This is according to a mathematical modelling study published in the PloS One medical journal this week.

Only about 10% of people with latent TB actually become ill with the active form of the disease because most people’s immune systems keep the disease dormant for life.

But for people with weak immune systems the risk of becoming ill with the disease rises dramatically. People living with HIV are of special concern as they are 20 to 30 times more likely to develop active TB from a latent infection, according to the WHO.

Weak immunity

However, it is not only people with weak immune systems who develop active disease, according to Dr Arne von Delft, from the organisation TB Proof.

“This containment process is not well understood and it is currently not possible to predict who will become sick or when. Anybody who is exposed is at risk,” he said.

A study to estimate the global burden of latent TB has not been done for 20 years and for two decades it has been thought that a third of the world’s population was affected.

Although the new global estimates are lower, 1.7 billion people are infected with latent TB including 100 million children.

But in places like South Africa latent TB poses a significant threat because of the high number of people living with HIV in the country who are at increased risk of becoming ill and infectious.

Latent TB in SA

Additionally, latent TB rates in South Africa are much higher than the global average.

According to a 2011 review published in the Journal of Infectious Diseases, as much as 89% of South African adults have latent TB, although some experts have contested this figure.

Two years ago the WHO released guidelines recommending latent TB be treated in countries with low TB burdens, which excludes South Africa.  In high burden countries the WHO only recommends treating latent infection in people living with HIV and children younger than five who have been in close contact with someone with TB.

Von Delft said this is simply not enough.

“We have approached the HIV epidemic aggressively, we have started treating people earlier and introduced preventative treatment for HIV and for TB in people living with HIV. But why are we so blasé about ramping up our TB response for everyone else? This is the leading infectious disease killer in the world and a leading cause of death in South Africa,” he said.

Additionally, there are no tools to identify if a latent TB infection is standard TB or drug-resistant TB (DR-TB). Von Delft suspects he is infected with latent DR-TB as he was exposed to this form of the disease when his wife fell ill in 2010.

Research into latent DR-TB is not a priority and considering the threat that poses to ending the epidemic – it’s a global embarrassment.

But, even as a doctor working in the TB field, he has no options for treating himself – other than undergoing the two-year toxic treatment regimen used to treat active DR-TB – a major side-effect of which is deafness.

Research not prioritised

“Research into latent DR-TB is not a priority and considering the threat that poses to ending the epidemic – it’s a global embarrassment.”

He hopes these issues will be high on the agenda at the 47th Union World Conference on Lung Health in Liverpool, United Kingdom this week.

According to the PloS One study, “even if all TB transmission stopped tomorrow, the current pool of latent infections alone would be enough to exceed the End TB global targets for TB control in 2035 and 2050”. – Health-e News.