Will Earth’s changing climate make TB spread faster?

10 Oct 2023

The world is far behind its TB targets. Hoping to reduce TB deaths by 75% by 2025, world leaders have only managed to bring it down by 5.6% so far. Climate change, however, can derail these targets even more – it increases poverty, overcrowding and malnutrition, the primary drivers of TB.

The world wants to end tuberculosis (TB) as a public health challenge by 2030. To do that, countries such as South Africa have signed up for World Health Organization (WHO) targets that will result in 90% fewer people dying of TB than in 2015, bring down new infections by 80% and make sure families affected by the disease aren’t left financially crippled.

But at the United Nations General Assembly’s high-level meeting on TB in September it was clear that governments are way behind.

Between 2015, when the targets were set, and 2021, the number of people dying from TB globally dropped by less than 6% – yet the 2025 target was 75%. In South Africa, TB deaths fell by 15% in that period.

Although countries have again vowed to make TB treatment easier to get, to work to address HIV and TB together, and to tackle the stigma that stops people from getting help, there will be obstacles to ending the disease.

At least one thing that will make the goals more difficult to reach is climate change.

Why?

Because pushing up the temperature dial is causing the climate to change, leading to more extreme weather events such as floods, droughts and storms, more often.

By 2030, experts say, our planet is likely to be 1.5°C warmer than before we started burning coal to fuel our lives about 200 years ago. This will probably deal a double blow to the fight against TB.

Here’s why.

A perfect storm

When people live or work in crowded spaces it’s easy for them to inhale TB germs. This is because the bacteria are found in small droplets that go into the air when someone with the disease coughs or speaks.

Climate disasters caused by excessive heat, rain or winds are likely to force many people from their homes to seek refuge in cramped makeshift housing – which creates perfect conditions for TB to spread. And when infrastructure such as electricity and water supply, roads and health services are already fragile because the government doesn’t have enough money to build, maintain or repair them, things get worse.

This is what happened in the Philippines in 2013, a lower-middle-income country according to the World Bank’s classification. (By comparison, South Africa is seen as a higher-middle-income country.)

In November 2013, this western Pacific island nation was hit by Super Typhoon Haiyan, a tropical storm on steroids. Instead of winds of about 120km/h, as with a usual typhoon, its big sister brings torrential rain and winds that rage at 240km/h or more.

While typhoons are common in the Philippines, what made the situation worse this time was that the country was recovering from another super typhoon, Bopha, which hit in December 2012, and a 7.2 magnitude earthquake thrown in the mix just three weeks before Haiyan made landfall.

In 2018, a study from Bohol, the Philippine province that bore the brunt of the earthquake and Haiyan’s wrath, found that one in 15 children tested positive for TB. About a third of them had been displaced from their homes, with one in five living in shelters where there were more than 25 other people.

Although the disasters alone didn’t cause the high number of TB cases (about a quarter of people with TB in the Philippines are younger than 25), the study found that living in poor, rural areas that are difficult to reach in the aftermath of a natural disaster and being in a crowded shelter, added to the chance of getting TB.

A vicious cycle

For countries with high TB infection rates, such as South Africa, the Philippines and India, climate change will be bad news.

In many of these places, people are poor, live in crowded spaces and don’t have enough healthy food – and poverty is a big part of how TB spreads.

When someone doesn’t get enough protein, starch and fresh fruit and vegetables, they don’t have energy to work and their body can’t grow well, repair damaged tissues or build a strong immune system. This means they can’t fight off germs such as TB, which in most people with a healthy body stay at low enough levels to not make them sick (latent infection). In fact, research shows that poor nutrition increases the chances of falling ill with TB.

The Rations study from India, in which 82% of 2,800 TB patients were underweight, shows how far a small change in eating better can go to help fight the disease.

After two months of getting a food package that included rice, milk powder, chickpea powder, vegetable oil and a vitamin supplement, more than half the participants had picked up 5% body weight – and their chances of dying from TB had dropped markedly. The results show that food aid that costs less than R10 a day can help to save lives, the researchers write, because people respond better to their treatment and get cured, and fewer patients slip through the system without being followed up.

With changing climate conditions, poor countries where there are many people with HIV are likely to grapple even more than they do now to keep TB under control.

In South Africa, research from the University of Cape Town estimates that half of South Africans between the ages of 12 and 18 could have latent TB, and earlier data from the Health Department suggests that in townships close to nine out of 10 people between the age of 30 and 39 could carry the TB germ.

When a latent infection flares up and overwhelms the immune system (meaning someone has active disease), poor people become even poorer because they have to spend money to travel to the clinic, for instance, or they could lose their jobs or income because they can’t work. With less money in a household, buying healthy food is even harder – as is the chance of fighting off TB.

Two of a kind

In 2021, 304,000 people in South Africa had TB and 56,000 died of the disease. Worse, though, is that models show that more than half of all new TB infections in the country are in people with HIV. This is because HIV weakens your immune system and the body therefore can’t fight off a TB infection well.

With changing climate conditions, poor countries where there are many people with HIV are likely to grapple even more than they do now to keep TB under control. The link between TB and HIV is so strong that the WHealthO recommends that plans to deal with one condition should also include the other.

When people with HIV take their medication every day, the levels of virus in their bodies are kept so low that their immune system can keep working well, which means their chance of falling ill with other infections, such as TB, drops.

However, when people have to go without their HIV medication because, say, roads are washed away or health facilities are destroyed by a storm, the virus can start multiplying in their bodies again and make them more susceptible to other infections.

If, on top of that, people have to flee their homes because of the weather disaster and have to stay in a shelter for long, and there’s lots of TB going around already, the most vulnerable will be hit even harder.

This happened in KwaZulu-Natal in April 2022 when the province was battered by floods that led to more than 40,000 people fleeing their homes, caused serious damage to 1,300 roads and disrupted health services.

Bhekisisa reported that Mfundo Shezi, then 32, had lost both his month’s packet of antiretrovirals and his ID book during the rains, which meant he couldn’t get a refill for his HIV pills. He had been on treatment since 2021, but “on that day, I missed a dose for the first time”.

In poor countries it can take years to rebuild after a natural disaster, as happened in the Philippines. This can make it even harder for governments to get back on track with their plans to curb simultaneous epidemics such as TB and HIV – and make the goals for ending either of these diseases nothing more than promises on paper.

But having plans in place to deal with such extreme events can help. For example, disaster relief teams working in the Ohangwena Region in Namibia, where floods occur often, begin to hand out six months’ worth of HIV treatment to people when it looks like heavy rains are on the way. Health workers remind their patients to collect more medication and nonprofits and home-based care organisations explain to people what to expect during floods and how they can stay safe and healthy.

The health department in Namibia has also set up a special registry for ARVs during the floods to try to keep track of patients receiving their treatment and, if they are too far away, move them closer to healthcare centres. Health information is also broadcast on the radio and at places where people gather such as schools and churches.

It’s not a perfect solution since some people are still unable to get their medication, but it helps, the study shows. And researchers say an approach like Namibia’s is a better way to prevent people from stopping their treatment during floods than an ill-prepared response.

What does the weatherman say?

Changing weather patterns are likely to have less of a direct effect on how quickly TB spreads – unlike in the case of insect-borne infections, such as malaria, when areas in which the carriers are found will change as they become drier, hotter or rainier. However, scientists say these factors could also contribute to TB’s spread, albeit to a lesser extent.

A 2016 study from Iran found that people who live in particularly dry places with little rainfall were more likely to get TB than those in rainier, more humid places. This is likely because when people breathe in very dry air, they produce less mucus (the watery fluid that keeps your airways and lungs moist), which makes it easier for the TB germ to grow.

If places with particularly dry air stay hotter for even longer, the chance of people getting sick with TB could climb.

Moreover, a 2021 study from China showed that in places where the air is less than 72% saturated with water vapour (an indication of humidity) and there is little wind, or where it gets very cold, TB infections become more common.

Researchers in India found that more people got sick with TB when the “dew point” – the temperature at which dew forms – was higher. Although it’s not to say that this temperature point will increase because of climate change, some research suggests that dew points tend to be higher just before or on the days of heavy, flood-like rains – which could be an early warning that people may have to flee their homes.

Read more in Daily Maverick: Better data and transparency needed if we are to live up to TB rhetoric at UN

Studies like these are important because they show how long-term changes in an area’s climate can alter trends in infections, which we wouldn’t have expected before. Iran, for instance, has warmed by an average of 1.3°C between 1951 and 2013. Heatwaves have become more common and cold spells less so. Scientists expect that there will be much less rain in the future, and that hot periods will become even longer. This means that if places with particularly dry air stay hotter for even longer, the chance of people getting sick with TB could climb.

Climate change will make it easier for TB to spread, both because of direct effects and the impact on people’s livelihoods.

To beat TB, said WHO director-general Tedros Adhanom Ghebreyesus at the UN meeting in September: “We need all hands on deck.”

This story was produced by the Bhekisisa Centre for Health Journalism. Sign up for the newsletter.

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World

A perfect storm

A vicious cycle

Two of a kind

What does the weatherman say?