Surprise Origin of Deadly Superbug MRSA Revealed

European hedgehogs were carrying ‘enhanced’ staph bacteria, MRSA, a century before artificial antibiotics were invented. But Israelis can still love our local spiky animals without fear

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The European hedgehog. Handle with care.
The European hedgehog. Handle with care.
Ruth Schuster
Ruth Schuster

A deadly superbug, methicillin-resistant Staphlycoccus aureus, didn’t originate in irresponsible use of antibiotics in humans or farm animals, as had been assumed.

It’s true that antibiotics abuse in human and veterinary medicine has elevated MRSA to the level of a global scourge. But the true origin of the variant called mecC-MRSA delivered quite the shock to science. It isn’t reckless doctors, it’s the European hedgehog.

Let us be crystal clear that there are many species of hedgehog, and so far the superbug has been found only in the European one, based on a study of hedgehogs in Denmark and Sweden.

Staphylococcus aureus is a normal resident of our skin (and lungs). Usually it causes nothing more malign than pimples, but infection can take a deadly turn and antibiotic-resistant staph variants are estimated to be responsible for about 50,000 premature deaths a year in the U.S. The variant MRSA specifically has been spreading worldwide.

No question, resistance in bacteria is exacerbated by irresponsible use of antibiotics. If we flood animals and people with drugs without good reason, we create conditions in which the only bacteria surviving the onslaught are ones that develop resistance genes. Every time a new antibiotic is born, an angel may get its wings but bacteria evolve resistance.

Yet in fact, antibiotic-resistance genes predate humanity, let alone artificial antibiotics, by eons, because antibiotics occur naturally. Penicillin, for instance, is made by certain molds.

So, the explosion of superbugs resistant to multiple antibiotics has been blamed on irresponsible doctors and suddenly we find the European hedgehog photobombing the picture.

Staphylococcus aureus on hedgehogs in Denmark and Sweden evolved resistance to methicillin (the MRSA variant) about 200 years ago, over a century before antibiotics were invented, according to a genetic analysis published in Nature by Prof. Jesper Larsen of the Statens Serum Institute in Copenhagen with an international team, including people from the University of Cambridge, the Wellcome Sanger Institute, the Serum Statens Institute and the Royal Botanic Gardens, Kew, of England.

The first man-made antibiotics are about 80 years old. The first known case of MRSA in humans appeared about 60 years ago.

Colonies of staphylococcus aureus grown on antibiotic-spiked agar: MRSA, methicillin resistant staph, grows; MSSA, non-resistant staph, doesn't grow

Again we stress, fear not the hedgehog – even though up to a whopping 60 percent of northern European ones carry mecC-MRSA. This variant only causes one in 200 of all MRSA infections in humans, the scientists explain.

With the hedgehog’s place in our hearts secure, now we can ask: How did these cutest of creatures develop a resistant bacterial guest? Where? And how did science figure this out?

When microbes go to war

“MRSA is a human pathogen,” explains Prof. Larsen, meaning as opposed to an animal pathogen. It was recognized in 1960. But around 15 years ago it was found in livestock, mainly pigs, in western Europe. “It probably emerged there because we use a lot of antibiotics in veterinary medicine,” he adds.

Then, reports suddenly appeared about MRSA in wild animals. Which begged the question, was there a nonhuman host of mecC-MRSA?

Various people began looking in various species. The superbug appeared in sheep and cattle, but at a very low prevalence of about 1 percent, Larsen says. Evidently they were not the reservoir.

MRSA spreads by contact, between European hedgehog and cattle and people, who get it by touching hedgehogs or cattleCredit: Jesper Larsen

Enter the picture a doctoral candidate studying hedgehogs in Denmark, by means of picking up dead ones found on the road, as one does. She was analyzing them to elucidate their relationships, cause of death and so on – and “asked if we would be interested in looking for MRSA,” Larsen explains. Why not?

They started checking deceased hedgehogs for the variant. “To our big surprise, we found that 60 percent were positive,” he says. “These were wild hedgehogs collected in nature, mainly roadkill. At the same time a similar study for Sweden reported the exact same thing – about 60 percent of their hedgehogs were positive for MRSA. That changed our understanding of the epidemiology.”

Why were the hedgehogs of Denmark and Sweden riddled with MRSA? What could be the mechanism of natural selection in this amiable animal that is unrelated to use of antibiotics in humans or animals? And was the problem unique to Denmark and Sweden?

No, it wasn’t. In fact, the highest rates of hedgehogs carrying mecC-MRSA is in Denmark and Britain. The New Zealand population is worthy of special mention, because they have it too. This is because the British imported hedgehogs to the island nation around 130 years ago, possibly to consume garden pests and also possibly because they’re adorable. Anyway, hedgehogs carrying mecC-MRSA are mainly in western and northern Europe, and New Zealand.

Now let us consider why hedgehogs developed methicillin-resistant staph 200 years ago.

Hedgehogs bear both bacteria and fungi on their skin, as do we all.

But how did MRSA happen to originate in the Scandinavian hedgehog? Their skin bacteria and fungi are at war, competing over the hedgehoggy resources, the scientists think. The dermal fungus Trichophyton erinacei, the agent of ringworm, living on the hedgehog skin attacks the bacteria with not one but two natural antibiotics.

You'll be surprised what you can find on the European hedgehog: Fungus secretes antibiotic, bacteria fight back with resistance

In response, the staph evolved resistance to the fungal attack and around 200 years ago the variant methicillin-resistant Staphylococcus aureus, aka MRSA, arose – today a problem in hospitals around the world. People hospitals, not hedgehog hospitals.

The Israeli hedgehog and the cat food

That 60 percent prevalence in the European hedgehog was much higher than expected, higher than among other European wild animals, and higher than among domestic animals. Hence the surmise that the origin of this specific superbug is the hedgehog, the team explains. They are ground zero for mecC-MRSA, it seems.

How actually did they deduce that hedgehogs developed this superbug around 200 years ago? “Using sequencing technology we have traced the genes that give mecC-MRSA its antibiotic resistance all the way back to their first appearance, and found they were around in the 19th century,” explains co-author Dr. Ewan Harrison of the Wellcome Sanger Institute and University of Cambridge.

Then, Harrison speculates, mecC-MRSA spread from hedgehogs to livestock, and from livestock to humans through direct contact.

In Israel, hedgehogs are one of the more common wild animals in the cities, often emerging at night to eat cat food. Many Israelis feed street cats and the hedgehogs get the leftovers, scorning their regular diet of invertebrates such as insects. Some Israeli hedgehogs have, as a result, become fat.

Sherman, an overweight hedgehog in Ramat GanCredit: AMIR COHEN/REUTERS
Feral cats eating in Tel AvivCredit: Daniel Tchetchik

But don’t worry that your local hedgehogs will infect you with ringworm (which, again, is a skin fungus) or mecC-MRSA. In any case: “I think you should treat wild animals with respect and use gloves when handling them for any reason – they also carry salmonella,” Larsen points out.

Ringworm is also infectious, but most hedgehogs who have it are asymptomatic carriers; few develop skin lesions. But to get sick from a hedgehog, the professor stresses, you have to “really touch” the animal and it doesn’t want you to – and most people don’t want to either. “In Denmark, we have 6 million people and only have maybe 30 cases of this MRSA a day in humans. Clearly this is not a big thing,” Larsen explains. Their paper is proof of concept, not a warning to scream and run when you see a hedgehog in the garden.

An Israel hedgehog. Partial to cat food.Credit: Oren Aharoni

No, they didn’t survey Israeli hedgehogs, of which there are three species, Larsen says – and none are the European hedgehog, which is the only one found to harbor mecC-MRSA so far. So there is no reason to suspect the Israeli hedgehogs of harboring deadly diseases, but feeding them cat food isn’t necessary either. Let them eat the bugs.

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