Mycobacterium marinum—not just ‘fish-tank’ disease but a real occupational problem for the 20th Century fishing industry in Hong Kong

I have caught a few diseases from animals over the years. The most irritating and long-lasting was  Mycobacterium marinum, aka fish tuberculosis or ‘fish-tank disease’. In the 1980s I caught a knuckle on the rockwork of a marine aquarium and several weeks later a nasty granular, ulcerating lesion appeared. The local dermatologist thought he recognised what it was and took a biopsy for culture. The dermatologist had read the then recent literature which showed a number of aquarists throughout the western world had caught M. marinum in a similar manner. Cases were also known in which a swimmer had grazed a hand or foot on a sharp edge of a tropical seawater swimming pool. The organism will only grow at the extremities of the human body because it is cool; it cannot survive at internal body temperatures. Unfortunately the bacteriologists had not read the literature and tried to culture the organism at 37° C. Eventually they got the conditions right and confirmed the presence of the organism.

In the meantime I had started a self-cure regime, realising the alternative was a long course of anti-microbials used to treated human tuberculosis. Using glutaraldehyde to kill the tissue and a scalpel to cut each layer of newly dead flesh I gradually got the upper hand. By the time I went to see the dermatologist who had eventually received the report from the bacteriologists, I had the organism in full retreat. He was delighted to find an alternative treatment and said he would write it up along with photographs. A couple of months later, I had won; normal skin completely replaced the ugly lesion. Physiologists, of course, are well-known for doing experiments on themselves—or a handy PhD student.

What I had not realised until recently was that fishermen and their familiies could also be victims of M. marinum. In general the literature deals with case of marine aquarists and swimmers who live in Europe and North America, although other cases, as in a New York fish market, get a mention. While looking for something else entirely, I came across an account compiled by our late great friend Dafydd Evans (1938-2006), a historian as well as former Dean of Law and founder of the Law School at the University of Hong Kong. In his centenary history of the medical school* of that University, he included accounts of work in the various departments. Under Microbiology I found:

The service provided by the Department has benefitted from a constant academic input…Recent examples include the occupational diseases such as the chronic hand diseases of fisherfolk caused by Mycobacterium marinum…

I am now trying to see if I can spot any lesions on the hands of the Hong Kong fisherfolk, who lived virtually their entire lives on their boats, in my own cine films of the 1960s or those of others like Michael Rogge in the 1950s. I do not know how prevalent the problem was, or still is, but clearly of sufficient importance for the local microbiologists to do something about it.

The Hong Kong boat people at the least crowded end of Aberdeen harbour in 1967-68.
How many of those handling fish caught M. marinum?

A view further to the right of the previous photograph showing the end of the harbour and the then new Ap Lei Chau Power Station which opened in 1968. It was closed in 1989.

*I had been looking for a copy of the book in U.K. for another line of research. I then spotted one on eBay from a seller in Norwich. As it wended its way to me I wondered how a bookseller in Norwich had acquired it. The only person in Norfolk who I could think might have had a copy was Brian Lofts (1929-2015), Professor of Zoology at HKU at the time Dafydd wrote the book. Sure enough, the inner cover is signed ‘Brian Lofts”. Also included was an invoice from the University Press stating that the discounted price (HK$120) would be deducted from his salary. Financial control at HKU was always tight!

Evans, Dafydd Emrys. 1987. Constancy of Purpose. An Account of the Foundation and History of the Hong Kong College of Medicine and the Faculty of Medicine of the University of Hong Kong 1887-1987. Hong Kong University Press.