Giardia duodenalis, a flagellated parasitic protozoan, the most common cause of parasite-induced diarrheal diseases worldwide. Codon usage bias (CUB) is an important evolutionary character in most species. However, G. duodenalis CUB remains unclear. Thus, this study analyzes codon usage patterns to assess the restriction factors and obtain useful information in shaping G. duodenalis CUB. The neutrality analysis result indicates that G. duodenalis has a wide GC3 distribution, which significantly correlates with GC12. ENC-plot result—suggesting that most genes were close to the expected curve with only a few strayed away points. This indicates that mutational pressure and natural selection played an important role in the development of CUB. The Parity Rule 2 plot (PR2) result demonstrates that the usage of GC and AT was out of proportion. Interestingly, we identified 26 optimal codons in the G. duodenalis genome, ending with G or C. In addition, GC content, gene expression, and protein size also influence G. duodenalis CUB formation. This study systematically analyzes G. duodenalis codon usage pattern and clarifies the mechanisms of G. duodenalis CUB. These results will be very useful to identify new genes, molecular genetic manipulation, and study of G. duodenalis evolution.

Neosporosis is caused by Neospora caninum (N. caninum), which mainly infects cattle and goats and severely threatens the animal industry. In this study, the inhibitory effects of polyclonal antiserum anti-NcSRS17, NcSRS2 and NcSRS52 were explored. Cytokines in mice or goat serum were detected after immunization. After infection, the survival of mice was recorded. The pathological changes and parasite loads were observed and detected in tissues. The results showed that anti-NcSRS2, NcSRS17 and NcSRS52 antibodies all inhibit the invasion and proliferation of N. caninum. The IFN-γ level in the NcSRS17 group was higher than that in the NcSRS2 and NcSRS52 groups, and higher in the NcSRS2-mIL-18 group than in the NcSRS2 group. The survival rates of mice were 16% in the positive control group, 67% in the SRS52 group, 83% in the SRS2 and mIL-18 groups and 100% in the SRS17 and SRS2-mIL-18 groups. Goats immunized with NcSRS17-gIL-18 developed high levels of IL-4, IL-12 and IFN-γ compared with those immunized with NcSRS-17. Parasite loads in the brains of animals in the NcSRS17 and NcSRS17-gIL-18 groups were significantly reduced, and were significantly lower in the NcSRS17-gIL-18 group (p ≤ 0.01). This study indicates that SRS17 may be an antigen candidate for vaccine development against neosporosis, and IL-18 can enhance the immune protective efficiency of antigen candidates.

Chicken coccidiosis is a parasitic disease caused mainly by Eimeria tenella, Eimeria acervulina, Eimeria maxima, and Eimeria necatrix, with most cases presenting as mixed infections. Currently, although a subunit vaccine (CoxAbic) targeting Eimeria maxima via maternal immunization is commercially available, no genetically engineered multivalent subunit vaccine exists against mixed infections caused by these four Eimeria species simultaneously. Therefore, we developed a tetravalent recombinant subunit vaccine (designated TEIN) by fusing key antigen genes (TA4, 3-1E, IMP1, NA4) from these four Eimeria species and expressing the construct in Pichia pastoris. A total of 500 chickens were randomly allocated into 25 experimental subgroups (n = 20 each), consisting of five groups (control, challenged, adjuvant, pPIC9K, and TEIN) and five challenge conditions (infection with Eimeria tenella, Eimeria acervulina, Eimeria maxima, Eimeria necatrix, or a mixture of four species). Immunization was performed via leg intramuscular injection at 14 and 21 days of age. At 28 days of age, all chickens except the controls were orally challenged with 1 × 10⁴ sporulated oocysts. Statistical analysis was performed using one-way or two-way ANOVA as appropriate. Results showed that chickens vaccinated with the TEIN subunit vaccine exhibited significantly elevated serum levels of IgY, IL-2, IL-10, and IFN-γ, as well as an increased splenic lymphocyte CD4⁺/CD8⁺ ratio. The anticoccidial indices (ACI) against Eimeria tenella, Eimeria acervulina, Eimeria maxima, and Eimeria necatrix, and their mixed infection reached 174.82, 174.58, 174.41, 180.61, and 175.95, respectively. Moreover, no significant differences were observed in hematological parameters, serum biochemical markers, or histopathological findings between the vaccinated and control groups. These results demonstrate the vaccine’s potential as a promising candidate for controlling mixed coccidial infections.

The impact of neosporosis on the livestock industry has worsening each year. Globally, annual losses were estimated to exceed $2.4 billion, with abortion rates reaching up to 47 % in affected herds. But no effective vaccines or drugs are currently available for prevention and treatment. This study aimed to investigate the inhibitory effects of emodin on Neospora caninum (N. caninum) infection and its potential mechanisms. The appropriates safe concentration of emodin was determined by the Cell Counting Kit-8 (CCK-8) assay. The anti-N. caninum effects of emodin in Vero cells, MDBK cells, macrophages, as well as the combined effects of emodin and niclosamide in Vero cells, were further verified using qPCR or Giemsa staining. Subsequently, the effects of direct incubation of tachyzoites with emodin on N. caninum invasion and proliferation were also examined. The activation of necroptosis by emodin was evaluated by measuring Lactate Dehydrogenase (LDH) levels in the supernatant and assessing cellular pMLKL levels. The CCK-8 results indicated that emodin exhibited low toxicity to Vero cells, MDBK cells, and macrophages. The qPCR results showed that emodin reduced the number of N. caninum in Vero cells, MDBK cells, and macrophages. Giemsa results showed that the number of tachyzoites within the parasitophorous vacuole was decreased accordingly. Notably, emodin directly affected tachyzoites, reducing its invasion capability by 55 %-63 % and its proliferation capacity by 62 %-88 %. Additionally, the combination of emodin with niclosamide significantly enhanced its antiparasitic effects compared with emodin alone. Western blot analysis showed that emodin significantly increased pMLKL levels and enhanced LDH release, assisting N. caninum in activating necroptosis. However, the inhibitory effects of emodin on N. caninum invasion and proliferation were not significantly altered in Mlkl^-/- macrophages. In conclusion, emodin inhibited N. caninum infection may through a necroptosis-independent mechanism by directly targeting the parasite, highlighting its potential as a therapeutic candidate for neosporosis.