Tuberculosis (TB) is an infection that is caused by the bacteria Mycobacterium tuberculosis and most commonly affect the lungs. TB is a topic that I’m close to because I’m from Jamaica, WI and was vaccinated (BCG) as a child for TB. Since moving to the US, I’ve had to go through the routine regimen of antibiotic treatment, occasional x-rays and more recently the quantiferon-TB-Gold blood test that detects levels of the bacteria Mycobacterium tuberculosis. I’ve been in the US since I was 8 so it’s been years of going through TB screening and at this point I’m pretty used to it. Also, TB is one of the leading cause of death in many parts of the world so it’s still a formidable disease, therefore I understand the need for caution and the endeavor to prevent the spread of this infectious disease. In fact, there are over 10 million cases of TB worldwide and almost 1.5 millions of death just in 2018 alone. Apparently, there are over 1.7 billion people living with TB worldwide. TB has become so rampant in parts of the world because it has become difficult to control. Tuberculosis (TB) is impeded by the problem of drug-resistance and in many cases the emergence of multi-drug resistance. Although most cases of TB in the United States (US) are from non-US natives, it is still a growing threat that the US has to contend with. In many parts of the world, TB is the number one killer of those infected with HIV and one-third of the world’s population has latent TB. Latent TB is a state where people are infected with TB but it is in its dormant state where the disease has the ability to be reactivated.
TB has become difficult to treat because the first-line antibiotic treatment that are commonly available have become ineffective against the bacteria due to drug resistance. Therefore, the current standard for treatment after a positive TB test is combination therapy for 6 months using first-line antibiotics for 2 months and 4 additional months with a different combination. Evidently, most Mycobacterium tuberculosis (Mtb) strains are defined as being resistant to at least isoniazid and rifampin, which are the two most commonly used bactericidal drugs and are essential for the treatment of the disease. What is the cause for the rise in drug resistance and even multi-drug resistance? Well, there are clinical, biological and microbiological factors that account for this problem; first, of these include patients not being compliant with the long duration of treatment advised by their physicians. Patients either stop taking the drug early or they frequently miss doses or they take the medication irregularly so that they don’t maintain serum levels high enough to effectively keep growth at bay. Another reason for drug-resistance relates to the complexity and poor vascularization of granulomatous lesions. Lacking proper vascularization means that the treatment drugs can not be properly distribution to some sites. When this happens resistance develop since the bacteria is shielded and can give rise to the formation of non-replicating, drug-tolerant bacilli inside the granulomas. Additionally, mutations can develop that provide a molecular mode of resistance or the bacilli can also have intrinsic drug resistance. Finally, in developing lands that may be financially deficient, physicians may have inferior regimen selection options, and inadequate drug supply that make adherence to the 6-months therapy virtually impossible.
Despite the challenge of drug resistance there is still a concerted effort being made to end the TB epidemic by 2030. Currently, globally, TB incidence is falling at about 2% per year. However, the desire is for this rate to increase to reach around 4–5% annually in order to reach the 2030 milestones towards ending TB. Not only is Tuberculosis a curable disease but it’s also very preventable. Currently, there are eight countries that carry the majority of the burden of TB and account for two thirds of the total cases; this includes India leading the count, followed by, China, Indonesia, the Philippines, Pakistan, Nigeria, Bangladesh and South Africa. TB is airborne and spread from person to person when people with lung TB cough, sneeze or spit, they propel the TB bacteria into the air. This infection has a very low ID50 since a person only needs to inhale a few of these bacteria to become infected. Therefore, it’s no wonder why Multidrug-resistant TB (MDR-TB) remains a public health threat and a community crisis. In 2018, WHO estimates that there were almost a half-million new cases with resistance to rifampicin, which is the most effective first-line drug, of which 78% had MDR-TB. Since adherence is such a key element to MDR-TB, consideration is being given to shortening the duration of therapy. A massive effort is being made to ramp up testing in high risk areas to help with diagnosis and early intervention and treatment. The political declaration of the UN indicated billions of dollars dedicated to TB preventive and treatment for a latent TB infection. Finally, in 2016, WHO recommended 4 new diagnostic tests that can provide a rapid molecular evaluation of type of TB a person is infected with. One of them is called the Xpert MTB/RIF. Also, there are 3 other tests to detect resistance to first- and second-line TB medicines. These test along with support to the patient by a health worker or trained volunteer are helping with treatment adherence and reducing deaths associated with the disease.
Microbiology and You 