Evaluation of antigenic variations between two virulent toxoplasma strains

Role of landscape context in Toxoplasma gondii infection of invasive definitive and intermediate hosts on a World Heritage Island

Free-ranging cats are invasive species threatening biodiversity worldwide. They may also impose an environmental risk to humans and livestock through the transmission of zoonotic diseases. We investigated antibody levels against Toxoplasma gondii in free-ranging cats and black rats (definitive and representative intermediate hosts) by ELISA and determined their relationships with landscape environmental factors on Tokunoshima Island, Japan, the Natural World Heritage site. We found a higher seroprevalence (>70%) in both cats and black rats in landscapes where the cattle barn density was high. This was consistent with higher density of rats revealed in our trapping survey. The spatial scale of landscape factors affecting infection was broader in cats (1 km buffer radius) than in black rats (100 m buffer radius). Both cats and rats showed an increasing trend in optical density (OD) values with increasing body weight and landscape cattle barn density, suggesting that the antibody concentration increases as the chance of exposure to T. gondii in the environment increases. Thus, management actions to stop humans from feeding cats and to control rat populations without using cats are both necessary to reduce the human health risk as well as to conserve endangered species on the island.

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High seroprevalence of T. gondii was found in cats and black rats on an island.

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Seroprevalence was high (>70%) in landscapes where there were many cattle barns.

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Antibody level in cats was lower in forests and higher around residential areas.

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Spatial scale of environmental factors affecting infection was broader in cats.

Diagnostic value of recombinant nanoluciferase fused Toxoplasma gondii antigens in Luciferase-linked Antibody Capture Assay (LACA) for Toxoplasma infection in pigs

Toxoplasmosis is a widespread protozoan zoonosis. Since ingesting undercooked meat harboring Toxoplasma gondii cyst is considered one of the major transmission routes to humans, the screening of T. gondii in meat-producing animals can reduce the risk of food-borne toxoplasmosis in humans. Among serological diagnostic methods, Luciferase-linked Antibody Capture Assay (LACA) has been found to be a promising platform with high sensitivity and specificity. In this study, we aimed to evaluate recombinant nanoluciferase fused-T. gondii antigens (rNluc-GRA6, rNluc-GRA7, rNluc-GRA8 and rNluc-BAG1) for their potential use in LACA for pigs. As a result, the sensitivity of GRA6-, GRA7-, GRA8- and BAG1-LACA were 70.0%, 80.0%, 80.0% and 30.0% with specificity 87.0%, 81.5%, 74.1% and 50.0%, respectively. The cocktail LACA using a mixture of rNluc-GRA6, rNluc-GRA7 and rNluc-GRA8 indicated higher sensitivity (90.0%) and a similar specificity (96.3%) in comparison with the commercial ELISA kit. Compared to the Dye-Test as a reference test, cocktail LACA showed strong agreement (kappa value=0.811) when we assessed pig sera collected at the slaughterhouse. In addition, we also successfully established the rapid LACA format for the detection of Toxoplasma infection in pigs (called Rapid-LACA) in which the test could be performed within 30 min. In Rapid-LACA, the protein A pre-coated/blocked plates could be preserved at −30°C, 4°C or room temperature conditions for at least two months without compromising on the quality of assay.

Prevalence of serum antibodies to Toxoplasma gondii in free-ranging cats on Tokunoshima Island, Japan

The prevalence of Toxoplasma gondii infection in free-ranging cats on Tokunoshima Island was assessed by testing 125 serum samples using anti-T. gondii IgG indirect enzyme-linked immunosorbent assay. The overall seropositivity rate was 47.2% (59/125). Seropositivity rates in cats with body weight >2.0 kg (57.4%) were significantly higher than in those with body weight ≤2.0 kg (12.5%, P<0.01). Analysis of the number of seropositive cats by settlement revealed the presence of possibly-infected cats in 17 of 23 settlements, indicating the widespread prevalence of T. gondii on the island. This is the first study to show the seroprevalence of T. gondii in free-ranging cats on Tokunoshima Island. The information revealed in this paper will help to prevent the transmission of T. gondii among cats and also in both wild and domestic animals and humans on the island.

A review of toxoplasmosis in humans and animals in Turkey

Infections by the protozoan parasite Toxoplasma gondii are widely prevalent in humans and animals in Turkey but little is known of the burden of their clinical toxoplasmosis. Many early papers on toxoplasmosis in Turkey were published in Turkish and often not available widely. Here, we review prevalence, clinical spectrum, epidemiology and diagnosis of T. gondii in humans and animals in Turkey. This knowledge should be useful to biologists, public health workers, veterinarians and physicians. Although one-third of the human population in Turkey is seropositive, the rate of congenital toxoplasmosis is unknown and no information is available in children 12 years old or younger. One large outbreak of acute toxoplasmosis has been reported in 14–18-year old school children in Turkey. An alarming rate (36%) of T. gondii tissue cysts were reported in tissues of sheep and water buffalo meats destined for human consumption; these reports require verification. Genetically, T. gondii strains from domestic cats and wild birds in Turkey were generally classical type II and III, like those prevalent in Europe. A separate genotype, Type 1 Africa, was isolated from two congenitally infected children and a domestic cat in Turkey.

Significance of a common 65 kDa antigen in the experimental fasciolosis and toxoplasmosis

In the current study, cross-reaction between two important zoonotic parasites; extracellular helminthes Fasciola gigantica and intracellular protozoa Toxoplasma gondii was proved by enzyme linked immunosorbent assay. Five antigens were used to identify and compare the cross-binding activities in the prepared antisera. Two F. gigantica antigens; adult flukes (FgA) and eggs (FgEA) were used to detect IgG in T. gondii naturally infected human sera (TgIHS) and experimentally infected sera of sheep (TgISS), mice (TgIMS) and rats (TgIRS). Three types of T. gondii antigens; RH (TgRHA), local sheep isolate (TgLA) and ME49 isolate (TgMEA) were used to detect cross binding activities in F. gigantica experimental infected rabbit sera (FgIRS) and F. gigantica naturally infected bovine sera (FgIBS). The cross-binding activities in the prepared antisera were strongly directed towards FgA and TgLA rather than the other antigens. The characterization of the five antigens using SDS-PAGE showed 4 common bands of FgA and TgLA; 165, 97, 76, and 65 kDa. While two common bands were observed between TgRHA, TgMEA and FgA; 165, and 65 kDa. Whereas, two common bands found between three types of T. gondii antigens and FgEA were identified; 165 and 65 kDa. The immunogenic cross-reactive bands between FgA and TgLA with F. gigantica infected bovine sera were identified by immunoblot. In FgA, the common immunogenic bands were 165, 65 and 14 kDa. While in TgLA, common immunogenic bands were 165 and 65 kDa. Whereas, the common immunogenic band between FgA and TgLA identified with T. gondii experimentally infected sheep sera was 65 kDa. The current research proves cross reaction between F. gigantica and T. gondii. One common band of 65 kDa showed broad immunogenic cross-reactivity with the developed antisera raising the prospect of being putative common immunodiagnostic candidate of both infections.

Ginsenoside Rg1 enhances immune response induced by recombinant Toxoplasma gondii SAG1 antigen

Ginsenoside, the most important component isolated from Panax ginseng, exhibits a variety of biological activities. Particularly, ginsenoside Rg1 is known to have immune-modulating activities such as increase of immune activity of T helper (Th) cells. In the present study, we evaluated the immunomodulatory potentials of the Rg1 at three dose levels on the cellular and humoral immune responses of ICR mice against T. gondii recombinant surface antigen 1 (rSAG1). ICR mice were immunized subcutaneously with 50 μg Rg1 alone, 100 μg rSAG1 alone or with 100 μg rSAG1 dissolved in saline containing ginsenoside Rg1 (10 μg, 50 μg or 100 μg). After immunization, we evaluated the immune response using lymphoproliferative assay, cytokine and antibody measurements, and the survival times of mice challenged lethally. The results showed that the groups immunized with rSAG1 and Rg1 (50 μg, 100 μg) developed a high level of specific antibody responses against T. gondii rSAG1, a strong lymphoproliferative response, and significant levels of cytokine production, compared with the other groups. After lethal challenge, the mice immunized with the rSAG1 and Rg1 (50 μg, 100 μg) showed a significantly increased survival time compared with control mice which died within 6 days of challenge. Our data demonstrate that by addition of ginsenoside Rg1, the rSAG1 triggered a stronger humoral and cellular response against T. gondii, and that Rg1 is a promising vaccine adjuvant against toxoplasmosis, worth further development.

The origin of intraspecific variation of virulence in an eukaryotic immune suppressive parasite

Occurrence of intraspecific variation in parasite virulence, a prerequisite for coevolution of hosts and parasites, has largely been reported. However, surprisingly little is known of the molecular bases of this variation in eukaryotic parasites, with the exception of the antigenic variation used by immune-evading parasites of mammals. The present work aims to address this question in immune suppressive eukaryotic parasites. In Leptopilina boulardi, a parasitic wasp of Drosophila melanogaster, well-defined virulent and avirulent strains have been characterized. The success of virulent females is due to a major immune suppressive factor, LbGAP, a RacGAP protein present in the venom and injected into the host at oviposition. Here, we show that an homologous protein, named LbGAPy, is present in the venom of the avirulent strain. We then question whether the difference in virulence between strains originates from qualitative or quantitative differences in LbGAP and LbGAPy proteins. Results show that the recombinant LbGAPy protein has an in vitro GAP activity equivalent to that of recombinant LbGAP and similarly targets Drosophila Rac1 and Rac2 GTPases. In contrast, a much higher level of both mRNA and protein is found in venom-producing tissues of virulent parasitoids. The F1 offspring between virulent and avirulent strains show an intermediate level of LbGAP in their venom but a full success of parasitism. Interestingly, they express almost exclusively the virulent LbGAP allele in venom-producing tissues. Altogether, our results demonstrate that the major virulence factor in the wasp L. boulardi differs only quantitatively between virulent and avirulent strains, and suggest the existence of a threshold effect of this molecule on parasitoid virulence. We propose that regulation of gene expression might be a major mechanism at the origin of intraspecific variation of virulence in immune suppressive eukaryotic parasites. Understanding this variation would improve our knowledge of the mechanisms of transcriptional evolution currently under active investigation.