Tuberculosis: A Persistent Cough

Mar 22, 2013 | Jason Hayes | Research & Policy

The disease caused by Mycobacterium tuberculosis, a strain of mycobacteria, has many names. Over the last two millennia, we’ve called it phthisis, the White Plague, consumption, tuberculosis, and, bluntly, TB. Although we no longer label it a plague, the World Health Organization estimates one third of the humans on earth are infected with TB, but are asymptomatic and cannot transmit it to others. For these people, there is a 10 percent chance their infection will develop into one of the 8.7 million cases of TB were diagnosed worldwide.

TB’s many pseudonyms reveal a little bit about the disease’s complex relationship with humans over the centuries. Indeed, TB was, at different times, both lamented and sought after. We possessed seemingly infallible cures only decades ago, and yet today there are strains of TB we cannot treat at all. In some ways, TB is as much a part of human history as, say, humans.

In 2009, German researchers exhaustively catalogued the genetic history of Mycobacterium tuberculosis and discovered that TB’s evolution probably shadowed our own. The study shows that modern TB evolved from a predecessor bacterium around 40,000 years ago when humans first departed the Horn of Africa. Over time, two specific clades – biological groups that share a common genetic ancestor – emerged. The first clade only infected humans and grew proportional to human populations in the Middle East and Asia. The second branched off to infect cattle and goats around 13,000 years ago, right about when humans began to domesticate animals. Unlike swine or avian flu, it appears this time we gave TB to the animals around us.

Over the centuries, TB infected people without prejudice. The disease afflicted the ancient Egyptians and the Greeks. But in those days, with no effective treatment, 66 percent of people who progressed to active TB died. We know about their encounters with TB from descriptions of telltale symptoms in their medical and general literature. The vast majority of active TB cases – 90 percent – are located in the lungs. The infection results in chronic cough, sometimes with blood, and the drawn, pallid face that signifies the body’s slow but steady deterioration. In the lungs, the infection forms cavities – literal holes – in the tissue. There is a reason the bacteria was called consumption: it consumes us.

When TB migrates from the lungs, which occurs often with HIV co-infection, it can attack the lymph nodes, joints, spine, and other structures. Frequently, these infections produce massive swelling.

These symptoms, specifically the wasting and chronic cough, created a cultural awareness of TB that persisted through the 1800s. During the industrial revolution, field workers moved to the cities for work. In the tightly crowded tenements, TB, which spreads on mucus or droplets from coughs and sneezes, spread easily.

At this point, the arts and science took very different outlooks on TB. During the late 19th century, Robert Koch used a staining technique to identify the Mycobacterium tuberculosis bacteria and finally identified the cause of all this death. While scientists had reached a new apex in TB research, artists revered the disease as a mark of noble artistic aspirations. Largely because many artists lived in squalor, many artists contracted TB. The English poet, Lord Byron, even told a fellow poet that he hoped to die of consumption because the well-known pallor would inspire admiration from on-looking women. Years later, he did, indeed, die of TB.

In the last century, scientific progress culminated, or so it seemed, in two effective antibacterial TB treatments: Isoniazid and Rifampin. We could, for the first time, cure the disease that followed our predecessors out of East Africa so many millennia ago. TB incidence dropped across the world, and after the eradication of smallpox in 1977, scientists speculated that maybe TB would soon be only a memory as well.

However, before TB was eliminated, the 1980s arrived with a new disease, human immunodeficiency virus, and another chapter in human history opened a door for TB. People with HIV are up to 34 percent more likely to contract active TB infections. Each disease compounds the other and their combined impacts are deadly. In 2011, TB caused 25 percent of all deaths among people living with HIV.

TB’s resurgence did not stop there. Perhaps caused by the confluence of HIV-related TB and the fact that TB treatment regimens can demand weeks of medication (which many do not follow to completion but instead until they feel better) TB developed drug-resistance. Scientists started combination therapies: mixing drugs and antibacterial treatments to combat the new, stronger bacteria. First there was multi-drug resistant TB (MDR), then extensively drug resistant TB (XDR). Reports in 2009 suggested a new strain of TB might be immune to all known treatments.

During the growing drug resistance, TB continued to be a leading cause of illness and death, disproportionally in developing countries.

Then, to confirm the rumors, a smattering of TB patients in Iran couldn’t be cured, followed by two in Italy. Recently, doctors in South Africa confirmed nine patients to have totally drug resistant TB (TDR). TDR TB is the newest face of TB: one that, yet again, we have no defense for other than early diagnosis and isolation. TB is not the only bacteria to develop drug resistance, but its dispassionate disregard for modern medicine seems to undermine our success in almost cutting TB incidence in half since the 1990s. We have made progress, but in some aspects it feels like we are back at square one – like we are trying to outrun our shadow. 

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