LS-7-P-2575 Morphometric Analysis of Granulomas in Nectomys squamipes Brants, 1827 (Rodentia: Sigmodontinae) naturally infected with Schistosoma mansoni Sambon, 1907 (Digenea: Schistosomatidae).

The semi-aquatic rodent Nectomys squamipes has been found naturally infected with Schistosoma mansoni and has a wide geographical distribution that coincides with endemic areas of human schistosomiasis in Brazil. Due to its susceptibility, high abundance and water-contact patterns, it contributes significantly with the epidemiology of the disease [1]. The pathological effects of schistosomiasis occur mainly because of the immunological reactions of the host due to the eggs of the parasite that are not excreted and are deposited on the tissues and later on are encapsulated to form the granulomas, which undergo several evolutional stages according to the phase of the infection [2]. In this process, the eosinophils, leukocytes of the innate immune system, are actively recruited and secrete cytotoxic products that cause damage to parasites [3]. In this study, we investigated the role of eosinophils in the formation of different stages of granulomas in this naturally infected rodent. Animals (n=3) were captured and immediately euthanized by deep anesthesia (animal ethical approval # L-0049/08). Liver fragments were processed for light microscopy. For the morphometric analysis, Histoquant software was used to measure parameters as area, perimeter, major and minor diameter of granulomas with visible eggs in the center. Liver sections showed inflammatory infiltrates and periovular lesions in pre-granulomatous stages, characterized by exudative reaction (7,93%) and exudative-necrotic reaction (1,22%) and a clear predominance of exudative-productive (48,78%) and productive (42,07%) granulomas. However, no significant differences were found in the areas of all types. Some granulomas around eggs containing well-preserved miracidium showed an acute inflammatory reaction, with many polymorphonuclear cells, mainly eosinophils. They presented the largest numbers of eosinophils (absolute numbers) and eosinophils per area (density of cells). More frequently, an inflammatory reaction of chronic type was seen, with cells as eosinophils, macrophages and fibroblasts and collagen deposition in varying amounts around empty eggshells or eggs containing degenerated miracidia. Finally, we observed that the degree of impairment of liver tissue (calculated as the sum of the area occupied by granulomas and that occupied by inflammatory infiltrates) was very small (mean = 5.05%), which explains the lack of symptoms observed in these rodents during schistosomiasis infection.  

References:
[1] Gentili, R. et al. Oecologia Australis, 14(3) (2010) 711-725.
[2] Lambertucci, J.R. 2010. Memórias do Instituto Oswaldo Cruz, 105(4) (2010) 422-435.
[3] Melo, R.C.N. et al. Journal of Leukocyte Biology, 83 (2008) 229-235.