PREVALENCE, ISOLATION, AND GENETIC CHARACTERIZATION OF TOXOPLASMA GONDII IN CHICKEN

Toxoplasma gondii (T. gondii) is one of the most successful parasites in the world because of its capability of infecting all warm-blooded animals. It has been reported that up to one third of the world population is infected with this parasite. Chickens are recognized as good indicators of the environmental T. gondii oocysts contamination because they obtain food from the ground. Thus, the prevalence of T. gondii in chicken provides more insight related to public health concern from T. gondii. Previous studies have shown a high isolation rate from free-range chickens raised in the United States. The objectives of this study were to evaluate the microbial safety and infection of T. gondii in free-range chickens available at the grocery stores and farms for the consumers to purchase and genotype T. gondii isolates. Chicken hearts were obtained from the local markets and also from the farms raising free- range chickens. Heart juice was obtained from cavities of each heart. Modified agglutination test (MAT) for detection of IgG antibodies was conducted with those heart juice samples with titer of 1:5, 1:25, and 1: 100. Each seropositive heart was pepsin digested and bioassayed into a group of two mice. Six weeks post inoculation (p.i.) mice were bled and euthanized to examine the infection of T. gondii. In addition, multiplex multilocus nested PCR-RFLP was performed to genetically characterize T. gondii isolates with eleven PCR-RFLP markers including SAG1, SAG2, altSAT2, SAG3, BTUB, GRA6, c22-8, c29-a, L358, PK1, and Apico. One hundred fifty from a total of 997 samples (15.0%) were found seropositive for T. gondii. No viable T. gondii was isolated from chicken hearts that were sampled. A total of four genotypes were identified, including one new genotype and three previously identified genotypes. The results suggest that T. gondii oocysts could present in the environment and infect the food animals. T. gondii prevalence in chicken hearts could reflect the environmental contamination of T. gondii and prevalence information can be used to manage T. gondii infection risk.

Experimentally Testing the Effect of Parent-Adolescent Conflict on HIV Risk, and Investigation of a Neurobiological Moderator of This Effect

Human immunodeficiency virus (HIV) is a condition in which immune cells become destroyed such that the body may become unable to fight off infections. Engaging in risk-taking behaviors (e.g., substance use) puts people at heightened risk for HIV infection, with mid-to-late adolescents at increasing risk (Leigh & Stall, 1993). Environmental and neurological reasons have been suggested for increased risk-taking among adolescents. First, family-level precursors such as parent-adolescent conflict have been significantly associated with and may pose risk for engaging in substance use and risk-taking (Duncan, Duncan, Biglan, & Ary, 1998). Thus, parent-adolescent conflict may be an important proximal influence on HIV risk behaviors (Lester et al., 2010; Rowe, Wang, Greenbaum, & Liddle, 2008). Yet, the temporal relation between parent-adolescent conflict and adolescent HIV risk-taking behaviors is still unknown. Second, at-risk adolescents may carry a neurobiological predisposition for engaging in trait-like expressions of disinhibited behavior and other risk-taking behaviors (Iacono, Malone, & McGue, 2008). When exposed to interpersonally stressful situations, their likelihood of engagement in HIV risk behaviors may increase. To investigate the role of parent-adolescent conflict in adolescent HIV risk-taking behaviors, 49 adolescents ages 14-17 and their parent were randomly assigned to complete a standardized discussion task to discuss a control topic or a conflict topic. Immediately after the discussion, adolescents completed a laboratory risk-taking measure. In a follow-up visit, eligible adolescents underwent electrophysiological (EEG) recording while completing a task designed to assess the presence of a neurobiological marker for behavioral disinhibition which I hypothesized would moderate the links between conflict and risk-taking. First, findings indicated that during the discussion task, adolescents in the conflict condition evidenced a significantly greater psychophysiological stress response relative to adolescents in the control condition. Second, a neurobiological marker of behavioral disinhibition moderated the relation between discussion condition and adolescent risk-taking, such that adolescents evidencing relatively high levels of a neurobiological marker related to sensation-seeking evidenced greater levels of risk-taking following the conflict condition, relative to the control condition. Lastly, I observed no significant relation between parent-adolescent conflict, the neurobiological marker of behavioral disinhibition and adolescent engagement in real-world risk-taking behavior.