Season 4, Episode 1: TB or not TB
While Rachel and Mayko try to find out what caused several people in an Illinois farming community to lose their ability to feel pain, David and Carlos travel to Chiapas in Mexico to investigate a sudden outbreak of severe tuberculosis (TB) among the revolutionary army of the Zapatistas. The patients don’t respond to the drugs most commonly used to fight TB, so the NorBAC team seeks to identify the bacterial strain to help them come up with a strategy to kill it and stop it from spreading.
CAN TUBERCULOSIS BE RESISTANT TO DRUG TREATMENT?
What is tuberculosis?
Tuberculosis, or TB, is a serious lung disease caused by the bacterium Mycobacterium tuberculosis. The bacteria are inhaled from tiny saliva droplets that are spread in the air when a person infected with TB sneezes or coughs nearby. Spread of the disease can be limited by wearing facemasks and by quarantines, where infected patients are isolated for as long as they are contagious.
|
|
 |
David and Isobel discuss the Zapatista TB patients. |
How is tuberculosis treated?
Tuberculosis can usually be cured by several months of treatment with antibiotics. Most strains of Mycobacterium tuberculosis are effectively killed this way, but some are resistant to the drugs that are most commonly used.
How does TB become drug resistant?
As you may recall from the ReGenesis: Science & Society installment from episode 7, last season, bacteria like those that cause TB can become resistant to antibiotics when infected patients are treated with too low dosages or when they don't complete the full drug treatment. When this happens, not all of the bacteria in the patient die, and the ones that survive - the drug resistant ones - will grow in the patient and can spread and continue to infect other patients.
These new infections are now resistant to the drug that the previous patient received, and can only be effectively treated with another drug that the bacteria haven't encountered before. If this drug isn't properly administered either, the strain can become resistant to the second drug as well.
What is multi-drug resistance or extensive drug resistance?
Multi-drug resistant tuberculosis (MDR-TB) bacteria are resistant to the two most commonly available drugs used to fight TB: isoniazid and rifampicin. These are called first-line drugs - the ones most readily available and most often used. When David and Carlos are sent to Chiapas, the Zapatistas have already tried to treat the patients with these drugs, and found that they didn't work.
 Image provided courtesy of Shaftesbury Films.
|
|
Carlos, Rico, Isobel and David examine an x-ray. |
To kill an MDR-TB strain, other antibiotics need to be used. The second-line drugs fluoroquinolone, amikacin, kanamycin, and capreomycin are the ones most commonly tried next.
If a strain is also resistant to several of the second-line drugs, it is considered extensively drug resistant (XDR). This form of TB is currently found worldwide in 40,000 new patients each year!
One way to find out if a strain of tuberculosis bacteria is XDR is to administer the second-line drugs and wait to see what happens. If the bacteria do not respond to the treatment, they are XDR.
But it's also possible to compare the DNA sequence of the strain in question with the genomic sequences of known TB strains to see if there is a match with a known XDR-TB strain. Through this method, Mayko found that the TB bacterium from the patients in Chiapas was identical to an XDR-TB strain from South Africa that is resistant to all first-line and second-line drugs.
So?
Sadly, yes, it's possible for tuberculosis to be resistant to all available first-line and second-line drugs. This happened in the South African province of KwaZulu-Natal, where a severe XDR-TB strain was first found in 1995. The strain killed more than 50 people in 2006 and is still active.
Until a drug that kills it is found or developed, the only way to fight it is to stop spread of the disease through containment of infected patients and vaccinations against TB. But even if a new drug becomes available, there is still a risk that continued improper treatment with antibiotics will cause resistance to that drug as well.
Researchers are currently using the genomic sequence of the KwaZulu-Natal XDR-TB strain to study genetic components that cause drug resistance in Mycobacterium tuberculosis.
DID YOU KNOW?
When Mayko is checking an Illinois farm for toxins that could possibly be related to several community members' inability to feel pain, the farmer tells her they only use biological insecticides. He mentions Saccharopolyspora spinosa. When fermented, these bacteria produce molecules called spinosyns, which attack the nervous system of insects that often damage farm crops, but are relatively safe to non-harmful species. The bacteria are grown industrially to produce these spinosyns, which are then collected and sold to farmers to use on the crops. So, S. spinosa itself is probably not directly used on the farm, just the spinosyns it produces.
-- Eva Amsen
Want to read and learn more?
To learn more about tuberculosis, try this link:
www.lung.ca/diseases-maladies/tuberculosis-tuberculose_e.php
More on the genomic sequence of XDR-TB used to study drug resistance can be found here:
www.sciencedaily.com/releases/2007/11/071121094524.htm
To learn more about using spinosyns as a pesticide, read this document from Dow Chemical:
www.umanitoba.ca/afs/agronomists_conf/2003/pdf/turnbull_success480SC.pdf
