Combination of cell culture and quantitative PCR (cc-qPCR) to assess disinfectants efficacy on Cryptosporidium oocysts under standardized conditions

Eimeria infections in domestic and wild ruminants with reference to control options in domestic ruminants

Eimeria infections are commonly seen in a variety of mammalian hosts. This genus of unicellular sporozoan parasites causes significant disease (coccidiosis) in different livestock species leading to economic losses for agricultural producers. Especially the production of cattle, sheep, and goat is strongly dependent on efficient coccidiosis control. However, many other livestock hosts like, e.g., camelids, bison, rabbits, and guinea pigs may benefit from reduced parasite transmission and targeted control measures as well. Besides livestock, also wildlife and pet animals may be affected by Eimeria infections resulting in clinical or subclinical coccidiosis. Wildlife herd health is crucial to conservation efforts, and Eimeria species are a prevalent pathogen in multiple mammalian wildlife species. This review aims to highlight the epidemiology of mammalian Eimeria infections in both wild and domestic ruminants, including host specificity, transmission, survival of environmental oocysts, occurrence, and risk factors for infection. Understanding general drivers of Eimeria infection may support adequate livestock and wildlife management. Furthermore, control options for livestock with reference to management factors, drug application, and alternative approaches are discussed. The goal of Eimeria control should be to reduce pathogen transmission in different host species and to improve sustainable livestock production. Controlling Eimeria infections in livestock is important considering both their animal welfare impact and their high economic relevance.

Dynamically expressed genes provide candidate viability biomarkers in a model coccidian

Eimeria parasites cause enteric disease in livestock and the closely related Cyclosporacayetanensis causes human disease. Oocysts of these coccidian parasites undergo maturation (sporulation) before becoming infectious. Here, we assessed transcription in maturing oocysts of Eimeria acervulina, a widespread chicken parasite, predicted gene functions, and determined which of these genes also occur in C. cayetanensis. RNA-Sequencing yielded ~2 billion paired-end reads, 92% of which mapped to the E. acervulina genome. The ~6,900 annotated genes underwent temporally-coordinated patterns of gene expression. Fifty-three genes each contributed >1,000 transcripts per million (TPM) throughout the study interval, including cation-transporting ATPases, an oocyst wall protein, a palmitoyltransferase, membrane proteins, and hypothetical proteins. These genes were enriched for 285 gene ontology (GO) terms and 13 genes were ascribed to 17 KEGG pathways, defining housekeeping processes and functions important throughout sporulation. Expression differed in mature and immature oocysts for 40% (2,928) of all genes; of these, nearly two-thirds (1,843) increased their expression over time. Eight genes expressed most in immature oocysts, encoding proteins promoting oocyst maturation and development, were assigned to 37 GO terms and 5 KEGG pathways. Fifty-six genes underwent significant upregulation in mature oocysts, each contributing at least 1,000 TPM. Of these, 40 were annotated by 215 GO assignments and 9 were associated with 18 KEGG pathways, encoding products involved in respiration, carbon fixation, energy utilization, invasion, motility, and stress and detoxification responses. Sporulation orchestrates coordinated changes in the expression of many genes, most especially those governing metabolic activity. Establishing the long-term fate of these transcripts in sporulated oocysts and in senescent and deceased oocysts will further elucidate the biology of coccidian development, and may provide tools to assay infectiousness of parasite cohorts. Moreover, because many of these genes have homologues in C. cayetanensis, they may prove useful as biomarkers for risk.

Selected Emerging Infectious Diseases of Squamata: An Update

This article details emerging infectious diseases that have devastating impacts on captive and wild squamates. Treatment advances have been attempted for Cryptosporidium infections in squamates. Gram-positive bacteria, Devriesea agamarum and Austwickia chelonae, are contributing to severe disease in captive and now in wild reptiles, some critically endangered. Nannizziposis, Paranannizziopsis, and Ophidiomyces continue to cause fatal disease as primary pathogens in wild and captive populations of squamates and sphenodontids. Nidovirus, bornavirus, paramyxovirus, sunshine virus, and arenavirus have emerged to be significant causes of neurorespiratory disease in snakes. Controlled studies evaluating environmental stability, disinfection, transmission control, and treatment are lacking.

Mouse Models for Use in Cryptosporidium Infection Studies and Quantification of Parasite Burden Using Flow Cytometry, qPCR, and Histopathology

Cryptosporidiosis threatens life of young children in developing countries and newborn calves around the world. No vaccine or therapy can prevent or cure this diarrhea-inducing enteric disease caused by Cryptosporidium spp. protozoan parasites. There is an essential need to discover new therapeutic drugs efficient in reducing parasite burden in infected individuals. Research therefore relies on reliable small animal models of cryptosporidiosis. Here, we present excellent mouse models which can efficiently mimic pathogenesis of human and bovine cryptosporidiosis. We also describe methods to purify C. parvum oocysts from stool and intestine of infected mice to facilitate oocyst quantification. Moreover, we present protocols using flow cytometry, quantitative polymerase chain reaction, and histopathology to accurately quantify parasite burden in stool or intestine samples.

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.

Toxoplasma gondii Oocyst Infectivity Assessed Using a Sporocyst-Based Cell Culture Assay Combined with Quantitative PCR for Environmental Applications

Toxoplasma gondii is a ubiquitous foodborne protozoan that can infect humans at low dose and displays different prevalences among countries in the world. Ingestion of food or water contaminated with small amounts of T. gondii oocysts may result in human infection. However, there are no regulations for monitoring oocysts in food, mainly because of a lack of standardized methods to detect them. The objectives of this study were (i) to develop a reliable method, applicable in biomonitoring, for the rapid detection of infectious oocysts by cell culture of their sporocysts combined with quantitative PCR (sporocyst-CC-qPCR) and (ii) to adapt this method to blue and zebra mussels experimentally contaminated by oocysts with the objective to use these organisms as sentinels of aquatic environments. Combining mechanical treatment and bead beating leads to the release of 84% ± 14% of free sporocysts. The sporocyst-CC-qPCR detected fewer than ten infectious oocysts in water within 4 days (1 day of contact and 3 days of cell culture) compared to detection after 4 weeks by mouse bioassay. For both mussel matrices, oocysts were prepurified using a 30% Percoll gradient and treated with sodium hypochlorite before cell culture of their sporocysts. This assay was able to detect as few as ten infective oocysts. This sporocyst-based CC-qPCR appears to be a good alternative to mouse bioassay for monitoring infectious T. gondii oocysts directly in water and also using biological sentinel mussel species. This method offers a new perspective to assess the environmental risk for human health associated with this parasite.IMPORTANCE The ubiquitous protozoan Toxoplasma gondii is the subject of renewed interest due to the spread of oocysts in water and food causing endemic and epidemic outbreaks of toxoplasmosis in humans and animals worldwide. Displaying a sensitivity close to animal models, cell culture represents a real alternative to assess the infectivity of oocysts in water and in biological sentinel mussels. This method opens interesting perspectives for evaluating human exposure to infectious T. gondii oocysts in the environment, where oocyst amounts are considered to be very small.

Bovine Cryptosporidium parvum field isolates differ in cytopathogenicity in HCT-8 monolayers

Suckling calves are prone to Cryptosporidium infection. The variable degree of clinical disease is influenced by keeping conditions and immune status of the host, but diversity of isolate virulence may also contribute. The aim of the current study was to evaluate the cytopathogenic effects of 26 C. parvum field isolates by using a MTT assay in HCT-8 cell monolayers. Cell viability of monolayers inoculated with oocysts of the field isolates varied considerably with values of 17.7% (± 5.1%) to 99.5% (± 7.1%). A standard deviation of 18.6% was detected for cell viability of the in house reference strain, which were tested alongside in every assay. Field isolates were grouped in three categories of cytopathogenicity. Probably the length of storage has an effect on the level of the cell destruction category detected post infection in vitro. The applied tool may help to better understand the variable course of cryptosporidiosis in the field.

Assessing viability and infectivity of foodborne and waterborne stages (cysts/oocysts) of Giardia duodenalis, Cryptosporidium spp., and Toxoplasma gondii: a review of methods

Giardia duodenalis, Cryptosporidium spp. and Toxoplasma gondii are protozoan parasites that have been highlighted as emerging foodborne pathogens by the Food and Agriculture Organization of the United Nations and the World Health Organization. According to the European Food Safety Authority, 4786 foodborne and waterborne outbreaks were reported in Europe in 2016, of which 0.4% were attributed to parasites including Cryptosporidium, Giardia and Trichinella. Until 2016, no standardized methods were available to detect Giardia, Cryptosporidium and Toxoplasma (oo)cysts in food. Therefore, no regulation exists regarding these biohazards. Nevertheless, considering their low infective dose, ingestion of foodstuffs contaminated by low quantities of these three parasites can lead to human infection. To evaluate the risk of protozoan parasites in food, efforts must be made towards exposure assessment to estimate the contamination along the food chain, from raw products to consumers. This requires determining: (i) the occurrence of infective protozoan (oo)cysts in foods, and (ii) the efficacy of control measures to eliminate this contamination. In order to conduct such assessments, methods for identification of viable (i.e. live) and infective parasites are required. This review describes the methods currently available to evaluate infectivity and viability of G. duodenalis cysts, Cryptosporidium spp. and T. gondii oocysts, and their potential for application in exposure assessment to determine the presence of the infective protozoa and/or to characterize the efficacy of control measures. Advantages and limits of each method are highlighted and an analytical strategy is proposed to assess exposure to these protozoa.

Improvement of in vitro evaluation of chemical disinfectants for efficacy on Cryptosporidium parvum oocysts

Cryptosporidium parvum has been suggested as a suitable target for in vitro efficacy testing of disinfectants. To improve validity of a method based on exposure of HCT-8 monolayers to C. parvum oocysts we here critically evaluate and we propose certain procedural steps needed for the validation of disinfectants. Within a range of 0.02% to 0.4%, sodium taurocholate at 0.2% stimulated infection most efficiently while preserving host cell integrity. The course of invasion was monitored for periods of 30-240min post infection (p.i.). FACS analysis revealed that the proportion of sporozoites liberated from oocysts in the presence of 0.2% sodium taurocholate increased within 120min of incubation but remained constant thereafter. Maximum invasion of cells measured by qPCR was reached 180min p.i. and therefore set as invasion endpoint. As monolayers harvested 24h or 48h p.i. did not differ in the quantity of parasite hsp70 gene copies, DNA extraction can be performed as early as 24h p.i. Incubation of oocysts with 20% H₂O₂ for 2h resulted in inactivation of more than 99.5% both at room temperature and 10°C and appeared thus suitable as positive chemical treatment control. Four washing procedures considered to remove potentially toxic residual disinfectant from oocyst suspensions were tested. An application of a combination of DMSO (Dimethylsulfoxid), Tween20 and WSH (water of standardized hardness) appeared most efficient without deleterious effect of disinfectant residuals on the cell monolayer viability when oocysts accordingly washed were applied. In conclusion, for standardized in vitro evaluation of chemical disinfectants in C. parvum infected HTC-8 monolayers. (i) excystation medium should contain 0.2 % sodium taurocholate. (ii) excystation medium should be replaced by growth medium after 180 min. (iii) monolayers should be harvested 24 h p.i. for DNA preparation. (iv) ocysts exposed to 20 % H₂O₂ should be included as positive controls. (v) disinfected oocysts should be washed with DMSO/Tween20/WSH before they are transferred to monolayers.

Quantitative analysis of Cryptosporidium growth in in vitro culture--the impact of parasite density on the success of infection

Cryptosporidium is an important waterborne pathogen for which no treatment or vaccination is available. This study set out to quantify DNA replication of Cryptosporidium parvum in vitro. Cryptosporidium DNA could be detected at up to 60 % of input level in both host-cell-free and host cell containing cultures 6 days after infection with living sporozoites, but was lost within 2 days in cultures inoculated with UV-inactivated sporozoites. Total DNA increased between days 2 and 6, evidence of successful DNA replication in both cell-free and host-cell-containing cultures. Overall however, only a small fraction (up to 5 %) of parasite DNA could be found associated with host cells or bound to plastic of the cell-free cultures, and the majority of parasite DNA was present in the cell culture medium, separable by simple decantation. After 2 days, in host-cell-containing cultures, the parasite DNA could be concentrated by slow centrifugation, suggesting that it was associated with intact parasite cells, but at 6 days, the majority could not be centrifuged and is therefore thought to have represented copies associated with dead and degraded parasites. In cell-free cultures and in larger plates, the majority of DNA was in this form. Performance of the parasite was best in small culture plates, and least in the largest plate sizes. We interpret these results as suggesting that Cryptosporidium sporozoites first bind to the host cell monolayer or to the plasticware, but then by 2 days, there has been a substantial release of parasites back into the medium. Host-cell-free cultures also supported modest replication and may have represented DNA synthesis in cells beginning merogony. The role of the host cells is unclear, as so much of the parasite DNA is released into the medium. Host cells may provide a feeder role, conditioning the medium for Cryptosporidium development.

Establishment of a germ carrier assay to assess disinfectant efficacy against oocysts of coccidian parasites

Parasites are a common threat to human and animal health. One option to combat parasites that produce infective environmental stages is to inactivate them by chemical disinfection. Standardised laboratory assays that enable proper evaluation of products suspected to be efficient are highly desirable to allow prudent selection and use of such potentially hazardous agents. Here, we present a newly developed in vitro germ carrier assay to evaluate inactivation of oocysts of the model organism Cryptosporidium parvum by chemical disinfectants. Stainless steel discs were used as carrier to mimic surface contamination by C. parvum oocysts. The germ carriers were incubated with approved chemical disinfectant for the specified time (2 h) and rinsed thereafter to remove the disinfectant and recover the exposed oocysts. Recovered oocysts were transferred to HCT-8 monolayers, and 48 h later, genomic DNA was extracted and quantified by real-time PCR targeting the hsp70 gene to estimate parasite reproduction. A panel of commercially available and approved disinfectants were examined and data compared with those of suspension assays and historical data obtained from efficacy assays based on infection of chicken with oocysts of Eimeria tenella. Altogether, data achieved by these divergent assays allowed similar conclusions although the sensitivity of the in vitro assay was higher. Consequently, a threshold of 99.5% inactivation is proposed to evaluate disinfectants in vitro using C. parvum as model organism as compared to the E. tenella animal infection assay (95%).

Inactivation of exogenous endoparasite stages by chemical disinfectants: current state and perspectives

Chemical disinfection is common practice and inevitable to achieve sufficient control over parasites particularly in intensive animal housing systems. To identify suitable chemicals, reliable data on antiparasitic efficacy of disinfectants are required. This review summarizes recently published experience with procedures applied to evaluate the viability of a variety of endoparasites following physical or chemical stress. It is concluded that laboratory models used to assess antiparasitic efficacy of e.g. commercial disinfectants should consider the most resistant stages of both helminths and protozoa, i.e. ascarid eggs and coccidia oocysts. To ensure reproducibility and transparency, standardized protocols are pivotal. Such protocols are established on a national level (e.g. DVG guidelines in Germany); however, internationally accepted certification procedures are currently lacking.

Efficacy of amine-based disinfectant KENO™COX on the infectivity of Cryptosporidium parvum oocysts

Cryptosporidium parvum is a zoonotic protozoan parasite that may cause severe neonatal diarrhoea or even mortality in newborn ruminants: its oocysts are extremely resistant to normal environmental conditions and to most common disinfectants. KENO™COX, a patent pending amine-based formula, was tested for its ability to inactivate C. parvum oocysts. The Daugschies assay (2002), a standardized assay for chemical disinfection initially described for Eimeria spp., was adapted for C. parvum oocysts. KENO™COX diluted in water at 2% and 3% concentration and incubated with oocyst suspensions for 2h, allowed a significant reduction in viability, lysing 89% and 91% of oocysts respectively. Infectivity of the remaining C. parvum oocysts was assessed by inoculation to C57 Bl/6 neonatal mice. Each mouse received 2.5 μl of a suspension initially containing 500,000 oocysts before contact with KENO™COX. Six days post inoculation, the intestinal parasite load was significantly reduced by 97.5% with KENO™COX 2% compared to that of the mice inoculated with untreated parasites. KENO™COX 3% completely eliminated infectivity of oocysts. The number of oocysts remaining infectious in the inoculum treated with KENO™COX 2% was calculated from an inoculated dose-response curve: it was estimated at about 48.6 oocysts among the 500,000 oocysts initially treated corresponding to 99.99% of inhibition. These results demonstrate the high efficacy of KENO™COX against C. parvum oocysts. Combined with an appropriate method of cleaning, the application of KENO™COX may be a useful tool to reduce cryptosporidial infectious load on farm level.

Age-stratified Bayesian analysis to estimate sensitivity and specificity of four diagnostic tests for detection of Cryptosporidium oocysts in neonatal calves

There is no gold standard diagnostic test for the detection of bovine cryptosporidiosis. Infection is usually highest in 2-week-old calves, and these calves also excrete high numbers of oocysts. These factors may give rise to variations in the sensitivity and specificity of the various diagnostic tests used to detect infection in calves of various ages. An age-stratified Bayesian analysis was carried out to determine the optimum diagnostic test to identify asymptomatic and clinical Cryptosporidium sp. infection in neonatal calves. Fecal samples collected from 82 calves at 1 week, 2 weeks, 3 weeks, and 4 weeks of age were subjected to the following tests: microscopic examination of smears stained with either phenol-auramine O or fluorescein isothiocyanate (FITC)-conjugated anti-Cryptosporidium monoclonal antibody, nested-PCR, and quantitative real-time PCR. The results confirmed a high prevalence of Cryptosporidium sp. infection, as well as a high level of oocyst excretion, in 2-week-old calves. The sensitivities of all the tests varied with the age of the calves. Quantitative real-time PCR proved to be the most sensitive and specific test for detecting infection irrespective of the age of the calf. The microscopic techniques were the least sensitive and exhibited only moderate efficiency with 2-week-old calves excreting large numbers of oocysts, the majority of which were diarrheic. It was concluded that, when interpreting the results of routine tests for bovine cryptosporidiosis, cognizance should be taken of the sensitivity of the tests in relation to the age of the calves and stage of infection.