Prologue

The USA was busy building its border wall and the country's right-wing media were in a state of absolute frenzy. It is strange how grimly odd North American television is: the anchors with their blocks of static hair and immoveable opinions, the manic shouting for no apparent reason, the agitated ticker scrolling endless anxiety across the bottom of the screen. It is a self-contained world; brightly lit, loud and paranoid. The screen filled with footage of cranes hauling huge black girders into a line that would end up snaking a great swathe of the US frontier to Mexico.

The news anchor lamented that progress was too slow; the number of immigrants escaping drought and crime in Central America had barely abated. The country was being 'swamped'. He welcomed a guest: David Ward, a former US Immigration and Customs Enforcement agent, popped up on a split screen as footage of people walking from Guatemala into Mexico played. With unblinking blue eyes and goatee on the verge of grey, Ward griped that an army was heading to US soil, 'not only from Central America but they're coming in from Africa, from the Middle East'. This is nonsense, I thought to myself.

As I went to change channels Ward thundered that, worse still, the caravans of immigrants harboured diseases such as 'leprosy and TB1 that are gonna infect our people in the United States'. It made me stop. I knew first-term President Donald Trump had claimed 'tremendous infectious diseases'2 were running rife because of immigration - it had become one of his minor refrains. Tuberculosis, maybe, at a push - but leprosy? Surely 'fake news', the newly minted phrase of the moment. Surely there is no leprosy now? In another time the question might have evaporated into the hyperbole it obviously was. Yet it lingered. The bait and switch Ward performed on-screen, between the othering of disease and the othering of the immigrant, seemed, and seems still, to be everywhere. The idea of leprosy began to consume my thoughts.

The next day, the day after. The immigrant as walking pathogen, the immigrant as criminal. Crime as a disease, disease as the other: build the wall, stop the boats, keep them out. It's a health emergency, it's a political calamity, it's a moral imperative. Our society is sick; the demigod populist has the cure. This book was born of this time, a moment in which, despite this shrinking world and our interconnected lives, the other is seen as more contagious than ever.

*

Leprosy, or Hansen's disease, is caused by an intracellular, rod-shaped, environmentally sensitive pathogenic bacterium known as Mycobacterium leprae, first identified in 1873 by Gerhard Armauer Hansen, a Norwegian physician. It is spread in water droplets transported by sneezes and coughs. The bacterium, which thirty-six million years ago shared a common ancestor3 with Mycobacterium tuberculosis, evades the immune system by seeking out the cooler extremities of the body, hiding as an outlaw in the nervous system. There were 202,485 new cases4 reported across more than a hundred countries in 2019. (Central American cases were in the single digits.) The global frequency in 2023 dropped dramatically to 182,815,5 but as with many health problems, the Covid-19 pandemic catastrophically skewed detection. Compared to other bacteria, Mycobacterium leprae is incredibly slow to replicate itself, and this has long hampered attempts to trace the spread of the infection: by the time it is visibly apparent, a person who has leprosy is likely to have been asymptomatically carrying and perhaps proliferating the disease for an average of five years, sometimes as many as twenty.

The first sign for the majority of patients will be numbness, most likely affecting the ability to gauge temperature, followed by sensitivity to light touch. A patient with tuberculoid leprosy - who will have better natural immunity to the attacking bacteria - might only exhibit a few discrete lesions, one- to two-centimetre red or white patches with slightly raised borders, possibly appearing decades after the initial signs. A person with untreated lepromatous leprosy (in which far more of the bacterium is present) is likely to suffer damage to the skin, the upper respiratory tract, toes and fingers, the eyes and the inside lining of the nose; they will experience blocked nostrils and swelling of the legs. If they seek medical attention, with luck, a doctor can order a slit skin smear, in which a small cut is made to the earlobe, forehead, chin, buttocks or, if they've already appeared, the lesions themselves. The doctor will scrape out a sample, which will be analysed under a microscope. The current multidrug cure - a combination of dapsone, rifampicin and clofazimine - has been available internationally since 1981. It was a major medical breakthrough and succeeded in reducing new cases from more than five million a year to the current hundreds of thousands.

Neither strain is as infectious as mythology dictates, and 95 per cent of the world's population is naturally immune to the bacillus. Most people with a good diet and the privilege of hygiene could spend a lifetime living with someone who is actively affected by the disease and not contract it. In areas where leprosy is still endemic - with India, Brazil and Indonesia topping that chart - a staggering 7.8 per cent of people have been found to carry the bacteria in their nasal passage.6

Yet the disease's dark reputation perseveres globally. In an 1886 essay, the French dermatologist Henri Leloir wrote that the leprosy patient suffers their condition twice,7 first as mycobacterial infection, second as stigma. A century later, in Illness as Metaphor, Susan Sontag notes: 'Nothing is more punitive than to give a disease a meaning - that meaning being invariably a moralistic one . In the name of the disease (that is, using it as a metaphor), that horror is imposed on other things. The disease becomes adjectival.'8 While this book does serve as a history of leprosy, Outcast is not a medical biography, but the story of this stigma - how the secondary infection identified by Leloir spread: how it came about, and how this particular stigma, the ur-stigma, was used as the blueprint for other forms of discrimination. Leprosy has become a geography, the world divided into ever-shifting territories of the unclean and clean; those who are subjects of Sontag's 'kingdom of the sick', and those looking across the border wall in abject fear.

*

A condition called 'leprosy' has much footprint in later translations of religious scripture, its sufferer hailed as ritually impure from Sanskrit hymns to the Old Testament, but these often prove unreliable evidence with which to trace the modern condition. A great deal of today's medical knowledge first emerged from the cultural and intellectual hub of third-century BC Alexandria. Among the ancient city's doctors was Straton, who, on encountering great sickness among Alexander the Great's soldiers returning from India (leprosy and war continue to dog each other today), described in detail a condition that resembles the effects of Mycobacterium leprae to a tee. 'Its symptoms are not hidden:9 they consist in livid and black embossments that resemble ecchymoses; some on the face, others on the arms, still others on the legs.' This bruising he named 'elephantiasis', long before the lymphatic infection that swells the legs took the name.

Attracted by Alexandria's reputation for tolerance, though keeping to their own quarter in which they might make their religious observances without hindrance, the Jewish scribes of the city were busy at their desks too, translating the Tanakh into Greek. Where today's reader finds reference to 'leprosy' there, and in the Old Testament, in the original text the Hebrew word tsa'arat (????) was used. The first use of tsa'arat these scholars needed to translate occurs in Leviticus 13, as God appears to Moses and issues a complex series of commands regarding ritual cleansing in the case of a person with a skin condition. Such a person is deemed unclean and is forbidden from entering the temple or touching sacred objects. They must live outside the camp. While symptoms persist, a priest must undertake regular examinations to see if the infection is spreading. 'If the priest look on it, and, behold, there be no white hair in the bright spot, and it be no lower than the other skin, but be somewhat dark; then the priest shall shut him up seven days.' For the examining religious man this was regarded as a risky job, and the passage not only forges the connection between this skin complaint and sin, but also charity and martyrdom. Crucially, however, we don't know what condition was being described, and nor would the rabbinic scholars have done - unlike Straton's scientific description, the verse is light on visual clues - but in their upper-case script, laid down on parchment, they inked their translation as lepra (??p?a), which at the time was a more generalised...