A lethal fungus that can rot human tissue from within is spreading rapidly across the US, and experts warn the problem could worsen as temperatures rise.

Aspergillus fumigatus is airborne and nearly impossible to avoid. Its spores are so tiny that people inhale them without noticing.

It can cause a serious lung infection called aspergillosis, which in vulnerable individuals can lead to organ failure and death.

Those with weakened immune systems, such as patients with cancer, asthma, or HIV, are especially at risk.

Scientists have found the fungus invading parts of the US, with Florida, Louisiana, Texas, Georgia, and California seeing the highest exposure due to hot, humid climates and farming activity.

Major cities like New York, Houston, and Los Angeles face added risks from dense populations and aging infrastructure.

Officials said that aspergillosis isn’t a reportable disease in the US, meaning infections, hospitalizations, and deaths aren’t tracked, making it hard to detect.

Doctors advise people with weakened immune systems to avoid soil, gardening, and moldy environments, wear masks in dusty areas, and maintain clean air in hospitals and homes. US hospitals have stepped up mold inspections and antifungal protocols.

Aspergillus fungus is a toxic fungus that produces aflatoxin, one of the most powerful naturally occurring carcinogens. This can cause cancers and disorders of the lung, liver, spleen, stomach, colon and kidney.

Co-author Norman van Rhijn, from the University of Manchester, told the Financial Times: ‘We’re talking about hundreds of thousands of lives, and continental shifts in species distributions.

‘In 50 years, where things grow and what you get infected by is going to be completely different.’ 

About 400,000 of these cases develop into chronic pulmonary aspergillosis, a long-term lung infection.

Invasive aspergillosis is less common but far deadlier. It mainly targets people with weakened immune systems and can spread from the lungs to the brain, heart, and kidneys.

One study found only 59 percent of organ transplant patients survived a year after infection, and just 25 percent of stem cell transplant patients.

Hospitalizations for invasive aspergillosis in the US rose about three percent annually from 2000 to 2013.

By 2014, nearly 15,000 hospital stays were recorded, costing an estimated $1.2 billion.

ICU autopsies show aspergillosis ranks among the top four infections likely to cause death.

The World Health Organization lists Aspergillus fumigatus as a ‘critical priority’ fungal threat due to rising drug resistance and high death rates.

The fungus thrives in warm, damp environments, even surviving temperatures above 120 degrees Fahrenheit in compost piles.

Close up of Aspergillus oryzae is a filamentous fungus, or mold that is used in food production, such as in soybean fermentation for education in laboratory.

Climate change is making it easier for the fungus to survive inside the human body as global temperatures rise.

A new study conducted by University of Manchester found that if fossil fuel use continues at current levels, the fungus could expand by more than 75 percent by 2100, putting millions more at risk in the southern US, where conditions mirror those forecasts.

Azole drugs, widely used to treat fungal infections in humans, are also heavily applied in agriculture to protect crops.

Experts warn this overuse may be driving drug resistance, which can transfer from the environment to humans and reduce treatment effectiveness.

A study published in the Applied and Environmental Microbiology, found azole-resistant, Aspergillus fumigatus in farm soil across at least seven US states, with many strains resistant to standard antifungal drugs.

Scientists warn the mixing of different fungal types is speeding resistance spread and suggests the problem is already deeply rooted in US soil.

The WHO urges immediate investment in safer drugs, faster testing, and better training for health workers, while calling on drug companies to prioritize fungal research and include children in clinical trials.

‘This isn’t science fiction,’ said Dr Vyas, an infectious disease expert at Columbia University. ‘These infections are real, and we’re not ready.’