Toxoplasma gondii infection is prevalent worldwide and considered one of the neglected parasitic infections targeted by Centers for Disease Control and Prevention. Most healthy individuals suffer no ill effects from toxoplasmosis, despite not undergoing treatment, as the host immunity helps to fight against the infection. However, most of the infected hosts will develop chronic toxoplasmosis as the parasite is capable of encyst itself and hiding themselves from attacks by the host immune system. Hence, understanding of host-parasite metabolic interaction is essential as the parasite strives to survive and grow in the host, while the host struggles to maintain homeostasis in many levels, such as the gut ecosystem, immune system and metabolic system. Here, we have established an animal model using BALB/c mice and Toxoplasma gondii strain ME49, to understand the interaction between both host and parasite using systems biology approaches: metagenomics, metabonomics and host immune response. This study showed a significant and distinctive profile between acute versus chronic phases of infection in terms of host immune system, gut microbiota and urinary metabolic profile. Observation on the change in gut microbe composition occurred during the acute but not chronic phase of infection. Nonetheless, significant changes in host metabolism can still be observed during the chronic phase of infection. Furthermore, our findings also demonstrated perturbation on the host immune responses. Continuous elevation of serum IFN-γ and decrease in levels of TNF-α indicated that IFN-γ plays a vital role in both acute and chronic infection phase of toxoplasmosis. Next, perturbation in the host immune system was also reflected in the urinary metabolic profile. Urinary levels of N-acetyls and O-acetyls of glycoproteins on the termination time point were significantly lower in the infected group. Moreover, infected animal also showed disruption in their host energy metabolism during toxoplasmosis. This was supported by the observation of a decrease in urinary citrate, 2-oxoglutarate and fumarate. Likewise, increase in urinary α-hydroxy N-valerate and β-aminoisobutyrate indicated that disruption of host amino acids catabolism occurred. Lastly, urinary excretion of short-chain fatty acids suggested a transient shift in energy metabolism towards oxidation of both gluconeogenic and ketogenic amino acids such as isoleucine, leucine, valine and nucleotide.

To address gaps in the understanding of host-parasite interactions, this study employed a systems biology approach to investigate system biological responses in Balb/c mice infected with Toxoplasma gondii and Trypanosoma brucei brucei. The study found distinct histopathological changes in Balb/e mouse organs post- infection. Spleen hyperplasia, chronic inflammation, and immune cell infiltrations were apparent in both infected arms. Cytokine profiling identified key players like tumour necrosis factor alpha, interferon-gamma, interleukin-2 in T. gondii group interleukin-6, and interleukin-IO in T. b. brucei group, providing insights into their roles in host defence or immunomodulation. Nuclear magnetic resonance metabolomics profiling was used to identify potential parasitic infection biomarkers, revealing alterations in metabolic profiles indicative of metabolic adaptations and gut microbiota dynamics during infection. Notably, short-chain fatty acids like acetate and butyrate, aromatic amino acid derivatives like phenylacetylglycine and tyrosine, and metabolites such as sueeinate and creatine were implicated in immune regulation and host-parasite interactions. This study also explores interactions between the gut microbiota and parasitic pathogens, highlighting their impact on disease outcomes. Specifically, Lactobacillus species were identified as key players in modulating the host's immune response and metabolic processes during parasitic infections. In conclusion, the systems biology approach enhances our understanding of host-pathogen interactions in Balb,/c mice, revealing potential therapeutic targets. While the findings are specific to the mouse model, they offer valuable insights that could inform strategies for managing parasitic infections in humans. This study thus lays a strong foundation for future research aimed at developing targeted interventions across various host systems, potentially bridging the gap from animal models to human disease management.