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There were several highly infectious viral diseases that affected many people around the world over the 19th and 20th centuries, including tuberculosis and influenza.

Tuberculosis

Tuberculosis spreads in the droplets of moisture from coughs and sneezes, and through unpasteurised cows’ milk. Until the mid-19th century it was known as ‘consumption’, due to the fact that tuberculosis sufferers gradually lost weight (ie the disease was thought to ‘consume’ them). In the 19th and early 20th centuries, it was associated with poor housing and unhealthy working conditions.

The tuberculosis bacterium was isolated in 1882, but finding a cure was difficult. During the late 19th century, a number of sanatoriums were set up to treat chronically ill patients. Fresh air was thought to be the cure. However, this only worked in about 50 per cent of cases.

In the 1950s the introduction of the streptomycin antibiotic, along with better sanitation and vaccination, reduced cases significantly. However, tuberculosis infections began to increase again after the 1980s for a number of reasons, such as growth in the number of drug-resistant strains of the disease, the dismantling of compulsory vaccination programmes in countries like Britain, and increased migration.

Tuberculosis in Britain

Poor sanitation and living conditions meant that one in four deaths in Britain were caused by tuberculosis in the early 19th century. There was an almost steady decline in the disease from 1912, as living and working conditions improved. However, it remained a disease that mostly affected poorer people.

In 2019 in Britain, 75 per cent of people who caught tuberculosis were born elsewhere. Nowadays, the main cause of tuberculosis infection in Britain is the disease being brought in from other places.

Influenza

The word ‘influenza’ comes from the medieval Italian word for ‘influence’. This is because some medieval doctors believed the disease was caused by the unfavourable influence of the planets. The word is commonly shortened to ‘flu’. The flu is a viral disease, which means that it can mutate. Therefore, a flu vaccine is only effective for a few years at the most, as more flu strains will develop.

The most serious known flu pandemic was the Spanish Flu of 1918-20. Beginning just as World War One was ending, this deadly flu virus claimed 50 to 100 million lives (between 3 and 5 per cent of the world’s population). This made it one of the deadliest diseases in human history. Unusually, it was most dangerous for 20- to 40-year-olds.

In most years a new strain of influenza spreads across the globe. This can result in about 250,000 to 500,000 deaths worldwide. Influenza still poses a serious health risk, particularly to the elderly.

Other viral diseases

Viral diseases remain a challenge for medical science. In the 1980s, the rapid spread of the HIV virus, which causes AIDS, came as a shock to many people. However, it is not like many epidemic diseases of the past, as it can only be spread through the blood or body fluids of infected people, eg through sexual contact or sharing needles with an infected person. More recently, the outbreaks of both the Zika virus in South America and the Ebola virus in West Africa have reminded us how dangerous viruses can be. Like the Black Death before, HIV, Zika and Ebola all seem to have originated in animals and spread to humans. In addition to this, the Sars-Cov-2 virus caused the disease Covid-19. This led to a worldwide pandemic in 2020.

The rapid spread of viral diseases like influenza and smallpox between humans has been made easier due to developments in:

• air travel
• motor cars
• rail networks
• passenger liners such as cruise ships

As a result, more epidemics, which are outbreaks of a disease in a particular country, have now become pandemics, which affect many countries at the same time.

For example, at the end of World War One in 1918, troops returning from France on troop ships were infected with Spanish Flu. They then spread the disease to people back in their own countries, including Britain and the USA. It was the mass movement of people like this that spread Spanish Flu, causing 20 per cent of the world’s population to be infected in just a few years.