In the UK we didn’t have an animal vector for leprosy until now… so who’s to blame… well apparently it’s our squirrels. In the UK we have two types of squirrel. The grey squirrel, a non-native introduced in the 1800s from North America, which has rapidly displaced our native species and is considered a bit of a pest. Whereas our native squirrel is the red squirrel. It is much smaller than the grey and in my opinion is considerably cuter! Unfortunately for our native red squirrel they have been found to carry Mycobacterium leprae and the headlines in the national press were “Red squirrels carrying medieval strain of human leprosy as people warned to stay away”. Really?! How many people in the UK have actually seen one of these rare and shy animals let alone got close to one? I’m not sure this really is a major threat to public health…! Ah, rant over…but it did make me realise that I know very little about the disease!
Leprosy is a chronic infection caused by the bacterium Mycobacterium leprae. This bacterium does not grow on artificial media and therefore cannot be grown in a normal laboratory. It is also very slow growing taking 12 days to divide and reproduce, it only grows inside other cells, and it prefers temperatures around 27-33oC. In humans it tends to affect cooler parts of the body such as the skin, respiratory mucous membranes and peripheral nerves. The genome of M. leprae is a very stable ancient bacterium which has changed little over the centuries.
Many people think leprosy is a disease of medieval times; remembering films where the “leper” was outcast from society forced to ring a bell shouting “unclean” and everyone shunned the unfortunate souls who had this disease. In fact my wife jokes all Microbiologists should carry bells but in fact Microbiologists just inform people of infection, they are not actually the ones infected! The first time I became aware of leprosy and its social stigmata was at the age of 11 when I read the Sci-fi fantasy books The Chronicles of Thomas Covenant by Stephen Donaldson, in which the “hero” has leprosy… Yep I am a bit of a Sci-Fi Geek!!
Contrary to popular belief leprosy is not highly infectious (see infection control below) and there is treatment available. The reason for the fear was the progressive nerve damage which leads to loss of body tissues from trauma and infection. This gave rise to the medieval notion that parts of a “leper’s” body would just fall off!
However, leprosy is not a disease of the past. In 1985 there were 5.2 million cases of leprosy worldwide; although this figure has reduced to 250,000 it hasn’t changed much in the last 10 years. In the UK however, leprosy is a very rare infection with only about 12 cases of “imported leprosy” being diagnosed each year. This makes it difficult to spot as we don’t expect it and therefore don’t think of it in a differential diagnosis. So could this patient actually be one of those twelve cases?
When should you think of leprosy?
The first trick to diagnosing leprosy is to have a clinical picture that fits with the diagnosis. The main clinical features include:
- Skin – a chronic itchy patch of skin which doesn’t respond to normal dermatology treatments, decreased sensation in a hypopigmented patch of skin, or widespread and persistent skin papules and nodules
- Nerve damage or pain that doesn’t fit another diagnosis
- Thickened peripheral nerves
- Ulceration on the sole of the foot
- Rarely – arthritis, erythema nodosum, orchitis and acute uveitis
The host’s immune response dictates how the disease presents:
- Tuberculoid leprosy – strong cell-mediated immunity resulting in obvious skin lesions containing few bacteria
- Lepromatous leprosy – no cell-mediated immunity leading to diffuse widespread lesions full of large amounts of bacteria
- Borderline leprosy – which has features of both tuberculoid and lepromatous leprosy
The WHO classifies leprosy as:
- Paucibacillary – 1-5 skin lesions with no viable bacteria in the lesions, this corresponds to tuberculoid and borderline leprosy above
- Multibacillary - > 5 skin lesions with lots of viable bacteria in the skin lesions, this also corresponds to lepromatous leprosy above
Leprosy is initially an asymptomatic infection but can present 2 to 12 years after exposure, which may be many years after leaving an endemic country (see below). However, once symptoms occur the disease is progressive without treatment.
If the patient has a potential diagnosis of leprosy, then consider how likely and whether they might have been exposed to the bacterium. We have not had a UK acquired case since 1925 so it means the patient is either from, or has been to another country where leprosy is more common. The countries with the highest incidence of leprosy are: India, Indonesia, Brazil, Angola, Central African Republic, Democratic Republic of Congo, Madagascar, Mozambique, Nepal and the United Republic of Tanzania. There are also some animals that carry M. leprae, in particular the nine-banded armadillo in America (which has a body temperature of 34oC and is therefore a perfect incubator); the biggest risk factor for developing leprosy from the nine-banded armadillo is hunting and eating this animal.
How is the diagnosis of leprosy confirmed?
Leprosy is confirmed by taking a biopsy of the skin lesions and seeing acid fast bacilli on microscopy. This is a specialist skill and in the UK patients should be referred to a specialist service such as at the Hospital for Tropical Diseases in London or the Liverpool School of Tropical Medicine. Don’t try and take biopsies yourself and send it to a local laboratory, let the experts do it.
What is the treatment of leprosy?
Patients with leprosy should be treated by someone with experience and expertise in this disease. In the UK the specialist centres above have “Consultant Advisors in Leprosy” who will manage these patients.
- Paucibacillary - (containing just a few bacilli) 6 month treatment - PO Rifampicin 600mg once a month PLUS PO Dapsone 1-2mg/kg OD
- Multibacillary – 12-24 month treatment - PO Rifampicin 600mg once a month PLUS PO Dapsone 100mg OD PLUS Clofazimine 300mg once a month PLUS Clofazimine 50mg OD
With effective treatment and careful attention to skin integrity of the denervated tissue, the “leper’s” body with its missing digits should no longer happen. Although if you travel widely you will still see many untreated cases begging on the streets of affected countries.
Patients with lepromatous or multibacillary leprosy are infectious and shed millions of viable bacteria in their nasal discharge; droplet transmission is thought to be the main mode of transmission. However, only about 5% of the population are able to acquire leprosy as there are specific genes that appear to allow infection to occur, this is why it is not considered highly infectious. There are no special precautions for patients admitted to hospital with untreated leprosy; universal precautions with gloves, masks, aprons and a side room are appropriate.
In the UK leprosy should be notified to Public Health England.
Relapse after treatment is very rare.
So the patient who comes to clinic thinking they might have leprosy is very unlikely to do so. I would suggest investigating and treating for other causes of skin diseases first. Then, if they don’t get better and they have suitable travel exposure, consider referring for a second opinion but please bear in mind that the UK sees on average 12 cases a year; that’s only 1 case per 500,000 population… it’s very rare.
For me the biggest tragedy about leprosy is that it is preventable and treatable. The problem is that those who most need the relevant treatment are in the poorest countries and have the most limited access to healthcare. The treatment is free of charge from the WHO, but there is still a cost to getting the medication to the patient and managing the complications of leprosy. As a result the poor countries of the world with less well developed healthcare continue to struggle to deal with this historical infection.
And please don’t blame the red squirrels… they have enough of a hard time dealing with their more rambunctious grey cousins who carry the deadly squirrel pox! …the last thing they need is to be blamed for such a socially stigmatising disease… and did I mention they’re really cute?!