Neither fleas nor rodents: how the plague spread and was stopped in Mallorca in the 19th century

BarcelonaThe previous plague epidemic in Mallorca had been in 1652. Almost 200 years later, in May 1820, the plague returned to the island. The disease arrived on board a ship from Tangier which clandestinely disembarked on the coasts of Son Servera. Until now, historiography had described it as a late case of classical bubonic plague: the disease transmitted by infected rats and passed on to humans through the bite of rodent fleas. A study led by the Autonomous University of Barcelona (UAB) and the Open University of Catalonia (UOC), published in the scientific journal the scientific journal PNAS, has overturned the version. The data show that rats had nothing to do with it and that the plague spread directly between humans at a devastating speed.

The research, led by professors Pere Puig (UAB and Centre for Mathematical Research) and Joana Pujadas-Mora (UOC and ICREA Acadèmia researcher), reconstructs the epidemic thanks to the analysis of unpublished historical documentation combined with advanced mathematical modeling tools. The results reveal that the outbreak reached a mortality rate of 78% among the infected population – more than 2,400 deaths out of a total of 7,500 inhabitants in the affected area – a figure incompatible with the usual dynamics of bubonic plague.

"In classical bubonic plague, the bite of the rat flea provides a margin of time and mortality is around 60%," explains Pere Puig. In the case of Mallorca, however, the patients' deterioration was fulminant. "The disease was transmitted so quickly that there was no time for a rodent-based dynamic. It spread via fleas from human to human and, above all, with a strong pneumonic and septicemic component, two variants that have a lethality close to 100%," details the UAB researcher. The pneumonic variant, transmitted through the air by saliva droplets, was largely responsible for the high mortality.

No port for rats

The reconstruction of events places the origin of the infection in a vessel that arrived on the coast of Son Servera, where there was no port, likely carrying contraband. The absence of port infrastructure has led researchers to dismiss the rodent theory. "The goods and contraband were transported from the ship in small rowing boats to the beach. It is impossible for rats to have reached dry land through these boats," states Puig.

The plague devastated nearby populations. There is a deeply rooted popular legend in the area that attributes the beginning of the tragedy to a shepherd boy who supposedly found an infected sailor's coat and put it on to go to the village. It is a myth so present in the collective memory that Son Servera preserves a sculpture dedicated to this figure in the main square.

A military closure that saved the island

Beyond the biological discovery, the study highlights the effectiveness of the political and administrative response of the time. Although in 1820 there were still decades to go before the birth of bacteriology and the existence of bacteria was unknown, the Balearic authorities quickly sensed the danger of contagion and decreed a sanitary cordon.

Populations such as Artà, Son Servera, Capdepera and, subsequently, Manacor were isolated and trade and movement of people were radically restricted. "In Mallorca, the epidemic was contained very well because very strict isolation belts were established," notes Pere Puig. "The historical message is clear: we must act quickly. They did not initially know it was the plague, but they made the right decision by confining the area and registering everything," he adds.

For demographer Joana Pujadas, this crisis marked a before and after in public health management in the Balearic Islands. "The epidemic could have ravaged the island, but the drastic action limited it. It represents a catalyst for the population's awareness of health as a common good," points out the UOC researcher. The lesson learned from that 1820, added to an outbreak of yellow fever that affected Palma the following year, endowed the archipelago with a unique culture of prevention. "While in inland Spain life expectancy in the mid-19th century barely reached 32 years, in the Balearic Islands it stood at 42, thanks to much lower infant mortality and an almost total containment of subsequent major epidemics," details Pujadas.

The key that has allowed the enigma of the plague in Mallorca in the mid-19th century to be solved has been an exceptional documentary archive: the daily records that the Superior Health Board obliged each cordoned-off municipality to fill out. On these specific sheets, the sick, the dead, the convalescents, and the recovered were counted daily. "This systematic work responded to the will of the emergent liberal state to analyze society through figures and statistics," highlights the demographer.