Introduction

Leprosy, which is also referred to as Hansen's disease, is a recurring infection caused by Mycobacterium leprae. It primarily targets the skin, the nasal lining, and the peripheral nerves. If left untreated, it may cause permanent disabilities. In certain regions of the world, particularly in low and middle-income countries, leprosy continues to be a public health concern despite being treatable and non-contagious, as it is transmitted via droplets.¹ 

The total number of leprosy patients has significantly reduced globally in recent times with the help of a treatment strategy known as multidrug therapy (MDT). On the other hand, drug resistance is a recent and emerging issue.² This article discusses how leprosy drug resistance develops, how to identify it, how to manage it currently and in the future, and what steps we can take to prevent & address this challenge.

Understanding drug resistance in leprosy

Drug resistance and its types

Drug resistance occurs when bacteria evolve so that antibiotics, which once killed them, are no longer effective. There are two main types:

• Primary drug resistance: when a person is infected with bacteria which is already resistant to a drug before starting any treatment
• Secondary drug resistance: when resistance arises during treatment, frequently, as a result of antibiotic misuse or incomplete therapy⁴

Mechanism of drug resistance

In leprosy, resistance typically arises from genetic changes (mutations) in the bacteria’s target genes, rather than through acquired resistance.

Gene mutations and drug targets

 These mutations happen in certain genes such as:

•  folP1 → dapsone (sulfonamide) resistance
•  rpoB → rifampicin (RNA polymerase inhibitor) resistance
•  gyrA → fluoroquinolone (DNA gyrase) resistance^3,4

Mutation effects

Changes in amino acid sequences at specific sites reduces drug-binding affinity, rendering treatment ineffective.⁴

Reasons for drug resistance

Some major reasons why drug resistance may develop include:

• Using only one drug instead of a combination (monotherapy)
• Overuse or misuse of antibiotics
• Patients not completing their treatment
• Inconsistent drug supply or poor-quality medicines
• Lack of awareness or support in treatment adherence⁵

Current treatment strategies and multidrug therapies

Various MDT regimens are recommended by the World Health Organisation (WHO) depending on the severity of the disease:

1. Treatment plan for paucibacillary (PB) leprosy (classified by fewer bacteria and less than 5 skin lesions):² it involves taking rifampicin once a month, and taking dapsone daily for six months⁶
2. Treatment plan for multibacillary (MB) leprosy (classified by increased bacteria and more than 5 skin lesions):² it consists of a 12-month long usage of rifampicin, dapsone, and clofazimine drugs⁶

Limitations of the current MDT in the context of resistance

Among all three antibiotics, rifampicin is considered the most effective. Although MDT has been fairly effective, the rising resistance of rifampicin and dapsone is concerning. People with leprosy may experience relapse or ongoing disease progression if these drugs are ineffective.⁶

Detection and monitoring of drug resistance

The leprosy-causing Mycobacterium leprae cannot be cultivated in lab cultures, as compared to other microorganisms. Traditionally, mice were infected & observed for a year to test for drug resistance, which is too slow for regular diagnosis. This meant many patients were not evaluated for resistance, increasing the chance of treatment failure.

To address this, researchers developed a quicker and simpler DNA-based test called genotype lepraeDR. It uses techniques like multiplex PCR (polymerase chain reaction) to detect certain genetic mutations, and DNA strip hybridisation to detect whether the bacteria is resistant to key antibiotics such as rifampin, dapsone, and ofloxacin. It’s also designed for simple & easy use in areas where leprosy is still widespread, and it has proven to give reliable results, matching those from traditional tests.^1,7

Clinical indicators of resistance

Doctors may suspect drug resistance if:

• Skin lesions don’t improve and they get worse
• Symptoms return after completing treatment
• The patient doesn’t respond to medicine after months of use¹

Laboratory detection methods

•  Molecular diagnostics (PCR-based tests, gene sequencing)
•  Surveillance systems supported by the WHO in high-risk regions to monitor and prevent the spread of resistant strains¹

Alternative and second-line therapies

These are drugs that are given in combinations to prevent further resistance in the following cases:

1. For serious multibacillary cases: the WHO recommends taking clofazimine, ofloxacin, and minocycline daily for 6 months, then continue with 2 of these drugs for another 18 months⁸
2. If clofazimine isn’t suitable, use rifampin, ofloxacin, and minocycline once a month for 2 years⁸
3. If dapsone causes side effects, replace it with clofazimine or adjust the combination based on the disease type

It is advised to start treatment without delay, even before resistance test results, and if resistance is confirmed, the treatment should be extended or modified accordingly.⁸

Programmatic and public health measures

Drug resistance management involves not only medicines, but also people and systems, too. Effective control of drug-resistant leprosy starts with a strong local surveillance system that works in coordination with national leprosy programs. Here are some important strategies:

• Designate testing and quality assurance lab: select national or international labs for resistance testing (rifampicin, dapsone, ofloxacin) and partner with WHO reference labs to ensure data accuracy and external validation⁹
• Select sites for sample collection: secondary and tertiary healthcare facilities managing MB and retreatment cases should be selected. The staffs should be trained on how to do slit-skin smears and biopsy techniques correctly⁹
• Collect and transport samples safely: standard & reliable methods should be used to collect, label, store, and transport samples without risking the quality
• Record and report information: use standardised reporting forms to record findings and upload them to the national AMR (antimicrobial resistance) databases, while also forwarding the reports to the WHO annually
• Monitor trends and update policies: continuously monitor trends of drug resistance and revise national policies accordingly. Also, active collaboration between healthcare facilities, laboratories, and public health officials is crucial for controlling drug-resistant leprosy⁹

Research and future directions

Drug-resistant leprosy remains a serious challenge, but new scientific researches offer hope and pave the way for better solutions.

1. Faster and smarter diagnosis: new molecular tools like PCR are improving early detection of both M. leprae and the newly found M. lepromatosis⁸
2. Exploring new drug options: with traditional drugs losing effectiveness, researchers are testing newer antibiotics like moxifloxacin and linezolid. While promising, some carry long-term side effects. Lab-grown models now help to test drug-resistant strains more efficiently⁸
3. Genome mapping for targeted treatment: by decoding the M. leprae genome, scientists are identifying resistance mutations, customised treatment plans, and tracking how the bacteria spreads globally⁸
4. Boosting immunity with vitamin D: studies suggest the bacteria may disrupt vitamin D pathways, weakening the immune system. Future treatments might combine vitamin D to restore immune defence¹⁰
5. Better tests and biomarkers for diagnosis: researchers have identified special proteins (biomarkers) that show up early in infection, that may improve diagnosis and could lead to vaccine development⁸
6. Vaccine research: the current BCG vaccine offers limited, short-term protection. Improved vaccines are being tested, but still need stronger and better results¹¹
7. Strengthening public health systems: tracking resistance patterns in national health programs can help identify resistant cases early, guide treatment, and control outbreak⁸

FAQs

Can drug-resistant leprosy spread to others like normal leprosy?

Yes, like normal leprosy, resistant strains can spread, but only via intimate, continuous contact.

Is drug-resistant leprosy more dangerous than normal leprosy?

It’s not always threatening, but it’s difficult to treat, takes longer to cure, and increases the chances of disability or relapse.

Is leprosy going to become completely untreatable in the future?

If its drug resistance keeps increasing and no new drugs are developed, treating leprosy could become very difficult. However, ongoing international research is working to prevent that. 

Can a person live a normal life with drug-resistant leprosy?

Yes, people can recover and live normally, with the right treatment and proper follow-up, though their therapy might take longer or require adjusting the drug regimen.

Can leprosy come back after treatment?

Yes, especially in cases where drug resistance is present or if the treatment course wasn’t followed properly.

Summary

Leprosy or Hansen’s disease is a recurring infection caused by the Mycobacterium leprae bacterium. Though it is curable with multidrug therapy (MDT), rising drug resistance, mainly to rifampicin and dapsone, has become a serious concern. Resistance can be either primary (before treatment) or secondary (develops during treatment), often due to misuse of antibiotics or incomplete therapy. Old methods of detecting resistance using PCR have been replaced by new genetic testing, such as genotype lepraeDR, which is faster. 

When resistance is suspected, other treatment options like ofloxacin, minocycline, and clofazimine are recommended. Effective management requires a multifaceted approach, early diagnosis, appropriate treatment, and strong public health systems. New antibiotics, enhanced diagnostic methods, improved vaccines, and the function of vitamin D in immunity are the subjects of ongoing study. It is possible to control and potentially eliminate drug-resistant leprosy with concerted international efforts.