Diarrhea is a common occurrence following vascular organ transplantation, including kidney transplants. It can be induced by non-infectious factors, adverse effects of immunosuppressive drugs, or infectious agents such as viruses, bacteria, fungi, or parasites. Intestinal protozoan parasites, include Cryptosporidium spp., are causes of infectious diarrhea particularly in immunocompromised patients. This review aims to summarize reports on epidemiology, pathogenesis, clinical presentation, diagnosis, and treatment of Cryptosporidium spp. infection in adult patients, particularly following kidney transplantation.

Cryptosporidiosis is a widespread disease caused by the parasitic protozoan Cryptosporidium spp., which infects various vertebrate species, including humans. Once unknown as a gastroenteritis-causing agent, Cryptosporidium spp. is now recognized as a pathogen causing life-threatening disease, especially in immunocompromised individuals such as AIDS patients. Advances in diagnostic methods and increased awareness have led to a significant shift in the perception of Cryptosporidium spp. as a pathogen. Nowadays, genomic and proteomic studies have played a main role in understanding the molecular biology of this complex-life-cycle parasite. Genomics has enabled the identification of numerous genes involved in the parasite's development and interaction with hosts. Proteomics has allowed for the identification of protein interactions, their function, structure, and cellular activity. The combination of these two approaches has significantly contributed to the development of new diagnostic tools, vaccines, and drugs for cryptosporidiosis. In this review, we summarize the major accomplishments in the field of Cryptosporidium research using genomics and proteomics.

Cryptosporidiosis is one of the most important causes of gastroenteritis in the world, especially in low- and middle-income countries. It is caused by the Apicomplexan parasite Cryptosporidium spp., and mainly affects children and immunosuppressed people, in whom it can pose a serious risk to their health, or even be life-threatening. In Honduras there are no data on parasite species or on molecular diversity or Cryptosporidium subtypes. Therefore, a cross-sectional study was conducted between September 2019 and March 2020 for the molecular identification of Cryptosporidium spp. in 102 patients living with HIV who attended a national hospital in Tegucigalpa. Stool samples were analysed by direct microscopy, acid-fast stained smears, and a rapid lateral flow immunochromatographic test. All samples that tested positive were molecularly analyzed to identify the species and subtype of the parasite using three different markers: gp60, cowp, and 18Sr. PCR products were also sequenced. Four out of 102 samples (3.92%) were positive for Cryptosporidium parvum, and all were assigned to subtype IIa. These findings suggest a possible zoonotic transmission in this population.

Cryptosporidium is comprised an apicomplexan parasitic protist, which infects a wide range of hosts, causing cryptosporidiosis. In cattle farms, the incidence of cryptosporidiosis results in high mortality in calves leading to considerable economic loss in the livestock industry. Infected animals may also act as a major reservoir of Cryptosporidium spp., in particular C. parvum, the most common cause of cryptosporidiosis in calves. This poses a significant risk to other farms via breeding centres, to trading of livestock and to human health. This study, funded by the Interreg-2-seas programme, is a part of a global project aimed at strategies to tackle cryptosporidiosis. To reach this target, it was essential to determine whether prevalence was dependent on the studied countries or if the issue was borderless. Indeed, C. parvum occurrence was assessed across dairy farms in certain regions of Belgium, France and the Netherlands. At the same time, the animal-to-animal transmission of the circulating C. parvum subtypes was studied. To accomplish this, 1084 faecal samples, corresponding to 57 dairy-farms from all three countries, were analysed. Well-established protocols amplifying the 18S rDNA and gp60 genes fragments, followed by DNA sequencing, were used for the detection and subtyping C. parvum; the DNA sequences obtained were further characterised using a combination of bioinformatics and phylogenetics methods. Our results show 25.7%, 24.9% and 20.8% prevalence of Cryptosporidium spp. in Belgium, France and the Netherlands respectively. Overall, 93% of the farms were Cryptosporidium positive. The gp60 subtyping demonstrated a significant number of the C. parvum positives belonged to the IIa allelic family, which has been also detected in humans. Consequently, this study highlights how widespread is C. parvum in dairy farms and endorses cattle as a major carrier of zoonotic C. parvum subtypes, which subsequently pose a significant threat to human health.

Cryptosporidium parvum is one of the major causes of neonatal calf diarrhoea resulting in reduced farm productivity and compromised animal welfare worldwide. Livestock act as a major reservoir of this parasite, which can be transmitted to humans directly and/or indirectly, posing a public health risk. Research reports on Cryptosporidium prevalence from the east Mediterranean region are scarce with even less originating from Cyprus. This study is the first to explore occurrence of Cryptosporidium spp. in young dairy calves on the island. A total of 242 faecal samples were collected from 10 dairy cattle farms in Cyprus, all of which were screened for Cryptosporidium spp. using nested-PCR amplification targeting the small subunit of the ribosomal RNA (18S rRNA) gene. The 60 kDa glycoprotein (gp60) gene was also sequenced for the samples identified as C. parvum positive to determine the subtypes present. Occurrence of Cryptosporidium was 43.8% (106/242) with at least one positive isolate in each farm sampled. Prevalence per farm ranged from 20¬‒64%, while C. bovis, C. ryanae and C. parvum were the only species identified. Amongst those, the latter was the predominant species, representing 51.8% of all positive samples. Four zoonotic subtypes were identified – IIaA14G1R1, IIaA15G1R1, IIaA15G2R1 and IIaA18G2R1. IIaA14G1R1 was the most abundant; representing 48.2% of all C. parvum positive samples and was also the most widespread. This is the first report of zoonotic subtypes of C. parvum circulating in Cyprus. These results highlight the need for further research into the parasite focusing on its diversity, prevalence, host-range and transmission dynamics on the island.

Enteric protozoan pathogenic infections significantly contribute to the global burden of gastrointestinal illnesses. Their occurrence is considerable within remote and indigenous communities and regions due to reduced access to clean water and adequate sanitation. The robustness of these pathogens means requirement of harsh treatment methods such as medicinal drugs or antibiotics. However, such treatments impact the gut microbiome, and create dysbiosis, often leading to opportunistic pathogens, anti-microbial resistance, or functional gastrointestinal disorders (FGIDs) such as irritable bowel syndrome (IBS). Recent studies have shown that these impacts do not remain confined to gut, and are reflected across the gut-brain, gut-liver, and gut-lung axes, among others. Therefore, apart from the medicinal treatment, nutritional supplementation is also a key aspect of providing the recovery from this dysbiosis. Future proteins, prebiotics, probiotics, synbiotics, and food formulations offer a good solution to remedy this dysbiosis. Furthermore, the nutritional supplementation also helps to build a resilience against the opportunistic pathogens and potential future infections and disorders that may arise due to the dysbiosis. Systems biology techniques have shown to be highly effective tools to understand the biochemistry of these processes. Systems biology techniques characterises the fundamental host-pathogen interaction biochemical pathways, at various infection and recovery stages. This same mechanism also allows to track the impact of abovementioned treatment methods of gut microbiome remediation. This manuscript is organised in sections delving into system biology approaches and upcoming developments to understand (1) Infection mechanism and current global status; (2) Cross-organ impacts of dysbiosis, particularly within gut-liver and gut-lung axes; (3) Nutritional interventions. It highlights the impact of antimicrobial resistance (AMR) and Multi-drug resistance (MDR) from a perspective of protozoal infections. It also highlights the role of nutritional interventions to add resilience against the chronic problems caused by these phenomena.