An outbreak of canine leptospirosis in Singapore made it to the news yesterday. There were 17 suspected and 1 confirmed case for the year to date (up from 2 cases in 2015), 12 of which were linked to a single dog daycare centre. There may also have been a case of dog-to-human transmission – According to the news report, a person who had a dog previously housed at the daycare centre in question developed leptospirosis this year. This outbreak highlights how human health is intricately linked to animal health, which is the key point of the “one health” paradigm. It seems evident from the report that many of our health officials have embraced this paradigm as well.
Leptospirosis is a fascinating disease with varied manifestations. It is caused by the bacterium Leptospira spp. (a spirochaete – corkscrew-shaped), which is found worldwide and has a huge and diverse animal reservoir. There are a large number of different leptospiral species (some of which have multiple serovars), of which only a minority can infect humans. The bacterium is primarily excreted from the urine of animals (and humans), contaminating the environment and water sources. The World Health Organization lists leptospirosis as a water-related disease, largely because the majority of reported human infections appear to have occurred as a result of urine-contaminated water (contact with mucous membrane, cut/abraded skin, or ingestion).
There are at least two comprehensive reviews that are worth reading for those who are interested, one published in Clinical Microbiology Reviews in 2001, and another in Current Topics in Microbiology and Immunology in 2015. The majority of human leptospiral infections probably results in mild or subclinical disease. The clinical presentation is classically described as being biphasic, with an acute or septic phase lasting approximately a week, followed by an immune phase which is when most of the complications of the disease occur. Many physicians will know of Weil’s disease, which is the most severe form of “classical” immune-phase leptospirosis with renal failure and liver injury (usually cholestatic hepatitis).
Mild leptospirosis is self-limiting and does not require antibiotic therapy. After this point, the evidence becomes conflicting and controversial. Fairly circumstantial evidence suggests that early administrative of antibiotics (intravenous penicillin) may shorten the duration of illness and reduce progression of renal failure. A Cochrane review in 2012 found only 4 placebo-controlled trials, based on which the authors concluded there was insufficient evidence to recommend for or against the use of antibiotics in severe leptospirosis. The choice of antibiotics based on 3 comparative trials (penicillin or ceftriaxone or doxycycline) also did not matter. The lack of success is easier to understand if one views severe leptospirosis as being largely immunologically driven (as opposed to bacterial virulence/invasion). Nonetheless, the “sin of omission” seems to be greater nowadays among us doctors and I believe most would err on the side of prescribing antibiotics. How about corticosteroids? There was only one (open-label) clinical trial, which failed to show any benefit.
Human leptospirosis is rare in Singapore largely due to good sanitation and the generally clean environment. Some occupations here may be at higher risk however – the seroprevalence of leptospirosis was six times higher in sewage workers compared to controls in a study done almost 3 decades ago in Singapore. The available vaccines are mostly for animal use, although there are at least a couple used in humans who are at risk for the disease in China and Cuba. Doxycycline is sometimes given as prophylaxis for travellers engaging in potentially high-risk activities such as white-wafting. Not unexpectedly, the benefit is unclear.