While an overt stroke causes obvious symptoms, such as weakness in one arm or speech problems that last more than a day, a covert stroke is not obvious except on brain scans, such as MRI. Each year, approximately 0.5 per cent of the 50 million people age 65 years or greater worldwide who have major, non-cardiac surgery will suffer an overt stroke, but until now little was known about the incidence or impacts of silent stroke after surgery.

The results of the NeuroVISION study were published today in The Lancet.

“We’ve found that ‘silent’ covert strokes are actually more common than overt strokes in people aged 65 or older who have surgery,” said Dr. PJ Devereaux, co-principal investigator of the NeuroVISION study. Dr. Devereaux is a cardiologist at Hamilton Health Sciences (HHS), professor in the departments of health research methods, evidence, and impact, and medicine at McMaster University, and a senior scientist at the Population Health Research Institute of McMaster University and HHS.

Dr. Devereaux and his team found that one in 14 people over age 65 who had elective, non-cardiac surgery had a silent stroke, suggesting that as many as three million people in this age category globally suffer a covert stroke after surgery each year.

NeuroVISION involved 1,114 patients aged 65 years and older from 12 centres in North and South America, Asia, New Zealand, and Europe. All patients received an MRI within nine days of their surgery to look for imaging evidence of silent stroke. The research team followed patients for one year after their surgery to assess their cognitive capabilities. They found that people who had a silent stroke after surgery were more likely to experience cognitive decline, perioperative delirium, overt stroke or transient ischaemic attack within one year, compared to patients who did not have a silent stroke.

“Over the last century, surgery has greatly improved the health and the quality of life of patients around the world,” said Dr. Marko Mrkobrada, an associate professor of medicine at University of Western Ontario and co-principal investigator for the NeuroVISION study. “Surgeons are now able to operate on older and sicker patients thanks to improvements in surgical and anesthetic techniques. Despite the benefits of surgery, we also need to understand the risks.”

“Vascular brain injuries, both overt and covert, are more frequently being detected, recognized and prevented through research funded by our Institute and CIHR,” says Dr. Brian Rowe, scientific director of the Institute of Circulatory and Respiratory Health, Canadian Institutes of Health Research (CIHR). “The NeuroVISION Study provides important insights into the development of vascular brain injury after surgery, and adds to the mounting evidence of the importance of vascular health on cognitive decline. The results of NeuroVISION are important and represent a meaningful discovery that will facilitate tackling the issue of cognitive decline after surgery.”

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The Bronze Age settlement at Must Farm, located near what is now the fenland city of Peterborough, consisted of wooden houses built on stilts above the water. Wooden causeways connected islands in the marsh, and dugout canoes were used to travel along water channels.

The village burnt down in a catastrophic fire around 3,000 years ago, with artefacts from the houses preserved in mud below the waterline, including food, cloth, and jewellery. The site has been called “Britain’s Pompeii.”

Also preserved in the surrounding mud were waterlogged “coprolites” — pieces of human faeces — that have now been collected and analysed by archaeologists at the University of Cambridge. They used microscopy techniques to detect ancient parasite eggs within the faeces and surrounding sediment.

Very little is known about the intestinal diseases of Bronze Age Britain. The one previous study, of a farming village in Somerset, found evidence of roundworm and whipworm: parasites spread through contamination of food by human faeces.

The ancient excrement of the Anglian marshes tells a different story. “We have found the earliest evidence for fish tapeworm, Echinostoma worm, and giant kidney worm in Britain,” said study lead author Dr Piers Mitchell of Cambridge’s Department of Archaeology.

“These parasites are spread by eating raw aquatic animals such as fish, amphibians and molluscs. Living over slow-moving water may have protected the inhabitants from some parasites, but put them at risk of others if they ate fish or frogs.”

Disposal of human and animal waste into the water around the settlement likely prevented direct faecal pollution of the fenlanders’ food, and so prevented infection from roundworm — the eggs of which have been found at Bronze Age sites across Europe.

However, water in the fens would have been quite stagnant, due in part to thick reed beds, leaving waste accumulating in the surrounding channels. Researchers say this likely provided fertile ground for other parasites to infect local wildlife, which — if eaten raw or poorly cooked — then spread to village residents.

“The dumping of excrement into the freshwater channel in which the settlement was built, and consumption of aquatic organisms from the surrounding area, created an ideal nexus for infection with various species of intestinal parasite,” said study first author Marissa Ledger, also from Cambridge’s Department of Archaeology.

Fish tapeworms can reach 10m in length, and live coiled up in the intestines. Heavy infection can lead to anemia. Giant kidney worms can reach up to a metre in length. They gradually destroy the organ as they become larger, leading to kidney failure. Echinostoma worms are much smaller, up to 1cm in length. Heavy infection can lead to inflammation of the intestinal lining.

“As writing was only introduced to Britain centuries later with the Romans, these people were unable to record what happened to them during their lives. This research enables us for the first time to clearly understand the infectious diseases experienced by prehistoric people living in the Fens,” said Ledger.

The Cambridge team worked with colleagues at the University of Bristol’s Organic Chemistry Unit to determine whether coprolites excavated from around the houses were human or animal. While some were human, others were from dogs.

“Both humans and dogs were infected by similar parasitic worms, which suggests the humans were sharing their food or leftovers with their dogs,” said Ledger.

Other parasites that infect animals were also found at the site, including pig whipworm and Capillaria worm. It is thought that they originated from the butchery and consumption of the intestines of farmed or hunted animals, but probably did not cause humans any harm.

The researchers compared their latest data with previous studies on ancient parasites from both the Bronze Age and Neolithic. Must Farm tallies with the trend of fewer parasite species found at Bronze Age compared with Neolithic sites.

“Our study fits with the broader pattern of a shrinking of the parasite ecosystem through time,” said Mitchell. “Changes in diet, sanitation and human-animal relationships over millennia have affected rates of parasitic infection.” Although he points out that infections from the fish tapeworm found at Must Farm have seen a recent resurgence due to the popularity of sushi, smoked salmon and ceviche.

“We now need to study other sites in prehistoric Britain where people lived different lifestyles, to help us understand how our ancestors’ way of life affected their risk of developing infectious diseases,” added Mitchell.

The Must Farm site is an exceptionally well-preserved settlement dating to 900-800 BC (the Late Bronze Age). The site was first discovered in 1999. The Cambridge Archaeological Unit carried out a major excavation between 2015 and 2016, funded by Historic England and Forterra Building Products Ltd.

She and fellow researchers have narrowed in a specific time during an era known as the Ordovician Radiation, showing that new species actually developed rapidly during a much shorter time frame than previously thought. The Great Biodiversification Event where many new species developed, they argue, happened during the Darriwilian Stage about 465 million years ago. Their research, “Coordinated biotic and abiotic change during the Great Ordovician Biodiversification Event: Darriwilian assembly of early Paleozoic building blocks,” was published in Palaeogeography, Palaeoclimatology, Palaeoecology as part of a special issue they are editing on the Great Ordovician Biodiversification Event.

New datasets have allowed them to show that what previously looked like species development widespread over time and geography was actually a diversification pulse. Picture a world before the continents as we know them, when most of the land mass was south of the equator, with only small continents and islands in the vast oceans above the tropics. Then picture ice caps forming over the southern pole. As the ice caps form, the ocean recedes and local, isolated environments form around islands and in seas perched atop continents. In those shallow marine environments, new species develop.

Then picture the ice caps melting and the oceans rising again, with those new species riding the waves of global diversification to populate new regions. The cycle then repeats producing waves of new species and new dispersals.

Lighting the Spark of Diversification

The early evolution of animal life on Earth is a complex and fascinating subject. The Cambrian Explosion (between about 540 to 510 million years ago) produced a stunning array of body plans, but very few separate species of each, notes Stigall. But nearly 40 million years later, during the Ordovician Period, this situation changed, with a rapid radiation of species and genera during the Great Ordovician Biodiversification Event.

The triggers of the GOBE and processes that promoted diversification have been subject to much debate, but most geoscientists haven’t fully considered how changes like global cooling or increased oxygenation would foster increased diversification.

A recent review paper by Stigall and an international team of collaborators attempts to provide clarity on these issues. For this study, Stigall teamed up with Cole Edwards (Appalachian State University), a sedimentary geochemist, and fellow paleontologists Christian Mac Ørum Rasmussen (University of Copenhagen) and Rebecca Freeman (University of Kentucky) to analyze how changes to the physical earth system during the Ordovician could have promoted this rapid increase in diversity.

In their paper, Stigall and colleagues demonstrate that the main pulse of diversification during the GOBE is temporally restricted and occurred in the Middle Ordovician Darriwilian Stage (about 465 million years ago). Many changes to the physical earth system, including oceanic cooling, increased nutrient availability, and increased atmospheric oxygen accumulate in the interval leading up to the Darriwilian.

These physical changes were necessary building blocks, but on their own were not enough to light the spark of diversification.

The missing ingredient was a method to alternately connect and isolate populations of species through cycles of vicariance and dispersal. That spark finally occurs in the Darriwilian Stage when ice caps form over the south pole of the Ordovician Earth. The waxing and waning of these ice sheets caused sea level to rise and fall (similar to the Pleistocene), which provided the alternate connection and disconnection needed to facilitate rapid diversity accumulation.

Stigall and her collaborators compared this to the assembly of building blocks required to pass a threshold.

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