Two stories of two deadly diseases

New studies shine new light on two infamous epidemics – one with possible lessons for our current global crisis.

Mathematical modelling of typhus infections in the Warsaw Ghetto during World War II reveals how public health interventions helped eradicate the disease, which was on track to be even more deadly than it turned out to be.

And on a grander scale, international scientists have reported the discovery of extinct strains of smallpox in the teeth of Viking skeletons, proving for the first time, they say, that the disease plagued humanity for at least 1400 years.

The first study, described in the journal Science Advances, was led by mathematician and disease modeller Lewi Stone from Australia’s RMIT University, with collaborators in Hong Kong, Amsterdam and Berlin.

When Nazi forces in Poland crammed more than 450,000 people into an area of little more than three square kilometres in 1941, as many as 120,000 were infected by typhus, with up to 30,000 dying directly from it and many more from starvation or a combination of both.

The new modelling shows that the epidemic was on track to become two to three times larger and peak in the middle of winter, but instead the curve “suddenly and unexpectedly nose-dived to extinction”, Stone says.

Epidemics typically crash when there are too few susceptible people remaining in a population, but at that stage less than 10% of the population of the Warwaw Ghetto had been infected.

“It was inexplicable at the time and many thought it was a miracle or irrational,” Stone says, but in reality, he adds, it likely reflects the success of behavioural interventions.

He and colleagues scoured the records and found evidence of well organised training courses covering public hygiene and infectious diseases, hundreds of public lectures on the fight against Typhus and an underground medical university for young students.

“In the end, it appears that the prolonged determined efforts of the ghetto doctors and anti-epidemic efforts of community workers paid off,” Stone says. “There is no other way we can find to explain the data.”

In the second study, described in the journal Science, an international team of scientists sequenced the genomes of newly discovered strains of smallpox after it was extracted from the teeth of Viking skeletons from sites across northern Europe.

Historians believed smallpox may have existed since 10,000 BCE but until now there has been no scientific proof that it was present before the 17th century.

“The timeline of the emergence of smallpox has always been unclear but by sequencing the earliest-known strain of the killer virus, we have proved for the first time that smallpox existed during the Viking Age,” says Martin Sikora from the University of Copenhagen, Denmark, one of the paper’s senior authors.

The researchers found smallpox, caused by the variola virus, in 11 Viking-era burial sites in Denmark, Norway, Russia and the UK and in multiple human remains from Öland, an island off the east coast of Sweden with a long history of trade. They were able to reconstruct near-complete variola virus genomes for four of the samples.

“While we don’t know for sure if these strains of smallpox were fatal and caused the death of the Vikings we sampled, they certainly died with smallpox in their bloodstream for us to be able to detect it up to 1400 years later,” Sikora says.

“It is also highly probable there were epidemics earlier than our findings that scientists have yet to discover DNA evidence of.”

Smallpox spread from person to person via infectious droplets, killing around a third of sufferers and leaving another third permanently scarred or blind. Around 300 million people died from it in the 20th century alone before it was officially eradicated in 1980 through a global vaccination effort – the first human disease to be wiped out.