Historically, most pandemics happened when the viruses were shipped away across the globe. The plague, the deadliest recurring pandemic in history, primarily happened because of rats, which travelled on the ships carrying the plague.
‘Ship Rats and Plague’, published in 1914 in Public Health Reports, states,
…the rat has become cosmopolitan, a globe trotter, so to speak. The grey or Norway rat and also the black rat have colonized in all parts of the world, and the globe-trotting on the part of these rodents still continues. It is for this reason that they are of particular significance in the spread of plague. The rat by traveling on ships has, since 1894, spread plague to all parts of the world.
The rat, however, was seen as having spread the plague to all parts of the world for centuries and not just since 1894. From the 1st great plague pandemic called the Justinian Plague in 541 AD that changed the course of the Roman Empire to the Black Death in the 14th century to the 3rd plague pandemic that spread across the world from the port town of Hong Kong in 1894, the rat had been carrying the plague.
Even when the bacteria that caused plague had not been identified, it was known that rats were the cause. That is why rat catchers had been employed by towns in medieval Europe. The legend of the Pied Piper of Hamelin is about a similar rat catcher employed to rid towns of rats. These rat catchers used to breed rats for the popular blood sport of those times, i.e. rat baiting in which bets would be placed on how many rats a dog could kill.
The most popular rat catcher of all time was Joe Black, the ‘Queen’s Official Rat Catcher’, who bred albino rats that were pets of Queen Victoria. These albino rats were the first rats that were studied scientifically in labs till the standardization of the lab-rat in 1906 at the Wistar Institute in Philadelphia.
The profession of rat catcher morphed into the Rat Officer on ships, who had to inspect the ships for rats. Ships also kept cats to rid them of rats. But it was almost impossible to rid ships of rats as ships provided rats with ample housing and food. The construction of ships made it easy for rats to find space and there was abundant food meant for passengers and in the cargo. The phrase, “even rats leave a sinking ship” suggests how much comfortable rats were otherwise in ships.
Because of this, C F White writes in The Proceedings of the Royal Society of Medicine in 1935:
“it is certain that good homes for rats will not long remain untenanted and the methods of deratization must be repeated again and again. The majority of rats in ships are probably born onboard…But I think that rats which are well housed and well fed will settle down to a comfortable family life and have large litters at frequent intervals. Our best method of waging war on rats is therefore to present them with an acute housing-problem and a food-shortage.”
However, with strict rat proofing and fumigation, the ships in the last century became safer. Meanwhile, scientific research on the plague helped identify how it spread. In 1894, Alexandre Yersin and his colleague identified the bacteria that caused the plague and that was later renamed as Yersinia Pestis in his honour. A year later, Paul Luis Simmond discovered while researching in India how the plague spread, i.e. the oriental rat flea carried the plague between rats and infected humans with it through their bites. This led to development of drugs and antibiotics such as streptomycin that helped attack the plague bacteria and the plague lost its potency though small outbreaks did happen.
Also Read: Pandemic In History: ‘Shipping’ The Virus