Molecular and morphological characterization of Echinococcus in cervids from North America

Northern host-parasite assemblages: history and biogeography on the borderlands of episodic climate and environmental transition

Diversity among assemblages of mammalian hosts and parasites in northern terrestrial ecosystems was structured by a deep history of biotic and abiotic change that overlies a complex geographic arena. Since the Pliocene, Holarctic ecosystems assembled in response to shifting climates (glacial and interglacial stages). Cycles of episodic dispersal/isolation and diversification defined northern diversity on landscape to regional scales. Episodes of geographic expansion and colonisation linked Eurasia and North America across Beringia and drove macroevolutionary structure of host and parasite associations. Asynchronous dispersal from centres of origin in Eurasia into the Nearctic resulted in gradients in parasite diversity in the carnivoran, lagomorph, rodent and artiodactyl assemblages we reviewed. Recurrent faunal interchange and isolation in conjunction with episodes of host colonisation have produced a mosaic structure for parasite faunas and considerable cryptic diversity among nematodes and cestodes. Mechanisms of invasion and geographic colonisation leading to the establishment of complex faunal assemblages are equivalent in evolutionary and ecological time, as demonstrated by various explorations of diversity in these high-latitude systems. Our ability to determine historical responses to episodic shifts in global climate may provide a framework for predicting the cascading effects of contemporary environmental change.

Morphological characteristics of Echinococcus granulosus derived from buffalo in Iran

Cystic echinococcosis is a significant parasitic disease in Iran, where a variety of animals act as intermediate hosts. In this study, 25 isolates of Echinococcus granulosus obtained from water buffalo from various parts of Iran were characterized on the basis of the morphology of the metacestode and the adult worm. The characteristics of protoscoleces from the different studied areas were nearly similar. They showed 2 rows of alternating large and small hooks and their shapes were smooth in outline. In contrast to the protoscoleces, the adult rostellar hooks showed a rough outline. The results showed that the total length, the blade lengths of the large and small hooks and the number of hooks are almost similar to those isolated from sheep but significantly different from those isolated from camels. The growth rates of adult E. granulosus (total worm length, segmentation and maturation) of buffalo origin, at 35 and 41 days post-infection of dogs, were nearly comparable to the common sheep strain. The form of the strobila and the morphology of the reproductive system were also similar to those of sheep origin. This suggests that the common sheep strain (G1) of E. granulosus may also use buffaloes as its intermediate host.

Rostellar hook morphology of larval Echinococcus granulosus isolates from the Indian buffalo and Iranian sheep, cattle and camel

Isolates of Echinococcus granulosus from the Indian buffalo and Iranian sheep, cattle and camels were characterized on the basis of rostellar hook morphology of the protoscolices. Results obtained indicated phenotypic polymorphism among parasites isolated from different host species. Isolates from buffalo are morphologically quite different from those of the more common sheep and cattle isolates and may represent a different strain, adapted to buffalo. In the Sari region of northern Iran, two morphologically distinct forms of E. granulosus, one in sheep and one in camels, were identified. Total length and handle length of both large and small hooks were considered the most variable characteristics which could be used not only for differentiating parasite isolates from different host species but also the origin of infection in the definitive host. We therefore suggest that larval hook morphology may be considered as a valid criterion for the identification of E. granulosus strains in Iran.

Emergence of sylvatic Echinococcus granulosus as a parasitic zoonosis of public health concern in an indigenous community in Canada

Within a remote Canadian Indigenous community, at least 11* of people had antibodies against Echinococcus granulosus and E. granulosus eggs were detected in 6* of environmentally collected canine fecal samples. Dog ownership, hunting, and trapping were not risk factors for seropositivity, suggesting that people are most likely exposed to E. granulosus through indirect contact with dog feces in the environment. In this situation, human exposure could be most effectively curtailed by preventing consumption of cervid viscera by free-roaming dogs.

Parasite zoonoses and wildlife: emerging issues

The role of wildlife as important sources, reservoirs and amplifiers of emerging human and domestic livestock pathogens, in addition to well recognized zoonoses of public health significance, has gained considerable attention in recent years. However, there has been little attention given to the transmission and impacts of pathogens of human origin, particularly protozoan, helminth and arthropod parasites, on wildlife. Substantial advances in molecular technologies are greatly improving our ability to follow parasite flow among host species and populations and revealing valuable insights about the interactions between cycles of transmission. Here we present several case studies of parasite emergence, or risk of emergence, in wildlife, as a result of contact with humans or anthropogenic activities. For some of these parasites, there is growing evidence of the serious consequences of infection on wildlife survival, whereas for others, there is a paucity of information about their impact.

A novel phylogeny for the genus Echinococcus, based on nuclear data, challenges relationships based on mitochondrial evidence

The taxonomic status of Echinococcus, an important zoonotic cestode genus, has remained controversial, despite numerous attempts to revise it. Although mitochondrial DNA (mtDNA) has been the source of markers of choice for reconstructing the phylogeny of the genus, results derived from mtDNA have led to significant inconsistencies with earlier species classifications based on phenotypic analysis. Here, we used nuclear DNA markers to test the phylogenic relationships of members of the genus Echinococcus. The analysis of sequence data for 5 nuclear genes revealed a significantly different phylogeny for Echinococcus from that proposed on the basis of mitochondrial DNA sequence data, but was in agreement with earlier species classifications. The most notable results from the nuclear phylogeny were (1) E. multilocularis was placed as basal taxon, (2) all genotypes of Echinococcus granulosus grouped as a monophyletic entity, and (3) genotypes G8 and G10 clustered together. We conclude that the analysis of nuclear DNA data provides a more reliable means of inferring phylogenetic relationships within Echinococcus than mtDNA and suggest that mtDNA should not be used as the sole source of markers in future studies where the goal is to reconstruct a phylogeny that does not only reflect a maternal lineage, but aims to describe the evolutionary history at species level or higher.

The molecular epidemiology of Cryptosporidium and Giardia infections in coyotes from Alberta, Canada, and observations on some cohabiting parasites

Coyotes from southern Alberta and Saskatchewan, Canada, were examined for the presence of Giardia and Cryptosporidium and cohabiting helminths. Toxascaris was present in over 90% of the 70 animals examined, and Taenia sp. in 6.5-25% of the two groups of animals studied. Giardia (12.5-21.7%) and Cryptosporidium (0-17.4%) were also common and molecular characterisation revealed both zoonotic and host-adapted genotypes of Giardia, whereas the Cryptosporidium proved to be a variant of the canine species C. canis. The seasonal variation observed in the occurrence of Cryptosporidium may be related to stress-induced shedding of the parasite.

First report of Echinococcus granulosus G8 in Eurasia and a reappraisal of the phylogenetic relationships of ‘genotypes’ G5-G10

In this study, we investigated the presence of the larval stage of the tapeworm Echinococcus granulosus in wild ungulates in Estonia, genetically characterized E. granulosus isolates using mitochondrial gene sequences and used the sequence data, together with those available in a public database, to infer the phylogenic relationships of E. granulosus ‘genotypes’ G5-G10. While 0·8% of the 2038 moose (Alces alces) examined were found to be infected with E. granulosus, the parasite was not detected in other wild ungulates, such as roe deer (Capreolus capreolus: 1044 specimens examined) and wild boar (Sus scrofa: 442 specimens). Genetic analyses of concatenated atp6, nad1 and cox1 gene (1028 bp) sequences revealed that 2 novel E. granulosus haplotypes, namely E8 (11 samples: 69%) and E10 (5 samples: 31%), grouped with E. granulosus G8 and G10, respectively, are present in Estonia. This is the first record of an E. granulosus G8 in Eurasia. Phylogenetic analyses, using 4 different methods, demonstrated with considerable statistical support that E. granulosus G6/7 forms a subgroup together with G10, whereas G8 is a sister taxon to G6/7-G10.

Characterization of Taenia madoquae and Taenia regis from carnivores in Kenya using genetic markers in nuclear and mitochondrial DNA, and their relationships with other selected taeniids

In the present study, we have extended earlier taxonomic, biochemical and experimental investigations to characterize two species of Taenia from carnivores in Kenya by use of the sequences of a variable domain (D1) of nuclear ribosomal DNA and the cytochrome c oxidase subunit 1 and NADH dehydrogenase 1 genes of mitochondrial DNA. Emphasis was placed on the characterization of Taenia madoquae from the silver-backed jackal (Canis mesomelas) and Taenia regis from the lion (Panthera leo), given the previous absence of any DNA sequence data for them, and on assessing their genetic relationships with socioeconomically important taeniids. The study showed that T. regis was genetically most closely related to T. hydatigena, and T. madoquae to T. serialis, T. multiceps or T. saginata. The present findings provide a stimulus for future work on the systematic relationships and epidemiology of lesser-known taeniid cestodes in Africa and other continents, employing mitochondrial sequence data sets.

Echinococcus granulosus from Mexican pigs is the same strain as that in Polish pigs

Samples of Echinococcus granulosus from seven pigs from Mexico were compared with isolates of the parasite from pigs in Poland and representative strains and species of Echinococcus. Isolates from pigs in Mexico were found to be genetically identical to E. granulosus from Polish pigs and distinct from other major genotypes by sequencing part of the mitochondrial cytochrome c oxidase I (COI) mtDNA locus, restriction fragment length polymorphism (RFLP) of the polymerase chain reaction (PCR) amplified rDNA internal transcribed spacer (ITS) 1 using five different enzymes, and random amplified polymorphic DNA (RAPD) analysis. These results were complemented by data on hook morphology and together strengthen the view that Echinococcus maintained in a cycle involving pigs and dogs is a distinct strain that is conserved genetically in different geographical areas. The present study supports the close relationship of the cervid, camel and pig strains and raises the question of their taxonomic status.

A molecular phylogeny of the genus Echinococcus inferred from complete mitochondrial genomes

Taxonomic revision by molecular phylogeny is needed to categorize members of the genus Echinococcus (Cestoda: Taeniidae). We have reconstructed the phylogenetic relationships of E. oligarthrus, E. vogeli, E. multilocularis, E. shiquicus, E. equinus, E. ortleppi, E. granulosus sensu stricto and 3 genotypes of E. granulosus sensu lato (G6, G7 and G8) from their complete mitochondrial genomes. Maximum likelihood and partitioned Bayesian analyses using concatenated data sets of nucleotide and amino acid sequences depicted phylogenetic trees with the same topology. The 3 E. granulosus genotypes corresponding to the camel, pig, and cervid strains were monophyletic, and their high level of genetic similarity supported taxonomic species unification of these genotypes into E. canadensis. Sister species relationships were confirmed between E. ortleppi and E. canadensis, and between E. multilocularis and E. shiquicus, regardless of the analytical approach employed. The basal positions of the phylogenetic tree were occupied by the neotropical endemic species, E. oligarthrus and E. vogeli, whose definitive hosts are derived from carnivores that immigrated from North America after the formation of the Panamanian land bridge. Host-parasite co-evolution comparisons suggest that the ancestral homeland of Echinococcus was North America or Asia, depending on whether the ancestral definitive hosts were canids or felids.

Taxonomic position and geographical distribution of the common sheep G1 and camel G6 strains of Echinococcus granulosus in three African countries

The taxonomic and phylogenetic status of Echinococcus granulosus strains are still controversial and under discussion. In the present study, we investigated the genetic polymorphism of E. granulosus isolates originating from three countries of Africa, including a region of Algeria, where the common G1 sheep and the camel G6 strains coexist sympatrically. Seventy-one hydatid cysts were collected from sheep, cattle, camels, and humans. Two mitochondrial markers (cox1 and nad1) were used for strain identification. Two nuclear markers (actII and hbx2) were used to study the possible occurrence of cross-fertilization. Despite the heterogeneity observed among the G1 isolates, they were all localized within one robust cluster. A second strong cluster was also observed containing all of the G6 isolates. Both strains appeared as two distinct groups, and no cases of interbreeding were found. Thus, the attribution of a species rank can be suggested. We also found the Tasmanian sheep G2 strain for the first time in Africa. Because of the slight variations observed between the common sheep and the Tasmanian sheep strains, further studies should be carried out to elucidate the epidemiological relevance of this genetic discrimination.