In 2006, a man in Scotland died from the first case of anthrax in Britain for 32 years. Then, in 2008, a man in London was fatally infected with the same disease. The properties of both men were sealed up while the authorities investigated where the anthrax spores had come from. The source in both cases? West African drums, made from animal hides.
Anthrax is very rare in the UK, but it is relatively common in livestock and wild animals in other parts of the world. The disease is caused by the bacterium Bacillus anthracis, which is found naturally in soil where it produces hardy spores that can lay dormant for decades. Anthrax isn’t contagious, but it’s these spores that make it so dangerous as a biological weapon – as in the 2001 anthrax attacks in the US, or the warfare testing that contaminated Gruinard Island in Scotland for almost 60 years.
If anthrax spores enter an animal or human, they can germinate to become active cells that rapidly multiply and spew out toxins, causing serious illness. Cutaneous anthrax (caused by spore entry through the skin) leads to painful sores and blisters, while inhalation anthrax causes flu-like symptoms and can lead to patients coughing up blood and haemorrhaging.
Human anthrax is usually caught by contact with contaminated animals or products. In fact, in the 1800s, anthrax was known as woolsorter’s disease, because people working with wool frequently became sick after inhaling spores. The risk of this happening in the UK today is very low, because animals with the disease are quickly spotted and dealt with. But spores can still be present on animal products from places where anthrax is more common, such as the animal hides used to make the drums in the two recent UK cases.
Dr Steven Pullan works on the Genomics of Rare and Emerging Human Pathogens at Public Health England. Steven is the lead author on a recent paper published in Microbial Genomics, which revisited the spores from these cases and analysed them using modern molecular techniques.
“There was some work done at the time to characterise what type of anthrax this was, to work out where it had come from in the world,” he explains. “But in the intervening period, it’s become cheaper and more feasible to sequence the entire genome. So that’s what we decided to do.”
Sequencing the entire genome of the spores from the drums gives a readout of the 5.2 million or so DNA base pairs found in each strain. These sequences can then be analysed by powerful computational methods and compared to other strains to look for patterns and commonalities.
“We showed from the whole genome sequencing that the strains from the two incidents were closely related, but they were distinct,” says Steve. “They were more closely related to each other than to any other previously published sequences.
“They also fell onto the same branch of the phylogeny – the anthrax evolutionary tree, you could call it. This branch was new; we hadn’t seen it before in other isolates that have been whole genome sequenced.”
The team then ran their sequences against a library of over 1,000 anthrax strains from Northern Arizona University and the Centers for Disease Control and Prevention (CDC) in the US. “They found one strain that was related to ours, which they whole genome sequenced. It had been isolated by the CDC, and it was from another animal drum skin case in New York in 2006.”
The fact the strains from these cases are all related isn’t surprising, and probably reflects their shared geographical origins – all the hides are thought to be imported from West Africa. But building up a library of anthrax strains is useful for dealing with future cases.
“It’s filling in the pieces of the jigsaw,” explains Steve. “Phylogeography is the word we use for it, using the genome sequence of a strain to link it to a part of the world where similar strains are found. In future, if we have cases of anthrax we don’t know much about, we might be able to infer information about the source by looking at what strains it’s similar to.”
So – should drummers be worried? According to the CDC, drums and hides made from healthy animals don’t pose a threat, and the risk of contracting anthrax from contact with infected drum hides is very low. It seems that the actual making of drums, rather than just playing them, is linked to a higher rate of infection.
A recent paper by the Biosafety Group at Public Health England measured the quantity of spores aerosolised from playing drums contaminated with anthrax. They found that only a very small percentage of spores were released. The authors conclude that the infections that did occur in the UK were unusual events, involving people that were highly susceptible to the disease.