Comparison of three Schistosoma mansoni strains: Infection, morphometry and susceptibility to treatment

Different Schistosoma mansoni strains exhibit distinct phenotypes, influencing parasite distribution, control strategies, and therapeutic alternatives for schistosomiasis. This study compared three Brazilian strains: Belo Horizonte/MG (SmBH), Ilha das Flores/SE (SmSE), and São José dos Campos/SP (SmSJ). To understand differences in infection, morphometry and response to praziquantel (PZQ) treatment, BALB/c mice were infected with each strain and treated 45 days post-infection (dpi) with praziquantel (PZQ) in different dosages. Egg elimination was monitored weekly from 30 dpi and euthanasia was performed 60 dpi. Untreated groups showed SmBH with the highest infection rates, with a larger number of recovered worms and a greater number of eggs. Morphometric analysis showed that SmSE females were significantly longer, while SmBH eggs were larger. Granuloma size was similar in SmBH- and SmSJ-infected mice, but SmSE-induced granulomas were smaller. SmBH infection resulted in a greater number of granulomas, suggesting higher pathogenicity. PZQ treatment at 150 or 300 mg/kg significantly reduced parasite burden, fecal egg count, and hepatic/intestinal granulomas in SmBH- and SmSJ-infected mice. SmBH infection also showed fewer immature and mature eggs and more dead eggs after treatment. However, SmSE-infected mice exhibited no significant differences between treated and untreated groups, suggesting higher resistance/tolerance to PZQ. These findings highlight phenotypic differences among S. mansoni strains: SmBH produced and retained more eggs, aggravating pathology; SmSJ had the lowest egg production; SmSE showed the highest resistance to PZQ. Understanding strain variability is crucial for improving schistosomiasis control and advancing drug development.