Student guest post by Jack Hamersky
After successfully completing a job interview I had the opportunity to take the next step in my employment process: taking a Tuberculosis or TB test. I have received the test before but never really understood the point of testing for a disease no one ever sees in my community. I always thought, “Why not focus all this effort and money on more prevalent infectious agents such as Ebola or HIV?” You know, focus on something important. So, as the nurse called me in from the waiting room I began to curse that hard little bubble that would soon be forming under my skin, and the inconvenience it would be to have to come back to this same clinic to have it read.
This same type of experience is known throughout the United States and other developed countries. However, many people like myself, do not know the importance of this test. They might not know that this test is a crucial part of the much larger goal of eradicating a deadly and common worldwide disease.
What is tuberculosis and why is it even important?
Tuberculosis is a contagious disease that is found in both animals and humans. The human form of the disease is caused by a group of three bacteria: Mycobacterium bovis, Mycobacterium avium, and Mycobacterium tuberculosis. This disease can come in two forms: latent and active. The active form of tuberculosis causes pockets of pus called granulomatous lesions in lungs and has a death rate around 50%. It is estimated that TB infects around one third of the human population on earth and is the second leading cause of death by infectious disease, behind HIV, killing around million people annually, according to the Center for Disease Control and Prevention; CDC (4). The greatest prevalence of TB occurs in developing countries and their low socioeconomic populations. This is likely due to the limited availability of health care, poor nutrition, and overcrowding conditions these people face on a daily basis. Immunosuppressed individuals, such as people infected with HIV, are also more likely to contract tuberculosis. TB is also very hard to treat and many forms of the disease are resistant to antibiotics.
Another reason TB is so dangerous is the threat of Mycobacterium bovis. M. bovis is another strain of tuberculosis that mainly infects cattle, cervids (deer like animals), elephants, bison, etc (7,10). What makes this bacterium interesting is its been known to infect people through the consumption of raw (unpasteurized) milk or products that were made from that raw milk (1,5,7,10). This zoonotic microorganism is responsible for two percent of all new cases of TB in the US (7) with an even a greater percentage worldwide (6). The zoonotic nature of M. Bovis allows for it to hide in wildlife populations which act as a reservoir for the disease (6,9). The good news is a campaign to eradicate M. Bovis from the US food supply began in 1993(5). The bad news is that TB remains endemic in wildlife and agricultural animal populations worldwide. The program in the United States has been a success and most of the United States is considered Bovine Tuberculosis free. However some states, such as Michigan, still find M. bovis in their wild deer herds making the continual threat of reemergence a reality.
So what have we done about this problem?
The United States government has taken a leading role in the fight against TB. It formed the Advisory Council for the Elimination of Tuberculosis to address the growing resurgence of TB in the 1980’s (5). It also passed legislation like the Comprehensive Tuberculosis Elimination Act which called for the increase of federal funding, education, and international collaboration in the fight against TB. Other non-governmental advancements have taken place over the years too. A vaccine was created and is now available throughout the world. Known as BCG, this vaccine is good at protecting children against the disease, however, it loses its effectiveness as children grow older and has not shown promising results in adults (8). This, coupled with the increasing amount of antibiotic resistant cases (known as Multi Drug Resistant Tuberculosis or MDR TB) once again proves the fight to eradication or even control might be more of an uphill battle then we once thought.
So how is the fight to end TB going?
Over the past few decades we have made progress and in 2011, the World Health Organization reported “The absolute number to TB cases has been falling since 2006”. However, in that same report, the WHO also stated, even though TB cases had dropped, “In 2009 there were almost 10 million children who were orphans as a result of parental deaths caused by TB” (12,13). As long as there TB is left to reside in our low income populations and in animal reservoirs it will continue to plague millions worldwide.
So where do we go from here?
The continuation and strengthening of surveillance and research projects worldwide is the key to combat tuberculosis. The more we know about the disease and its ecology the better prepared we will be to face the challenges we may encounter during its eradication process. Will we ever get to total world eradication of tuberculosis? This writer thinks so but to quote the great Robert Frost it seems that “we have miles to go before we can sleep”.
1) http://www.aphis.usda.gov/animal_health/animal_diseases/tuberculosis/
2) http://www.cdc.gov/tb/publications/factsheets/general/mbovis.htm
3) http://www.cdcnpin.org/scripts/tb/eliminate.asp
4) http://www.cdc.gov/tb/statistics/default.htm
5) http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5412a1.htm
6) http://wwwnc.cdc.gov/eid/article/19/6/12-0543_article.htm
7) http://www.cfsph.iastate.edu/Factsheets/pdfs/bovine_tuberculosis.pdf
9) http://www.mayoclinic.com/health/tuberculosis/DS00372/DSECTION=tests-and-diagnosis
10) http://www.lung.org/lung-disease/tuberculosis/factsheets/multidrug-resistant.html
11) http://www.ncbi.nlm.nih.gov/pubmed/20819249
12) http://www.who.int/tb/publications/global_report/2011/gtbr11_full.pdf
13) http://www.who.int/mediacentre/factsheets/fs104/en/index.html
14) http://en.wikisource.org/wiki/Comprehensive_Tuberculosis_Elimination_Act_of_2008
15) http://en.wikipedia.org/wiki/Mycobacterium_tuberculosis
16) http://en.wikipedia.org/wiki/Mycobacterium_avium-intracellulare_infection
17) http://en.wikipedia.org/wiki/Tuberculosis
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In addition to MDR-TB, there are two further strains, one "extensively drug resistant" and the other "extremely drug-resistant" or "totally drug-resistant" (darn, I know the names and acronyms for these but I'm multi-tasking and can't recall them at the moment).
One of the key problems is that TB-infected humans often don't follow doctors' orders properly, and stop taking their antibiotics prematurely, thereby ending up with resistant strains. Here in the San Francisco Bay Area, there is even a bus route in San Francisco that is colloquially known as "the TB run" because a high percentage of people who take that bus are infected (and presumably spreading it to others on the bus).
The unpleasant and inevitable necessity is that people who are either unwilling or incapable of following doctors' orders and taking their meds properly, should be subject to custodial confinement for the duration, against their will if need be (there is no constitutional right to spread deadly diseases to others). What's needed is legislation whereby when a drug-resistant strain of any disease emerges, a public health emergency is declared, in which people who are judged to be recalcitrant or impaired in a manner that endangers public health, can be confined to hospital under civil commitment, until they are no longer a risk to others.
Pragmatically, any hint of such a policy will be met by howls of outrage, and we will suffer one or more deadly pandemics before the situation is recognized and acted upon. That, or your pessimistic headline will prove to have been an accurate forecast.
While researchers continue to work on both new antibiotics for TB as well as TB vaccines, I ultimately think that a vaccine would be the best solution because, as you mentioned, TB has a sizable animal reservoir including cattle and wild animals like deer.
Also, the claim that 1/3 of the world is infected with TB is a problematic one. That data comes from a 1999 paper that used PPD (TB skin test) positivity as a way to estimate disease prevalence (as well as another statistical method), but this test is prone to false positives.
In the words of the study's authors: "given the poor quality of much of the underlying data, they are better thought of as plausible estimates. They represent a consensus among many TB experts around the world but will certainly be subject to improvement when better data are available"
http://www.ncbi.nlm.nih.gov/pubmed/10517722