Hansen’s Disease in Florida: Is This Ancient Disease Coming to a Lab Near You?

For many people, Hansen’s disease, also known as leprosy, conjures up frightening images from old Hollywood movies, set in biblical times. Despite its ancient origins, this disease has not been eradicated, and while easily curable, it still has devastating consequences for people in many parts of the world. 

While rare in the U.S., a recent increase in cases in Florida has brought Hansen’s disease to the forefront for the medical community.¹ It’s not thought that numbers of cases in the U.S. will increase dramatically, but for the afflicted, recognizing and diagnosing leprosy early is essential for staving off its worst outcomes.  

If Hansen’s hasn’t been seen in your laboratory, it may be, and soon. Here’s what pathologists and laboratory professionals should know about this infectious disease.  

What is Hansen’s disease? 

Hansen’s disease is a chronic bacterial disease caused by Mycobacterium leprae (M. leprae), a slow-growing bacteria that typically takes years to cause noticeable symptoms. Symptoms typically manifest between four and eight years after exposure. In some instances, incubation may persist over decades. “Since the time between exposure to symptoms is so long, it is often difficult to trace exposures and most cases in the U.S. are thought to result from exposures that occurred internationally in areas where Hansen’s disease is endemic,” says Wesley Long, MD, Medical Director of microbiology for Houston Methodist. 

As with so many conditions, leprosy’s cause was first discovered in the laboratory. For centuries, Hansen’s disease was assumed to be hereditary. That changed in 1873, when Norwegian scientist G.H. Armauer Hansen identified leprosy’s causative organism under a microscope. This groundbreaking discovery was was one of the early recognitions of a bacterium that could generate disease in humans.²    

Leprosy primarily affects the skin, eyes, mucosa of the upper respiratory tract, and peripheral nerves of the hands and feet. Thickened skin, numb skin lesions and nodules, eye problems that can lead to blindness, and numb ulcers on the soles of the feet are common symptoms.  

These symptoms often have other, more likely causes. In the U.S., this makes getting a speedy diagnosis less likely to occur. Medical professionals should consider leprosy as a differential diagnosis when patients present with hypopigmented or red skin lesions, combined with peripheral neuropathy, and paresthesia. Travel to endemic regions may be a clue to a source of leprosy infection but isn’t essential for making a diagnosis. “We often say when you hear hoofbeats think of horses and not zebras, but it is important to remember that sometimes you can find a zebra,” says Dr. Long.  

Hansen’s disease has several subtypes, which can be identified via biopsy. Tuberculoid, or paucibacillary, leprosy is the least severe type. Lepromatous, or multibacillary, leprosy can cause more generalized damage to the skin, body, and internal organs, including the kidneys. Borderline, or dimorphous, leprosy is the most common form and is of intermediate severity. 

Most importantly, leprosy is curable. When caught early, treatment consists of several months of antibiotic multidrug therapy. When left untreated, the devastating long-term effects of leprosy cannot be undone. These included amputations, blindness, and skin deformity. 

How is Hansen’s disease diagnosed in the lab? 

A definitive diagnosis of leprosy requires either a skin biopsy taken from the edge of an infected lesion, or a nerve biopsy taken from a thickened nerve. Skin smears can sometimes be useful in detecting multibacillary disease. “Unfortunately, the best diagnostic tests for Hansen’s disease are biopsies, which are more invasive than a simple blood test,” says Dr. Long. 

M. leprae is an acid-fast bacterium. Acid fastness enables a bacterium to resist decolorization by acids during staining procedures. In the laboratory, a diagnosis of leprosy can be considered through testing of a nasal or slit-skin smear from an active lesion. It can only be confirmed, however, through a full-thickness skin or nerve biopsy done with a Fite stain.³ 

The antibody response to phenolic glycolipid-1 (PGL-1) is currently the most widely used biomarker for Hansen’s disease.⁴ PGL-1 is a cell wall component that is specific to M. leprae. PGL-1 is detectable through serologic assays, provided the affected person has more than five leprosy lesions (multibacillary disease). Serologic assays are not sensitive enough to diagnose patients with fewer than five lesions (paucibacillary disease). This test, while helpful, is not the gold standard for diagnosis.  

Molecular probes of genetic material may identify multibacillary leprosy, when earlier histological evaluations fail to detect it. They are not considered effective for the identification of paucibacillary leprosy. 

The Ridley-Jopling scale is typically used in the U.S. to measure the density of bacilli on biopsy. This helps identify the subtype and level of disease from indeterminant to lepromatous (severe).⁵ 

How contagious is leprosy? 

When left untreated, leprosy can cause devastating physical deformity and disability. For this reason, the most contagious aspects of leprosy are fear and stigma, not the disease itself. “What everyone should know is that the old fears of Hansen’s disease being highly contagious are baseless. In reality, Hansen’s disease is not particularly contagious and human to human transmission is exceedingly rare,” Dr. Long says.   

Despite the way it was portrayed in those old movies you may have loved, leprosy is not easily transmissible by casual contact. It cannot be transmitted by shaking hands or hugging, sitting next to each other on a bus or plane, or sitting together at a meal. It is not transmissible by sexual contact or from mother to child during pregnancy.