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Tuberculosis on the rise globally, second most infectious killer disease- WHO

Wednesday December 17 2014
EATUBERCULOSIS

A doctor prepares a BCG vaccine, which is typically given to infants. Poor healthcare systems have been blamed for the spread of TB in developing countries. PHOTO | FILE

There is growing concern over the rate at which the number of tuberculosis cases are increasing globally.

According to the World Health Organisation’s 2014 TB report, more than nine million people developed tuberculosis in 2013 globally, and 1.5 million of them died. Some 8.6 million TB cases and 1.3 million TB deaths were reported in 2012.

In East Africa, Kenya, Uganda and Tanzania face the highest disease burden. For example, in 2013, Kenya recorded the highest number of new cases at 89,796, followed by Tanzania with 65,732 and third Uganda with 47,650.

According to WHO, TB is now the second most infectious killer disease after the Aids virus and remains one of the world’s deadliest communicable disease. Health experts say a lack of investment in health care systems has allowed the disease persist and spread in developing countries.

READ: Rwanda sets new target to eliminate tuberculosis

Head of the Division of Leprosy, Tuberculosis and Lung Diseases at Kenya’s Ministry of Health Joseph Sitenei, said TB is especially insidious and hard to fight because people can be infected for years without showing symptoms and it takes weeks if not months of treatment with antibiotics to eradicate it.

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“TB spreads in the air and when untreated kills up to 70 per cent of those who contract it, although this can take a decade,” said Dr Sitenei.

Despite people getting vaccinated against TB with Bacille Calmette-Guérin (BCG) — given at infancy — Dr Sitenei said that the vaccine does not protect everyone it is administered to. It is thought to protect up to 80 per cent of people for a maximum of 15 years.

“The vaccine targets young children and protects them against the severe form of TB like meningitis and after the 15 years it is no longer effective,” he said.

“The vaccine is a weakened strain of TB, which builds up immunity and encourages the body to fight it. Though BCG gives some people protection against TB, it cannot prevent everyone who comes into contact with it from falling ill.”

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He said that most people in Kenya for example who get TB got the BCG vaccine as children. However, the vaccine is less effective in countries nearer the equator where TB is more common and that is why Kenya, Uganda and Tanzania are mainly affected.

“It is not possible to control the disease using the BCG as there will always be people who fall ill despite having had the vaccine, and they will continue to pass it on. Until a better vaccine is developed the best control we have for TB is to make sure people know what the symptoms are so they visit a doctor and get diagnosed as early as possible, and to make sure they take all their medication,” said Dr Sitenei.

However, he said boosters cannot be developed for the TB vaccine as in the case of polio and tetanus. There is currently ongoing research on a new tuberculosis vaccine for adults.

The trial, scheduled to start early next year in South Africa, will be jointly conducted by the global non-profit biotech Aeras and health care company GlaxoSmithKline (GSK) and aims to examine the prevention of Mycobacterium tuberculosis (Mtb), the bacterium that causes TB infection, through vaccination in adults for three years.

The trial will also evaluate the revaccination of the BCG vaccine. That is, evaluate the effectiveness of the vaccine when it is given for a second time.

According to Dr Sitenei, TB cases are on the increase but prevention is the better option in fighting the disease. The first step in TB prevention is to stop transmission from one adult to another, which is done by identifying people with active TB and then administering the drug treatment.

“In Kenya, testing and treatment of TB is free in all public hospitals,” said Dr Sitenei adding with proper treatment people with active TB will not be infectious and so can no longer spread the disease to others.

“Prevention of TB also involves stopping people with latent TB from developing active, infectious TB.”

He said that anything that increases the number of infectious people, such as the presence of TB and HIV infection together, or which increases the number of people infected by each infectious person, such as ineffective treatment because of drug resistant TB, reduces the overall effect of TB prevention efforts.

For TB prevention, WHO recommends the drug isoniazid to be taken daily for at least six months and preferably for nine months.
Isoniazid is a cheap drug, but in a similar way to the use of the BCG vaccine, it is mainly used to protect individuals rather than to interrupt transmission between adults. This is because children rarely have infectious TB, and it is hard to administer isoniazid on a large scale to adults who do not exhibit any symptoms.

It costs from $100 to $500 to treat normal TB in countries that have the most cases — almost all of them poor countries in Africa and Asia. If TB is eradicated before it can mutate into drug-resistant forms, it is cheaper and easier for all involved, experts say.

“Taking isoniazid daily for six months is difficult in respect of adherence, and as a result many individuals who could benefit from the treatment stop taking the drug before the end of the six-month period,” said Dr Sitenei. “This then leads to multi-drug resistant TB (MDR-TB).”

At a paediatric HIV/Aids conference in Kampala, doctors were unable to agree on whether children infected with HIV should be given isoniazid as preventative treatment for TB. Those arguing for the drug treatment as prevention, claimed that in children co-infected with HIV and TB, up to 50 per cent of exposed children ended up developing the disease.

There have also been concerns about the possible impact of TB treatment on prevention programmes because of drug resistance. However, a review of scientific evidence has now shown that there is no need for this to be a concern.

The benefit of isoniazid preventative therapy for people living with HIV, and who have, or may have had latent TB, has also recently been emphasised.

Although the differences between drug-susceptible and drug-resistant TB, as well as HIV status, affect the risk of TB transmission, Dr Sitenei said that people with drug-resistant TB remain infectious for much longer, even if treatment has been started, and this may prolong the risk of transmission in the household.

The WHO advocates directly observed therapy (DOTS) under the supervision of health care workers to reduce the emergence of drug resistance.

“Every TB patient is supposed to be supervised when taking medication in order to increase adherence and decrease emergence of drug resistance,” said Dr Sitenei.

The MDR-TB treatment takes 20-30 months to work depending on the stage and extent of infection. The drugs administered include an injection and five types of tablets to be taken daily. The entire treatment regimen costs between $18,000 and $36,000.

However, Dr Sitenei said that treatment options are limited and expensive; the recommended medicines are not always available and patients experience many adverse side effects from the drugs. In some cases, even more severe drug-resistant tuberculosis can develop.

The other challenge to the MDR-TB treatment is the emergence of extensively drug-resistant TB, XDR-TB, a form of multidrug-resistant tuberculosis with additional resistance to more anti-TB drugs that therefore responds to even fewer available medicines.

It has been reported in 100 countries worldwide. Kenya has so far reported three cases of XDT-TB and has managed to treat one.

Drug resistance can be detected using special laboratory tests that assess the bacterium for sensitivity to the drugs or detect resistance patterns. These tests can be molecular in type (Xpert MTB/RIF) or culture-based. Molecular techniques can provide results within hours and have been successfully implemented even in low resource settings.

WHO recommends the use of GeneXpert machine, which provides a two-hour diagnosis. The machine can also detect TB/HIV co-infection as well as drug-resistant strains. Because it is DNA-specific, it only detects the TB bacterium that infects humans only, compared with other tests that also pick up other strains such as bovine TB, which is found in cow’s milk.

Kenya, Uganda and Tanzania have already adopted the use of the GeneXpert machines to detect TB. Kenya has 100 machines being used in public hospitals and plans to buy more next year.

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