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Treatment

Treatment for TB uses antibiotics to kill the bacteria. The two antibiotics most commonly used are rifampicin and isoniazid. However, instead of the short course of antibiotics typically used to cure other bacterial infections, TB requires much longer periods of treatment (around 6 to 12 months) to entirely eliminate mycobacteria from the body. Latent TB treatment usually uses a single antibiotic, while active TB disease is best treated with combinations of several antibiotics, to reduce the risk of the bacteria developing antibiotic resistance. People with these latent infections are treated to prevent them from progressing to active TB disease later in life. However, treatment using Rifampin and Pyrazinamide is not risk-free. The Centers for Disease Control and Prevention (CDC) notified healthcare professionals of revised recommendations against the use of rifampin plus pyrazinamide for treatment of latent tuberculosis infection, due to high rates of hospitalization and death from liver injury associated with the combined use of these drugs.

Drug resistant tuberculosis is transmitted in the same way as regular TB. Primary resistance occurs in persons who are infected with a resistant strain of TB. A patient with fully-susceptible TB develops secondary resistance (acquired resistance) during TB therapy because of inadequate treatment, not taking the prescribed regimen appropriately, or using low quality medication.Drug-resistant TB is a public health issue in many developing countries, as treatment is longer and requires more expensive drugs. Multi-drug resistant TB (MDR-TB) is defined as resistance to the two most effective first line TB drugs: rifampicin and isoniazid. Extensively drug-resistant TB (XDR-TB) is also resistant to three or more of the six classes of second-line drugs.

In ancient times, available treatments focused more on dietary parameters. Pliny the Elder described several methods in his Natural History: "wolf's liver taken in thin wine, the lard of a sow that has been fed upon grass, or the flesh of a she-ass taken in broth". While these particular remedies haven't been tested scientifically, it has been demonstrated that malnourished mice receiving a 2% protein diet suffer far higher mortality from tuberculosis than those receiving 20% protein receiving the same infectious challenge dose, and the progressively fatal course of the illness could be reversed by restoring the mice to the normal diet.Moreover, statistics for immigrants in South London reveal an 8.5 fold increased risk of tuberculosis in (primarily Hindu Asian) lacto vegetarians, who frequently suffer protein malnutrition, compared to those of similar cultural backgrounds who ate meat and fish daily.

Prevention

TB prevention and control takes two parallel approaches. In the first, people with TB and their contacts are identified and then treated. Identification of infections often involves testing high-risk groups for TB. In the second approach, children are vaccinated to protect them from TB. Unfortunately, no vaccine is available that provides reliable protection for adults. However, in tropical areas where the incidence of atypical mycobacteria is high, exposure to>nontuberculous mycobacteria gives some protection against TB.

Vaccines

Many countries use BCG vaccine as part of their TB control programs, especially for infants. This was the first vaccine for TB and developed at the Pasteur Institute France between 1905 and 1921. However, mass vaccination with BCG did not start until after World War II. The protective efficacy of BCG for preventing serious forms of TB (e.g. meningitis) in children is greater than 80%; its protective efficacy for preventing pulmonary TB in adolescents and adults is variable, ranging from 0 to 80%.

In South Africa, the country with the highest prevalence of TB, BCG is given to all children under the age of three. However, the effectiveness of BCG is lower in areas where mycobacteria are less prevalent, therefore BCG is not given to the entire population in these countries. In the USA, for example, BCG vaccine is not recommended except for people who meet specific criteria:

  • Infants or children with negative skin-test results who are continually exposed to untreated or ineffectively treated patients or will be continually exposed to multidrug-resistant TB.
  • Healthcare workers considered on an individual basis in settings in which a high percentage of MDR-TB patients has been found, transmission of MDR-TB is likely, and TB control precautions have been implemented and were not successful.

BCG provides some protection against severe forms of pediatric TB, but has been shown to be unreliable against adult pulmonary TB, which accounts for most of the disease burden worldwide. Currently, there are more cases of TB on the planet than at any other time in history and most agree there is an urgent need for a newer, more effective vaccine that would prevent all forms of TB – including drug resistant strains – in all age groups and among people with HIV.

Several new vaccines to prevent TB infection are being developed. The first recombinant tuberculosis vaccine entered clinical trials in the United States in 2004, sponsored by the National Institute of Allergy and Infectious Diseases (NIAID). A 2005 study showed that a DNA TB vaccine given with conventional chemotherapy can accelerate the disappearance of bacteria as well as protect against re-infection in mice; it may take four to five years to be available in humans. A very promising TB vaccine, MVA85A, is currently in phase II trials in South Africa by a group led by Oxford University, and is based on a genetically modified vaccinia virus. Many other strategies are also being used to develop novel vaccines. In order to encourage further discovery, researchers and policymakers are promoting new economic models of vaccine development including prizes, tax incentives and advance market commitments.

The Bill and Melinda Gates Foundation has been a strong supporter of new TB vaccine development. Most recently, they announced a $200 million grant to the Aeras Global TB Vaccine Foundation for clinical trials on up to six different TB vaccine candidates currently in the pipeline.

 

 

Epidemiology

Annual number of new reported TB cases. Data from WHO.
World TB incidence. Cases per 100,000; Red = >300, orange = 200–300; yellow = 100–200; green 50–100; blue = <50 and grey = n/a. Data from WHO, 2006.

According to the World Health Organization (WHO), nearly 2 billion people—one–third of the world's population—have been exposed to the tuberculosis pathogen.Annually, 8 million people become ill with tuberculosis, and 2 million people die from the disease worldwide.In 2004, around 14.6 million people had active TB disease with 9 million new cases. The annual incidence rate varies from 356 per 100,000 in Africa to 41 per 100,000 in the Americas.Tuberculosis is the world's greatest infectious killer of women of reproductive age and the leading cause of death among people with HIV/AIDS.

In 2005, the country with the highest estimated incidence of TB was Swaziland, with 1262 cases per 100,000 people. India has the largest number of infections, with over 1.8 million cases. In developed countries, tuberculosis is less common and is mainly an urban disease. In the United Kingdom, TB incidences range from 40 per 100,000 in London to less than 5 per 100,000 in the rural South West of England; the national average is 13 per 100,000. The highest rates in Western Europe are in Portugal (42 per 100,000) and Spain (20 per 100,000). These rates compare with 113 per 100,000 in China and 64 per 100,000 in Brazil. In the United States, the overall tuberculosis case rate was 4.9 per 100,000 persons in 2004.

The incidence of TB varies with age. In Africa, TB primarily affects adolescents and young adults. However, in countries where TB has gone from high to low incidence, such as the United States, TB is mainly a disease of older people.

There are a number of known factors that make people more susceptible to TB infection: worldwide the most important of these is HIV. Co-infection with HIV is a particular problem in Sub-Saharan Africa, due to the high incidence of HIV in these countries. Smoking more than 20 cigarettes a day also increases the risk of TB by two- to four-times. Diabetes mellitus is also an important risk factor that is growing in importance in developing countries.. http://www.wikipedia.org