The 1894 Hong Kong Plague: Kitasato Shibasaburō's Race with Yersin to Discover the Bubonic Plague Bacillus

The Hong Kong Plague of 1894 and the Race for a Discovery

The year 1894 marked a terrifying chapter in medical history, as a violent pandemic of bubonic plague, the same Black Death that had decimated medieval Europe, erupted in the bustling port city of Hong Kong, then a British colony. The outbreak, which had spread from its endemic home in China's Yunnan province, struck fear across the globe, threatening to become a worldwide catastrophe. In response to desperate pleas from the British colonial government, two of the era's most brilliant bacteriologists embarked on a high-stakes mission to Hong Kong: the renowned French scientist Alexandre Yersin, working for the Pasteur Institute, and the already-famous Japanese pioneer, Kitasato Shibasaburō, who was dispatched by the Japanese government. Their arrival in June 1894 set the stage for a fierce scientific race conducted under the most grueling and hazardous conditions imaginable, a race that would culminate in the discovery of the microbial cause of one of humanity's most feared diseases.

Kitasato Shibasaburō was, by 1894, a scientific celebrity. A student of the great Robert Koch in Berlin, he had already co-discovered the toxin and, crucially, the antitoxin for tetanus, a breakthrough that laid the very foundation for the field of serology and modern immunology. He had also developed a pure culture method for the anaerobic Clostridium tetani bacterium, a significant technical achievement. Flush with this success and having recently returned to Japan to found his own Institute for Infectious Diseases, Kitasato was the epitome of the new, world-class Japanese scientific community that had emerged during the Meiji Restoration. He arrived in Hong Kong with a team of assistants, granted full facilities and access to patients by the British authorities, who provided him with a dedicated room in the Kennedy Town Hospital at the heart of the outbreak. His methodology was meticulous and rooted in the Kochian principles he had mastered in Germany. He performed numerous autopsies on victims of the plague, carefully extracting tissue samples from the characteristic swollen lymph nodes, or buboes, and from the blood and organs of the deceased. Using state-of-the-art staining techniques and culture methods, he observed and described a plethora of microorganisms. However, his central and most famous finding was a stout, bipolar-staining, non-motile bacillus that he consistently found in the buboes and the blood of plague victims. He successfully grew this bacterium in pure culture and noted its characteristics. Most importantly, he conducted experiments where he injected these pure cultures into laboratory animals—mice and guinea pigs—which subsequently developed symptoms mirroring human plague and died. Upon their death, he recovered the same bacterium from their tissues, thus fulfilling several of Koch's postulates, the rigorous standard for proving a pathogen causes a specific disease.

With great speed, Kitasato and his team compiled their findings. On July 7, 1894, a preliminary communication from Kitasato was read before the Medical Society of Hong Kong. Shortly thereafter, on August 25, 1894, his comprehensive paper, "The Bacillus of Bubonic Plague," was published in the prestigious British medical journal The Lancet. In this detailed article, which ran for multiple pages, Kitasato described the clinical progression of the disease he observed, his autopsy findings, and his meticulous laboratory work. He provided detailed descriptions of the bacterium's morphology, its growth characteristics on different media, and the results of his animal inoculation experiments. He firmly stated that this bacillus was the causative agent of the plague. However, his report was complex and contained a significant point of confusion. Alongside the plague bacillus, he also described the presence of other microbes, including streptococci and pneumococci, and he did not entirely dismiss the possibility that they might play a contributing or synergistic role. This nuance, combined with the immense pressure and the primitive working conditions (extreme heat, overwhelming numbers of the dying, and the constant risk of infection), likely led to a less than perfectly clear presentation of his primary discovery.

Simultaneously, Alexandre Yersin was working under vastly different circumstances. Lacking the official support granted to Kitasato, Yersin was forced to conduct his investigations in a makeshift bamboo hut near the hospital. Crucially, however, his outsider status may have worked to his advantage. While Kitasato focused on blood samples from deceased patients, which were often contaminated with other bacteria, Yersin gained permission to perform his autopsies more discreetly and focused on sampling the intact buboes themselves, which were more likely to contain the primary pathogen in pure form. Yersin also made a key technical adjustment: suspecting the plague bacterium might be sensitive to heat, he cultured his samples at room temperature rather than at 37°C, which was standard practice but which inadvertently killed the plague bacillus (Yersinia pestis) while allowing contaminating microbes to flourish. Within days of Kitasato's first report, Yersin too had isolated a single, consistent bacterium from the buboes. He described it as a small, gram-negative rod with bipolar staining, and he too fulfilled Koch's postulates with animal experiments. His findings were sent to the Pasteur Institute in Paris and were published in the Annales de l'Institut Pasteur in September 1894, slightly after Kitasato's Lancet paper.

The Aftermath and Resolution of Priority

For much of the subsequent decade, a vigorous dispute over priority raged within the international scientific community. Kitasato had published first, and his reputation was immense. For a time, the bacterium was often referred to as Kitasato's plague bacillus or Bacterium pestis. However, as microbiology advanced and scientists around the world began to study the organism, problems with Kitasato's initial description became apparent. The bacterium he described in his 1894 paper was not entirely consistent with the organism universally accepted as the true cause. It was later argued that the cultures Kitasato had identified and used for his animal experiments were likely a mixed culture, possibly containing the true plague bacillus but also contaminated with pneumococci, which led to his confused conclusions about multiple potential agents. Yersin's description, by contrast, was precise, accurate, and perfectly matched the properties of the organism we know today. By the early 20th century, the scientific consensus had shifted decisively in Yersin's favor. The bacterium was formally named Pasteurella pestis in honor of the Pasteur Institute, and later reclassified as Yersinia pestis, finally giving Yersin unambiguous credit.

Nevertheless, to relegate Kitasato's role to mere footnote would be a profound historical injustice. His journey to Hong Kong at great personal risk, his rapid and diligent work, and his publication of the first major report were acts of tremendous scientific courage. He was undoubtedly one of the first two men to isolate the plague bacillus, and his initial identification, though muddled, was fundamentally correct in pointing to a specific bacillus as the primary cause. The 1894 episode is now correctly viewed not as a story of a single winner, but as a dramatic example of simultaneous discovery, a common phenomenon in science where two brilliant minds arrive at the same truth independently, albeit with differing levels of clarity and accuracy in their initial reports. The legacy of 1894 is therefore a dual one: the bacterium rightly bears the name of Alexandre Yersin, but the historical record must always honor Kitasato Shibasaburō for his pivotal role in the terrifying and urgent investigation that finally unmasked the ancient scourge of bubonic plague, a monumental achievement that propelled the world into a new era of understanding and eventually combating infectious disease.

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