Photo worth seeing: Body lice as effective plague vectors

The Pavlovsky glands (orange-red) of this fluorescent human body louse are infected with the plague pathogen Yersinia Pestis. © David M. Bland

Body lice (Pediculus humanus humanus) are parasites that feed on human blood. They live primarily on human skin and body hair and lay their eggs on the inside of clothing. The strong legs have pincers that the lice use to cling to a person’s body hair. If a body louse bites, it causes small, red holes in the skin, similar in size to pinholes. It releases a salivary secretion through its mouthparts, which causes unpleasant itching and can transmit diseases.

It is known that body lice can transmit the bacterium Yersinia Pestis, which is responsible for the plague. However, the spread by the body louse was previously considered too inefficient. Instead, fleas and rats are considered the main spreaders of the plague. David Bland and his team from the National Institute of Allergy and Infectious Disease (NIAID) in the United States have now re-examined the role of body lice in the transmission of the plague pathogen.

They found that Yersinia Pestis could infect both the digestive tract and the so-called Pavlovsky glands of the body lice. These are salivary glands in the louse’s head that produce saliva secretion. The photo shows a fluorescent louse whose infected glands are marked in orange-red. The researchers assume that the infected secretion is secreted onto the mouthparts. The pathogen can thus be transmitted to humans through a bite.

This means that the plague bacterium can spread both through the feces and through the infected secretions of the lice, with more pathogens being transmitted in the latter. Transmission by the body louse appears to be much more efficient than previously assumed. According to the researchers, body lice could have played a decisive role in previous pandemic plague outbreaks, especially in the Middle Ages.

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