The adoption of woolen clothing in prehistoric times inadvertently opened a new avenue for a hazardous pathogen, transforming its transmission route adn contributing to the spread of recurring fever. This shift, occurring between 6,000 and 4,000 years ago in West Asia, coincided with the rise of sheep cultivation for wool and the subsequent use of woolen garments.

Prior to this period, the bacterium responsible for recurring fever was primarily transmitted by ticks. However, the introduction of woolen clothing created a new ecological niche for a specialized strain of the bacterium.

The Rise of the Louse-Borne Variant

Around the time humans began wearing wool, Borrelia duttoni, the tick-borne bacterium, underwent a significant evolutionary split. This resulted in Borrelia recurrentis, a variant specifically adapted for transmission by human body lice. These lice thrive in woolen clothing, which they prefer over plant-based fibers like flax or hemp.

This adaptation led to the emergence of two distinct forms of recurring fever: a tick-borne variant and a louse-borne variant. The louse-borne variant, carried by Borrelia recurrentis, causes a disease nearly identical to that caused by the tick-borne strain but is exclusively transmitted through body lice.

DNA Analysis Provides Evidence

The evolutionary history of these bacterial types is supported by DNA analysis, including the study of ancient DNA extracted from lice found in English graves dating back 500 to 2,000 years. This research, published in Science, highlights the genetic divergence between Borrelia recurrentis and Borrelia duttoni.

The Impact of Louse-Borne Recurring Fever

The louse-borne bacterium, Borrelia recurrentis, causes a disease similar to the tick-borne version but can only survive in body lice. This bacterium is suspected to be responsible for the “Sweat fever” epidemic that swept through Europe in the 16th century.

According to the Dutch National Institute for Public Health and the Habitat (RIVM), a characteristic symptom of the disease is a high fever of a few days that returns after a week. While the tick-borne variant recurs about 11 times, the louse-borne variant recurs slightly less often. The high fever can lead to severe complications, including heart and liver failure, and even death.

Current Prevalence and Related Diseases

Thanks to improved hygiene practices, the louse-borne variant of recurring fever has largely disappeared from Europe. However, it remained a significant health concern during the World Wars and continues to be a major cause of mortality in Ethiopia and Sudan. The tick-borne variant is more widespread, especially in warmer climates.

Notably,the bacteria responsible for recurring fever are related to those that cause syphilis and Lyme disease,highlighting a shared evolutionary history and potential similarities in thier mechanisms of infection.

The origins of Woolen Clothing

The period between 6,000 and 4,000 years ago, coinciding with the start of the Bronze Age, marked the widespread adoption of woolen clothing in West Asia. While it is certain that woolen clothing became popular during this time, the precise origins of sheep cultivation for wool remain debated. Some theories suggest it began on the steppes of Ukraine, associated with the Yamnaya culture, while others point to earlier practices in the organized cities of Mesopotamia. Sheep where initially raised for meat starting around 10,000 years ago.

Archaeological evidence of woolen clothing dates back approximately 5,000 years in Iran and 4,800 years in the northern Caucasus.Around 6,000 years ago, there was a noticeable increase in the number of rams raised in the Middle East, as rams produce more and better wool than ewes. By 4,500 years ago, the Proto-Indo-European word for “fur” also began to encompass the meaning of wool. Interestingly, this word shares similarities with terms used for wool in Middle Eastern languages like Sumerian and Akkadian, although it remains unclear whether this indicates borrowing or a shared linguistic origin.