De-Hua Lai

Clonorchiasis: a key foodborne zoonosis in China

The oriental liverfluke, Clonorchis sinensis, is of major socioeconomic importance in parts of Asia, including China, Japan, Korea, Taiwan, and Vietnam. The parasite is transmitted via snails to freshwater fish, and then to human beings and other piscivorous mammals, and causes substantial clinical or subclinical disease, known as clonorchiasis. There is considerable evidence for an aetiological relation between clonorchiasis and cholangiocarcinoma in human beings. It is estimated that about 35 million people are infected globally, of whom approximately 15 million are in China. Although very little information from China has been published in the English language, recent analyses of epidemiological data sets suggest that clonorchiasis is having an increased human-health impact due to the greater consumption of raw freshwater fish. To gain an improved insight into clonorchiasis in China, this review provides a background on the parasite and its life cycle, summarises key aspects regarding the pathogenesis, diagnosis, and treatment of clonorchiasis, describes the geographic distribution and prevalence of clonorchiasis, and makes some recommendations for future research and the control of this important disease.

Adaptations of Trypanosoma brucei to gradual loss of kinetoplast DNA: Trypanosoma equiperdum and Trypanosoma evansi are petite mutants of T. brucei

Trypanosoma brucei is a kinetoplastid flagellate, the agent of human sleeping sickness and ruminant nagana in Africa. Kinetoplastid flagellates contain their eponym kinetoplast DNA (kDNA), consisting of two types of interlocked circular DNA molecules: scores of maxicircles and thousands of minicircles. Maxicircles have typical mitochondrial genes, most of which are translatable only after RNA editing. Minicircles encode guide RNAs, required for decrypting the maxicircle transcripts. The life cycle of T. brucei involves a bloodstream stage (BS) in vertebrates and a procyclic stage (PS) in the tsetse fly vector. Partial [dyskinetoplastidy (Dk)] or total [akinetoplastidy (Ak)] loss of kDNA locks the trypanosome in the BS form. Transmission between vertebrates becomes mechanical without PS and tsetse mediation, allowing the parasite to spread outside the African tsetse belt. Trypanosoma equiperdum and Trypanosoma evansi are agents of dourine and surra, diseases of horses, camels, and water buffaloes. We have characterized representative strains of T. equiperdum and T. evansi by numerous molecular and classical parasitological approaches. We show that both species are actually strains of T. brucei, which lost part (Dk) or all (Ak) of their kDNA. These trypanosomes are not monophyletic clades and do not qualify for species status. They should be considered two subspecies, respectively T. brucei equiperdum and T. brucei evansi, which spontaneously arose recently. Dk/Ak trypanosomes may potentially emerge repeatedly from T. brucei.

Trypanosoma evansi and Surra: A Review and Perspectives on Origin, History, Distribution, Taxonomy, Morphology, Hosts, and Pathogenic Effects

Trypanosoma evansi, the agent of “surra,” is a salivarian trypanosome, originating from Africa. It is thought to derive from Trypanosoma brucei by deletion of the maxicircle kinetoplastic DNA (genetic material required for cyclical development in tsetse flies). It is mostly mechanically transmitted by tabanids and stomoxes, initially to camels, in sub-Saharan area. The disease spread from North Africa towards the Middle East, Turkey, India, up to 53° North in Russia, across all South-East Asia, down to Indonesia and the Philippines, and it was also introduced by the conquistadores into Latin America. It can affect a very large range of domestic and wild hosts including camelids, equines, cattle, buffaloes, sheep, goats, pigs, dogs and other carnivores, deer, gazelles, and elephants. It found a new large range of wild and domestic hosts in Latin America, including reservoirs (capybaras) and biological vectors (vampire bats). Surra is a major disease in camels, equines, and dogs, in which it can often be fatal in the absence of treatment, and exhibits nonspecific clinical signs (anaemia, loss of weight, abortion, and death), which are variable from one host and one place to another; however, its immunosuppressive effects interfering with intercurrent diseases or vaccination campaigns might be its most significant and questionable aspect.

Trypanosoma evansi and Surra: A Review and Perspectives on Transmission, Epidemiology and Control, Impact, and Zoonotic Aspects

This paper reviews the transmission modes of Trypanosoma evansi. Its worldwide distribution is attributed to mechanical transmission. While the role of tabanids is clear, we raise questions on the relative role of Haematobia sp. and the possible role of Stomoxys sp. in delayed transmission. A review of the available trypanocidal drugs and their efficacy in various host species is useful for understanding how they interact in disease epidemiology, which is complex. Although there are similarities with other mechanically transmitted trypanosomes, T. evansi has a more complex epidemiology due to the diversity of its hosts and vectors. The impact of clinical and subclinical disease is difficult to establish. A model was developed for buffaloes in the Philippines, which could be transferred to other places and livestock systems. Since Trypanosoma evansi was reported in humans, further research is required to investigate its zoonotic potential. Surra remains a potentially emerging disease that is a threat to Australia, Spain, and France. A number of questions about the disease have yet to be resolved. This brief review of the basic knowledge of T. evansi suggests that there is renewed interest in the parasite, which is spreading and has a major economic impact.

Morphology and ultrastructure of multiple life cycle stages of the photosynthetic relative of apicomplexa, Chromera velia.

Chromera veliais a photosynthetic alga with a secondary plastid that represents the closest known photosynthetic relative of the apicomplexan parasites. The original description of this organism was based on brownish, immotile coccoid cells, which is the predominating stage ofC. veliain the culture. Here we provide a detailed light and electron microscopy description of coccoid cells ofC. veliaand a previously undocumented bi-flagellated stage that is highly motile and moves in a characteristic zig-zag pattern. Transformation from a coccoid into a flagellate stage occurs in exponentially growing cultures, and is accelerated by exposure to light. TheC. veliacells contain a pseudoconoid, which is likely homologous to the corresponding structure in the apical complex of Apicomplexa, cortical alveoli subtended by subpellicular microtubules, mitochondrion with tubular cristae, a micropyle, and a distinctive chromerosome, an apparently novel type of extrusion organelle. Ultrastructural analysis of the flagellate supports its close association with colpodellids and apicomplexans and provides important insight into their evolution.

Genome and phylogenetic analyses of Trypanosoma evansi reveal extensive similarity to T. brucei and multiple independent origins for dyskinetoplasty

Two key biological features distinguish Trypanosoma evansi from the T. brucei group: independence from the tsetse fly as obligatory vector, and independence from the need for functional mitochondrial DNA (kinetoplast or kDNA). In an effort to better understand the molecular causes and consequences of these differences, we sequenced the genome of an akinetoplastic T. evansi strain from China and compared it to the T. b. brucei reference strain. The annotated T. evansi genome shows extensive similarity to the reference, with 94.9% of the predicted T. b. brucei coding sequences (CDS) having an ortholog in T. evansi, and 94.6% of the non-repetitive orthologs having a nucleotide identity of 95% or greater. Interestingly, several procyclin-associated genes (PAGs) were disrupted or not found in this T. evansi strain, suggesting a selective loss of function in the absence of the insect life-cycle stage. Surprisingly, orthologous sequences were found in T. evansi for all 978 nuclear CDS predicted to represent the mitochondrial proteome in T. brucei, although a small number of these may have lost functionality. Consistent with previous results, the F1FO-ATP synthase γ subunit was found to have an A281 deletion, which is involved in generation of a mitochondrial membrane potential in the absence of kDNA. Candidates for CDS that are absent from the reference genome were identified in supplementary de novo assemblies of T. evansi reads. Phylogenetic analyses show that the sequenced strain belongs to a dominant group of clonal T. evansi strains with worldwide distribution that also includes isolates classified as T. equiperdum. At least three other types of T. evansi or T. equiperdum have emerged independently. Overall, the elucidation of the T. evansi genome sequence reveals extensive similarity of T. brucei and supports the contention that T. evansi should be classified as a subspecies of T. brucei.

Split Photosystem Protein, Linear-Mapping Topology, and Growth of Structural Complexity in the Plastid Genome of Chromera velia

The canonical photosynthetic plastid genomes consist of a single circular-mapping chromosome that encodes a highly conserved protein core, involved in photosynthesis and ATP generation. Here, we demonstrate that the plastid genome of the photosynthetic relative of apicomplexans, Chromera velia, departs from this view in several unique ways. Core photosynthesis proteins PsaA and AtpB have been broken into two fragments, which we show are independently transcribed, oligoU-tailed, translated, and assembled into functional photosystem I and ATP synthase complexes. Genome-wide transcription profiles support expression of many other highly modified proteins, including several that contain extensions amounting to hundreds of amino acids in length. Canonical gene clusters and operons have been fragmented and reshuffled into novel putative transcriptional units. Massive genomic coverage by paired-end reads, coupled with pulsed-field gel electrophoresis and polymerase chain reaction, consistently indicate that the C. velia plastid genome is linear-mapping, a unique state among all plastids. Abundant intragenomic duplication probably mediated by recombination can explain protein splits, extensions, and genome linearization and is perhaps the key driving force behind the many features that defy the conventional ways of plastid genome architecture and function.

Trypanosoma brucei: two steps to spread out from Africa

Trypanosoma brucei equiperdum and Trypanosoma brucei evansi are typically considered separate species, although a recent study suggested that these organisms can be classified as subspecies of Trypanosoma brucei, which we also favor. Here we present a scenario that attempts to explain the continuing evolution of the dyskinetoplastic and akinetoplastic strains, as a consequence of loss of selective pressure(s) leading to the loss of kinetoplast DNA.

Divergent Mitochondrial Respiratory Chains in Phototrophic Relatives of Apicomplexan Parasites

Four respiratory complexes and ATP-synthase represent central functional units in mitochondria. In some mitochondria and derived anaerobic organelles, a few or all of these respiratory complexes have been lost during evolution. We show that the respiratory chain of Chromera velia, a phototrophic relative of parasitic apicomplexans, lacks complexes I and III, making it a uniquely reduced aerobic mitochondrion. In Chromera, putative lactate:cytochrome c oxidoreductases are predicted to transfer electrons from lactate to cytochrome c, rendering complex III unnecessary. The mitochondrial genome of Chromera has the smallest known protein-coding capacity of all mitochondria, encoding just cox1 and cox3 on heterogeneous linear molecules. In contrast, another photosynthetic relative of apicomplexans, Vitrella brassicaformis, retains the same set of genes as apicomplexans and dinoflagellates (cox1, cox3, and cob).

Molecular genetic profiles among individual Clonorchis sinensis adults collected from cats in two geographic regions of China revealed by RAPD and MGE-PCR methods

Clonorchis sinensis causes the important food-borne zoonosis, clonorchiasis, which is endemic in East Asia, especially in China mainly in Guangdong, Guangxi and Heilongjiang provinces and Korea. Although comparisons on isoenzymes and some molecular profiles of C. sinensis collected from different parts of China and Korea have been studied, few works on the genetic variation among the individuals from different regions of China has been reported. In the present study, individual adults of C. sinensis were collected from cats in two geographic locations (Guangdong province in the South and Heilongjiang province in the North) of China and 44 of them were examined by using random amplified polymorphic DNA (RAPD)-PCR and mobile genetic elements (MGEs)-PCR techniques to assess the individual genetic variability within and between the two groups of this parasite. Six arbitrary primers and two pairs of MGE primers were employed in the genomic DNA amplification. The molecular patterns showed significant polymorphism among the individuals. The RAPD data displayed that the similarity coefficient (SC) of the individuals within Heilongjiang group was much higher than that of the Guangdong group, which was further confirmed by MGE-PCR results. Individuals from Heilongjiang were found genetically closer with lesser polymorphisms than those collected from Guangdong province. These results demonstrated that RAPD and MGE-PCR techniques, particularly RAPD method, could be useful for investigating genetic variations among C. sinensis individuals. They may also indicate that the genetic variation of C. sinensis occurs in the subtropical region--Guangdong--faster than that in the cold-region--Heilongjiang province--due to more generations (life cycle) occurred.