Isospora suis had 3 asexual and 1 sexual intra-intestinal conventional life cycle. The first asexual generation was most prominent at 2 days p.i. (post inoculation). The use of Isospora suis, a sister taxon to T. gondii and the causative agent of piglet coccidiosis, could provide a solution for this. In the present. I. suis were seen within the intestinal epithelium and oocysts were recovered from the and identified a new species of porcine coccidia as Isospora suis [2].

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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. 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.

It is assumed that neonates are particularly prone to clinical disease because infections with C. Clostridia have been especially inferred to profit from the altered intestinal environment during parasite infection.

Suid tools, particularly in the area of genomics, might illustrate the interactions between C. The first reference genome for C. 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. Isospora suisan apicomplexan parasite of swine, is the causative agent of isosporx porcine cystoisosporosis coccidiosis.

The parasite was first described in 1but it received recognition only after the introduction of intensive, high-throughput pig breeding facilities in the mids 2 — 4. Suckling piglets are the most affected age group and frequently show pasty-to-watery non-hemorrhagic diarrhea and marked weight loss, while older pigs are less susceptible and excrete few or no oocysts without clinical signs upon infection.

Life cycle of Isospora suis in gnotobiotic and conventionalized piglets.

Despite high rates of morbidity, piglets exhibit high individual variability in the development of disease 56which leads to uneven weaning weights 78. Infected piglets usually recover within 2 weeks post-infection 9 — Although cystoisosporosis has a ubiquitous distribution 12 — 15the diagnosis is still cumbersome because of variations in the excretion intensity 16 and short individual oocyst excretion periods Several species of the genera Eimeria and C ystoisospora sui infect swine.

Unlike in other livestock, where mixed infections with various Eimeria species are common 17 — 20C. Economic losses associated with coccidiosis in livestock are mainly due to impaired performance, retarded growth, mortality, and cost of treatment. Moreover, cystoisosporosis is thought to predispose the piglet to infection with secondary bacterial and viral pathogens, which subsequently increase morbidity, mortality, and managerial costs There are no vaccines available so far, and toltrazuril is the only licensed drug for metaphylaxis that can effectively suppress oocyst excretion and improve piglet health both under experimental conditions 823 and in the field However, rapid emergence of resistance against all introduced anticoccidials in chicken Eimeria 25 is also of concern regarding porcine cystoisosporosis, and there is an urgent need to develop new and sustainable intervention strategies against C.

An experimental model mimicking the field situation 10 in conventional piglets gave isosproa insight into neonatal porcine cystoisosporosis. This was further strengthened by the establishment of an in vitro culture system supporting the entire lifecycle of C.

Moreover, gnotobiotic piglets are available as infection models for specific applications 3 Like other Cystoisospora species, C. Suie after ingestion, sporulated oocysts undergo excystation and sporozoites invade the small intestine epithelium 1228 to reproduce within a parasitophorus vacuole 29 suiis, Asexual reproduction merogony peaks at day 4 and 5 iospora.

Unlike Eimeriamerogonic stages are not assigned to generations but to types defined by the number of nuclei, shape, size, and time of appearance 2627 From day 5, mature sexual stages can be identified 3 After fusion to form a zygote, the unsporulated oocyst is excreted with the feces and undergoes sporogony outside the host 2728 Proposed model of C. A Oocysts are excreted with feces and undergo sporulation in the environment. B Sporulated oocysts excyst upon ingested by host to release sporozoites.


C Sporozoites invade intestinal epithelium and develop to become merozoites 1. In contrast to Eimeriamerogony in C. It is currently not known which type could act as extraintestinal resting stage. D Merogony is followed by gamogony resulting in fusion of macro- and micro-gametes to form a zygote and subsequently an oocyst. E The desynchronization of the merogonic development may also be responsible for the characteristic oocyst excretion occurring in two or more peaks, when some of the merozoites may undergo rapid development to gamogonic stages, while others enter into a development lag phase to undergo the sexual maturation for the next peak.

G Intake of colostrum and milk, rich in antibodies and cellular components could partially confer passive humoral immunity against C. I The existence of extraintestinal stages of C. Various environmental conditions influence the sporulation time. Rapid multiplication of sporozoites and merozoites inside the intestinal epithelium leads to isosproa histological alterations including atrophy, necrosis, and fusion of villi, hyperplasia of crypts, and desquamation of epithelial cells 122934 These changes persist for a considerable time after parasite development 8which may contribute to the reduction in body weight gain due to lasting impairment of nutrient absorption.

Cystoisospora suis completes its life cycle within 5—6 days Clinical signs can be seen as early as 3 days post-infection dpishedding of oocysts typically starts on fifth dpi 610212831 However, these periods may differ, probably due to the age and health condition of the piglets and the virulence of the parasite strain 310 Oocyst excretion and symptoms show typical peaks auis 5th—9th and 11th—14th dpi 212830which might be due to extraintestinal stages re-entering the intestines 3.

It has been shown for several Cystoisospora species C.


These extraintestinal stages have been found in definitive as well as in paratenic hosts 327 Suiw hosts do not show clinical signs but act as carriers, since parasites can survive for at least 2 ispspora within their tissues However, no study could so far unequivocally demonstrate the existence of C.

Previous studies 313739 could not provide evidence of extraintestinal stages in tissues of experimentally infected piglets or mice.

Still, gnotobiotic piglets shed oocysts after intraperitoneal inoculation of liver, spleen, and lymph node homogenates from experimentally infected piglets 3. In a preliminary study, C. In spleen and mesenteric lymph nodes, it could first be detected on the second dpi.

In kidney tissues, it was detected on the second and in kidney and liver tissue isospoea the fifth to the ninth dpi.

In jejunal mucosa, it was found from the 1st dpi until the end of the study on 13th dpi Although detection of DNA does not prove the presence of viable, infectious parasitic cells, these results indicate trafficking of C.

Many aspects, such as isosporx, maturation of the gut immune system, as well as the immune status of the infected piglet, influence resistance to C. Also, when piglets were infected at 3rd vs. Therefore, the authors concluded that age resistance based on the maturation of the innate immune system suiz a more important role than acquired immunity.

However, in some mammalian species, susceptibility increases with the age of the animal before it decreases again 4445which may isospra be related to changing immune responses in older animals Maturation of the porcine immune system can also influence the clinical outcome.

Piglets are born with a premature immune system, which only starts to develop during the first few weeks of age. Likewise, the small intestinal mucosa of new-born piglets is characterized by the absence of lymphoid cells with the exception of a few antigen presenting cells and T cells 47which may explain the severity of the disease in young piglets due to the inability to adequately respond to the parasite.


In older piglets, by contrast, Worliczek et al. For other coccidian parasites, humoral suiw response seems to have a minor role in the protection mechanism. Stimulation of humoral immunity by Eimeria is known but its effectiveness in controlling the infection is still unclear Immune sera from E.

In spite of the fact that piglets are born with an immature immune system 47cellular immune responses might be involved in the development of immunity against coccidian parasites including C. The role of passive immune response and the transmission of immune components from infected sows to piglets had been neglected by many authors 4156 However, earlier works have shown that colostral antibodies may participate in resistance against natural infections with C.

Recently, Schwarz et al. It is currently unclear whether the detected immunoglobulins have a protective function by themselves or are merely markers for protection conveyed by other, not yet explored, mechanisms. While the genomes of many coccidian species are available in the ToxoDB database 61C.

Moreover, the number of chromosomes is also unknown. To date, only few ribosomal and mitochondrial sequences of Cystoisospora species were zuis for phylogenetic studies, which established that the genus Cystoisospora constitutes a monophyletic clade with the Sarcocystidae, and it is closely related to Toxoplasma and Neospora 62 — These studies also confirmed the hypothesis ixospora heteroxeny is an evolutionary derived character in Cystoisospora First estimates based on NGS data showed that the genome of C.

Isospora suis enteritis in piglets.

Thus, to generate a comprehensive gene catalog of C. This will also allow for identification of genes involved in life stage transitions, as similarly performed in E. Intervention strategies isowpora also be aided by genomics.

Currently, the drug toltrazuril is the only treatment available against C. The availability of the gene catalog of C. Typically, annotation of gene function can be inferred on the basis of orthologous proteins, suuis tools such as Blast2GO Suls, screening for drug targets can be performed on the basis of the functions of candidates identified as drug targets in other coccidia. These include protein kinases 71 — 73apicoplast proteins 74enzymes involved in fatty acid biosynthesis 75 and shikimate metabolism 76mitochondrial proteins 77and others, reviewed in Ref.

Another approach to identify drug targets involves comparing the metabolic pathways of parasite and host isospporafor example, selecting pathways that are present in C. An alternative control sis might be vaccination; however, there is at present no vaccine available against C. In this regard, genomics can also contribute to vaccine discovery: This approach has been successfully applied in various bacterial species However, the inherent complexity of eukaryotic pathogens has hindered the application of this strategy in such organisms.

Recently, the feasibility of reverse vaccinology has been reviewed in the coccidian parasite N. In parallel, bioinformatics tools and pipelines have finally emerged to address the specific issue of detecting vaccine candidates in eukaryotic pathogens 84 — An overview of the in silico analysis of wuis C.

Schematic view of the in silico analysis of genomic data for C. The genome sequence can be isospor with next generation sequencing using a combination of short and long reads libraries. C 3D structure of drug candidates can be reconstructed by homology using Swiss-Model 96 ; screening of virtual libraries of compounds can be performed with AutoDock D Vaccine candidates can be identified using Vacceed 86 and validated by proteomics approaches, such as mass spectrometry, with the aid of the software PEAKS Bioinformatics Solutions Inc.