Parasites and immune responses: memory illusion?

Protective humoral immunity induced by virus-like particles expressing Toxoplasma gondii CST1 or MIC8

Protective efficacy assessment of toxoplasmosis vaccines, at least at the preclinical level, frequently involves lethal dose challenge infection. Nonetheless, their efficacies remain largely unexplored against low infection doses which better reflects how humans become infected in the real world. In this study, we compared the immunity elicited in mice that were heterologously immunized with recombinant baculovirus and virus-like particles expressing either the cyst wall protein (CST1) or microneme protein 8 (MIC8) of Toxoplasma gondii (T. gondii). We also investigated how these vaccines fared against both light and heavy infection intensities of T. gondii ME49. Interestingly, under light infection intensity, vaccines expressing CST1 induced significantly higher mucosal antibody responses than MIC8. Germinal center B (GC B) cell responses were elicited to a greater extent following immunization with either antigen, regardless of the infection dose. Similarly, both antigens suppressed IFN-γ production in the brains upon heavy infection. The overall vaccine-induced protection was also similar for the two vaccine antigens under heavy infection. However, in lightly infected mice, CST1 conferred improved GC B cell induction and further inhibited IFN-γ and cyst burden than those elicited by MIC8, thereby contributing to better protection. These findings indicated that light infection could be used to identify optimal vaccine candidates, thus highlighting the impact of infection intensity in vaccine efficacy evaluations.

Gastrointestinal parasites of indigenous pigs (Sus domesticus) in south-central Nepal

BACKGROUND

Intestinal parasites have a significant impact on productivity of pigs. Additionally, presence of zoonotic parasites in pig faeces used as fertilizer and ingestion of raw or undercooked pork products originated from parasite-infested pigs pose a risk to human health.

OBJECTIVES

The aim of the study was to estimate the prevalence and diversity of gastrointestinal (GI) parasites in indigenous pigs (Sus domesticus) maintained under traditional rearing system in Nepal.

METHODS

Fresh faecal samples (n = 100) were collected from the pigs of varying age and sex maintained in 18 small-scale farms in south-central Nepal. Samples were processed using various standard methods and examined for parasite eggs, cysts or oocysts.

RESULTS

Prevalence of GI parasites in indigenous pigs was 91%, comprising of 14 different genera of protozoans and helminths. Male pigs generally had a higher (97.5%) prevalence of GI parasites than females (87%). While 90% of the suckling and weaner piglets were positive for the GI parasites, all growers and 85% the adult pigs were infected with the parasites. Entamoeba spp. were the primary protozoans in all age groups. Strongyloides sp. was more prevalent helminths in suckling and weaner piglets, whereas Ascarid spp. were higher in both growers and adults. Triplet infection was higher (33.3%) in suckling and weaner piglets, while quadruplet and pentuplet infections were higher (p < .05) among growers (46.7%) and adults (30%), respectively.

CONCLUSIONS

The indigenous pigs harbour a higher prevalence and greater diversity of GI parasites. GI parasitism varies by sex and age of the pigs.

Infection and treatment immunizations for successful parasite vaccines

Since the advent of techniques for the expression of recombinant peptide antigens, the availability of human vaccines for parasitic diseases has been ‘imminent’. Yet vaccines based on recombinant proteins are still largely aspirations, not realities. It is now apparent that vaccine development needs additional knowledge about host protective immune response(s), antigen characteristics, and the delivery required to induce those responses. The most successful immune protection against parasites has been generated by infection and treatment, the induction of protective immunity by truncating the course of an infection with drug treatment. Here, we consider the characteristics of an effective, protective anti-parasite vaccine and propose a conceptual framework to aid parasite vaccine development using malaria and schistosomiasis as examples.

Protozoan and helminth infections in pregnancy. Short-term and long-term implications of transmission of infection from mother to foetus

This review of protozoan and helminth infections in pregnancy focuses on the impact on the immune response in the newborn infant to maternal infection. Studies of protozoan and helminth infections in pregnant women and in their offspring have shown that children exposed to antigens or microorganisms during pregnancy often have a reduced immune response to these infections. The most common finding is a reduced IFN gamma response to specific antigens regardless of specific infection studied. In some studies the impaired immune response disappeared before the age of one year, while in other studies the impaired immune response was present as much as two decades after birth. Data from chronic viral infections like Rubella, cytomegalovirus and hepatitis B also show that congenital or perinatal infections may result in a life-long inability to control the infections. Studies of both helminth and protozoan infections show that children exposed to antigens during gestation have a microorganism-specific impaired immune response which is characterized by reduced IFN-gamma and stimulation of responses to specific antigens.

Respiratory syncytial virus infects and abortively replicates in the lungs in spite of preexisting immunity

Respiratory syncytial virus (RSV) is a major cause of bronchiolitis and viral pneumonia in young children and a serious health risk in immunocompromised individuals and the elderly. Immunity to RSV is not completely understood. In this work, we established a method for monitoring RSV infection by real-time PCR and applied this method for analysis of RSV replication in vivo in the cotton rat model in naïve animals and in animals rendered immune to RSV by prior RSV infection. We found that even though no virus could be isolated from the lungs of RSV-challenged immune animals, RSV infection in fact took place and an accumulation of viral RNA transcripts was observed. This type of replication, therefore, can be termed "abortive," as RSV is capable of entering the cells in the lungs of immune animals, yet the production of progeny viruses is impaired. Similar patterns of RSV gene expression gradient were observed between naïve and reinfected animals, indicating that the skewing of mRNA gradient of viral gene expression, a mechanism documented during latent infection by other viruses, is not likely to be responsible for abortive replication of RSV during reinfection. We found that passive administration of antibodies to RSV prevents productive infection normally accompanied by viral release in the lung, but it does not prevent abortive replication of the virus. To the best of our knowledge, this is the first evidence of abortive replication of RSV in vivo.

Frontal and stealth attack strategies in microbial pathogenesis

Interactions between microbes and human hosts can range from a benign, even symbiotic collaboration to a competition that may turn fatal--resulting in death of the host, the microbe or both. Despite advances that have been made over the past decades in understanding microbial pathogens, more people worldwide still die every year from infectious disease than from any other cause. This highlights the relevance of continuing to probe the mechanisms used by microorganisms to cause disease, and emphasizes the need for new model systems to advance our understanding of host-pathogen interactions.