I was on a small mammals training course and the professor was warning of the dangers of Leptospirosis. Apparently 5-40% of Rats have it and an unknown proportion of other animals. The warning sheet they handed out listed farmers, gardeners, etc as 'at risk' groups. I looked it up on the NHS website out of interest but it said there were only about 25 cases a year in the UK, even of the mild form.

I understand that it dies when it's dried out, but still, in notoriously rainy Britain, I can't seem to make sense of the numbers. There are at least half a million farmers in our country, probably a similar amount of gardeners, at least several thousand homeless and poverty stricken who must live in very close proximity to the huge urban Rat population, not to mention the potential for rodents to get into domestic water tanks. In rainy weather everything can stay wet for days. Also, if I remember rightly, an Olympic athlete recently died from it, so it obviously doesn't require a weak physiology to get in.

So, the question is, given what seems to me to be a massive prevalence (40% of all Rats), vast contact opportunities (all land workers during spells of wet weather), and seemingly a tough little organism (can kill an Olympic athlete), why is it so rare (25 cases in 70,000,000 people)?

  • $\begingroup$ Leptospira, the bacteria is largely found in the urine. So the urine from the rat has to get into cuts or wounds of a human. That seems rather unlikely. For such a thing to happen, you need ample rains, improper sewage and lots of rats. So apart from occupational groups, the disease also has an epidemic nature. During heavy rains in Mumbai, rodent infested sewers overflow and there's sudden spike in leptospirosis cases. I don't know the nos. but my micro txt calls it the most widespread zoonosis. Spells of wet weather aren't enough, there needs to be water logging combined with contamination. $\endgroup$ – Polisetty Aug 12 '16 at 20:26
  • $\begingroup$ Yes, Leptospirosis is, of course, a major problem in tropical areas, but as far as I know, there has never been an epidemic in Britain, yet we have some floods as well as all the other things I listed in my question. What puzzles me is there seems to be nothing in the bacterium's characteristics or mode of transmission that would account for the lack of epidemic in Britain. A little further reading I've done since asking the question seems to even imply that it can survive in moist soil phac-aspc.gc.ca/lab-bio/res/psds-ftss/msds95e-eng.php, we shouldn't even need a rainy season. $\endgroup$ – Isaacson Aug 13 '16 at 6:52
  • $\begingroup$ An epidemiologist must be able to answer this question but id like to point out that the presence of bacteria doesn't necessarily lead to infection. Something as ubiquitous as Clostridium tetani in the soil doesn't cause tetanus in everyone (even in pre-vaccination era). $\endgroup$ – Polisetty Aug 13 '16 at 9:07
  • $\begingroup$ That's true, but the mode of transmission with C.tetani is what prevents it from reaching epidemic scales, it requires a relatively deep wound. What I seem to be missing is the equivalent characteristic of Leptospires which prevents Leptospirosis from reaching epidemic proportions in Britain. $\endgroup$ – Isaacson Aug 14 '16 at 6:48
  • $\begingroup$ Both deep and superficial wounds can cause tetanus. In recent times superficial wounds have become the main mode infection, more than deep wounds. This may be because deeper wounds receive more attention. I know this is off-track but still... $\endgroup$ – Polisetty Aug 14 '16 at 7:33

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