HIV and bubonic plague: a false comparison?

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For the past 20 years journalists have sought out similarities between the impact of HIV and epidemic diseases from earlier centuries, most notably the Black Death (bubonic plague), which from the 14th to early 18th centuries caused crisis mortality throughout Europe. Such comparisons have often been the hallmark of scaremongering and sensationalist writing in tabloid newspapers, eager to find an attention grabbing headline rather than engage in a serious discussion of the issues which the AIDS pandemic presents.

Last week however, an article in the prestigious British Medical Journal suggested that the current HIV was set to become the biggest pandemic in human history, outstripping bubonic plague both in the number of lives it claims and also in its social and economic impact. Unsurprisingly, the appearance of such a suggestion in such an internationally respected publication, received serious news attention from broadsheet newspapers and national broadcasters. However, it is arguable that the BMJ's comparison between bubonic plague and HIV will be just as unhelpful as the 'gay plague' headlines of the British tabloid press in the early 1980's in the fight against HIV.

There is no doubt that AIDS is having a devastating impact - last year over 3 million people died of an HIV related condition and over 40 million are now living with HIV worldwide. What's more, HIV disproportionately affects the world's poorest, with over 90 per cent of all infections in the developing world.

Glossary

morbidity

Illness.

sensitivity

When using a diagnostic test, the probability that a person who does have a medical condition will receive the correct test result (i.e. positive). 

mathematical models

A range of complex mathematical techniques which aim to simulate a sequence of likely future events, in order to estimate the impact of a health intervention or the spread of an infection.

opportunistic infection (OI)

An infection that occurs more frequently or is more severe in people with weakened immune systems, such as people with low CD4 counts, than in people with healthy immune systems. Opportunistic infections common in people with advanced HIV disease include Pneumocystis jiroveci pneumonia; Kaposi sarcoma; cryptosporidiosis; histoplasmosis; other parasitic, viral, and fungal infections; and some types of cancer. 

epidemiology

The study of the causes of a disease, its distribution within a population, and measures for control and prevention. Epidemiology focuses on groups rather than individuals.

The authors's intentions are laudable - to further draw the attention of policy makers to the need to take HIV prevention in the developing world seriously. But by making such apocalyptic predictions, and specifically by making the comparison with the plague, they may well be storing up problems for the future of HIV prevention, treatment and care programmes across the globe. If the rate at which HIV is spreading slows thanks to the increased prevention efforts in place or planned and/or morbidity and mortality from the disease slows as basic health care improves and antiretrovirals and treatments for opportunistic infections become more available, will the world's press applaud this achievement - or denounce `the AIDS lobby' once more for exaggerating the threat?

A cautionary tale is provided from the early years of HIV in the UK, when mathematical models based upon the assumed sexual behaviour of the British people, backed by eminent statisticians and government epidemiologists, suggested that up to a quarter of the UK population would be infected with HIV by now. In fact, there have been a little over 40,000 cases of HIV in a UK population of over 60 million, and although the frightening predictions may have helped to jolt transient changes in general sexual behaviour and top level government attention, it was at the cost of a huge media backlash against HIV prevention campaigns and HIV care and treatment services. In the early 1990's it became clear that the impact of HIV on the UK population was going to be much less than previously thought, thanks mainly to government backed (and then highly controversial) needle exchange programmes and the community-led safer sex campaigns amongst gay men.

Indeed, is it appropriate to compare the impact of the Black Death and HIV at all? Although it might seem attractive to try and find shared features between these two diseases, in effect we are looking at very different diseases (not least because plague is a curable bacteria, HIV an incurable virus), with vastly differing epidemiological structures, patterns of morbidity and mortality and different economic and social impacts.

In 1348/9 an estimated 50 per cent of the population of England died as the Black Death made its first visitation to these shores. Over the next 300 years, at roughly 20 year intervals until its final outbreak in 1665, the plague returned killing between 30 and 50 per cent of the population of London and other large population centres. Smaller outbreaks happened at intervals of five years, leaving around five percent of the urban population dead, and in other years, poor crowded areas of large cities would normally see one or two deaths attributed to plague. Plague's distinct patterns of mortality can in part be explained by the disease's sensitivity to environmental conditions and the role played by the black rat as host to the plague carrying rat-flea.

It should also be emphasised that the rat-flea connection in plague was not discovered until the final years of the 19th century and consequently our medieval and early modern ancestors had no effective prevention measures against the spread of plague.

By contrast, the weather and vermin play no role in the HIV pandemic. It is human behaviour which spreads the disease, and our behaviour can be modified to affect its spread.

What's more, plague and HIV have very different clinical outcomes. If left untreated, plague kills with a week of infection, with only a statistically insignificant number of people surviving. Compare this to the years which HIV can take to kill its host, and the current impossibility of a cure.

In addition, plague killed huge numbers of people in a relatively short period of time. In a bad plague year, such as 1665, a third of London's population died between May and November. Even with such huge mortality concentrated into the space of six months, the government of the city and its economy continued to function - there was no break down in order or cases of starvation. Again, compare this to HIV, where mortality is occurring at a much more even and protracted rate.

It is also instructive to compare who died from plague and who is killed by HIV. Although plague mortality was concentrated in poor, crowded areas, severe outbreaks of the disease would leave rich and poor alike defenceless against he disease and ultimately lying in the same grave yard. Again compare this to HIV which has affected specific groups within societies and particular countries and regions.

Although there are some comparisons, notably the willingness of people to find scapegoats for the diseases or to fall back on moralising about the lifestyles and beliefs of others, comparisons between plague and HIV are unhelpful in the fight against the disease and historically dubious.