Parasite distribution and associated immune response during the acute phase of Toxoplasma gondii infection in sheep

Evaluation of the Protective Efficacy of Different Doses of a Chlamydia abortus Subcellular Vaccine in a Pregnant Sheep Challenge Model for Ovine Enzootic Abortion

Chlamydia abortus causes the disease ovine enzootic abortion, which is one of the most infectious causes of foetal death in small ruminants worldwide. While the disease can be controlled using live and inactivated commercial vaccines, there is scope for improvements in safety for both sheep and human handlers of the vaccines. We have previously reported the development of a new prototype vaccine based on a detergent-extracted outer membrane protein preparation of C. abortus that was determined to be more efficacious and safer than the commercial vaccines when administered in two inoculations three weeks apart. In this new study, we have developed this vaccine further by comparing its efficacy when delivered in one or two (1 × 20 µg and 2 × 10 µg) doses, as well as also comparing the effect of reducing the antigen content of the vaccine by 50% (2 × 5 µg and 1 × 10 µg). All vaccine formulations performed well in comparison to the unvaccinated challenge control group, with no significant differences observed between vaccine groups, demonstrating that the vaccine can be administered as a single inoculation and at a lower dose without compromising efficacy. Future studies should focus on further defining the optimal antigen dose to increase the commercial viability of the vaccine.

Screening of apical membrane antigen-1 (AMA1), dense granule protein-7 (GRA7) and rhoptry protein-16 (ROP16) antigens for a potential vaccine candidate against Toxoplasma gondii for chickens

Toxoplasmosis is a zoonotic disease caused by the protozoan parasite, Toxoplasma gondii known to infect almost all animals, including birds and humans globally. This disease has impacted the livestock industry and public health, where infection of domestic animals increases the zoonotic risk of transmission of infection to humans, threatening public health. Hence the need to discover novel and safe vaccines to fight against toxoplasmosis. In the current study, a novel multiepitope vaccine was designed using immunoinformatics techniques targeting T. gondii AMA1, GRA7 and ROP16 antigens, consisting of antigenic, immunogenic, non-allergenic and cytokine inducing T-cell (9 CD8⁺ and 15 CD4⁺) epitopes and four (4) B-cell epitopes fused together using AAY, KK and GPGPG linkers. The tertiary model of the proposed vaccine was predicted and validated to confirm the structural quality of the vaccine. The designed vaccine was highly antigenic (antigenicity = 0.6645), immunogenic (score = 2.89998), with molecular weight of 73.35 kDa, instability and aliphatic index of 28.70 and 64.10, respectively; and GRAVY of -0.363. The binding interaction, stability and flexibility were assessed with molecular docking and dynamics simulation, which revealed the proposed vaccine to have good structural interaction (binding affinity = -106.882 kcal/mol) and stability when docked with Toll like receptor-4 (TLR4). The results revealed that the Profilin-adjuvanted vaccine is promising, as it predicted induction of enhanced immune responses through the production of cytokines and antibodies critical in blocking host invasion.

Recombinant AMA1 Virus-like Particle Antigen for Serodiagnosis of Toxoplasma gondii Infection

Toxoplasmosis diagnosis predominantly relies on serology testing via enzyme-linked immunosorbent assay (ELISA), but these results are highly variable. Consequently, various antigens are being evaluated to improve the sensitivity and specificity of toxoplasmosis serological diagnosis. Here, we generated Toxoplasma gondii virus-like particles displaying AMA1 of T. gondii and evaluated their diagnostic potential. We found that AMA1 VLPs were highly sensitive and reacted with the sera acquired from mice infected with either T. gondii ME49 or RH strains. The overall IgG and IgM antibody responses elicited by AMA1 VLPs were substantially higher than those induced by the conventionally used T. gondii lysate antigen (TLA). Importantly, AMA1 VLPs were capable of detecting parasitic infection with T. gondii RH and ME49 as early as 1 week post-infection, even when mice were exposed to low infectious doses (5 × 10³ and 10 cysts, respectively). AMA1 VLPs also did not cross-react with the immune sera acquired from Plasmodium berghei-infected mice. Compared to TLA, stronger antibody responses were induced by AMA1 VLPs when tested using T. gondii-infected human sera. The sensitivities and specificities of the two antigens were substantially different, with AMA1 VLPs demonstrating over 90% sensitivity and specificity, whereas these values were in the 70% range for the TLA. These results indicated that AMA1 VLPs can detect infections of both T. gondii ME49 and RH at an early stage of infection caused by very low infection doses in mice, and these could be used for serological diagnosis of human toxoplasmosis.

Seroprevalence of Toxoplasma gondii infection in sheep and goats from different geographical regions of the world: Systematic review and meta-analysis

The Toxoplasma gondii is an obligate intracellular protozoan parasite which significantly impact small ruminant productivity, international animal trade and transboundary movement of animal across the globe. The seroprevalence of T. gondii infection (toxoplasmosis) in sheep and goats is widely studied in many parts of the world and there is a lack of comprehensive information on prevalence estimates considering the global and regional perspectives. The aim of the study was to use systematic review and meta-analysis methods to estimate the global and regional pooled seroprevalence of T. gondii infection in sheep and goats, as well as factors that influence prevalence estimations. Relevant articles reporting the seroprevalence of toxoplasmosis in sheep and/goats were searched in five electronic databases, including PubMed, Web of Science, Scopus, Embase and ProQuest. After the publications were checked to verify they fit the inclusion criteria, a total of 225 articles were included in the systematic review and meta-analysis, reflecting data from 70 countries/regions. The pooled prevalence was estimated using a random effect meta-analysis model. Overall, the seroprevalence of T. gondii infection was 33.86% (95% CI: 30.47-37.25%) in sheep and 31.78% (95% CI: 28.99-34.58%) in goats, with significant variation in prevalence estimates across geographical locations (p < .001). Substantial heterogeneity (I²  > 75%) was observed in most pooled seroprevalence estimates. The T. gondii infection in global sheep and goat population showed uptrend over the period. This information would be useful for epidemiologist, health authorities and farmers in order to plan future T. gondii survey and infection management strategies both locally and internationally.

Advances in vaccine development and the immune response against toxoplasmosis in sheep and goats

Toxoplasmosis is a zoonotic, parasitic infection caused by the intracellular, apicomplexan parasite Toxoplasma gondii, which infects all homeothermic animals including humans. The parasite has a major economic impact on the livestock industry. This is especially true for small ruminants (sheep, goats) as it is one of the most likely reasons for reproductive disorders in these animals. Primary infection in sheep and goats can result in a fetus that is mummified or macerated, fetal embryonic death, abortion, stillbirth, or the postnatal death of neonates, all of which threaten sheep and goat rearing globally. Humans can also become infected by ingesting bradyzoite-containing chevon or mutton, or the contaminated milk of sheep or goats, highlighting the zoonotic significance of this parasite. This article reviews the advances in vaccine development over recent decades and our current understanding of the immune response to toxoplasmosis in small ruminants (sheep, and goats).

Anatomical distribution of Toxoplasma gondii in naturally and experimentally infected lambs

Consumption of raw or undercooked meat containing Toxoplasma gondii tissue cysts is one of the main sources of infection for humans worldwide. Among the various species intended for human consumption, sheep appear to be a high risk for human infection. The present study focused on the detailed anatomical distribution of Toxoplasma gondii in naturally and experimentally infected lambs using fresh and frozen samples of various pieces of meat, from a public health perspective. The first objective was to rank the edible parts intended for human consumption according to the detectable parasite burden by real-time PCR targeting the 529-bp repeated element. The second objective was to evaluate the impact of freezing by comparing the detection efficiency of the quantitative PCR between fresh and frozen tissues, as imports of lamb carcasses/cuts may arrive frozen or chilled. The highest estimated parasite loads were observed in skeletal muscles, and more particularly in edible portions such as quadriceps femoris muscle, intercostal muscles, deltoid muscle and diaphragm, with a significant difference in detectable parasite burden between fresh and frozen samples (p < 0.0001) or natural and experimental infection (p < 0.0001). Thoracic and pelvic limbs (3278-1048 parasites/g muscle) were ranked at the top of the list. Toxoplasma gondii DNA was detected in all the edible parts of lamb studied. These results suggest that lamb meat represents a risk for consumers. Further investigations are needed in order to confirm these differences in larger numbers of animals and in different breeds.

Seroprevalence of Toxoplasma gondii and Neospora caninum in sheep intended for human consumption in the Rondônia state, Western Brazilian Amazon

The aim of this study was to carry out a seroepidemiological study of anti-T. gondii and anti-N. caninum antibodies in serum samples from sheep intended for human consumption in the Rondônia state, in the Western Brazilian Amazon, and identify possible risk factors associated with seropositivity. The analysis of the 616 sheep serum samples revealed animal-level seroprevalence of T. gondii in the order of 52.4 % and of N. caninum of 60.6 %. Prevalence of co-infections was 33.4 %. The herd-level seroprevalence was 100 % for both the parasites. Applying of multivariate logistic regression analysis, test of the association between seroprevalence of T. gondii infection and the potential predictors showed that feed, fetal malformation, abortion, neurological problems (lambs), presence of rodents were the significant (P < 0.05) predictors. The variables presence of rodents, cats, wild animals and main activity showed statistical association (P < 0.05) with the seroprevalence of N. caninum. Due to the high prevalence of T. gondii and N. caninum found in this study, the absence of specific slaughterhouses for sheep and raw or undercooked sheep meat for human consumption we concluded that sheep can represent an important source of infection for humans.

Key Limitations and New Insights Into the Toxoplasma gondii Parasite Stage Switching for Future Vaccine Development in Human, Livestock, and Cats

Toxoplasmosis is a parasitic disease affecting human, livestock and cat. Prophylactic strategies would be ideal to prevent infection. In a One Health vaccination approach, the objectives would be the prevention of congenital disease in both women and livestock, prevention/reduction of T. gondii tissue cysts in food-producing animals; and oocyst shedding in cats. Over the last few years, an explosion of strategies for vaccine development, especially due to the development of genetic-engineering technologies has emerged. The field of vaccinology has been exploring safer vaccines by the generation of recombinant immunogenic proteins, naked DNA vaccines, and viral/bacterial recombinants vectors. These strategies based on single- or few antigens, are less efficacious than recombinant live-attenuated, mostly tachyzoite T. gondii vaccine candidates. Reflections on the development of an anti-Toxoplasma vaccine must focus not only on the appropriate route of administration, capable of inducing efficient immune response, but also on the choice of the antigen (s) of interest and the associated delivery systems. To answer these questions, the choice of the animal model is essential. If mice helped in understanding the protection mechanisms, the data obtained cannot be directly transposed to humans, livestock and cats. Moreover, effectiveness vaccines should elicit strong and protective humoral and cellular immune responses at both local and systemic levels against the different stages of the parasite. Finally, challenge protocols should use the oral route, major natural route of infection, either by feeding tissue cysts or oocysts from different T. gondii strains. Effective Toxoplasma vaccines depend on our understanding of the (1) protective host immune response during T. gondii invasion and infection in the different hosts, (2) manipulation and modulation of host immune response to ensure survival of the parasites able to evade and subvert host immunity, (3) molecular mechanisms that define specific stage development. This review presents an overview of the key limitations for the development of an effective vaccine and highlights the contributions made by recent studies on the mechanisms behind stage switching to offer interesting perspectives for vaccine development.

Toxoplasmosis of the central nervous system: Manifestations vary with immune responses

Toxoplasmosis is an opportunistic infection caused by Toxoplasma gondii (TG), which affects one third of the global human population and commonly involves the central nervous system (CNS)/brain despite the so-called CNS immune privilege. Symptomatic clinical disease of TG infection is much more commonly associated with immunodeficiency; clinicopathological manifestations of CNS toxoplasmosis are linked to individual immune responses including the CNS infiltration of T-cells that are thought to prevent the disease. In patients with autoimmune diseases, immune status is complicated mainly byimmunosuppressant and/or immunomodulatory treatment but typically accompanied by infiltration of T-cells that supposedly fight against toxoplasmosis. In this article, we review characteristics of CNS toxoplasmosis comparatively in immunocompromised patients, immunocompetent patients, and patients with coexisting autoimmune diseases, as well as CNS immune responses to toxoplasmosis with a representative case to demonstrate brain lesions at different stages. In addition to general understanding of CNS toxoplasmosis, our review reveals that clinical manifestations of CNS toxoplasmosis are commonly nonspecific, and incidental pathological findings of TG infection are relatively common in immunocompetent patients and patients with autoimmune diseases (compared to immunocompromised patients); CNS immune responses such as T-cell infiltrates vary in acute and chronic lesions of brain toxoplasmosis.

Effective Nanoparticle-Based Nasal Vaccine Against Latent and Congenital Toxoplasmosis in Sheep

Toxoplasma gondii is a parasitic protozoan of worldwide distribution, able to infect all warm-blooded animals, but particularly sheep. Primary infection in pregnant sheep leads to millions of abortions and significant economic losses for the livestock industry. Moreover, infected animals constitute the main parasitic reservoir for humans. Therefore, the development of a One-health vaccine seems the best prevention strategy. Following earlier work, a vaccine constituted of total extract of Toxoplasma gondii proteins (TE) associated with maltodextrin nanoparticles (DGNP) was developed in rodents. In this study we evaluated the ability of this vaccine candidate to protect against latent and congenital toxoplasmosis in sheep. After two immunizations by either intranasal or intradermal route, DGNP/TE vaccine generated specific Th1-cellular immune response, mediated by APC-secretion of IFN-γ and IL-12. Secretion of IL-10 appeared to regulate this Th1 response for intradermally vaccinated sheep but was absent in intranasally-vaccinated animals. Finally, protection against latent toxoplasmosis and transplacental transmission were explored. Intranasal vaccination led to a marked decrease of brain cysts compared with the non-vaccinated group. This DGNP/TE vaccine administered intranasally conferred a high level of protection against latent toxoplasmosis and its transplacental transmission in sheep, highlighting the potential for development of such a vaccine for studies in other species.

Economic and public health importance of Toxoplasma gondii infections in sheep: 2009-2020

Toxoplasma gondii infections are common in humans and animals worldwide. The present review summarizes worldwide information on the prevalence of clinical and subclinical infections, epidemiology, diagnosis, control, and genetic diversity of T. gondii in sheep in the past decade. There is debate and uncertainty concerning repeat congenital infection as evidenced by finding T. gondii DNA in progeny of chronically infected sheep. However, there is no concrete evidence that T. gondii is the cause of repeated abortions in sheep. Recent data concerning pathogenesis of abortion in acutely infected sheep are reviewed. PCR-RFLP typing of T. gondii DNA derived from viable T. gondii isolates or tissues of infected sheep revealed low genetic diversity in sheep in Europe, Africa, Asia and North America but high diversity in South America. This review will be of interest to biologists, parasitologists, veterinarians, and public health workers.

Early Kinetics of Intestinal Infection and Immune Responses to Two Toxoplasma gondii Strains in Pigs

Toxoplasma gondii is an obligate intracellular parasite, able to infect all homeothermic animals mostly through ingestion of (oo)cysts contaminated food or water. Recently, we observed a T. gondii strain-specific clearance from tissues upon infection in pigs: while the swine-adapted LR strain persisted in porcine tissues, a subsequent infection with the human-isolated Gangji strain cleared parasites from several tissues. We hypothesized that intestinal immune responses shortly after infection might play a role in this strain-specific clearance. To assess this possibility, the parasite load in small intestinal lymph node cells and blood immune cells as well as the IFNγ secretion by these cells were evaluated at 2, 4, 8, 14, and 28 days post oral inoculation of pigs with tissue cysts of both strains. Interestingly, at day 4 post inoculation with the LR strain the parasite was detected by qPCR only in the duodenal lymph node cells, while in the jejunal and ileal lymph node cells and PBMCs the parasite was detected from day 8 post inoculation onwards. Although we observed a similar profile upon inoculation with the Gangji strain, the parasite load in the examined cells was much lower. This was reflected in a significantly higher T. gondii-specific serum IgG response in LR compared to Gangji infected pigs at day 28 post inoculation. Unexpectedly, this was not reflected in the IFNγ secretion upon re-stimulation of the cells where almost equal IFNγ secretion was observed in both groups. In conclusion, our results show that T. gondii first enters the host at the duodenum and then probably disseminates from this site to the other tissues. How the early immune response influences the clearance of parasite from tissues needs further study.

QuilA-Adjuvanted T. gondii Lysate Antigens Trigger Robust Antibody and IFNγ+ T Cell Responses in Pigs Leading to Reduction in Parasite DNA in Tissues Upon Challenge Infection

Toxoplasma gondii is an intracellular parasite of all mammals and birds, responsible for toxoplasmosis. In healthy individuals T. gondii infections mostly remain asymptomatic, however this parasite causes severe morbidity and mortality in immunocompromised patients and congenital toxoplasmosis in pregnant women. The consumption of raw or undercooked pork is considered as an important risk factor to develop toxoplasmosis in humans. Since effective therapeutic interventions to treat toxoplasmosis are scarce, vaccination of meat producing animals may prevent T. gondii transmission to humans. Here, we evaluated the elicited immune responses and the efficacy of a potential vaccine candidate, generated by size fractionation of T. gondii lysate proteins, to reduce the parasite burden in tissues from experimentally T. gondii infected pigs as compared to vaccination with total lysate antigens (TLA). Our results show that both the vaccine candidate and the TLA immunization elicited strong serum IgG responses and elevated percentages of CD4+CD8+IFNγ+ T cells in T. gondii infected pigs. However, the TLA vaccine induced the strongest immune response and reduced the parasite DNA load below the detection limit in brain and skeletal muscle tissue in most animals. These findings might inform the development of novel vaccines to prevent T. gondii infections in livestock species and humans.

Peripheral and placental immune responses in sheep after experimental infection with Toxoplasma gondii at the three terms of gestation

Although it is known that gestation could influence the clinical course of ovine toxoplasmosis, the precise effect of the term of gestation when sheep are infected are yet mostly unknown. The aim of this study was to evaluate the peripheral and placental immune responses developed in pregnant sheep after experimental infection with Toxoplasma gondii at different times of gestation. Thirty-six pregnant sheep were allocated in different groups, orally inoculated with sporulated oocysts of T. gondii at early, mid and late gestation and culled within 30 days post-infection. The peripheral humoral and cytokine responses were evaluated, as well as the transcription of cytokines at the placenta. Serological analysis revealed that, regardless the term of gestation when infected, specific IgG against T. gondii were detected from day 8 post-infection and there was an early peripheral release of IFN-γ at the first week post-infection followed by a short peak of IL10 and TNF-α at the second week post-infection. There were no significant differences in this response between infected groups. At the placenta, a similar increase in transcription of IFN-γ, and TNF-α was found at the three terms of gestation, while IL-4 increased mainly at the first and second terms and IL-10 transcription was higher at the last term. While these findings show that both Th1 and Th2 cytokines play a key role in the pathogenesis of ovine toxoplasmosis and that placental and peripheral immune responses do not closely correlate, there seems to be no clear modulation of these responses along the gestation.

Immunological interaction between Giardia cyst extract and experimental toxoplasmosis

Toxoplasmosis is mostly associated with other intestinal parasitic infections especially Giardia due to shared mode of peroral infection. Toxoplasma and Giardia induce a strong T-helper 1- immune response. Our aim was to induce a protective immune response that results in significant impact on intestinal and extra-intestinal phases of Toxoplasma infection. This study was conducted in experimental animals and assessment of Giardia cyst extract effect on Toxoplasma infection was investigated by histopathological examination of small intestine and brain, Toxoplasma cyst count and iNOS staining of the brain, measurement of IFN-γ and TGF-β in intestinal tissues. Results showed that the brain Toxoplasma cyst number was decreased in mice infected with Toxoplasma then received Giardia cyst extract as compared to mice infected with Toxoplasma only. This effect was produced because Giardia cyst extract augmented the immune response to Toxoplasma infection as evidenced by severe inflammatory reaction in the intestinal and brain tissues, increased levels of IFN-γ and TGF-β in intestinal tissues and strong iNOS staining of the brain. In conclusion, Giardia cyst extract generated a protective response against T. gondii infection. Therefore, Giardia antigen will be a suitable candidate for further researches as an immunomodulatory agent against Toxoplasma infection.

Dextran sulfate inhibits acute Toxoplama gondii infection in pigs

Background

Toxoplasma gondii is a highly prevalent protozoan that can infect all warm-blooded animals, including humans. Its definitive hosts are Felidae and its intermediate hosts include various other mammals and birds, including pigs. It is found in the meat of livestock which is a major source of human infection. Hence the control of toxoplasmosis in pigs is important for public health. We previously showed that dextran sulfate (DS), especially DS10 (dextran sulfate MW 10 kDa), is effective against T. gondii infection both in vitro and in mice. In this study, we asked whether DS affects T. gondii infection of pigs, one of the main animal sources of toxoplasmosis transmission to humans.

Methods

Fourteen-day-old male pigs (n = 10) were infected with T. gondii and then immediately treated with different doses of DS10; clinical, pathological, and immunological analyses were performed 5 days post-infection.

Results

DS10 had an inhibitory effect on toxoplasmosis in pigs. Intravenous injection of DS10 prevented the symptoms of toxoplasmosis and reduced the parasite burden and inflammation induced by T. gondii infection. High-dose DS10 (500 μg per head) caused reversible hepatocellular degeneration of the liver; middle-dose DS10 (50 μg per head) was effective against toxoplasmosis in pigs without causing this side effect.

Conclusions

Our data suggest that middle-dose DS10 led to minimal clinical symptoms of T. gondii infection and caused little hepatocellular degeneration in our pig model, thereby demonstrating its potential as a new treatment for toxoplasmosis. These data should be very beneficial to those interested in the control of toxoplasmosis in pigs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1421-9) contains supplementary material, which is available to authorized users.

Interferon-gamma expression and infectivity of Toxoplasma infected tissues in experimentally infected sheep in comparison with pigs

Livestock animals are a potential risk for transmission of toxoplasmosis to humans. Sheep and pigs still remain an important source because their meat is often eaten undercooked which has been regarded as a major route of infection in many countries. Moreover, porcine tissues are processed in many food products. In the current study, the IFN-gamma (T-helper 1 cells), IL-4 (Th2 cells) and IL-10 mRNA (Treg cells) expression by blood mononuclear cells, and the serum antibody response against Toxoplasma gondii total lysate antigen, recombinant T. gondii GRA1, rGRA7, rMIC3 and rEC2, a chimeric antigen composed of MIC2, MIC3 and SAG1, was studied in sheep the first two months after a T. gondii infection and compared with these responses in pigs. At the end of this period, the parasite distribution in heart, brain and two skeletal muscles in sheep was compared with this in pigs. Whereas the parasite distribution was similar in sheep and pigs, the antibody response differed considerably. In sheep, antibodies appeared against all tested T. gondii antigens, but mainly against rGRA7, rMIC3234307 and TLA whereas in pigs only rGRA7-specific antibodies could be demonstrated. Also, the cytokine response differed. Both in sheep and pigs an IFN-gamma response occurred which seemed to be a slightly more pronounced in sheep. In sheep, also IL-10 and IL-4 mRNA expression showed an increase, but later than IFN-gamma and with more variation. However, in pigs no such increase was seen. As concerning diagnosis, results indicate that serum antibodies against GRA7 in live sheep and pigs and heart tissue for bioassay and qPCR in slaughtered animals are the best targets to demonstrate presence of T. gondii infection.