IN THE current coronavirus pandemic it’s easy to forget that other diseases still persist, yet even with the disruptions of working from home and fluctuating lockdowns, scientists are still working on new research. 

In the last week a team of researchers from across the world reported the first ever recorded cases of leprosy in wild chimpanzees.

Wild chimpanzees have now conclusively joined a short but diverse list of animals that are known to be affected by forms of leprosy, including nine-banded armadillos and red squirrels. 

Leprosy is a bacterial infection that causes symptoms over a very long period of time. 

In humans there are often no symptoms at all until around five years after initial infection. 

A minority of infected individuals develop lesions on their skin, which becomes dry and thick. 

The bacteria invade host cells, which are damaged when the host’s immune system fights back. 

This leads to nerve damage which causes a loss of sensation. The dry skin can crack, or cuts can happen due to the lack of feeling. These openings lead to other bacterial infections that cause further damage.

Leprosy in humans is an ancient disease. A skeleton in India dating back to 2000 BC showed skeletal damage associated with leprosy. 

It is also highly stigmatised, even though it has been part of human life for millennia. 

People living with leprosy are represented throughout the Bible as spurned lepers (a term now avoided). 

The Gospel of Matthew reports Jesus’s miracle of healing someone of leprosy as an example of kindness even to the social outcast. 

Despite the stigma, which has often led to people affected by leprosy being forced to live in colonies with other sufferers, leprosy is not a particularly transmissible disease. 

Transmission requires prolonged, close contact with an infected person. It is now treatable. 

Unfortunately, the stigma often leads to people avoiding seeking treatment until the disease has reached an advanced stage.

While leprosy is now considered a historical disease in Britain, there are still over 200,000 cases diagnosed worldwide each year. 

The majority occur in India and Brazil. It is classed as a neglected tropical disease by the World Health Organisation, because it primarily affects only the poorest populations.

As a result it receives low levels of funding for treatment and research. That is part of the reason we are only now finding out about some of the other animals affected by leprosy. 

It was the disfigurement of faces and hands caught in photos used to monitor wild populations of chimpanzees in two different national parks that led to the eventual suspicion of leprosy. 

This suspicion was confirmed by testing for the leprosy bacteria in samples of faeces.

The fact that the chimpanzees at these sites have been monitored for over a decade allowed researchers to notice the gradual development of leprosy symptoms, but it also raises further questions. 

How were the chimpanzees infected? It is tempting to suspect that they could have been infected by a human with leprosy. 

However, the same constant monitoring rules out the kind of prolonged contact with humans that would be required for transmission. 

On top of this, after isolating the genetic code of the leprosy-causing bacteria, it was a bacterial strain that is not very commonly seen in humans. 

What this suggests is another, currently unknown, species that can also act as a host. 

Researchers call such species “reservoirs”: they are where a disease is maintained in circulation, only occasionally “spilling over” into other species. 

For the wild chimpanzees affected by leprosy, the future is unclear. Since this is a relatively recent discovery we don’t know how leprosy will progress in the chimps. 

Treating leprosy in humans requires taking a mixture of several antibiotics for up to a year, so this treatment cannot be replicated in wild animals without disrupting their free lives. 

Thankfully, the rates of leprosy infection among the chimpanzees remains quite small. 

What this discovery shows is how much more we have to learn about infectious disease. 

It’s easy to forget humility, as we act to dominate and shape the natural world, that species and places hold much that is unknown, and to which we’re not immune. 

Finding ways to stay healthy, for ourselves and other animals, is a valuable work in progress.