Porcine isosporosis: infection dynamics, pathophysiology and immunology of experimental infections

Variations in extracellular vesicle shedding of Cystoisospora suis stages (Apicomplexa: Coccidia)

Cystoisospora suis, a porcine enteral parasite of the order Coccidia, is characterized by a complex life cycle, with asexual and sexual development in the epithelium of the host gut and an environmental phase as an oocyst. All developmental stages vary greatly in their morphology and function, and therefore excrete different bioactive molecules for intercellular communication. Due to their complex development, we hypothesized that the extracellular vesicles (EVs) cargo is highly dependent on the life cycle stages from which they are released. This study aimed to characterize and compare EVs of all developmental stages of C. suis. Nanoparticle tracking analysis and microscopy were used to determine particle numbers and size distributions of stage-specific parasite EVs. Furthermore, Fourier-transform infrared spectral analysis was employed for the metabolic fingerprinting of EVs, and the lipid and protein profiles of all parasite stages were determined. Overall, the study revealed that asexual, sexual and transmissible stages of C. suis release different EVs during the parasite's life cycle. EVs of endogenous asexual and sexual stages were found to be more similar to each other than to those of the transmissible environmental stage, the oocyst. Furthermore, the ratio of fatty acids to polysaccharides and proteins changed during parasite development. In particular, proteins associated with the Apicomplexa and those involved in vesicle shedding showed changes in expression in all parasite stages. Lipid analysis showed that fatty acids were found in the same concentration through all parasite stages, whereas the amount of stereolipids, sphingolipids and glycerolipids changed between the parasite stages. In conclusion, this study, which presents the first known characterization of C. suis EVs, demonstrates a link between EVs and the respective developmental stages of the parasite, and putative functions in the parasite-parasite and host-parasite interplays.

Epidemiology and distribution of gastrointestinal parasites in fattening pig farms in northern Italy

In Italy, pig breeding is characterised by intensive farms in which parasitic diseases often present a subclinical pattern, while being responsible for decreased animal welfare and great economic losses. The present study aimed to assess the prevalence of major parasites in pigs, and, for this purpose, 880 faecal samples of fattening pigs raised in 22 intensive farms located in northern Italy were collected in two different sampling sessions, at the beginning and end of the fattening cycle. For the detection of helminth eggs and coccidian oocysts, a quantitative flotation technique was used, whereas a conventional PCR was performed to confirm the identification of cestode eggs found by copromicroscopic analysis. Moreover, data regarding herd management were collected to assess risk factors for parasite occurrence. A total of 95 samples were positive for at least one parasitic taxon (10.8%); the most detected parasite was Ascaris suum (7.6%), followed by Trichuris suis (1.7%) and Cystoisospora suis (0.9%). Further, eggs with morphometric features compatible with those of Hymenolepis diminuta were detected in 16 samples (1.8%), and the analysis of sequences confirmed the identification of cestode eggs. Statistical analysis showed that large farms and those applying the all-in/all-out system were associated with a lower risk of nematode infection. This study provided data on prevalence and burden of gastrointestinal parasites in two different times of the fattening cycle. It was evidenced that endoparasites are persistent, albeit with low prevalences, and would need specific measures to reduce their effects on both animal health and productivity.

In vitro cultivation methods for coccidian parasite research

The subclass Coccidia comprises a large group of protozoan parasites, including important pathogens of humans and animals such as Toxoplasma gondii, Neospora caninum, Eimeria spp., and Cystoisospora spp. Their life cycle includes a switch from asexual to sexual stages and is often restricted to a single host species. Current research on coccidian parasites focuses on cell biology and the underlying mechanisms of protein expression and trafficking in different life stages, host cell invasion and host-parasite interactions. Furthermore, novel anticoccidial drug targets are evaluated. Given the variety of research questions and the requirement to reduce and replace animal experimentation, in vitro cultivation of Coccidia needs to be further developed and refined to meet these requirements. For these purposes, established culture systems are constantly improved. In addition, new in vitro culture systems lately gained considerable importance in research on Coccidia. Well established and optimized in vitro cultures of monolayer cells can support the viability and development of parasite stages and even allow completion of the life cycle in vitro, as shown for Cystoisospora suis and Eimeria tenella. Furthermore, new three-dimensional cell culture models are used for propagation of Cryptosporidium spp. (close relatives of the coccidians), and the infection of three-dimensional organoids with T. gondii also gained popularity as the interaction between the parasite and host tissue can be studied in more detail. The latest advances in three-dimensional culture systems are organ-on-a-chip models, that to date have only been tested for T. gondii but promise to accelerate research in other coccidians. Lastly, the completion of the life cycle of C. suis and Cryptosporidium parvum was reported to continue in a host cell-free environment following the first occurrence of asexual stages. Such axenic cultures are becoming increasingly available and open new avenues for research on parasite life cycle stages and novel intervention strategies.

Porcine Deltacoronavirus Infection Disrupts the Intestinal Mucosal Barrier and Inhibits Intestinal Stem Cell Differentiation to Goblet Cells via the Notch Signaling Pathway

Goblet cells and their secreted mucus are important elements of the intestinal mucosal barrier, which allows host cells to resist invasion by intestinal pathogens. Porcine deltacoronavirus (PDCoV) is an emerging swine enteric virus that causes severe diarrhea in pigs and causes large economic losses to pork producers worldwide. To date, the molecular mechanisms by which PDCoV regulates the function and differentiation of goblet cells and disrupts the intestinal mucosal barrier remain to be determined. Here, we report that in newborn piglets, PDCoV infection disrupts the intestinal barrier: specifically, there is intestinal villus atrophy, crypt depth increases, and tight junctions are disrupted. There is also a significant reduction in the number of goblet cells and the expression of MUC-2. In vitro, using intestinal monolayer organoids, we found that PDCoV infection activates the Notch signaling pathway, resulting in upregulated expression of HES-1 and downregulated expression of ATOH-1 and thereby inhibiting the differentiation of intestinal stem cells into goblet cells. Our study shows that PDCoV infection activates the Notch signaling pathway to inhibit the differentiation of goblet cells and their mucus secretion, resulting in disruption of the intestinal mucosal barrier. IMPORTANCE The intestinal mucosal barrier, mainly secreted by the intestinal goblet cells, is a crucial first line of defense against pathogenic microorganisms. PDCoV regulates the function and differentiation of goblet cells, thereby disrupting the mucosal barrier; however, the mechanism by which PDCoV disrupts the barrier is not known. Here, we report that in vivo, PDCoV infection decreases villus length, increases crypt depth, and disrupts tight junctions. Moreover, PDCoV activates the Notch signaling pathway, inhibiting goblet cell differentiation and mucus secretion in vivo and in vitro. Thus, our results provide a novel insight into the mechanism underlying intestinal mucosal barrier dysfunction caused by coronavirus infection.

Diagnostic Approach to Enteric Disorders in Pigs

The diagnosis of enteric disorders in pigs is extremely challenging, at any age. Outbreaks of enteric disease in pigs are frequently multifactorial and multiple microorganisms can co-exist and interact. Furthermore, several pathogens, such as Clostridium perfrigens type A, Rotavirus and Lawsonia intracellularis, may be present in the gut in the absence of clinical signs. Thus, diagnosis must be based on a differential approach in order to develop a tailored control strategy, considering that treatment and control programs for enteric diseases are pathogen-specific. Correct sampling for laboratory analyses is fundamental for the diagnostic work-up of enteric disease in pigs. For example, histology is the diagnostic gold standard for several enteric disorders, and sampling must ensure the collection of representative and optimal intestinal samples. The aim of this paper is to focus on the diagnostic approach, from sampling to the aetiological diagnosis, of enteric disorders in pigs due to different pathogens during the different phases of production.

Pharmacokinetics, bioavailability, and excretion of ponazuril in piglets

Ponazuril is a triazine anticoccidial drug which is the main metabolite of toltrazuril in animals, it has excellent activity against many protozoa, including Cystoisospora suis, and has broad application prospects in the control of swine coccidiosis. To evaluate the pharmacokinetic and excretion characteristics of ponazuril, 12 healthy piglets aged 10-14 days were divided into 2 groups for pharmacokinetic studies, which were given 20 mg/kg body weight ponazuril orally and intravenously, respectively. And 6 other piglets were housed individually in metabolic cages and given the same oral dose of ponazuril. After administration, the concentration of ponazuril in plasma, fecal, and urine samples collected was determined using high-performance liquid chromatography (HPLC). The plasma concentration profiles of ponazuril obtained after intravenous and oral administration were analyzed simultaneously by the nonlinear mixed-effects (NLME) model. Following the results, the pharmacokinetics of ponazuril exhibited a Michaelis-Menten elimination with Michaelis-Menten constant K_m and maximum metabolic rate V_m of 10.8 μg/mL and 0.083 mg/kg/h. The apparent volume of distribution was calculated to be 735 mL/kg, and the final estimated oral bioavailability was 81%. Besides, cumulatively 86.42 ± 2.96% of ponazuril was recovered from feces and 0.31% ± 0.08% from urine during 0-1,020 h after oral administration. These findings indicated a good oral absorption of ponazuril in piglets with nonlinear disposition and slow excretion largely via feces, implying sustained drug concentration in vivo and long-lasting anticoccidial effects.

Study of the effect of intestinal immunity in neonatal piglets coinfected with porcine deltacoronavirus and porcine epidemic diarrhea virus

Porcine deltacoronavirus (PDCoV) and porcine epidemic diarrhea virus (PEDV) have often been detected simultaneously in piglets with coronavirus diarrhea. However, the intestinal immune response to the interaction between circulating PDCoV and PEDV is unknown. Therefore, this study was conducted to investigate the intestinal immunity of neonatal piglets that were exposed first to PDCoV and then to PEDV. The amounts and distribution of CD3⁺ T lymphocytes, B lymphocytes, and goblet cells (GCs) in the small intestine were analyzed by immunohistochemistry and periodic acid–Schiff staining, respectively. The expression levels of pattern recognition receptors and downstream mediator cytokines were analyzed by qPCR and ELISA. The results showed that the numbers of GCs, CD3⁺ T lymphocytes, and B lymphocytes in the duodenum and jejunum of the PDCoV + PEDV coinoculated piglets were increased compared with those of piglets inoculated with PEDV alone. The piglets in the PDCoV + PEDV group had significantly upregulated IFN-α and IFN-λ₁ compared with the PEDV single-inoculated piglets. These results suggest that PDCoV + PEDV-coinfected piglets can activate intestinal antiviral immunity more strongly than piglets infected with PEDV alone, which provides new insight into the pathogenesis mechanism of swine enteric coronavirus coinfection that may be used for vaccination in the future.

Prevalence and Risk Factors of Intestinal Parasite Infections in Greek Swine Farrow-To-Finish Farms

Intestinal parasites, helminths, and protozoa challenge health and welfare of pigs and deteriorate the sustainability of swine farms leading to monetary losses. A multicentric survey was conducted for approximately one year. Overall, 1150 fecal samples were collected from eight intensive farms in Greece at regular intervals and examined by flotation and Ziehl-Neelsen techniques. Age, season, and time of last recorded antiparasitic treatment were assessed as possible risk factors using binary regression models. The overall prevalence of intestinal parasitism in pigs was 44.7%. The most frequently detected parasites in the studied population were the protozoa Balantidium coli (37.8%), followed by Entamoeba spp. (8.3%), Cystoisospora suis (6.0%), and the nematodes Ascaris suum (3.7%), Trichuris suis (2.5%), and Oesophagostomum spp. (1.4%). Distribution of intestinal parasites in different age groups was as expected. In autumn, the prevalence of Balantidium coli infection enhanced whereas the prevalence of Entamoeba spp. and Cystoisospora suis infections increased in spring. Time of last recorded antiparasitic treatment influenced Balantidium coli and Trichuris suis infection levels. Our results demonstrated that swine intestinal parasitism in intensive farms of Greece seems to be relatively common and highlighted the importance of proper laboratory examinations, as well as the need for tailored made control programs.

Antibody and cytokine response to Cystoisospora suis infections in immune-competent young pigs

Background

To date, investigations on the immune response to Cystoisospora suis infections focused on suckling piglets, the age group clinically most affected. Actively immunizing piglets is unfeasible due to their immature immune system and the typically early infection in the first days after birth. Therefore, understanding and possibly enhancing the immune response of immune-competent animals is the prerequisite to develop a passive immunization strategy for piglets which currently rely on very limited treatment options.

Methods

To investigate antibody and cytokine responses of immune-competent animals and the impact of the oral immunization protocol on their immune response, growers with unknown previous exposure to C. suis (10–11 weeks-old) were infected one or three times with different doses (600 and 6000 or 200 and 2000, respectively) of C. suis oocysts, and compared to uninfected controls. Oocyst excretion was evaluated, and blood and intestinal mucus antibody titers were determined by IFAT. Systemic production of Th1, Th2, inflammatory and regulatory cytokines was determined in different immune compartments at mRNA and (after stimulation with a recombinant merozoite-protein) at protein level by PCR and multiplex fluorescent immunoassay, respectively.

Results

Infection generated significantly increased serum IgA and IgG levels against C. suis sporozoites and merozoites, irrespective of infection mode, with IgG against merozoites showing the strongest increase. No clinical signs and only occasional excretion were observed. The systemic cytokine response to C. suis was only weak. Nonetheless, in white blood cells, IL-4, IL-6 and IL-10 mRNA-levels significantly increased after infection, whereas IFN-ɣ, IL-2 and TGF-β expression tended to decrease. In mesenteric lymph nodes (MLN), IL-10 and TNF-α levels were elevated while splenic cytokine expression was unaltered upon infection. Stimulated MLN-derived lymphocytes from infected pigs produced slightly more IL-12 and less IFN-α than controls.

Conclusions

An infection and a subsequent systemic immune response can be induced in immune-competent animals by all evaluated infection models and growers can be used as models to mimic sow immunizations. The immune response to C. suis, although mild and with considerable variation in cytokine expression, was characterized by a Th2-associated and regulatory cytokine profile and antibody production. However, none of the parameters clearly stood out as a potential marker associated with protection. Antibody titers were significantly positively related with oocyst excretion and might thus serve as correlates for parasite replication or severity of infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2974-6) contains supplementary material, which is available to authorized users.

Occurrence, clinical involvement and zoonotic potential of endoparasites infecting Swiss pigs

In order to estimate the diversity, clinical involvement and zoonotic potential of parasites in pigs submitted for diagnosis to the PathoPig project of the Swiss Federal Food Safety and Veterinary Office, faeces (n=125) from suckling piglets (n=39), weaners (n=60) and piglets beginning fattening (n=26) from 74 Swiss farms were examined by 3 coproscopical methods (i.e. sedimentation/zinc chloride-flotation; SAFC and Ziehl-Neelsen staining). Samples microscopically positive for Cryptosporidium were further tested by PCR/sequencing for species assessment. The most frequently detected parasite was Balantidium coli, a facultative pathogenic ciliate with zoonotic potential, in 5.1, 36.7 and 50.0% of suckling, weaners and fatteners and 43.2% of farms; however, no association with disease was observed. Isospora (syn. Cystoisospora) suis infections were detected in 13.3 and 11.1% of suckling piglets with and without diarrhoea, and in 10.0 and 13.3% of weaners and fatteners with diarrhoea, respectively, and were significant associated with emaciation. Cryptosporidium infections were detected in 10.3, 15.0 and 19.2% of sucklings, weaners and fatteners, respectively, and in 18.9% of the farms. Interestingly, two age-related species were identified: C. suis in younger piglets (2 to 6weeks) and C. scrofarum in older ones (6 to 17weeks). None of the pigs infected with C. scrofarum (n=8), but 3 of 4 piglets infected with C. suis (co-infection with I. suis in 2 cases) had diarrhoea. The zoonotic species C. parvum was not detected, nevertheless, sporadic cases of human infection with the porcine-adapted species have been reported. Ascaris suum, Trichuris suis and Strongylida were rarely detected (<4%) in all age categories.

Presence and characterization of pig group A and C rotaviruses in feces of Belgian diarrheic suckling piglets

The importance of group A and C rotaviruses (RVA and RVC) in the pathogenesis of diarrhea in Belgian suckling pigs is poorly investigated, and it is not known which strains are circulating in the Belgian suckling pig population. Obtaining better insights in the occurrence of both viral species in the swine population is essential in order to develop accurate diagnostic, therapeutic and prophylactic strategies to protect suckling pigs against diarrhea in a durable manner. In the present study, viral loads of RVA and RVC were quantified in diarrhea samples of suckling piglets less than 2 weeks old, collected on 36 different Belgian farms. On 22 of 36 farms tested (61%), high viral loads of RVA (6.96-11.95 log10 copies/g feces) and/or RVC (5.40-11.63 log10 copies/g feces) were detected. Seventeen RVA isolates were genotyped for their outer capsid proteins VP7 and VP4. Four different G-genotypes (G3, G4, G5 and G9) for VP7 were found together with 4 different P-genotypes (P[6], P[7], P[13] and P[23]) for VP4, in 8 different G/P combinations. All characterized RVC strains belonged to genotype G6 (VP7), except for one strain possessing the G1 genotype. VP4 genes of Belgian RVC strains were genetically heterogeneous, but were classified in the genotype P5. Most rotavirus positive samples also contained Escherichia coli, whereas Clostridium perfringens infections were mainly detected in rotavirus negative samples. Results of the present study offer better insights in the occurrence of RVA and RVC infections in Belgian diarrheic suckling piglets. As a conclusion, routine diagnostic testing for both viral species in cases of diarrhea in suckling pigs is highly recommended. Furthermore, the present findings also offer valuable information for the development of new prophylactic measures against rotavirus. Finally, the relatedness between RVC strains from pigs and other host species is described, and their possible implications in interspecies transmission events are discussed.

Cystoisospora suis - A Model of Mammalian Cystoisosporosis

Cystoisospora suis is a coccidian species that typically affects suckling piglets. Infections occur by oral uptake of oocysts and are characterized by non-hemorrhagic transient diarrhea, resulting in poor weight gain. Apparently, primary immune responses to C. suis cannot readily be mounted by neonates, which contributes to the establishment and rapid development of the parasite, while in older pigs age-resistance prevents disease development. However, the presence of extraintestinal stages, although not unequivocally demonstrated, is suspected to enable parasite persistence together with the induction and maintenance of immune response in older pigs, which in turn may facilitate the transfer of C. suis-specific factors from sow to offspring. It is assumed that neonates are particularly prone to clinical disease because infections with C. suis interfere with the establishment of the gut microbiome. Clostridia have been especially inferred to profit from the altered intestinal environment during parasite infection. New tools, particularly in the area of genomics, might illustrate the interactions between C. suis and its host and pave the way for the development of new control methods not only for porcine cystoisosporosis but also for other mammalian Cystoisospora infections. The first reference genome for C. suis is under way and will be a fertile ground to discover new drugs and vaccines. At the same time, the establishment and refinement of an in vivo model and an in vitro culture system, supporting the complete life cycle of C. suis, will underpin the functional characterization of the parasite and shed light on its biology and control.

Which factors influence the outcome of experimental infection with Cystoisospora suis?

For reliable predictions of clinical and parasitological outcome of experimental infections with parasites, different models must be evaluated for possible influences of infection time point, infection dose and host-specific parameters such as breed or litter size. To address these issues for Cystoisospora (syn. Isospora) suis, the causative agent of porcine neonatal coccidiosis, 181 piglets from 90 litters (hybrid crosses of different breeds) were included in a retrospective study to evaluate differences in time point and dose of infection in four different experimental models ((1) 1,500 oocysts on the 4th day of life, d.o.l.; (2) 1,000 oocysts, 4th d.o.l.; (3) 1,000 oocysts, 1st d.o.l.; (4) 5,000 oocysts, 4th d.o.l.). The target variables body weight gain, faecal consistency and oocyst excretion were evaluated during the acute phase of infection (5-10 days post infection), and the influences of the dependent variables breed or litter size were estimated. Despite differences in the time course of excretion and faecal consistency, neither the average amount of excretion nor the average faecal consistency differed among models, breeds or litters of different size. High individual variability was seen in all four models as described earlier for higher infection doses. When infections on the 1st vs. 4th day of life were compared, no differences in averages could be found, in contrast to previous observations on the influence of age. Other, not yet defined, variables appear to have a greater impact on the outcome of infection than doses and time points in the tested range, despite the reliable outcome of infection with high excretion rates and signs of clinical disease.

Subversion of host cellular functions by the apicomplexan parasites

Rhoptries are club-shaped secretory organelles located at the anterior pole of species belonging to the phylum of Apicomplexa. Parasites of this phylum are responsible for a huge burden of disease in humans and animals and a loss of economic productivity. Members of this elite group of obligate intracellular parasites include Plasmodium spp. that cause malaria and Cryptosporidium spp. that cause diarrhoeal disease. Although rhoptries are almost ubiquitous throughout the phylum, the relevance and role of the proteins contained within the rhoptries varies. Rhoptry contents separate into two intra-organellar compartments, the neck and the bulb. A number of rhoptry neck proteins are conserved between species and are involved in functions such as host cell invasion. The bulb proteins are less well-conserved and probably evolved for a particular lifestyle. In the majority of species studied to date, rhoptry content is involved in formation and maintenance of the parasitophorous vacuole; however some species live free within the host cytoplasm. In this review, we will summarise the knowledge available regarding rhoptry proteins. Specifically, we will discuss the role of the rhoptry kinases that are used by Toxoplasma gondii and other coccidian parasites to subvert the host cellular functions and prevent parasite death.

Changes in lymphocyte populations in suckling piglets during primary infections with Isospora suis

Isospora suis, a common intestinal parasite of piglets, causes neonatal porcine coccidiosis, which results in reduced and uneven weaning weights and economic losses in pig production. Nevertheless, there are no detailed studies available on the immune response to I. suis. The aim of this study was to carry out phenotypical characterization of lymphocytes during primary infections on day 3 after birth. Infected and noninfected piglets were investigated between days 7 and 16 after birth. Lymphocytes from the blood, spleen and mesenteric lymph nodes (flow cytometry) and of the jejunal mucosa (immunohistochemistry) were analysed. A decrease in T cells, especially with the phenotype of resting T-helper cells, T-cell receptor-gammadelta-T cells, and regulatory T cells in the blood, spleen and mesenteric lymph nodes was noticeable. An increase in cells with the phenotype of natural killer cells in the spleen of infected animals was found, and the subset of TcR-gammadelta-T cells was strongly increased in the gut mucosa. Our findings suggest an accelerated migration of those cells into the gut. This study provides a strong indication for the involvement of adaptive and innate immune response mechanisms in the primary immune response to I. suis, especially of TcR-gammadelta-T cells as a linkage between innate and adaptive immunity.