ability could be only a few mutations away for the virus. One subfamily of the virus is already able to infect humans, but luckily, it is still isolated from the main group. However, if these two were to come into contact, MERS could start the next pandemic.

Just one unlucky break

Pandemics, or the plagues of yore, usually start from zoonoses. These aren’t noses that like zoos at all. Rather, they’re pathogens that specialize in infecting animals but evolved to also infect human beings, at one point or another. Historically speaking, livestock is the main source of zoonoses, and the reason plagues used to ravage medieval Europe, where people and animals used to live in tight proximity with poor hygiene. Another element that makes zoonoses so dangerous is that, being a ‘new’ pathogen to humans, virtually nobody has any natural defenses against them.

SARS-CoV-2 was also a zoonosis, most likely originating from bats. The speed and ferocity with which the virus spread across the world, and the devastating effects it had on patients, are tragic reminders of just how dangerous such pathogens can become. But it’s not the only virus out there, not by far. Its big break, so to speak, what set it apart from other animal-borne viruses, was that it evolved the ability to infect a human cell — probably by accident.

MERS-CoV, a virus first seen in 2012 in Saudi Arabia, also has the potential to follow in its footsteps, according to a new study. During its initial outbreak, MERS killed around 40% of the patients it infected. However, it’s unlucky break was that it couldn’t pass from one person to another. Analyses at the time showed that virtually all cases of  infection originated from dromedaries (camels). These animals, in turn, likely got it from bats.

Despite its lethality, the MERS outbreak remained a footnote of history, as it remained quite small in scope. Testing since then also seems to indicate that the danger is passing, as around 80% of the dromedaries tested so far — 70% of which live in Africa — have antibodies against the virus in their blood.

But, in a bid to find out why this virus didn’t infect many more people — especially curious considering how many dromedaries there are around, and how often people in Africa and Saudi Arabia interact with them — an international team of researchers took samples of the virus from multiple sites across the Middle East and Africa. Their goal was to identify and isolate individual strains (‘variants’) of the virus.

Those from Africa and the Middle East were separated into different clades, and were then compared from a genetic standpoint, and under lab conditions, using cultures of human lung cells. To their surprise, they found that African clades wouldn’t readily infect human cells. Those in the Arabian clade, however, would.

It all comes down to differences in the amino acids each clade uses in a particular protein — the S, or ‘spike’ protein. The team showed that African clade variants engineered to have the same amino acids in this protein as the Arabian clade had a much easier time infecting human cells.

One possible explanation for the difference between these two clades is that dromedary trade is “virtually one-way”, from Africa to the Middle East. In essence, this means that changes in the Arabian clade can’t percolate back into the African one, even if African clades do come into contact with Arabian ones. If the trade was to be reversed, however, or if a carrier animal makes its way back to Africa, the local population of viruses could become highly infectious to humans, sparking a new and deadly pandemic.

The paper “Phenotypic and genetic characterization of MERS coronaviruses from Africa to understand their zoonotic potential” has been published in the journal Proceedings of the National Academy of Sciences.