Until a viable vaccination has been licensed, the only control measure for humans is to use antibiotics. If a patient becomes ill then a program of antibiotics will be given, but they can also be used to control infections before patients show clinical symptoms. This preventative use of medication is called ‘prophylaxis’.
For adult humans at risk from leptospirosis the standard prophylaxis is a single 200mg oral dose of an antibiotic called Doxycycline. It provides protection for about a week, so in some cases (such as natural disasters) one tablet is issued per week, for as long as necessary. however it is not a good idea to use antibiotics like this for more than a few weeks at a time, as there are significant risks of creating resistance.
Doxycycline does not totally prevent an infection – patients can still show a mild illness, and can also be infectious to others via their urine for a short time, however in most cases the infection is controlled to a very low level and the patient feels no clinical symptoms. It’s important to realise that taking prophylactics is not the same as being vaccinated – it doesn’t give you a safe ticket to drink contaminated water!
Children under 8 are usually not allowed to take doxycycline due to the potential for side effects, such as the permanent staining of their unerupted teeth, and so in cases where young patients must receive prophylaxis we often give a short course of penicillin instead. It’s not as simple to administer as a single tablet, but just as effective.
Note that giving prophylactic antibiotics is not permitted in the workplace as a measure to permit hazardous work, so employees routinely exposed to the bacteria must be given protective clothing and education, but cannot be medicated except after specific accidents. Long-term use of small doses of antibiotics is very likely to cause resistant infections that can be life-threatening. The only exception to this rule is where the workers are engaged in short-term essential operations, such as the emergency services attending sites of natural disasters and some military special forces teams.