Identification of a Sporozoite-Specific Antigen from Toxoplasma gondii

Abstract

Reduction of risk of human and food animal infection with Toxoplasma gondii is hampered by the lack of epidemiological data documenting the predominant routes of infection (oocyst versus tissue cyst consumption) in horizontally transmitted toxoplasmosis. Existing serological assays can determine previous exposure to the parasite, but not the route of infection. We have used difference gel electrophoresis in combination with tandem mass spectroscopy and Western blot to identify a sporozoite-specific protein (Toxoplasma gondii embryogenesis-related protein, TgERP) which elicited antibody and differentiated oocyst- versus tissue cyst-induced infection in pigs and mice. The recombinant protein was selected from a cDNA library constructed from T. gondii sporozoites, and this protein was used in Western blots and probed with sera from T. gondii infected humans. Serum antibody to TgERP was detected in humans within 6–8 mo of initial oocyst-acquired infection. Of 163 individuals in the acute stage of infection (anti-Toxoplasma IgM detected in sera, or <30 in the IgG avidity test), 103 (63.2%) had detectable antibodies that reacted with TgERP. Of 176 individuals with unknown infection route and in the chronic stage of infection (no anti-Toxoplasma IgM detected in sera, or >30 in the IgG avidity test), antibody to TgERP was detected in 31 (17.6%). None of the 132 uninfected individuals tested had detectable antibody to TgERP. These data suggest that TgERP may be useful in detecting exposure to sporozoites in early Toxoplasma infection and implicates oocysts as the agent of infection.

Epidemiology of and Diagnostic Strategies for Toxoplasmosis

“…Persons may be unaware of their exposure or may have difficulty recalling specific risks that occurred. The recent discovery of a sporozoite-or oocyst-specific protein, which elicited antibody production and differentiated oocyst-versus tissue cyst-induced experimental infection in pigs and mice, may help to solve this problem (168). Serum antibodies to the sporozoite protein were detected in humans within 6 to 8 months of an initial oocystacquired infection.…”

Toxoplasma gondii Seroprevalence in the United States 2009–2010 and Comparison with the Past Two Decades

“…Recent findings by Dr. Hill and colleagues using a sporozoite antigen test suggest that the oocyst form of T. gondii, which is associated with soil and cat feces exposure, may be responsible for a majority of human infections in the United States. 22,23 If this is currently the case, one possibility is that some of the reduction in human exposure to T. gondii in the past 20 years was caused by a reduction of T. gondii in meats such as pork, which has been documented, 24 or less exposure from meat in general because of changes in preparation or freezing practices. An increase in frozen pre-prepared meals and freezing of meat helps reduce exposure to infectious T. gondii cysts because cysts are inactivated by adequate freezing.…”

Diagnosis, Treatment, and Prevention of Congenital Toxoplasmosis in the United States

“…53 Recent studies suggested that oocysts were the predominant route of transmission of T gondii infections in the United States; 78% (59 of 76) of pregnant women with acute primary T gondii infections during pregnancy who gave birth to infants with CT had serologic evidence suggestive of being infected by oocysts. 23,54 Different types of locally produced meat from retail meat stores in the United States (eg, pork, lamb, goat, wild game meat) have been found to be contaminated with T gondii. 39, 46, 56 -59 Moreover, with the globalization of the food market, imported meats from other countries (that could be infected even with atypical, more virulent T gondii strains) also can be found in the United States and Europe.…”