How genome sequences tracked down an ancient disease Premium

Scientists have traced the prehistoric trail of many major human pathogens in recent years, providing an unparalleled view of the evolution and adaptation of human pathogens. This article takes a closer at the origins of the cause of the bubonic plague.

This article is part of a fortnightly column exploring contemporary concepts and issues in genetics.

The ‘black death’, or the Great Plague, of the 14th century was one of the deadliest epidemics in human history. It’s a clear example of the profound influence infectious disease outbreaks can have on society, economy, and culture. It was also probably one of the most impactful epidemics, considering it left an indelible mark on humankind and shaped the collective memory of many subsequent generations.

The ‘black death’ is believed to have killed more than 25 million people in Europe and possibly up to 40-50% of the population in some of the continent’s major cities.

The ‘black death’ was caused by a bacterium called Yersinia pestis, which infects mammals. This bacteria’s discovery has been attributed separately to Alexandre Yersin, a Swiss-French physician, and Kitasato Shibasaburō, a Japanese physician and microbiologist during the plague outbreak in Hong Kong in 1894. Humans typically get infected through fleas or through close handling/contact with an infected human or animal.

One possible reason for the humongous proportions of the ‘black death’ outbreak is the human-to-human transmission of the bacteria. While the plague remains a serious disease today, it’s also quite treatable. After the discovery of antibiotics, in fact, its modern mortality is quite small.

India has experienced plague epidemics of varying intensities from as early as 1896 in Bombay to outbreaks in Karnataka (1966) and Surat (1994), and to a more recent isolated outbreak (2004) in a village in Uttarakhand. India also prominently figures in the history of the plague. The plague vaccine was developed by Waldemar Haffkine in 1897 during the outbreaks in Bombay; the country also initiated mass vaccination programmes, with at least 20 million doses estimated to have been administered to date.

While the ‘black death’ is probably not the earliest recorded epidemic, there are old records of its occurrence. Historical archives suggest the Plague of Justinian in the sixth century A.D. was possibly the first to be documented. Plague epidemics continue to occur around the world and are today endemic in some regions.