Prevalence of Toxoplasmosis in Thika region, Kenya and the Immunopathology associated with Toxoplasma gondii infection in BALB/c mice

Abstract

Toxoplasma gondii is an important food and waterborne opportunistic pathogen that causes severe disease in immunocompromised individuals. The detection of T. gondii in free range chickens is a good indicator of environmental contamination with T. gondii and possible risk to human beings. The pathology and immune responses associated with the ensuing disease has not been well described in strains from different parts of Kenya. The present study aimed at determining the prevalence of toxoplasmosis in Thika region and development of a neurological mouse model in BALB/c mice to assess the changes of IgG, Ig M, cytokines and organ pathology. In order to accomplish this, 105 free range chicken were collected; deoxyribonucleic acid extracted from brain and analyzed using PCR to detect presence of T. gondii. For experimental infections, BALB/c mice were infected intraperitoneally with 15 cysts of a T. gondii isolate; monitored for 42 days and euthanized at different time points. Another group of mice were orally treated with dexamethasone [DEX: 2.66mg/kg daily (Group 1); 5.32mg/kg daily (Group 2)] at 42 days after infection and followed by monitoring for a further 42 days. The control groups consisted of infected and untreated (positive control, Group 3) and uninfected and untreated (negative control, Group 4) mice. After euthanasia, blood was collected for serum and assessed for IgG, IgM, IL-10 and IFN- levels. The brain tissue was also collected and divided in halves; one half was used for cyst enumeration, while the other half was used for histology. The liver, heart and spleen were also collected and processed for histopathology. Results indicated that the overall prevalence of T. gondii infection in chicken was 79.0% (95% CI: 70.0-86.4%). A mortality rate of 15% and 28.6% was observed in mice given 2.66mg/kg/day and 5.32mg/kg/day of dexamethasone, respectively. The number of cysts in the brain of DEX treated mice increased up to twofold compared with chronically infected untreated mice. During the acute and chronic phases, there was an increase in both IgM and IgG levels but following dexamethasone treatment, IgM levels declined but IgG levels continued to rise peaking on 42 days post-treatment. Elevated levels of interferon-gamma (IFN-) (P<0.05) and IL-10 (P<0.01) were observed between 7 and 42 days post infection (dpi). After dexamethasone treatment, IFN-γ and IL-10 levels declined significantly (P<0.05) at time points between 42 and 84 dpi. The decrease was higher (P>0.05) in Group 2 compared to Group 1, mice. Mice in the infected non-treated group had significantly (P<0.01) elevated IFN-γ and IL-10 levels compared to the dexamethasone treated mice at all time points. The brain of toxoplasmosis infected mice showed inflammatory infiltrations, neuronal necrosis, and cuffing. The severity of pathology was higher in mice treated with dexamethasone compared to the positive control groups. In conclusion, the study showed that T.gondii infection is highly endemic in free range chicken from Thika region. Further studies should be carried out to determine the possible role of roaming chickens in the epidemiology of the disease among humans in the area. The findings of this study also demonstrate that dexamethasone-induced reactivation of chronic toxoplasmosis may be a useful development of laboratory animal model in outbred mice used for in vivo studies. The results of this study also demonstrate that toxoplasmosis in mice was associated with elevated IFN- and IL-10 levels, and myocarditis, hepatitis characterized by mononuclear inflammatory cellular infiltration. Further work on other cytokines involved in the pathology should be carried out. Research to investigate the potential of IFN- and IL-10 as diagnostic and therapeutic tools should be undertaken.