The disability caused by a tropical parasitic worm infection is far greater than previously thought, warn experts.
About 80% of the worm infection occurs in sub-Saharan Africa
Schistosomiasis is a slow, debilitating infection, caught from contaminated fresh water.
The centimetre-long worms live around the human bladder and intestine and can cause massive damage.
Scientists are calling for more resources to fight the disease, which affects more than 200m people globally, but mostly in sub-Saharan Africa.
Once released into water supplies from the body via faeces and urine, the worm infects water snails.
A second generation then hatches and hunts out another human host, entering through the skin of those wading, swimming, bathing, or washing in the contaminated water.
Maturing in the person's liver, the worms can get lost on their journey back to the bladder or intestine, causing untold damage if they reach the brain or spine.
Schistosomiasis, also known as bilharzia, can be treated with drugs. Although they are relatively cheap, resources tend to go to more urgent diseases, such as malaria, TB and HIV, say health experts.
Dr Charles King and colleagues at the Centre for Global Health and Diseases in Ohio set out to evaluate the true burden of schistosomiasis.
By looking at available data they estimate that the disability it causes is closer to 2-15% rather than the 0.5% stated by the World Health Organization (WHO).
While it is rarely fatal, it can cause disabling anaemia, diarrhoea, pain, fatigue and malnutrition, say the researchers.
"It is a prominent, chronic, recurring infection in endemic areas and its effect on health status of infected individuals is clearly not negligible," said Dr King.
He said priority and resources allocated to the disease should be reassessed.
Lorenzo Savioli of WHO agreed, saying: "A WHO expert committee concluded that the current figure for disability-adjusted life years lost to schistosomiasis was considerably underestimated.
"We hope now more resources will be allocated to this important disease."
He urged countries to tackle communicable diseases the poor, such as schistosomiasis and lymphatic filariasis, together, in a coordinated way.