Compression of parasite load data of multiple tissues uncovers relationships of parasite burden with clinical signs and hematological, biochemical and oxidative stress markers in dogs with visceral leishmaniasis

Thirty-seven dogs naturally infected with Leishmania spp. were examined in order to establish relationships between parasite load (PL) in multiple tissues and common clinical and laboratory findings in canine visceral leishmaniasis (CVL). Quantitative polymerase chain reaction was employed to determine PL in conjunctival swabs, ear skin, peripheral blood and buffy coat. Additionally, a series of hematological, biochemical and oxidative stress markers were quantified. Contribution of total parasite burden to clinical signs and variation in laboratory parameters was assessed through a new statistical approach, namely Compressed Parasite Load Data (CPLD), which uses dimension reduction techniques from multivariate statistics to summarize PL across tissues into a single variable. The analysis revealed that elevation in PL substantially contributes to the probability of occurrence of clinical sings commonly observed in CVL, such as skin lesions, ophthalmic alterations, onycogriphosis, popliteal lymphadenomegaly and low body mass. Furthermore, increase in PL was found to be followed by intensification of non-regenerative anemia, neutrophilia, eosinopenia, hepatic injury and oxidative imbalance. These results suggest that routinely used clinical and laboratory exams are predictive of parasite burden, thus highly infected dogs in endemic areas can be reliably identified even in the absence of PL quantification.