Progress 07/01/02 to 06/30/05
Outputs
Brucella abortus strain RB51 expressing the surface antigen of T. gondii TgSAG2 and excretory/secretory granules (syn. Dense granule) TgGRA2 and TgGRA6 antigens was genetically engineered. Western blots confirmed that the appropriate antigens were incorporated in to the B. abortus vaccine. Groups of C3H/HeJ mice were immunized subcutaneously using these candidate vaccines, or 200 gy irradiated RH strain tachyzoites and challenged orally with 25 tissue cysts of the VEG strain of T. gondii. The ability of vaccinated mice to protect against tissue cyst formation was evaluated 4 weeks post challenge. Results indicated that only mice vaccinated with irradiated tachyzoites had significantly (P less than 0.05) fewer tissue cysts than non-vaccinated controls.
Impacts
Our studies indicate that vaccination against T. gondii is possible. Single antigen vaccines are less effective that are inactivated (irradiated) vaccines. Future work on antigen delivery and antigen expression by Brucella abortus RB51 strain is needed.
Publications
- Bandara, A. M. N. Selem, C. N.Jordan, G. G. Shurig, N. Sriranganathan, and D. S. Lindsay. 2006. Vaccination of mice with Brucella abortus strain RB51 expressing TgSAG2, TgGRA2 and TgGRA6 antigens of Toxoplasma gondii. J. Eukaryotic Microbiology. supplement from the International Workshops on Opportunistic Protists, Lisbon, Portugal (in press).
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Progress 10/01/03 to 09/30/04
Outputs
Toxoplasma gondii is an important opportunistic protozoan parasite. Most animals develop resistance to T. gondii infection and associated T helper 1 (Th1) cell mediated responses leading to protective immunity. We examined a novel approach to vaccination using Brucella abortus strain RB51 to deliver protective antigens of T. gondii intracellularly, in a manner mimicking natural infection. The TgSAG2, TgGRA2 and TgGRA6 antigens of T. gondii were chosen for incorporation into the vaccine strain of B. abortus RB51 and examined for their demonstrated ability to induce protective immunity. A plasmid, pNSGroE, was used for the expression of putative T. gondii protective antigens. Groups of 5 each, female C3H/HeJ mice were immunized using these candidate vaccines, or 200 gy irradiated RH strain tachyzoites and challenged orally with 25 tissue cysts of the VEG strain of T. gondii. The ability of vaccinated mice to protect against tissue cyst formation was evaluated 6 weeks
post challenge. Mortality occured in all vaccinated groups and in controls. Results indicated that only mice vaccinated with irradiated tachyzoites had significantly (P less than 0.05) fewer tissue cysts than non-vaccinated controls. These preliminary vaccine-challenge studies did not demonstrate substantial protection against clinical signs or indicate a reduction in tissue cyst numbers in vaccinated mice when compared to non-vaccinated controls. This may have been due to lack of high expression of the inserted T. gondii genes. Irradiated T. gondii tachyzoites offered protection from clinical disease and reduced the numbers of tissue cysts in vaccinated mice. This is similar to results found by others in the past using irradiated tachyzoites and indicates that irradiated tachyzoites can serve as a good positive control in vaccine studies. Future studies will seek ways to increase expression of the T. gondii genes placed in B. abortus RB51 and on placing additional potentially
protective T. gondii genes in B. abortus RB51.
Impacts
Toxoplasmosis is the third leading cause of death due to foodborne pathogens in the United State. It has been estimated that two-thirds of all human toxoplasmosis cases are caused by ingestion of infected meat. Potentially meat from any warm-blooded vertebrate can contain T. gondii tissue cysts. Studies indicate that T. gondii tissues can survive for many years and probably the life of infected animals. A vaccine that prevents tissue cyst formation would greatly reduce the prevalence of T. gondii in meat.
Publications
- Bandara, A.M., M. N. Selem, C. N. Jordan, G. G. Shurig, D. S. Lindsay, and N. Sriranganathan. 2004. Brucell abortus strain RB51 expressing antigens of Toxoplasma gondii as a potential dual vaccine. American Society for Tropical Medicine and Hygiene annual meeting (Miami, FL, Nov).
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Progress 07/01/02 to 06/30/03
Outputs
Researchers at Virginia Tech have successfully used PCR to obtain 8 genes from Toxoplasma gondii for use as potential vaccines. The surface associated genes TgSAG1, TgSAG2, TgSRS1 and TgSRS2 and dense granule genes TgGRA2, TgGRA5, TgGRA6 and TgGRA7 were selected because they have shown promise in other systems. Seven of the 8 genes (all but SRS2) have been placed into pBBGroE vectors and introduced in E. coli. We have successfully moved 4 of these genes (TgSAG2, TgSRS1, TgGRA2, and TgGRA6) from E. coli in to the B. abortus RB51 vaccine strain. Expression of all 4 have been confirmed by western blot. Additional work is under way to confirm expression of the other genes. Vaccine and challenge studies will be done with these constructs in December of 2003.
Impacts
Toxoplasmosis is the third leading cause of death due to foodborne pathogens in the United State. It has been estimated that two-thirds of all human toxoplasmosis cases are caused by ingestion of infected meat. Potentially meat from any warm-blooded vertebrate can contain T. gondii tissue cysts. Studies indicate that T. gondii tissues can survive for many years and probably the life of infected animals. A vaccine that prevents tissue cyst formation would greatly reduce the prevalence of T. gondii in meat.
Publications
- No publications reported this period
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Progress 07/01/02 to 10/24/02
Outputs
We have identified potentially protective Toxoplasma gondii antigens and obtained the appropriate DNA sequences. We have conducted one pilot study and determined that vaccination with our bacterial vector alone has no protective effect against toxoplasmosis in mice.
Impacts
If successful our recombinant vaccines will help protect consumers against toxoplasmosis by reducing their exposure to infected meat.
Publications
- No publications reported this period
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