Relationship between Canine Visceral Leishmaniosis and the Leishmania (Leishmania) chagasi Burden in Dermal Inflammatory Foci

SummaryThe skin is the first point of contact with organisms of the genus Leishmania from sand fly vectors, and apparently normal skin of sick dogs harbours amastigote forms of Leishmania chagasi. In relation to canine visceral leishmaniosis (CVL), the ear skin was examined in 10 uninfected dogs (UDs) and in 31 dogs dogs naturally infected with L. chagasi. The infected animals consisted of 10 symptomless dogs (SLDs), 12 mildly affected dogs (MADs) and nine affected dogs (ADs). A higher parasite burden was demonstrated in ADs than in SLDs by anti-Leishmania immunohistochemistry (P<0.01), and by Leishman Donivan Unit (LDU) indices (P=0.0024) obtained from Giemsa-stained impression smears. Sections stained with haematoxylin and eosin demonstrated a higher intensity of inflammatory changes in ADs than in SLDs (P<0.05), and in the latter group flow cytometry demonstrated a correlation (P=0.05/r=0.7454) between the percentage of CD14+ monocytes in peripheral blood and chronic dermal inflammation. Extracellular matrix assessment for reticular fibres by staining of sections with Masson trichrome and Gomori ammoniacal silver demonstrated a decrease in collagen type I and an increase in collagen type III as the clinical signs increased. The data on correlation between cellular phenotypes and histological changes seemed to reflect cellular activation and migration from peripheral blood to the skin, mediated by antigenic stimulation. The results suggested that chronic dermal inflammation and cutaneous parasitism were directly related to the severity of clinical disease.