Researchers say that diabetes suppresses the immune system, giving latent TB germs the chance to multiply and cause disease.
"Diabetes is fueling the spread of TB," declares a white paper on the looming "co-epidemic" released at the 45th Union World Conference on Lung Health in Barcelona on Wednesday.
"Having diabetes increases the risk that a person will become sick with TB," the report says. "Diabetes is also more difficult to manage in people who have TB. And a person sick with both diseases is likely to have complications that do not typically exist when either is present on its own."
Dr. Anthony Harries, a coauthor of the report, tells Goats and Soda there's a new urgency to head off the dual epidemic in countries with high levels of TB, such as Brazil, China, India, Indonesia and the Russian Federation.
Harries, who spent years in Malawi as the HIV/TB epidemic unfolded, doesn't want to repeat history. "Looking back, we were a bit late in our response to the HIV/TB epidemic. It took a while to wake up to the fact that HIV was driving that."
Warnings about the deadly interaction of HIV and TB were sounded in the early 1990s, but no global strategy was developed until 2004. The AIDS virus kills off CD4 cells in the immune system, which are necessary to fight TB infection.
The TB/diabetes double-whammy has at least two important differences from the TB/HIV co-epidemic:
It involves the interaction of an infectious disease (TB is the world's second-deadliest, next to HIV/AIDS) and a non-communicable chronic disease, rather than two infections.
It has potentially more global impact. The TB/HIV co-epidemic was concentrated in sub-Saharan Africa, where 18 countries saw TB rates quadruple because of HIV. Many more countries have high rates of TB and, increasingly, of diabetes.
And while low- and middle-income countries with most of the world's population is at risk for the TB/diabetes problem, wealthy countries such as the United States are hardly immune in an increasingly mobile world.
Akbar Anthony is a case in point. A 62-year-old Pakistani, he's lived with his family in the Bronx for more than 14 years, working as a welder.
This spring he developed a fever and malaise — although not the coughing that sometimes signals a lung disease. A trip to the emergency room and a lung x-ray revealed TB.
"I was in the hospital for 70 days, in an isolated room," Anthony tells Goats and Soda. "If somebody come inside, they had to wear a mask. I never go outside for 70 days. It was not easy."
Drugs eventually cleared his TB. But blood tests showed he had diabetes — and apparently has suffered from the metabolic disorder for years. It has caused blindness in one eye and numbness in his feet, side effects of longstanding diabetes.
A study presented in Barcelona on Thursday finds that one in five TB patients in the Indian state of Kerala also had diabetes.
So, as Akbar Anthony's case also shows, people with newly diagnosed TB should be tested for unsuspected diabetes.
And a large Korean study presented at the Barcelona meeting shows that TB is frequently diagnosed within a year of diabetes — a finding that argues for screening newly diagnosed diabetics for TB.
Such "bi-directional" screening seems like simple logic. But it represents a big shift in thinking among doctors and public health workers. Infectious and non-communicable diseases are thought of as occurring in separate "silos," treated by different kinds of doctors and addressed (if at all) by different programs or agencies that don't talk to one another.
Nobody knows whether Akbar Anthony caught TB in New York City or brought it from his native Pakistan. Of the two billion people in the world with latent TB infection, 90 percent will never get sick from it. But the risk soars among people who develop diabetes.
"Obviously diabetes does something to your immunity, but we don't understand what," Harries says. "We're trying to understand the mechanisms."
One thing is clear: Having both diseases complicates the treatment and compromises the outcome of both. For one thing, diabetes drugs interfere with those needed to cure TB, and vice versa.
"This makes it more difficult to treat TB," Harries says. "There's an increased chance of relapse and death, and it takes longer to go from infectious to non-infectious. And controlling diabetes becomes more difficult."
The dual infection may also increase patients' risk of getting hard-to-treat multi-drug resistant TB, although there's conflicting evidence about that.
But there's reason to be skeptical that heading off the co-epidemic will come cheap.
"You can say, 'How on earth are we going to implement this?' And I don't think we've got that worked out yet," Harries says.
India, which has a high incidence of both TB and diabetes, has recently set up a system to provide free diabetes testing. But newly diagnosed patients have to pay for their own diabetes drugs, which are beyond the means of many Indians.
In China, patients must bear the cost of both diabetic testing and treatment.
This, too, is different from the situation with TB/HIV. Harries says HIV and TB diagnosis and treatment are generally free, thanks to the belated realization that no-cost treatment was necessary to fight that co-epidemic. "That's not the case with noncommunicable diseases like diabetes," he says.