Enterocytozoon bieneusi is the most common cause of human microsporidiosis and it also infects a wide range of mammals and birds worldwide. The role of animals in the transmission of this parasite to ...humans and its public health importance remain poorly elucidated. This review summarizes all E. bieneusi genotypes identified thus far based on sequence analysis of the ribosomal internal transcribed spacer (ITS) from specimens obtained from humans, domestic and wild animals, and water sources; it examines genotypes, host and geographical distribution, analyzes inter- and intragenotype group host specificity, and interprets the public health significance of genotype groups and major zoonotic genotypes, with the goal of improving our understanding of host specificity in E. bieneusi and its implications for interspecies and zoonotic transmission.
High genetic diversity for E. bieneusi has been revealed using genetic polymorphisms at the ITS locus with almost 500 genotypes identified in humans, livestock, companion animals, wild mammals, birds, and water worldwide.
E. bieneusi genotypes vary in genetic or hereditary traits and 11 phylogenetic groups have been recognized using ITS genotyping data.
Genotypes in Group 1 and Group 2 have been found in a broad range of hosts including humans and are probably responsible for most zoonotic or cross-species E. bieneusi infections, whereas host adaptation seems to be more common in genotypes of Groups 3 to 11.
MLST and population genetic data have provided important insights into the host adaptation mechanism for some genotypes, but additional MLST tools and genomic data are required to elaborate the host specificity of E. bieneusi and its public health implications.
Cryptosporidium species differ in host range. Parasite–host coevolution, host adaptation, and geographic segregation have led to the formation of subtype families with unique phenotypic traits within ...the major human-pathogenic species C. parvum and C. hominis. Transmission intensity, genetic diversity, and occurrence of genetic recombination and selective pressure have further shaped their population genetic structures. Panmixia appears to be common within the zoonotic C. parvum, especially its hypertransmissible IIaA15G2R1 subtype. Genetic recombination in C. hominis, in contrast, is more restricted to virulent subtypes, especially IbA10G2. Nonhuman primates and equine animals are commonly infected with genetically divergent C. hominis populations. Systematic studies of these and other host-adapted Cryptosporidium spp. are likely leading to improved understanding of population structures underlying various transmission patterns and intensities of Cryptosporidium.
Cryptosporidium species and subtypes differ in host range and public health significance.
Host-adapted subtype families exist in the human-pathogenic species C. parvum and C. hominis.
Genetic recombination is common within the zoonotic C. parvum, especially its hypertransmissible IIaA15G2R1 subtype.
Genetic recombination in C. hominis is mostly restricted to its virulent subtypes, especially IbA10G2.
Host and geographical segregation, genetic recombination, and selective pressure shape the population structure of C. parvum and C. hominis, leading to the emergence of host-adapted, virulent, and hypertransmissible subtypes with public health significance.
Giardia duodenalis
is a common intestinal parasite in various hosts, with the disease giardiasis being a zoonosis. The use of molecular typing tools has improved our understanding of the distribution ...and zoonotic potential of
G. duodenalis
genotypes in different animals. The present review summarizes recent data on the distribution of
G. duodenalis
genotypes in humans and animals in different areas. The dominance of
G. duodenalis
assemblages A and B in humans and common occurrence of host-adapted assemblages in most domesticated animals suggests that zoonotic giardiasis is probably less common than believed and could be attributed mainly to contact with or contamination from just a few species of animals such as nonhuman primates, equines, rabbits, guinea pigs, chinchillas, and beavers. Future studies should be directed to advanced genetic characterization of isolates from well-designed epidemiological investigations, especially comparative analyses of isolates from humans and animals living in the same household or community. This will likely lead to better understanding of zoonotic transmission of
G. duodenalis
in different environmental and socioeconomic settings.
Molecular epidemiology of cryptosporidiosis is an active research area in China. The use of genotyping and subtyping tools in prevalence studies has led to the identification of unique ...characteristics of
infections in humans and animals. Human cryptosporidiosis in China is exemplified by the high diversity of
spp. at species and subtype levels, with dominant
and
subtypes being rarely detected in other countries. Similarly, preweaned dairy calves, lambs, and goat kids are mostly infected with non-pathogenic
species (
in calves and
in lambs and goat kids), with
starting to appear in dairy calves as a consequence of concentrated animal feeding operations. The latter
species is dominated by IId subtypes, with IIa subtypes largely absent from the country. Unlike elsewhere, rodents in China appear to be commonly infected with
IId subtypes, with identical subtypes being found in these animals, calves, other livestock, and humans. In addition to cattle, pigs and chickens appear to be significant contributors to
contamination in drinking water sources, as reflected by the frequent detection of
, and
in water samples. Chinese scientists have also made significant contributions to the development of new molecular epidemiological tools for
spp. and improvements in our understanding of the mechanism involved in the emergence of hyper-transmissible and virulent
and
subtypes. Despite this progress, coordinated research efforts should be made to address changes in
transmission because of rapid economic development in China and to prevent the introduction and spread of virulent and zoonotic
species and subtypes in farm animals.
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•We present a review of 50 years of Cryptosporidium and Giardia taxonomy.•Historical and current understanding of Cryptosporidium and Giardia epidemiology are compared.•Research needs ...including more comparative genomic analysis and studies in developing countries are discussed.
The protozoan parasites Cryptosporidium and Giardia are significant causes of diarrhoea worldwide and are responsible for numerous waterborne and foodborne outbreaks of diseases. Over the last 50 years, the development of improved detection and typing tools has facilitated the expanding range of named species. Currently at least 44 Cryptosporidium spp. and >120 genotypes, and nine Giardia spp., are recognised. Many of these Cryptosporidium genotypes will likely be described as species in the future. The phylogenetic placement of Cryptosporidium at the genus level is still unclear and further research is required to better understand its evolutionary origins. Zoonotic transmission has long been known to play an important role in the epidemiology of cryptosporidiosis and giardiasis, and the development and application of next generation sequencing tools is providing evidence for this. Comparative whole genome sequencing is also providing key information on the genetic mechanisms for host specificity and human infectivity, and will enable One Health management of these zoonotic parasites in the future.
Molecular diagnostic tools have played an important role in improving our understanding of the transmission of Cryptosporidium spp. and Giardia duodenalis, which are two of the most important ...waterborne parasites in industrialized nations. Genotyping tools are frequently used in the identification of host-adapted Cryptosporidium species and G. duodenalis assemblages, allowing the assessment of infection sources in humans and public health potential of parasites found in animals and the environment. In contrast, subtyping tools are more often used in case linkages, advanced tracking of infections sources, and assessment of disease burdens attributable to anthroponotic and zoonotic transmission. More recently, multilocus typing tools have been developed for population genetic characterizations of transmission dynamics and delineation of mechanisms for the emergence of virulent subtypes. With the recent development in next generation sequencing techniques, whole genome sequencing and comparative genomic analysis are increasingly used in characterizing Cryptosporidium spp. and G. duodenalis. The use of these tools in epidemiologic studies has identified significant differences in the transmission of Cryptosporidium spp. in humans between developing countries and industrialized nations, especially the role of zoonotic transmission in human infection. Geographic differences are also present in the distribution of G. duodenalis assemblages A and B in humans. In contrast, there is little evidence for widespread zoonotic transmission of giardiasis in both developing and industrialized countries. Differences in virulence have been identified among Cryptosporidium species and subtypes, and possibly between G. duodenalis assemblages A and B, and genetic recombination has been identified as one mechanism for the emergence of virulent C. hominis subtypes. These recent advances are providing insight into the epidemiology of waterborne protozoan parasites in both developing and developed countries.
•Molecular tools are widely used to characterize isolates of Cryptosporidium and Giardia.•Methods differ in resolution capability, purpose, and technical complexity.•Molecular characterization has significantly improved knowledge of cryptosporidiosis epidemiology.•Cryptosporidium transmission is significantly different between developing and industrialized nations.•Improved molecular tools are needed to delineate Giardia duodenalis transmission in humans.
The enteric parasite, Cryptosporidium is a major cause of diarrhoeal illness in humans and animals worldwide. No effective therapeutics or vaccines are available and therefore control is dependent on ...understanding transmission dynamics. The development of molecular detection and typing tools has resulted in the identification of a large number of cryptic species and genotypes and facilitated our understanding of their potential for zoonotic transmission. Of the 44 recognised Cryptosporidium species and >120 genotypes, 19 species, and four genotypes have been reported in humans with C. hominis, C. parvum, C. meleagridis, C. canis and C. felis being the most prevalent. The development of typing tools that are still lacking some zoonotic species and genotypes and more extensive molecular epidemiological studies in countries where the potential for transmission is highest are required to further our understanding of this important zoonotic pathogen. Similarly, whole-genome sequencing (WGS) and amplicon next-generation sequencing (NGS) are important for more accurately tracking transmission and understanding the mechanisms behind host specificity.
Sheep and goats are commonly infected with three
Cryptosporidium
species, including
Cryptosporidium parvum
,
Cryptosporidium ubiquitum
, and
Cryptosporidium xiaoi
, which differ from each in ...prevalence, geographic distribution, and public health importance. While
C. parvum
appears to be a dominant species in small ruminants in European countries, its occurrence in most African, Asian, and American countries appear to be limited. As a result, zoonotic infections due to contact with lambs and goat kids are common in European countries, leading to frequent reports of outbreaks of cryptosporidiosis on petting farms. In contrast,
C. xiaoi
is the dominant species elsewhere, and mostly does not infect humans. While
C. ubiquitum
is another zoonotic species, it occurs in sheep and goats at much lower frequency. Host adaptation appears to be present in both
C. parvum
and
C. ubiquitum
, consisting of several subtype families with different host preference. The host-adapted nature of
C. parvum
and
C. ubiquitum
has allowed the use of subtyping tools in tracking infection sources. This has led to the identification of geographic differences in the importance of small ruminants in epidemiology of human cryptosporidiosis. These tools have also been used effectively in linking zoonotic transmission of
C. parvum
between outbreak cases and the suspected animals. Further studies should be directly elucidating the reasons for differences in the distribution and public health importance of major
Cryptosporidium
species in sheep and goats.
The current outbreak of coronavirus disease-2019 (COVID-19) poses unprecedented challenges to global health
. The new coronavirus responsible for this outbreak-severe acute respiratory syndrome ...coronavirus 2 (SARS-CoV-2)-shares high sequence identity to SARS-CoV and a bat coronavirus, RaTG13
. Although bats may be the reservoir host for a variety of coronaviruses
, it remains unknown whether SARS-CoV-2 has additional host species. Here we show that a coronavirus, which we name pangolin-CoV, isolated from a Malayan pangolin has 100%, 98.6%, 97.8% and 90.7% amino acid identity with SARS-CoV-2 in the E, M, N and S proteins, respectively. In particular, the receptor-binding domain of the S protein of pangolin-CoV is almost identical to that of SARS-CoV-2, with one difference in a noncritical amino acid. Our comparative genomic analysis suggests that SARS-CoV-2 may have originated in the recombination of a virus similar to pangolin-CoV with one similar to RaTG13. Pangolin-CoV was detected in 17 out of the 25 Malayan pangolins that we analysed. Infected pangolins showed clinical signs and histological changes, and circulating antibodies against pangolin-CoV reacted with the S protein of SARS-CoV-2. The isolation of a coronavirus from pangolins that is closely related to SARS-CoV-2 suggests that these animals have the potential to act as an intermediate host of SARS-CoV-2. This newly identified coronavirus from pangolins-the most-trafficked mammal in the illegal wildlife trade-could represent a future threat to public health if wildlife trade is not effectively controlled.
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