Cryptosporidium sp. of the starred lizardAgama stellio: Ultrastructure and life cycle

The Cryptosporidium signaling kinase CDPK5 plays an important role in male gametogenesis and parasite virulence

The protozoan parasite Cryptosporidium is a leading cause of diarrhea in young children. The parasite's life cycle involves a coordinated and timely progression from asexual to sexual stages, leading to the formation of the transmissible oocyst. Underlying molecular signaling mechanisms orchestrating sexual development are not known. Here, we describe the function of a signaling kinase in Cryptosporidium male gametogenesis. We reveal the expression of Cryptosporidium parvum calcium-dependent protein kinase 5 (CDPK5) during male gamete development and its important role in the egress of mature gametes. Genetic ablation of this kinase results in viable parasites, indicating that this gene is dispensable for parasite survival. Interestingly, cdpk5 deletion decreases parasite virulence and impacts oocyst shedding in immunocompromised mice. Using phosphoproteomics, we identify possible CDPK5 substrates and biological processes regulated by this kinase. Collectively, these findings illuminate parasite cell biology by revealing a mechanism controlling male gamete production and a potential target to block disease transmission.

Immunity to Cryptosporidium: insights into principles of enteric responses to infection

Cryptosporidium parasites replicate within intestinal epithelial cells and are an important cause of diarrhoeal disease in young children and in patients with primary and acquired defects in T cell function. This Review of immune-mediated control of Cryptosporidium highlights advances in understanding how intestinal epithelial cells detect this infection, the induction of innate resistance and the processes required for activation of T cell responses that promote parasite control. The development of a genetic tool set to modify Cryptosporidium combined with tractable mouse models provide new opportunities to understand the principles that govern the interface between intestinal epithelial cells and the immune system that mediate resistance to enteric pathogens.

Parasite microtubule arrays

Microtubules are a key component of eukaryotic cell architecture. Regulation of the dynamic growth and shrinkage of microtubules gives cells their shape, allows cells to swim, and drives the separation of chromosomes. Parasites have developed intriguingly divergent biology, seemingly expanding upon and reinventing microtubule use in fascinating ways. These organisms affect life on the planet at scales that are often overlooked: there are likely more parasitic than free-living organisms on Earth, and they have a sizeable influence across ecosystems. As parasites can cause devastating diseases, this in turn drives evolutionary adaptations and species diversity. Parasites are varied, living in all environments and at all scales - from the tiny 2 μm single-celled Plasmodium merozoite that invades red blood cells to the 40 m long Tetragonoporus, a large intestinal tapeworm of whales. To survive in their various niches, parasites have undergone striking adaptations and developed complex life cycles, often involving two or more host species. This diversity is reflected at the cellular level, where unique molecular mechanisms, cytoskeletal structures and organellar compositions are found. Hence, the study of parasite cell biology provides a biological playground for understanding diversity and species diversification. It also facilitates the identification of specific targets to develop urgently needed therapeutics: for example, drugs targeting microtubules are used at large scale to treat intestinal worms and parasites that form tissue cysts in our livers and brains. Here, we discuss some of the curious microtubule arrays found in a small, select number of human-infecting, single-celled parasites of medical importance (Table 1). Our aim is to put a spotlight on distinctive molecular features in a field that promises exciting cell-biological discoveries with the potential for therapeutic breakthroughs.

p25alpha Domain-Containing Proteins of Apicomplexans and Related Taxa

TPPP (tubulin polymerization promoting protein)-like proteins contain one or more p25alpha (Pfam05517) domains. TPPP-like proteins occur in different types as determined by their length (e.g., long-, short-, truncated-, and fungal-type TPPP) and include the protein apicortin, which possesses another domain, doublecortin (DCX, Pfam 03607). These various TPPP-like proteins are found in various phylogenomic groups. In particular, short-type TPPPs and apicortin are well-represented in the Myzozoa, which include apicomplexans and related taxa, chrompodellids, dinoflagellates, and perkinsids. The long-, truncated-, and fungal-type TPPPs are not found in the myzozoans. Apicortins are found in all apicomplexans except one piroplasmid species, present in several other myzozoans, and seem to be correlated with the conoid and apical complex. Short-type TPPPs are predominantly found in myzozoans that have flagella, suggesting a role in flagellum assembly or structure.

Cryptosporidium uses multiple distinct secretory organelles to interact with and modify its host cell

Cryptosporidium is a leading cause of diarrheal disease in children and an important contributor to early childhood mortality. The parasite invades and extensively remodels intestinal epithelial cells, building an elaborate interface structure. How this occurs at the molecular level and the contributing parasite factors are largely unknown. Here, we generated a whole-cell spatial proteome of the Cryptosporidium sporozoite and used genetic and cell biological experimentation to discover the Cryptosporidium-secreted effector proteome. These findings reveal multiple organelles, including an original secretory organelle, and generate numerous compartment markers by tagging native gene loci. We show that secreted proteins are delivered to the parasite-host interface, where they assemble into different structures including a ring that anchors the parasite into its unique epicellular niche. Cryptosporidium thus uses a complex set of secretion systems during and following invasion that act in concert to subjugate its host cell.

Live imaging of the Cryptosporidium parvum life cycle reveals direct development of male and female gametes from type I meronts

Cryptosporidium is a leading infectious cause of diarrhea around the world associated with waterborne outbreaks, community spread, or zoonotic transmission. The parasite has significant impact on early childhood mortality, and infection is both a consequence and cause of malnutrition and stunting. There is currently no vaccine, and treatment options are very limited. Cryptosporidium is a member of the Apicomplexa, and, as typical for this, protist phylum relies on asexual and sexual reproduction. In contrast to other Apicomplexa, including the malaria parasite Plasmodium, the entire Cryptosporidium life cycle unfolds in a single host in less than 3 days. Here, we establish a model to image life cycle progression in living cells and observe, track, and compare nuclear division of asexual and sexual stage parasites. We establish the length and sequence of the cell cycles of all stages and map the developmental fate of parasites across multiple rounds of invasion and egress. We propose that the parasite executes an intrinsic program of 3 generations of asexual replication, followed by a single generation of sexual stages that is independent of environmental stimuli. We find no evidence for a morphologically distinct intermediate stage (the tetraploid type II meront) but demonstrate direct development of gametes from 8N type I meronts. The progeny of each meront is collectively committed to either asexual or sexual fate, but, importantly, meronts committed to sexual fate give rise to both males and females. We define a Cryptosporidium life cycle matching Tyzzer’s original description and inconsistent with the coccidian life cycle now shown in many textbooks.

Cryptosporidium rhoptry effector protein ROP1 injected during invasion targets the host cytoskeletal modulator LMO7

The parasite Cryptosporidium invades and replicates in intestinal epithelial cells and is a leading cause of diarrheal disease and early childhood mortality. The molecular mechanisms that underlie infection and pathogenesis are largely unknown. Here, we delineate the events of host cell invasion and uncover a mechanism unique to Cryptosporidium. We developed a screen to identify parasite effectors, finding the injection of multiple parasite proteins into the host from the rhoptry organelle. These factors are targeted to diverse locations within the host cell and its interface with the parasite. One identified effector, rhoptry protein 1 (ROP1), accumulates in the terminal web of enterocytes through direct interaction with the host protein LIM domain only 7 (LMO7) an organizer of epithelial cell polarity and cell-cell adhesion. Genetic ablation of LMO7 or ROP1 in mice or parasites, respectively, impacts parasite burden in vivo in opposite ways. Taken together, these data provide molecular insight into how Cryptosporidium manipulates its intestinal host niche.

The Biology of the Intestinal Intracellular Parasite Cryptosporidium

Cryptosporidium emerged as a leading global cause of severe diarrheal disease in children. The parasite occupies a unique intracellular niche at the brush border of intestinal epithelial cells, where it undergoes a complex sexual life cycle. How this life cycle unfolds and how host and parasite interact remain largely to be discovered. A series of technical advances now offer genetic and immunological tools for mechanistic investigation of the parasite. Here we introduce the pathogen and disease and highlight important questions to tackle onward. We invite scientists to consider this versatile parasite model to probe the biology and immunology of the intestine.

Life cycle progression and sexual development of the apicomplexan parasite Cryptosporidium parvum

The apicomplexan parasite Cryptosporidium is a leading global cause of severe diarrhoeal disease and an important contributor to early childhood mortality. Currently, there are no fully effective treatments or vaccines available. Parasite transmission occurs through ingestion of oocysts, through either direct contact or consumption of contaminated water or food. Oocysts are meiotic spores and the product of parasite sex. Cryptosporidium has a single-host life cycle in which both asexual and sexual processes occur in the intestine of infected hosts. Here, we genetically engineered strains of Cryptosporidium to make life cycle progression and parasite sex tractable. We derive reporter strains to follow parasite development in culture and in infected mice and define the genes that orchestrate sex and oocyst formation through mRNA sequencing of sorted cells. After 2 d, parasites in cell culture show pronounced sexualization, but productive fertilization does not occur and infection falters. By contrast, in infected mice, male gametes successfully fertilize female parasites, which leads to meiotic division and sporulation. To rigorously test for fertilization, we devised a two-component genetic-crossing assay using a reporter that is activated by Cre recombinase. Our findings suggest obligate developmental progression towards sex in Cryptosporidium, which has important implications for the treatment and prevention of the infection.

Infection with Cryptosporidium parvum is a leading cause of severe diarrhoeal disease and childhood mortality worldwide. Using tools they recently developed to genetically engineer Cryptosporidium, the authors define life cycle stage-specific markers and generate reporter parasites, making life cycle progression and parasite sex tractable.

Captive Agamid lizards in Germany: Prevalence, pathogenicity and therapy of gastrointestinal protozoan and helminth infections

Reptiles are becoming popular pets in many parts of the world. They are also known to harbor numerous gastrointestinal parasites. We used faecal smears to examine 748 stool samples from 14 different agamid lizard species. In addition, we used coproantigen ELISA tests (11 samples) and immunofluorescence assays (IFA) (19 samples) to detect reptile Cryptosporidium infections. In 28 cases, veterinarians requested therapy to treat oxyurid- and/or Isospora amphiboluri-infections and resent fecal samples after proposed therapy and anti-parasitic treatments had been applied. We also performed complete dissections of 24 deceased agamas in order to specify protozoan and helminth parasite infections. Overall, the examined fecal samples contained 6 different taxa. Oxyurids (Pharyngodonidae) were the most prevalent nematodes (41.2%), followed by I. amphiboluri (17.0%), Entamoeba spp. (0.8%), Choleoeimeria spp. (0.5%), Trichomonas spp. (0.3%), Cryptosporidium spp. (0.3%) and Strongyloides-like nematodes (0.1%). I. amphiboluri infections were significantly more prevalent (Chi-square test: χ² = 21,5, df = 1, P <  0.001) in juvenile agamid lizards (31.9%) than in adults (14.2%). One of 11 (9.1%) coproantigen ELISA-examined samples was positive for Cryptosporidium. In 10.5% of the samples we found oocysts of Cryptosporidium. Thirteen (54.2%) of necropsied agamid lizards were infected with endoparasites and it is likely that three (12.5%) of them died due to severe parasitic infections. 74.0% of the samples that were submitted after therapy had been applied were negative. The high prevalences and pathological findings of several clinical parasitoses observed in these exotic reptiles calls for more detailed investigations on agamid gastrointestinal parasite fauna.

Budding of the Alveolate Alga Vitrella brassicaformis Resembles Sexual and Asexual Processes in Apicomplexan Parasites

Ease of cultivation and availability of genomic data promoted intensive research of free-living phototrophic relatives of apicomplexans, i.e. Chromera velia and Vitrella brassicaformis. Chromera and Vitrella differ significantly in their physiology, morphology, phylogenetic position and genomic features, but Vitrella has not gained as much attention. Here we describe two types of Vitrella zoosporangia. One contains zoospores surrounded by roughly structured matter, with an intracytoplasmic axoneme predicted to develop into a mature flagellum upon spore release, similarly to Plasmodium microgametes; in the second type, cells concurrently bud off the center of the sporangium, surrounded by smooth matter, and flagella develop extracellularly. This process of budding is reminiscent of microsporogenesis as seen in Toxoplasma. We suggest one (or both) of these processes generates gamete-like flagellate progeny. Based on live staining, fusion of zoospores does occur in cultures of V. brassicaformis. We failed to find an apical structure similar to the pseudoconoid in any life stage. V. brassicaformis may therefore either represent an ancestral state lacking an apical complex or has lost the apical complex secondarily. We propose that the common ancestor of Apicomplexa and "chrompodellids" exhibited a complex life cycle, which was reduced in chromerids and colpodellids as dictated by their environment.

Ultrastructural Comparison of Hepatozoon ixoxo and Hepatozoon theileri (Adeleorina: Hepatozoidae), Parasitising South African Anurans

To date, only two haemogregarine parasite species have been described from South African anurans: Hepatozoon ixoxo, infecting toads of the genus Sclerophrys (syn. Amietophrynus); and Hepatozoon theileri, parasitising the common river frog, Amietia quecketti. Both species have been characterised using limited morphology, and molecular data from PCR amplified fragments of the 18S rRNA gene. However, no ultrastructural work has been performed thus far. The aim of this study was to add descriptive information on the two species by studying their ultrastructural morphology. Mature gamont stages, common in the peripheral blood of infected frogs, were examined by transmission electron microscopy. Results indicate that H. ixoxo and H. theileri share typical apicomplexan characteristics, but differ markedly in their external cellular structure. Hepatozoon ixoxo is an encapsulated parasite presenting a prominent cap at the truncate pole, and shows no visible modifications to the host cell membrane. In comparison, H. theileri does not present a capsule or cap, and produces marked morphological changes to its host cell. Scanning electron microscopy was performed to further examine the cytopathological effects of H. theileri, and results revealed small, knob-like protrusions on the erythrocyte surface, as well as notable distortion of the overall shape of the host cell.

The fine structure of sexual stage development and sporogony of Cryptosporidium parvum in cell-free culture

The sexual stages and new oocysts development of Cryptosporidium parvum were investigated in a cell-free culture system using transmission electron microscopy (TEM). Sexual development was extremely rapid after inoculation of oocysts into the medium. The process began within 1/2-12 h and was completed with new oocyst formation 120 h post-inoculation. The macrogamonts were bounded by two membranes and had amylopectin granules and two distinct types of wall-forming bodies. The microgamonts had a large nucleus showing lobe projections and condensation of chromatin, giving rise to peripherally budding microgametes. The microgametes contained a large area of granular substance containing groups of microtubules surrounding the electron-dense nucleus. In some instances, the dividing microgamy was observed in cell-free cultures with no preceding merogonic process. Fertilization was observed with the bullet-shaped microgamete penetrating an immature macrogamont at 24 and 216 h. The new thin- and thick-walled oocysts had a large residuum with polysaccharide granules and sporogony noted inside these oocysts. Novel immature four-layer walled thick oocysts with irregular knob-like protrusions on the outer layer resembling the immature Eimeria oocysts were also observed. The present study confirms the gametogony and sporogony of C. parvum in cell-free culture and describes their ultra-structure for the first time.

Electron microscopic observation of the early stages of Cryptosporidium parvum asexual multiplication and development in in vitro axenic culture

The stages of Cryptosporidium parvum asexual exogenous development were investigated at high ultra-structural resolution in cell-free culture using transmission electron microscopy (TEM). Early C. parvum trophozoites were ovoid in shape, 1.07 × 1.47 μm(2) in size, and contained a large nucleus and adjacent Golgi complex. Dividing and mature meronts containing four to eight developing merozoites, 2.34 × 2.7 μm(2) in size, were observed within the first 24h of cultivation. An obvious peculiarity was found within the merozoite pellicle, as it was composed of the outer plasma membrane with underlying middle and inner membrane complexes. Further novel findings were vacuolization of the meront's residuum and extension of its outer pellicle, as parasitophorous vacuole-like membranes were also evident. The asexual reproduction of C. parvum was consistent with the developmental pattern of both eimerian coccidia and Arthrogregarinida (formerly Neogregarinida). The unique cell-free development of C. parvum described here, along with the establishment of meronts and merozoite formation, is the first such evidence obtained from in vitro cell-free culture at the ultrastructural level.

An essential role of the basal body protein SAS-6 in Plasmodium male gamete development and malaria transmission

Gametocytes are the sole Plasmodium parasite stages that infect mosquitoes; therefore development of functional gametes is required for malaria transmission. Flagellum assembly of the Plasmodium male gamete differs from that of most other eukaryotes in that it is intracytoplasmic but retains a key conserved feature: axonemes assemble from basal bodies. The centriole/basal body protein SAS-6 normally regulates assembly and duplication of these organelles and its depletion causes severe flagellar/ciliary abnormalities in a diverse array of eukaryotes. Since basal body and flagellum assembly are intimately coupled to male gamete development in Plasmodium, we hypothesized that SAS-6 disruption may cause gametogenesis defects and perturb transmission. We show that Plasmodium berghei sas6 knockouts display severely abnormal male gametogenesis presenting reduced basal body numbers, axonemal assembly defects and abnormal nuclear allocation. The defects in gametogenesis reduce fertilization and render Pbsas6 knockouts less infectious to mosquitoes. Additionally, we show that lack of Pbsas6 blocks transmission from mosquito to vertebrate host, revealing an additional yet undefined role in ookinete to sporulating oocysts transition. These findings underscore the vulnerability of the basal body/SAS-6 to malaria transmission blocking interventions.

ELECTRON MICROSCOPIC OBSERVATION OF THE INVASION PROCESS OF CRYPTOSPORIDIUM PARVUM IN SEVERE COMBINED IMMUNODEFICIENCY MICE

Cryptosporidium parvum mainly invades the intestinal epithelium and causes watery diarrhea in humans and calves. However, the invasion process has not yet been clarified. In the present study, the invasion process of C. parvum in severe combined immunodeficiency (SCID) mice was examined. Infected mice were necropsied; the ilea were double-fixed routinely and observed by scanning and transmission electron microscopy. In addition, the microvillus membrane was observed by ruthenium red staining. Scanning electron micrographs showed elongation of the microvilli at the periphery of the parasite. The microvilli were shown to be along the surface of the parasite in higher magnification. Transmission electron microscopy confirmed that the invading parasites were located among microvilli. Parasites existed in the parasitophorous vacuole formed by the microvillus membrane. The parasite pellicle attached to the host cell membrane at the bottom of the parasite, and then the pellicle and host cell membrane became unclear. Subsequently, the pellicle became complicated and formed a feeder organelle. In addition, invasion of the parasite was not observed in either a microvillus or the cytoplasm of the host cell. Therefore, C. parvum invades among microvilli, is covered with membranes derived from numerous microvilli, and develops within the host cell.

Chronic cryptosporidiosis in Australian elapid snakes: control of an outbreak in a captive colony

An outbreak of chronic cryptosporidiosis resulting in hypertrophic gastritis occurred in a captive colony of Australian elapid snakes. Two species of the genus Notechis were involved: Notechis ater (Black Tiger Snake) and Notechis scutatus (Eastern or Mainland Tiger Snake). The infection was eventually fatal in all 9 affected snakes. Typical histopathological findings of the stomach included mucosal thickening with cystic dilatation of gastric glands, moderate oedema and fibrosis of the lamina propria, and a mild to moderate patchy infiltration of inflammatory cells. Procedures implemented to contain the outbreak included the use of a formaldehyde-based disinfectant, prompt removal of faecal matter, uneaten and regurgitated food from enclosures, and examination of faecal specimens for Cryptosporidium oocytes and other pathogens.

Sexual stage development of cryptosporidia in the Caco-2 cell line

We used the spontaneously differentiated human intestinal epithelial cell line Caco-2 to develop an in vitro model of Cryptosporidium sp. infection. The mean cell infection rate was 3% +/- 2%. Asexual stages of cryptosporidia were observed on day 2 postinoculation. Transmission electron microscopy showed the presence of macrogametes at day 5. This cell line appears to be suited to the study of the mechanisms by which biological agents inhibit both sexual and asexual development of cryptosporidia.