Undetectable Mycobacterium leprae complex in European Pallas's squirrels

Eurasian red squirrels were acknowledged as a reservoir for secular leprosy in the British Isles, after detection of Mycobacterium leprae in specimens dating back to the 11th century. In order to question the situation of Pallas's squirrels (Callosciurus erythraeus) recently introduced to the European continent, we investigated a series of 522 samples (241 liver, 241 spleen, and 40 faecal samples) collected from 281 deceased C. erythraeus specimens by means of controlled quantitative PCR targeting the M. leprae specific RLEP repetitive element, the M. lepromatosis RLPM repetitive element, and the most closely related Mycobacterium uberis ESX-1 locus gene. Successful amplification of the internal control certified the absence of PCR inhibition in any samples, which all tested negative for M. leprae complex DNA. Because tissues potentially involved in localized infection were not studied in the absence of clinical signs and the study was geographically restricted, these results cannot be extrapolated beyond dismissed systemic leprosy in tested animals. Nevertheless, the congruency of present data with equally negative ones reported in various continental squirrel populations suggests that, in Europe zoonotic leprosy is restricted to British Islands' red squirrel population.