الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Toxoplasmosis is a worldwide disease caused by an obligate intracellular parasite, Toxoplasma gondii. It is a protozoan belonging to the phylum Apicomplexa. The parasite is capable of infecting many species of mammals, including man, and birds. It is globally distributed, transmitted by eating raw or undercooked meat containing tissue cysts or through ingesion of oocysts form soil contaminated with infected cat’s feces. Toxoplasmosis can be also transmitted transplacentally, accidentally in the laboratory, through blood transfusion or organ transplantation.
Infection with this parasite can evoke different types of clinical manifestations varying from asymptomatic self limited infection to a fatal disease. This is particularly evident in neonates and in immunocompromised patients where it can be considered as one of the most common opportunistic infections. The diagnosis of such cases as well as their prevention are of prime importance.
Vaccination trials with live attenuated, killed, antigen fractions or lastly DNA vaccines have been made with varying success.
In this study two types of killed vaccines were tried, Autoclaved Toxoplasma vaccine and Toxoplasma lysate vaccine in combination with Freund’s incomplete adjuvant (FIA). The efficacy of each vaccine was studied in both immunocompetent and immunosuppressed mice.
The virulent RH-strain of T. gondii was used to carry out this study and was maintained in the laboratory by serial intraperitoneal passage in mice. This strain was used for animal inoculation and vaccine preparation. FIA was used in combination with each vaccine to enhance the immune response . Cyclophosphamide in a dose of 70 mg/kg twice seven days apart was used for immunosuppression which was maintained by the same dose every two weeks over the whole period of the experiment.
Animals were divided into two main groups: control and experimental groups. The control group was subdivided into five subgroups: normal non-infected, infected immunocompetent, adjuvant infected immunocomptent, infected immunosuppressed and adjuvant infected immunosuppressed control subgroups. The experimental groups included two main groups: immunocompetent and immunosuppressed vaccinated groups which were further subdivided into subgroups receiving autoclaved Toxoplasma vaccine and subgroups receiving Toxoplasma lysate vaccine. Each experimental subgroup received three doses of each vaccine on days one, ten and the last dose was on day 30, then challenge with Toxoplasma tachyzoites was done four weeks after the last immunization dose. Vaccination was done subcutaneously over the sternum. Immunocompetent animals were sacrificed five days post challenge and for immunosuppressed animals three days post challenge.
Assessment of vaccine efficacy were done through parasitological, histopathological and immunological studies. Parasitological studies included; survival rate parasite count from; liver, lung, spleen, and brain. Histopathologic studies was done for the following organs; lymph nodes, liver, lung, spleen, and brain. Immunological assay was through counting CD8+ T-cell.
Immunocompetent mice that received autoclaved Toxoplasma vaccine showed the highest survival rate with maximum survival time of 13 days, followed by immunocompetent mice that received Toxoplasma lysate vaccine with maximum survival time of eight days. Also immunosuppressed vaccinated group, showed higher survival rates as compared to their control counterparts.
Parasite count which were done in impression smears of liver, lung, spleen, and brain showed statistically significant reduction in experimental groups whether immunocompetent or immunosuppressed when compared to their control counterparts. Histopathologic examination of different organs showed lesser areas of necrosis, inflammatory infiltrate and less frequent tachyzoite collections in experimental groups. Immunological assay showed statistically significant increase in the mean percentage of CD8+ T-cells, in experimental groups, as regards to their control counterpart.
Regarding all evaluation parameters, experimental groups received autoclaved Toxoplasma vaccine whether immunocompetent or immunosuppressed showed significantly better results when compared to experimental groups received Toxoplasma lysate vaccine.
Therefore, results of this study encourage continuation of the task to assess the efficacy of such vaccines against avirrulent Toxoplasma strain and congenital toxoplasmosis.