Hair fungus clouds forensic evidence
The presence of fungi in hair samples is often misinterpreted in forensic investigations, say researchers.
Their study, on the causes and effects of biological degradation of hair, is reported today in the Proceedings of the Royal Society B.
"There's a lot you can tell from hairs just by looking at them," says forensic biologist Silvana Tridico, who has carried out a study of 95 samples of hair from mammals across the ages -- from ancient woolly mammoths to modern humans.
Keratin-containing mammalian hair is one of the most common biological materials found at crime scenes and can also so be found in archaeological sites.
"Hair can withstand the test of time, often surviving for millennia due to the resilience of the keratin biopolymer," write Tridico and colleagues in their paper.
But although it can survive freezing, burial and mummification, hair does degrade, with filamentous fungi that live mainly in soils playing a key role in digesting keratin, say the researchers.
Tridico and colleagues found fungal invasions in the hairs of ancient humans, and an extinct woolly rhino and woolly mammoth. A scanning electron microscope showed one hair "peppered" with damage caused by fungi invading the hair.
They say the presence of fungi on archaeological or forensic samples can indicate the season during which the animal or person died and was buried, since fungus thrives in warm humid conditions.
But, while scientists have generally believed that this only happens once people are dead, Tridico says such fungi can invade the hair of healthy living animals, and even people.
"The finding that these fungal species colonise the hair of the living and not just the dead has implications for forensic science," they write.
For example if the hair of a missing person is found at the house of a suspect and has a fungal invasion, it would have generally been concluded that the missing person was dead, that the suspect had moved the body after it had been buried, and a search for the grave would begin.
"In reality, the missing person might still be alive, albeit with an infection of fungus."
What the fungal invasion tells you is the hair has been in contact with soil at some stage, says Tridico. This could be because the person it belongs to had frequented playgrounds, stables and zoos.
The most useful process for determining whether a human or animal was dead at the time they shed their hair, says Tridico, is a phenomenon known as post-mortem banding where invading bacteria leave a dark band at the root of the hair.
"So if someone is lost in the bush and you find this post-mortem banding it's going to be a recovery not a rescue mission," she says.
Tridico and colleagues also found evidence that misinterpretation of fungal invasion of hair could affect conservation efforts.
For example particular finger-like or 'stellate' patterns in wombat hairs, actually caused by fungal invasion, have been wrongly used to identify endangered wombats, says Tridico.
"Conservation biologists think it's a genetic feature of wombat hairs and therefore if you see it, it can only come from a wombat," she says.
"It's nonsense. It's an acquired artefact and a reflection of the environment the animals live in," says Tridico. "Any creature that has this in their hair has to have quite a bit of contact with the soil, and of course wombats are subterranean."
Tridico says the stellate pattern is also seen in the hair of voles and some polar bears housed in zoos.
These polar bears sometimes have green hair due to algae invading tunnels in the hair formed by the fungi, she says.
Hair colour can also be misleading, says Tridico, because it can be affected by factors such as exposure to sunlight or bacterial films.
Archaeological hair samples from both humans and animals, frequently appear red, but this does not mean a 'red-head' has been unearthed, she says.
For example, a woolly mammoth dug out of the permafrost appeared to have strawberry red hair, but her examination showed the mammoth hair was colourless.
"They did not have any pigmentation whatsoever," she says. "The colour is acquired not genetic."
Tridico suggests perhaps the colour of the mammoth hair was due to changes in the hair due to humidity or a bacterial biofilm that had formed over the hair.