Further thoughts on 'Asymptomatic dogs are highly competent to transmit Leishmania (Leishmania) infantum chagasi to the natural vector'

摘要

We appreciate the reply of Laurenti and Marcondes (2014), but our interpretation was (see Dantas-Torres and Otranto, 2014) and is (in the current letter) based on data presented in their original paper (Laurenti et al., 2013). Firstly, they should be aware that the classifications of the Canine Leishmaniasis Working Group (Paltrinieri et al., 2010) and LeishVet (Solano-Gallego et al., 2011) are different, not complementary. Secondly, the new analysis provided in their letter is equally misleading as the first. Stating that “The average percentage infected sand flies from asymptomatic, asymptomatic with mild popliteal lymph node enlargement and symptomatic groups were 43.57%, 33.43% and 24.67%”, indicates that they have now divided dogs into three groups rather than the initial two, and continue to classify dogs with mild popliteal lymph node enlargement as “asymptomatic” (=healthy) which is incorrect as previously stated. Surely they should have classified dogs with mild popliteal lymph node enlargement as symptomatic dogs and then compared those with truly healthy dogs. An elegant study recently published in PLOS Neglected Tropical Diseases by Courtenay et al. (2014) reported that total parasite abundance and relative numbers in ear skin compared to bone marrow increased with the duration and severity of infection in dogs. They also show that infectiousness to the sand flies was associated with high parasite numbers in ear skin accessible to sand flies. In that study they base this conclusion on both average numbers of flies infected by dogs in repeated xenodiagnoses through the time-course of infection, as well as at single point xenodiagnosis. The authors also stated that “crab-eating foxes, which typically present asymptomatic infection and are non-infectious, had parasite numbers comparable to those of non-infectious dogs.” As observed in that longitudinal study, parasite detection and infectiousness to sand flies can be highly variable from one day to the next (O. Courtenay, pers. com.) representing a further difficulty in interpreting data from cross-sectional studies.