Assessment of drugs against Cryptosporidium parvum using a simple in vitro screening method

Molecular identification and antiprotozoal activity of silver nanoparticles on viability of Cryptosporidium parvum isolated from pigeons, pigeon fanciers and water

Cryptosporidium is a protozoan that causes acute gastroenteritis, abdominal pain, and diarrhea in many vertebrate species, including humans, animals and birds. A number of studies have reported the occurrence of Cryptosporidium in domestic pigeons. Thus, this study aimed to identify Cryptosporidium spp. in samples collected from domestic pigeons, pigeon fanciers, and drinking water, as well as to investigate the antiprotozoal activity of biosynthesized silver nanoparticles (AgNPs) on the viability of isolated Cryptosporidium parvum (C. parvum). Samples were collected from domestic pigeons (n = 150), pigeon fanciers (n = 50), and drinking water (n = 50) and examined for the presence of Cryptosporidium spp. using microscopic and molecular techniques. The antiprotozoal activity of AgNPs was then assessed both in vitro and in vivo. Cryptosporidium spp. was identified in 16.4% of all examined samples, with C. parvum identified in 5.6%. The highest frequency of isolation was from domestic pigeon, rather than from pigeon fanciers or drinking water. In domestic pigeons, there was a significant association between Cryptosporidium spp. positivity and pigeon's age, droppings consistency, housing, hygienic and heath conditions. However, Cryptosporidium spp. positivity was only significantly associated with pigeon fanciers' gender and heath condition. The viability of C. parvum oocysts was reduced using AgNPs at various concentrations and storage times in a descending manner. In an in vitro study, the highest reduction in C. parvum count was observed at the AgNPs concentration of 1000 µg/mL after a 24 h contact time, followed by the AgNPs concentration of 500 µg/mL after a 24 h contact time. However, after a 48 h contact time, a complete reduction was observed at both 1000 and 500 µg/mL concentrations. Overall, the count and viability of C. parvum decreased with increasing the AgNPs concentration and contact times in both the in vitro and in vivo studies. Furthermore, the C. parvum oocyst destruction was time-dependent and increased with increasing the contact time at various AgNPs concentrations.

Phenotypic screening techniques for Cryptosporidium drug discovery

Introduction: Two landmark epidemiological studies identified Cryptosporidium spp. as a significant cause of diarrheal disease in pediatric populations in resource-limited countries. Notably, nitazoxanide is the only approved drug for treatment of cryptosporidiosis but shows limited efficacy. As a result, many drug discovery efforts have commenced to find improved treatments. The unique biology of Cryptosporidium presents challenges for traditional drug discovery methods, which has inspired new assay platforms to study parasite biology and drug screening. Areas covered: The authors review historical advancements in phenotypic-based assays and techniques for Cryptosporidium drug discovery, as well as recent advances that will define future drug discovery. The reliance on phenotypic-based screens and repositioning of phenotypic hits from other pathogens has quickly created a robust pipeline of potential cryptosporidiosis therapeutics. The latest advances involve new in vitro culture methods for oocyst generation, continuous culturing capabilities, and more physiologically relevant assays for testing compounds. Expert opinion: Previous phenotypic screening techniques have laid the groundwork for recent cryptosporidiosis drug discovery efforts. The resulting improved methodologies characterize compound activity, identify, and validate drug targets, and prioritize new compounds for drug development. The most recent improvements in phenotypic assays are poised to help advance compounds into clinical development.

Assessment of differences between DNA content of cell-cultured and freely suspended oocysts of Cryptosporidium parvum and their suitability as DNA standards in qPCR

BACKGROUND

Although more modern methods are available, quantitative PCR (qPCR) is reproducible, sensitive and specific with instruments and expertise readily available in many laboratories. As such, the use of qPCR in Cryptosporidium research is well established and still widely used by researchers globally. This method depends upon the generation of standards at different concentrations to generate standard curves subsequently used for the quantification of DNA.

METHODS

We assessed four types of DNA template used to generate standard curves in drug screening studies involving Cryptosporidium spp.: (i) serially diluted Cryptosporidium parvum oocysts (106-1); (ii) diluted template DNA from pure oocysts (×10-×106 dilution of 106 oocyst DNA template); (iii) oocysts incubated in human ileocecal adenocarcinoma (HCT-8) cells (105-1 and 5 × 104-50); and (iv) diluted DNA template (5 × 104) from cell culture incubated parasites (×10-×1000).

RESULTS

Serial dilutions of both cell culture and pure oocyst suspension DNA template yielded better linearity than cell culture derived standards, with dilutions of 106 oocysts exhibiting similar quantification cycle (Cq) values to those obtained from DNA template dilutions of 106 oocysts. In contrast, cell culture incubated oocysts demonstrated significantly higher DNA content than equivalent freely suspended oocysts and diluted DNA template from both cell culture derived and freely suspended oocysts across numerous concentrations.

CONCLUSIONS

For many studies involving Cryptosporidium, only relative DNA content is required and as such, the superior linearity afforded by freely suspended oocysts and diluted DNA template (from either cell culture derived standards or freely suspended oocysts) will allow for more accurate relative quantification in each assay. Parasite division in the cell culture standards likely explains the higher DNA content found. These standards, therefore, have the potential to more accurately reflect DNA content in cell culture assays, and despite more modern methods available for absolute quantification, i.e. droplet digital PCR (ddPCR), the ubiquity of qPCR for the foreseeable future encourages further investigation into the reduced linearity observed in these standards such as varying oocyst seeding density, non-linear growth rates and assay efficiency.

Discovery of Novel Anti-cryptosporidial Activities From Natural Products by in vitro High-Throughput Phenotypic Screening

Cryptosporidium parvum is a globally distributed zoonotic protozoan parasite of both medical and veterinary importance. Nitazoxanide is the only FDA-approved drug to treat cryptosporidiosis in immunocompetent people, but it is not fully effective. There is no drug approved by FDA for use in immunocompromised patients or in animals. In the present study, we conducted phenotypic screening of 800 nature products with defined chemical structures for potential novel activity against the growth of C. parvum in vitro. We identified a large number of compounds showing low to sub-micromolar anti-cryptosporidial activity, and fully characterized 16 top hits for anti-parasitic efficacies in vitro [EC₅₀ values from 0.122 to 3.940 μM, cytotoxicity (TC₅₀) values from 6.31 to >100 μm] and their safety margins. Among them, 11 compounds were derived from plants with EC₅₀ values from 0.267 to 3.940 μM [i.e., cedrelone, deoxysappanone B 7,4'-dimethyl ether (Deox B 7,4), tanshinone IIA, baicalein, deoxysappanone B 7,3'-dimethyl ether acetate, daunorubicin, dihydrogambogic acid, deacetylgedunin, deacetoxy-7-oxogedunin, dihydrotanshinone I, 2,3,4'-trihydroxy-4-methoxybenzophenone, and 3-deoxo-3beta-hydroxy-mexicanolide 16-enol ether]. Three compounds with sub-micromolar EC₅₀ values (i.e., cedrelone, Deox B 7,4, and baicalein) were further investigated for their effectiveness on various parasite developmental stages in vitro. Cedrelone and baicalein were more effective than Dexo B 7,4 when treating parasite for shorter periods of time, but all three compounds could kill the parasite irreversibly. These findings provide us a large selection of new structures derived from natural products to be explored for developing anti-cryptosporidial therapeutics.

Inhibitory activity of chitosan nanoparticles against Cryptosporidium parvum oocysts

Cryptosporidium is a ubiquitous harsh protozoan parasite that resists many disinfectants. It remains viable and infective for a long time in water and food causing global outbreaks. Chitosan (the deacetylated chitin molecule) was used in its nanosuspension form to evaluate its effect against Cryptosporidium parvum. The experiments were performed in vitro in serial concentrations and confirmed in mice in vivo infectivity assay. Chitosan nanoparticles (Cs NPs) were toxic to Cryptosporidium oocysts. The effect appeared to decrease the number of Cryptosporidium oocysts and altered their content. The destruction rate of oocysts was dependent on the dose of chitosan and the time of exposure (P < 0.05). Higher doses of Cs NPs over a prolonged period exhibited a significantly higher destruction rate. Using staining and light microscopy, remarkable destructive changes were observed in the oocysts' morphology. The minimal lethal dose for > 90% of oocysts was 3000 μg/ml, no mice infections in vivo were observed. The results in this study elucidate Cs NPs as an effective anti-cryptosporidial agent.

Oleylphosphocholine (OlPC) arrests Cryptosporidium parvum growth in vitro and prevents lethal infection in interferon gamma receptor knock-out mice

Cryptosporidium parvum is a species of protozoa that causes cryptosporidiosis, an intestinal disease affecting many mammals including humans. Typically, in healthy individuals, cryptosporidiosis is a self-limiting disease. However, C. parvum can cause a severe and persistent infection that can be life-threatening for immunocompromised individuals, such as AIDS patients. As there are no available treatments for these patients that can cure the disease, there is an urgent need to identify treatment options. We tested the anti-parasitic activity of the alkylphosphocholine oleylphosphocholine (OlPC), an analog of miltefosine, against C. parvum in in vitro and in vivo studies. In vitro experiments using C. parvum infected human ileocecal adenocarcinoma cells (HCT-8 cells) showed that OlPC has an EC₅₀ of 18.84 nM. Moreover, no cell toxicity has been seen at concentrations ≤50 μM. C57BL/6 interferon gamma receptor knock-out mice, were infected by gavage with 4000 C. parvum oocysts on Day 0. Oral treatments, with OlPC, miltefosine, paromomycin or PBS, began on Day 3 post-infection for 10 days. Treatment with OlPC, at 40 mg/kg/day resulted in 100% survival, complete clearance of parasite in stools and a 99.9% parasite burden reduction in the intestines at Day 30. Doses of 30 and 20 mg/kg/day also demonstrated an increased survival rate and a dose-dependent parasite burden reduction. Mice treated with 10 mg/kg/day of miltefosine resulted in 50% survival at Day 30. In contrast, control mice, treated with PBS or 100 mg/kg/day of paromomycin, died or had to be euthanized between Days 6 and 13 due to severe illness. Results of parasite burden were obtained by qPCR and cross-validated by both flow cytometry of stool oocysts and histological sections of the ileum. Together, our results strongly support that OlPC represents a potential candidate for the treatment of C. parvum infections in immunocompromised patients.

A review of the global burden, novel diagnostics, therapeutics, and vaccine targets for cryptosporidium

Cryptosporidium spp are well recognised as causes of diarrhoeal disease during waterborne epidemics and in immunocompromised hosts. Studies have also drawn attention to an underestimated global burden and suggest major gaps in optimum diagnosis, treatment, and immunisation. Cryptosporidiosis is increasingly identified as an important cause of morbidity and mortality worldwide. Studies in low-resource settings and high-income countries have confirmed the importance of cryptosporidium as a cause of diarrhoea and childhood malnutrition. Diagnostic tests for cryptosporidium infection are suboptimum, necessitating specialised tests that are often insensitive. Antigen-detection and PCR improve sensitivity, and multiplexed antigen detection and molecular assays are underused. Therapy has some effect in healthy hosts and no proven efficacy in patients with AIDS. Use of cryptosporidium genomes has helped to identify promising therapeutic targets, and drugs are in development, but methods to assess the efficacy in vitro and in animals are not well standardised. Partial immunity after exposure suggests the potential for successful vaccines, and several are in development; however, surrogates of protection are not well defined. Improved methods for propagation and genetic manipulation of the organism would be significant advances.

A review of chemotherapeutic approaches to the treatment of cryptosporidiosis

This review focuses on chemotherapies used against the parasite, Cryptosporidium parvum, the causative agent of cryptosporidiosis. Populations at risk from severe morbidity or mortality from cryptosporidiosis are discussed with particular reference to those infected with HIV. The review then examines chemotherapies used in the clinical setting, as well as a number of in vitro and in vivo experimental studies. It begins with a discussion of the targets within Cryptosporidium that have been the foci of past treatments and then examines novel target sites that may present an exploitable alternative. Some of the novel target sites discussed include the recently discovered apicomplexan plastid and its associated pathways. Lastly, the review examines tubulin as a potential anticryptosporidial target in view of the fact that it has been exploited successfully for almost 50 years for the treatment of helminthiasis. The review concludes with a five-year outlook on the future of anticryptosporidial drug design.

A cysteine protease inhibitor rescues mice from a lethal Cryptosporidium parvum infection

Cryptosporidiosis, caused by the protozoan parasite Cryptosporidium parvum, can stunt infant growth and can be lethal in immunocompromised individuals. The most widely used drugs for treating cryptosporidiosis are nitazoxanide and paromomycin, although both exhibit limited efficacy. To investigate an alternative approach to therapy, we demonstrate that the clan CA cysteine protease inhibitor N-methyl piperazine-Phe-homoPhe-vinylsulfone phenyl (K11777) inhibits C. parvum growth in mammalian cell lines in a concentration-dependent manner. Further, using the C57BL/6 gamma interferon receptor knockout (IFN-γR-KO) mouse model, which is highly susceptible to C. parvum, oral or intraperitoneal treatment with K11777 for 10 days rescued mice from otherwise lethal infections. Histologic examination of untreated mice showed intestinal inflammation, villous blunting, and abundant intracellular parasite stages. In contrast, K11777-treated mice (210 mg/kg of body weight/day) showed only minimal inflammation and no epithelial changes. Three putative protease targets (termed cryptopains 1 to 3, or CpaCATL-1, -2, and -3) were identified in the C. parvum genome, but only two are transcribed in infected mammals. A homology model predicted that K11777 would bind to cryptopain 1. Recombinant enzymatically active cryptopain 1 was successfully targeted by K11777 in a competition assay with a labeled active-site-directed probe. K11777 exhibited no toxicity in vitro and in vivo, and surviving animals remained free of parasites 3 weeks after treatment. The discovery that a cysteine protease inhibitor provides potent anticryptosporidial activity in an animal model of infection encourages the investigation and development of this biocide class as a new, and urgently needed, chemotherapy for cryptosporidiosis.

Pomegranate (Punica granatum) peel is effective in a murine model of experimental Cryptosporidium parvum ultrastructural studies of the ileum

The current treatments for cryptosporidiosis are ineffective, and there is an urgent need to search for more effective and safer alternatives. One such alternative may be treatments derived from natural resources. The pomegranate peel has been used effectively in traditional medicine to cure diarrhea and dysentery. The purpose of this study was to examine the effectiveness of a Punica granatum (pomegranate) peel suspension as a treatment for Cryptosporidium parvum infection. In this study, the effects of this treatment on the ultrastructure of both the intestinal epithelial layer of infected nursling mice and the parasite were observed with a transmission electron microscope. The histological study focused on the examination of the microvilli, columnar epithelium, goblet cells, lamina propria, and crypts of Lieberkuhn. Examination of the ileums of infected mice that received the pomegranate peel suspension demonstrated that the general structure of the ileal tissue of these mice was similar to that of the control group. In the infected mice treated with the suspension, but not the infected/untreated mice, there was an improvement in all ultrastructure aspects at 28days post-inoculation. The study of the ultrastructure of the parasite (C. parvum) in mice treated with the suspension showed that there was decomposition in the parasite to the extent that in some cases we were unable to identify the stage of the parasite due to the severe degeneration. Significant decomposition of the nutrition organ was also observed. Additionally, microgamonte and macrogamonte were not observed in the suspension-treated group, explaining the disappearance of the sexual phases of the parasite in the lumens of this group. In all, this examination demonstrated the restoration of the normal structures of villi and the disappearance of acute symptoms in the suspension-treated mice and showed that the suspension directly affected the parasite at various stages of its development and led to its decomposition and death.

Drug repurposing screen reveals FDA-approved inhibitors of human HMG-CoA reductase and isoprenoid synthesis that block Cryptosporidium parvum growth

Cryptosporidiosis, a diarrheal disease usually caused by Cryptosporidium parvum or Cryptosporidium hominis in humans, can result in fulminant diarrhea and death in AIDS patients and chronic infection and stunting in children. Nitazoxanide, the current standard of care, has limited efficacy in children and is no more effective than placebo in patients with advanced AIDS. Unfortunately, the lack of financial incentives and the technical difficulties associated with working with Cryptosporidium parasites have crippled efforts to develop effective treatments. In order to address these obstacles, we developed and validated (Z' score = 0.21 to 0.47) a cell-based high-throughput assay and screened a library of drug repurposing candidates (the NIH Clinical Collections), with the hopes of identifying safe, FDA-approved drugs to treat cryptosporidiosis. Our screen yielded 21 compounds with confirmed activity against C. parvum growth at concentrations of <10 μM, many of which had well-defined mechanisms of action, making them useful tools to study basic biology in addition to being potential therapeutics. Additional work, including structure-activity relationship studies, identified the human 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitor itavastatin as a potent inhibitor of C. parvum growth (50% inhibitory concentration [IC(50)] = 0.62 μM). Bioinformatic analysis of the Cryptosporidium genomes indicated that the parasites lack all known enzymes required for the synthesis of isoprenoid precursors. Additionally, itavastatin-induced growth inhibition of C. parvum was partially reversed by the addition of exogenous isopentenyl pyrophosphate, suggesting that itavastatin reduces Cryptosporidium growth via on-target inhibition of host HMG-CoA reductase and that the parasite is dependent on the host cell for synthesis of isoprenoid precursors.

In vitro determination of anticryptosporidial activity of phytogenic extracts and compounds

Cryptosporidiosis caused by Cryptosporidium spp. is an important diarrhoeal disease observed in farm animals and humans, especially in young or immunocompromised individuals. A novel cell culture assay for testing extracts and pure compounds against Cryptosporidium parvum in 96-well microplate format was established and evaluated. It is based on previously described indirect fluorescent antibody techniques and was optimised for higher sample throughput. Rapid assessment of minimal inhibitory concentrations (MICs) was done by checking each well microscopically for the presence or absence of parasite stages. As a novelty, parasite development was quantified by enumeration of clusters of secondary infection (CSI), which typically appeared upon infection with a distinct parasite inoculum after a defined incubation time. Host cell (HCT-8) viability was measured by an integrated non-destructive water-soluble tetrazolium salt assay (WST-1), which facilitated discrimination of antiparasitic activity from possible cytotoxic effects of a test compound against the host cells. Host cell viability was regarded unimpaired when cultures had 75% or more viability when compared to control cultures without test substance. In this study, a maximum density of distinguishable CSI was obtained when cultures were infected with 2.5 × 10(3) oocysts and incubated for 48 h. The applicable inoculum has to be optimised for each batch of oocysts and before each experimental series. Parasite development was inhibited completely by monensin at 134 nM and silymarin at 50 mg/mL. These concentrations were non-toxic to the host cells and comparable to literature data. The percentages of parasite inhibition were determined for monensin and a 50% inhibitory concentration (IC(50)) of 36.6 nM (27.4-45.5) and a 90% inhibitory concentration of 65.9 nM (54.8-90.2) were calculated. The introduced assay is economic because relatively low parasite numbers may be used. If MICs are determined, evaluation is fast, as each well is viewed only briefly under the fluorescence microscope for presence or absence of CSI. Furthermore it is highly critical because only full parasite inhibition is assessed. Counting of CSI is more laborious and time-consuming, but it allows calculation of parasite inhibition rates and parameters like the half maximal inhibitory concentration (IC(50)). This assay shall be used to assess anticryptosporidial activities of various plant waste materials and by-products from the food and the pharmaceutical industries in the course of the EU project SAFEWASTES. Comparison with in vivo models should be performed to further corroborate the results. Automated evaluation by flow cytometry might facilitate higher sample throughput and reduce operator bias.

Characterization of trifluralin binding with recombinant tubulin from Trypanosoma brucei

The binding kinetics of five novel trifluralin analogs with recombinant alpha- and beta-tubulin proteins from Trypanosoma brucei rhodesiense was determined. Native tubulin from rats was used to determine the extent of binding of each analog to mammalian tubulin. The results of this study clearly demonstrate two important characteristics of the binding of these trifluralins to tubulin. Firstly, they have specific affinity for trypanosomal tubulin compared with mammalian tubulin irrespective of the chemical composition of the trifluralin analog tested. Secondly, they have a stronger affinity for trypanosomal alpha-tubulin compared with trypanosomal beta-tubulin. In addition, compounds 1007, 1008, 1016, and 1017 have strong binding affinities for alpha-tubulin, with limited binding affinity for mammalian tubulin, which indicates that these compounds selectively bind to trypanosomal tubulin.

Efficacy of pyrvinium pamoate against Cryptosporidium parvum infection in vitro and in a neonatal mouse model

No effective approved drug therapy exists for Cryptosporidium infection of immunocompromised patients. Here we investigated the nonabsorbed anthelmintic drug pyrvinium pamoate for inhibition of the growth of the intestinal protozoan parasite Cryptosporidium parvum. The concentration of pyrvinium that effected 50% growth inhibition in human enterocytic HCT-8 cells by a quantitative alkaline phosphatase immunoassay was 354 nM. For comparison, in the same assay, 50% growth inhibition was obtained with 711 microM paromomycin or 27 microM chloroquine. We used a neonatal mouse model to measure the anti-Cryptosporidium activity of pyrvinium pamoate in vivo. Beginning 3 days after infection, pyrvinium at 5 or 12.5 mg/kg of body weight/day was administered to the treatment group mice for 4 or 6 consecutive days. Nine days after infection, the mice were sacrificed, and drug efficacy was determined by comparing the numbers of oocysts in the fecal smears of treated versus untreated mice. The intensities of trophozoite infection in the ileocecal intestinal regions were also compared using hematoxylin-and-eosin-stained histological slides. We observed a >90% reduction in infection intensity in pyrvinium-treated mice relative to that in untreated controls, along with a substantial reduction in tissue pathology. Based on these results, pyrvinium pamoate is a potential drug candidate for the treatment of cryptosporidiosis in both immunocompetent and immunocompromised individuals.

Development and validation of a cell culture based assay for in vitro assessment of anticryptosporidial compounds

In vitro culture of Cryptosporidium parvum oocysts in HCT-8 cells was combined with immunofluorescent labelling and digital image analysis to quantify the development of the parasite by detecting and measuring the labelled area in the respective cell cultures. The number of inoculated oocysts and the labelled area correlated reliably and significantly (R (2), 0.98-0.99). The effects of various concentrations of halofuginone bromide (0.00039 to 50 microM) and monensin (0.00225 to 0.144 microM) on in vitro parasite development were determined in further trials in cultures inoculated each with 10(5) oocysts. Monensin reduced the detected area in a dose-dependant manner. In comparison to the untreated controls, the area positive for C. parvum in the cultures treated with 0.144 to 0.009 microM monensin reached a maximum of 17%, and inhibition of 40% was observed at 0.0045 microM. Halofuginone bromide also efficiently inhibited parasite in vitro reproduction, albeit at higher concentrations. At 12.5 microM or more, inhibition was at least 90%; 0.05 microM still yielded 80% inhibition, whereas at concentrations below 0.00625 microM, labelled areas abruptly increased. Both drugs appeared efficient under in vitro conditions; the applied system is suited to screen drugs for their anti-cryptosporidial capacity.

Integrated mapping, chromosomal sequencing and sequence analysis of Cryptosporidium parvum

The apicomplexan Cryptosporidium parvum is one of the most prevalent protozoan parasites of humans. We report the physical mapping of the genome of the Iowa isolate, sequencing and analysis of chromosome 6, and approximately 0.9 Mbp of sequence sampled from the remainder of the genome. To construct a robust physical map, we devised a novel and general strategy, enabling accurate placement of clones regardless of clone artefacts. Analysis reveals a compact genome, unusually rich in membrane proteins. As in Plasmodium falciparum, the mean size of the predicted proteins is larger than that in other sequenced eukaryotes. We find several predicted proteins of interest as potential therapeutic targets, including one exhibiting similarity to the chloroquine resistance protein of Plasmodium. Coding sequence analysis argues against the conventional phylogenetic position of Cryptosporidium and supports an earlier suggestion that this genus arose from an early branching within the Apicomplexa. In agreement with this, we find no significant synteny and surprisingly little protein similarity with Plasmodium. Finally, we find two unusual and abundant repeats throughout the genome. Among sequenced genomes, one motif is abundant only in C. parvum, whereas the other is shared with (but has previously gone unnoticed in) all known genomes of the Coccidia and Haemosporida. These motifs appear to be unique in their structure, distribution and sequences.

Intra-isolate variation of Cryptosporidium parvum small subunit ribosomal RNA genes from human hosts in England

Cryptosporidium parvum is a protozoan parasite responsible for a number of water-borne outbreaks of human gastrointestinal infection. The importance of this parasite for human health has led to several investigations into its epidemiology. In the present study, sequence and PCR-RFLP analyses were performed on cloned SSU rRNA genes from human and bovine C. parvum isolates. Each cloned gene was assigned a genotype using AseI restriction digestion profiles. Although sequence heterogeneity was observed, six of seven human isolates contained human genotype SSU rRNA genes and one human isolate contained bovine genotype genes. No intra-isolate variation was observed between the SSU rRNA genes analysed from a single bovine (Iowa) isolate. Intra-isolate variation did not occur at the Ase I restriction sites and therefore did not interfere with the assignment of C. parvum genotypes by RFLP. Mixed RFLP genotypes (human and bovine) were not observed in any of the C. parvum isolates analysed.

Identification of a novel Cryptosporidium genotype in pigs

Over a 3-year period, a total of 646 fecal samples from pigs in 22 indoor and outdoor herds from Western Australia were screened for Cryptosporidium spp. by microscopy. Results revealed that 39 of 646 samples (6.03%) were positive for Cryptosporidium. Cryptosporidium was much more common in outdoor herds (17.2%) than in indoor herds (0.5%) and was more common in animals between the ages of 5 and 8 weeks (69.2%) than in younger animals (P < 0.0001). Molecular characterization of the positive samples at the 18S ribosomal DNA locus identified two distinct genotypes of Cryptosporidium: the previously identified pig genotype I and a novel pig genotype (pig genotype II), both of which warrant species status.

A comparison of the effects of two dinitroanilines against Cryptosporidium parvum in vitro and in vivo in neonatal mice and rats

The effects of two dinitroanilines, oryzalin and trifluralin, were compared against Cryptosporidium parvum, in vitro using HCT-8 cells and in vivo using neonatal Swiss ARC mice and Wistar neonatal rats. In vitro, oryzalin and trifluralin exhibited IC(50) values (concentration necessary to cause a 50% inhibition) of 750 and 800 nM, respectively. A viability assay showed that neither compound produced a cytotoxic effect on the host cells at concentrations as high as 1 microM. The in vivo component of this study consisted of inoculation of neonatal mice and neonatal rats with 10(5) viable oocysts of C. parvum per animal and the subsequent treatment of this infection with trifluralin and oryzalin administered via gastric intubation. At doses of 100 mg kg(-1) body weight administered twice daily for 3 consecutive days, trifluralin had no statistically significant effect on the number of oocysts recovered from the gut of either rats or mice compared with controls, whereas at the same concentration, oryzalin caused 90 and 79% inhibition of oocysts recovered from mice and rats, respectively.