Farooq Riaz (2008-VA-231)

Isolation Of Surface Antigen 1 Gene Of Toxoplasma Gondii And Its Cloning In The Expression Plasmid - 2015. - 47p.;

Toxoplasma gondii is an obligate intracellular protozoan parasite which comes under the classification of phylum Apicomplexa, subclass Coccidiasina (Cornelissen et al. 1984). Toxoplasmosis is one of the more common parasitic zoonoses world-wide caused by Toxoplasma gondii which is a facultatively heteroxenous, polyxenous protozoon that has developed several potential routes of transmission within and between different host species (Tenter et al. 2000). It is the most important source of toxoplasmosis in humans and animals, with cat as definite host and warm-blooded animals as intermediate host (Frenkel et al. 1970). It was first described by Nicolle, Manceaux and Splendore in 1908 from rodents Ctenodactylus gondii (Black and Boothroyd 2000).
Toxoplasmosis is a worldwide parasitic disease and it is estimated that about one-third total population of the world is seropositive for Toxoplasma gondii (Tenter et al. 2000). Prevalence of infection varies between countries, geographical areas and ethnic groups living within a specific region. In Humans, infection rates range from 50% to 83% in Brazil (Tenter et al. 2000; Dubey et al. 2012). Seropositivity of Toxoplasma gondii in China is about 8% with continuously increase while in USA its 10-15%, 50-70% in France and 20% in UK (Dubey and Jones 2008; Zhou et al. 2008; Jones et al. 2009). Prevalence of toxoplasmosis is higher in males (79%) as compared to females (63.4%) and the age dependent sero-prevalence reaches >92% in age group of 40 to 50 (Coêlho et al. 2003).
Transmission occurs through the ingestion of contaminated vegetable /water with oocysts, as well as the ingestion of contaminated raw/undercooked meat with tissue cysts (Gajadhar et al. 2006). Transmission may also occurs by ingestion of sporulated oocysts, or bradyzoites within cysts present in the tissues of numerous food animals (Esteban-Redondo et al. 1999). In humans, transmission of Toxoplasma gondii happens mainly by eating raw or undercooked contaminated meat, raw cow’s milk and birds eggs, swallowing oocysts dis-charged in feces of infected cats, inoculation of trophozoites through the skin, or by inhalation (Wallace 1971; Wallace 1973; Bannister 1982).
In humans, mostly infections (congenitally or post-natally acquired) are asymptomatic. Congenital infection occurs only when a woman becomes infected during pregnancy. Congenital infections acquired during the first trimester are more severe than those acquired in the second and third trimester (Desmonts and Couvreur 1974). The main clinical signs associated with toxoplasmosis are anorexia, weight loss, lethargy, dyspnea, ocular signs, pyrexia, vomiting and diarrhea, jaundice, myositis, encephalitis and abortion. Humans become infected when they ingest the toxoplasma at infective stages (oocysts and tissue cysts) found in some cat feces and in raw meats.
In addition to being hazardous to livestock animals, the T. gondii infection is also important due to its zoonotic implications (Jittapalapong et al. 2005). Congenital abnormalities in humans, such as microcephaly, hydrocephaly, chorioretinitis, convulsion, cerebral calcification, epilepsy, blindness, deafness, and mental retardation may occur if the mother acquires infection during pregnancy (Jones et al. 2003). In addition to congenital anomalies, T. gondii also causes severe neuropathologic infections in immuno-compromised hosts, such as AIDS and cancer patients receiving chemotherapy (Del Valle and Piña-Oviedo 2005).
Seroprevalence studies of T. gondii among domestic animals in South-Western Pakistan has indicated considerable prevalence (25% in cattle, 2.5% sheep) (Zaki 1995) and suggesting potential transmission to the human community. Small scale study in urban area of Rahim Yar Khan (Punjab), Pakistan has revealed that the overall prevalence of toxoplasmosis in food animals is 19% (Ramzan et al. 2009). Another study has already been published that untreated patients with leprosy in Pakistan have shown significant seroprevalence (29.6%) of antibodies against T. gondii (Hussain et al. 1992).
Vaccine against toxoplasmosis is not available yet with one exception (“Toxovax” for sheep). Vaccine against T. gondii in animals used for human consumption may block the possible transmission to humans (Bhopale 2003). SAG1, among one of the major antigenic components of Toxoplasma gondii is a major surface antigen identified on the surface membrane of this parasite using a monoclonal antibody (Handman et al. 1980). SAG1 is an important surface antigen, expressed by tachyzoite form of T. gondii and is a putative candidate for vaccine and diagnostic against toxoplasmosis (Sharma et al. 1983; Godard et al. 1990). Immunization with SAG1 adjuvanted with saponin Quil A or incorporated in lysosomes provided total protection after challenge (Bülow and Boothroyd 1991; Khan et al. 1991). SAG1 is single copy gene with no introns (Burg et al. 1988), regulates both humoral as well as cellular Th1 immune responses (Liu et al. 2008) and is powerful candidate for vaccine against toxoplasmosis. SAG1 is a potent candidate of diagnostics for detection of serum antibodies against toxoplasmosis in Man and animals (Abu-Zeid 2002).

Department of Parasitology


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