The disinfection of mail was not an occasional happening, like disaster mail resulting from the sinking of ships or the crash of an aircraft. It was rather the ‘logical’ outcome of a near-universal belief that infectious diseases could be brought into a healthy country by susceptible goods, including paper.
This belief, which was still held by many countries until late in the 19th century, was unfounded, in so far as none of the diseases against which disinfection had been practised – plague, yellow fever, typhus fever, cholera and leprosy included – could be transmitted on dry paper. But this was not established scientifically until modern times : in the 1880s in the case of cholera, and the first decade of the 20th century for yellow fever. Ironically, smallpox, a disease against which disinfection was hardly ever employed, can be so conveyed ; and the virus can be very easily destroyed by heat, even a hot iron.
The Republics of Venice and Ragusa, (Dubrovnik), enforced quarantine from the 1370s. Out of this grew a complex of health passports, ships’ bills of health, quarantine guards and lazarettos. The same States introduced the ‘perfuming’ of mail from the Levant with sweet-smelling herbs and flowers a half-century later : a treatment which left no discernible traces. With the advent of the terrible plagues of the mid-17th c., most Mediterranean ports smoked or scorched mail from suspect vessels, sometimes after dousing it with vinegar. Wafers or seals, legitimising the opening of covers to treat the contents, are seldom seen before the 1720s. The earliest cachets to certify treatment appeared in the 1780s. These measures were mainly directed at plague, though England and France also quarantined ships against yellow fever.
Europe (other than Russia and the Balkans) was generally spared plague after the end of the 18th c., though there were isolated outbreaks in the Ionian Islands and at Noja, near Bari in Italy But yellow fever, which had occasioned disinfection of mail from the Caribbean in particular, visited ports in Italy in 1801, and several Mediterranean ports in 1805, resulting in a short-lived resurgence of the treatment of mail, even in Northern European countries.
After a period of relatively few scares, in 1831 the western world faced a new threat : cholera, which had escaped from India, (its reservoir even now, as it was then). It came to Europe via Persia and Russia in the contamination of water sources. In the ensuing panic, even countries like Germany, which had been sceptical of the virtues of treatment of mail, rushed into action. The old Cordon Sanitaire against plague was resurrected by Austria and mail was treated in virtually every country in the known world : but by the mid-1840s disinfection was little used, except in eastern Europe and Malta against plague.
An epidemic of cholera in Egypt in 1883-4 resulted in a brief renewal of measures especially in Italy, but most countries had anticipated the verdict of the 1893 International Sanitary Congress, that ‘letters, news-papers and books should be free of all restrictions’ – but only against cholera. The Americans still disinfected mail against yellow fever and bubonic plague on isolated occasions, most notably in Hawaii, and the Russians redoubled their efforts against Persia and the Far East in the 1890s when both plague and cholera raged, until 1911. Austrian Poland was treating selected mail from the east in 1879 and 1892.
In the 20th century, mail was very sensibly treated to prevent transmission of smallpox until its final eradication in the 1970s, most notably in Austrian military hospitals in W.W.1 :. but it was also used in American T.B. Sanatoria, in leper colonies, and even against foot-and-mouth disease in a Swiss canton in the 1920s. Australia treated letters from quarantine up to 1935. The anthrax scare in the U.S.A., on the heels of the terrorist outrages of September 2001, resulted in measures to irradiate mail there which continued for a few years ; and some rather half-hearted inspection in Europe and Australia. This has resulted in 21st century examples of collectable items, a hitherto unimaginable development.