The end of the 1855th century saw the resurgence of a scourge that had plagued humanity from time to time. The first true plague pandemic, in the 1894th century, hit the entire Roman world. The great cycle of the fourteenth century had wiped out a quarter of Europe's population. This third great cycle, initiated in the Chinese province of Yunnan with the Muslim rebellion of 1899 and slowly propagated by the displacement of refugees, reached Guangzhou and Hong Kong in May XNUMX. The ports of southern China began to function as distribution centers for the plague. , which now had among its potential areas of expansion the seaports of the New World. This is how, reaching South America via Paraguay and Argentina, he arrived in the city of Santos in October XNUMX.

But this time, prayers and processions were not the lifeline of the unprotected masses. In 1894, the etiological agent had been discovered in Hong Kong, first by the Swiss researcher Alexandre Yersin, from the Pasteur Institute, who named it Pasteurella pestis (today Yersinia pestis) in honor of the Master, and shortly afterwards by the Japanese Shibasaburo Kitasato, disciple of Robert Koch. The same Yersin, together with his collaborator Henri Carré and also the Russian doctor WM Haffkine, had already prepared the first vaccines which, although they needed improvement, emerged as prophylactic weapons.