K24 T. gondii isolate is a hybrid and has the virulence of lineage I isolates
1Department of Biology and Wildlife Diseases, University of Veterinary and Pharmaceutical Sciences, Brno, Czech Republic. bartovae@vfu.cz
Abstract:
A permanently high virulence was found in tachyzoites of T. gondii K24 after serial passage in mice (90 passages during 324 days). Virulence tests revealed that a single tachyzoite of the 50th passage represented LD100 for mice. Analysis of genotype of K24 isolate was done by PCR/RFLP with ROP1/Ddel, SAG1/Ddel, 850/Rsal and IGS/Rsal and by RFLP/DNA with TGR1E sequence and Pstl enzyme. K24 isolate had an atypical genotype, with an association of type II (for ROP1, SAG1 genes and TGR1E sequence) and type I (for 850 gene) alleles, and a new pattern observed for IGS. All tested PCR/RFLP did not change through 2, 10, 20, 28, 40, 50, 60, 70, 81 and 90 tested passages. In RFLP/DNA with Pstl enzyme and TGR1E probe, K24 isolate produced a pattern with seven fragments of the size ranging from one to 23 kb and did not change through 7, 56, 70 and 83 tested passages. K24 T. gondii isolate is a hybrid and has the virulence of lineage I isolates.
Insights
Toxoplasma gondii K24 tachyzoites maintained high virulence in mice over 90 passages. Genetic analysis revealed an atypical hybrid genotype, combining Type II and Type I alleles, consistent with high virulence.
Area of Science:
- Parasitology
- Genetics
- Infectious Diseases
Background:
- Toxoplasma gondii is an opportunistic parasite with varying virulence.
- Understanding the genetic basis of virulence is crucial for disease control.
Purpose of the Study:
- To investigate the long-term virulence and genetic stability of the T. gondii K24 isolate in a mouse model.
- To characterize the genotype of the K24 isolate and its correlation with virulence.
Main Methods:
- Serial passage of T. gondii K24 tachyzoites in mice for 90 passages.
- Virulence assays to determine the lethal dose (LD100).
- Genotyping using PCR/RFLP and RFLP/DNA with specific gene targets (ROP1, SAG1, 850, IGS, TGR1E) and enzymes (DdeI, RsaI, PstI).
Main Results:
- The T. gondii K24 isolate consistently exhibited high virulence, with one tachyzoite of the 50th passage being lethal (LD100) to mice.
- Genetic analysis revealed an atypical hybrid genotype, with Type II alleles for ROP1, SAG1, and TGR1E, and a Type I allele for the 850 gene.
- The observed genotype remained stable throughout all tested passages, indicating genetic consistency.
Conclusions:
- The T. gondii K24 isolate is a stable hybrid with a genotype associated with high virulence, characteristic of lineage I isolates.
- This study highlights the genetic stability of virulence factors in T. gondii under prolonged host passage.
