Anatomical MRI and [18F]FDG PET/CT imaging of Schistosoma mansoni in a NMRI mouse model

Abstract

Schistosomiasis represents one of the most devastating worm parasitosis in the world. Current diagnostic methods are insufficient to determine the infection grade and the disease related organ damage. We herein investigated whether discrimination of infection grade and its correlation to liver damage could be accurately performed by multimodal imaging in a mouse model of Schistosoma mansoni infection. Therefore, groups of uninfected and infected mice underwent MRI and [18F]FDG PET/CT imaging. Anatomical MRI images were used for liver volumetry and for quantification of hepatic granulomas. For PET/CT images a volume of interest based analyses were employed to calculate the [18F]FDG uptake in liver, portal vein, spleen and abdomen. Herein, we demonstrate that the combined use of [18F]FDG-PET/CT and MRI represents an appropriate diagnostic tool for Schistosoma mansoni infection, but fails to discriminate the infection grade and the linked organ damage. Only the splenic [18F]FDG uptake in the 25 cercariae group (5.68 ± 0.90%ID/cc) and 50 cercariae group (4.98 ± 1.43%ID/cc) was significantly higher compared to the control group (2.13 ± 0.69%ID/cc). Nevertheless, future multimodal imaging studies with new radiopharmaceuticals could build a highly sensitive and specific basis for the diagnosis and evaluation of organ damage of schistosomiasis.

Recent Advances in the Diagnosis of Schistosomiasis

“…These cercaria are then discharged from the snail into the water, where they can infect the ultimate host once more, thus perpetuating the cycle (Fig. 1) (Lindner et al 2020).…”

Medical Imaging in the Diagnosis of Schistosomiasis: A Review

“…As early as 1950 physiology experiments demonstrated that schistosomes are large consumers of glucose [ 63 ]: therefore 18 F-FDG PET/CT imaging, as reported in a study with mice infected with S. mansoni , could be useful for the evaluation of worm burden in schistosomiasis infection [ 64 ]. Particularly noteworthy are also the results obtained in a study conducted by Lindner and collaborators, using mice infected with S. mansoni : the authors found a significantly higher uptake of 18 F-FDG in the spleen of infected mice in comparison to the control group, suggesting a possible role of splenic uptake in the determination of infection grade [ 8 ].…”

“…At this moment, the egg releases miracidia (the initial larval stage) which penetrates the intermediate host (aquatic snail) and undergoes several cycles of asexual reproduction, up to reaching the cercaria stage. Hence, cercaria is released by snail into the water, infecting again the final host [ 1 , 2 , 4 , 8 ].…”

“…As regards laboratory evaluation, an important technique is represented by the microscopic examination of stools (for S. japonicum and S. mansoni ) and filtered urines (for S. haematobium ) to find the eggs with the Kato-Katz technique, since egg excretion is considered a marker of active infection [ 22 ]: this is the most used method in endemic countries due to its rapidity and cost-effectiveness (even if it has a variable sensitivity) and it is also recommended by WHO in case of intestinal schistosomiasis [ 23 ]. Laboratory evaluation also comprises serology (to find serum antibodies), which is non-specific because it cannot differentiate between active infection and former one [ 2 , 8 ], molecular assays such as polymerase chain reaction (PCR) for circulating DNA of the parasite in blood, stool, urine, saliva, tissues, which is proved to be a sensitive and specific method even in the non-endemic countries [ 24 ] or immunodiagnostic assays such as enzyme-linked immunosorbent assay (ELISA) for the detection of schistosomulae antigens (which helps the diagnosis in the early infection) [ 22 ] and of eggs antigens in blood (which is the standard screening method). Moreover, another important tool for the diagnosis is represented by tissue biopsy, especially for intestinal ( S. japonicum and S. mansoni ) and urinary schistosomiasis ( S. haematobium ) [ 1 ].…”