Genetic variability in ESAG6 genes among Trypanosoma evansi isolates and in comparison to other Trypanozoon members

Molecular characterization of trypanocide-resistant strains derived from a single field isolate of Trypanosoma evansi

Four strains (SB-PR, SB-RS, SB-RD, and SB-RM) of Trypanosoma evansi (T. evansi) were used in this study. SB-PR is known to be trypanocide-sensitive, while the others are trypanocide-resistant to suramin, diminazene diaceturate, and melarsomine hydrochloride, respectively. SB-RS, SB-RD, and SB-RM are derivatives of a single field isolate of SB-PR. Trypanocide resistance will not only increase costs and decrease production efficiency but will also affect effective treatment strategies. Therefore, studies on this topic are important to avoid inefficient production and ineffective treatment. This paper aims to presents a comparative molecular characterization of the trypanocide-resistant strains compared to the parent population. Comparative molecular characterization of these strains based on a protein profile analysis performed with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), DNA fingerprinting of random amplified polymorphic DNA (RAPD), and the molecular characterization of expression-site-associated 6 (ESAG6), variant surface glycoprotein (VSG), and T. evansi adenosine transporter-1 (TevAT1) gene sequences. The results show three derived strains (SB-RS, SB-RD, and SB-RM) exhibit different banding patterns than SB-PR. According to the RAPD results, SB-RS and SB-RD are different strains with DNA fingerprint similarities of about 77.8 %, while the DNA fingerprint of SB-RM has a similarity of 44.4 % to SB-RS and SB-RD. No differences in VSG were found among the four strains; however, ESAG6 showed differences in both nucleotide and amino acid sequences, as well as in its secondary and 3D structure. In conclusion, all molecular analyses of the ESAG6 gene showed that SB-PR, SB-RS, SB-RD, and SB-RM are different strains. Furthermore, SB-PR, SB-RS, SB-RD, and SB-RM did not exhibit the TevAT1 gene, so the resistance mechanism was determined to be unrelated to that gene.

Trypanosoma brucei Plimmer & Bradford, 1899 is a synonym of T. evansi (Steel, 1885) according to current knowledge and by application of nomenclature rules

Proper application of the principles of biological nomenclature is fundamental for scientific and technical communication about organisms. As other scientific disciplines, taxonomy inherently is open to change, thus species names cannot be final and immutable. Nevertheless, altering the names of organisms of high economical, medical, or veterinary importance can become a complex challenge between the scientific need to have correct classifications, and the practical ideal of having fixed classifications. Trypanosoma evansi (Steel, 1885), T. brucei Plimmer & Bradford, 1899 and T. equiperdum Doflein, 1901 are important parasites of mammals. According to current knowledge, the three names are synonyms of a single trypanosome species, the valid name of which should be T. evansi by the mandatory application of the Principle of Priority of zoological nomenclature. Subspecies known as T. brucei brucei Plimmer & Bradford, 1899, T. b. gambiense Dutton, 1902 and T. b. rhodesiense Stephens & Fantham, 1910 should be referred to respectively as T. evansi evansi (Steel, 1885), T. e. gambiense and T. e. rhodesiense. The polyphyletic groupings so far known as T. evansi and T. equiperdum should be referred respectively to as surra- and dourine-causing strains of T. e. evansi. Likewise, trypanosomes so far known as T. b. brucei should be referred to as nagana-causing strains of T. e. evansi. Though it modifies the scientific names of flagship human and animal parasites, the amended nomenclature proposed herein should be adopted because it reflects phylogenetic and biological advancements, fixes errors, and is simpler than the existing classificatory system.

Intra and inter species genetic variability of transferrin receptor gene regions in Trypanosoma evansi isolates of different livestock and geographical regions of India

Trypanosoma evansi, the aetiological agent of Surra affects a wide range of livestock and wild animals in India. In the present study, we studied intra- and inter species genetic variability in the transferrin receptor encoding gene regions (ESAG6/7 gene region) of T. evansi isolates by cloning, sequencing and phylogenetic study collected from camel, cattle, donkeys and ponies from North-Western and Central India. The nucleotide sequence variation of ESAG6/7 gene region between Indian T. evansi isolates was up to 17.7% and amino acid sequence variation was up to 31%. Twenty nine clones from six T. evansi isolates from geographical regions of India were included into Clade 1, 5, 6, 7 and 9 consisting of ESAG6 variants reported among T. evansi isolates from South-east Asia and South America. The cladogram indicated a relation between the host species and the genetic variability in the hyper-variable region of ESAG6 gene. Analysis of the Indian ESAG6 variants and their respective Clade positions presented a host specific distribution indicating homogenous parasite population in their respective animal hosts.

Phylogeny of Trypanosoma brucei and Trypanosoma evansi in naturally infected cattle in Nigeria by analysis of repetitive and ribosomal DNA sequences

In continuing efforts to better understand the genetics of bovine trypanosomosis, we assessed genetic diversity of Trypanosoma brucei and Trypanosoma evansi in naturally infected Nigerian cattle using repetitive DNA and internal transcribed spacer 1 of rDNA sequences and compared these sequences to species from other countries. The length of repetitive DNA sequences in both species ranged from 161 to 244 bp and 239 to 240 bp for T. brucei and T. evansi, respectively, while the ITS1 rDNA sequences length range from 299 to 364 bp. The mean GC content of ITS1 rDNA sequences was 33.57 %, and that of repetitive sequences were 39.9 and 31.1 % for T. brucei and T. evansi, respectively. Result from sequence alignment revealed both T. brucei and T. evansi repetitive DNA sequences to be more polymorphic than ITS1 rDNA sequences, with moderate points of deletion and insertions. T. brucei separated into two clades when subjected to phylogenetic analysis. T. evansi repetitive DNA sequences clustered tightly within the T. brucei clade while the ITS1 rDNA sequences of T. brucei were clearly separated from T. theileri and T. vivax individually used as outgroups. This study suggest that ITS1 rDNA sequences may not be suitable for phylogenetic differentiation of the Trypanozoon group and also suggest that T. evansi may be a phenotypic variant of T. brucei which may have potential implications in designing prevention and therapeutic strategies.

Molecular identification and phylogenetic analysis of Trypanosoma evansi from dromedary camels (Camelus dromedarius) in Egypt, a pilot study

Animal trypanosomiasis is one of the major constraints of livestock industry in developing countries. In the present study, prevalence of Trypanosome evansi was assessed in the blood of dromedary camels (Camelus dromedarius) brought to Al Bassatein abattoir, Cairo, Egypt, by mouse inoculation test out of 84 tested camels, 4 animals (4.7%) were infected. Molecular analysis was achieved by PCR amplification and sequence analysis of part of ribosomal RNA gene including 18S, ITS1, 5.8S and ITS2 regions. Despite the conserved nature of 18S region, ITS region showed obvious heterogeneity compared to analogous sequences in database. Analysis of transferrin receptor encoding gene (ESAG6) showed variable repertoire in the studied isolates, which may indicate to a novel structure of T. evansi population from Egypt and/or a difference in host range. Furthermore, analysis of variable surface glycoprotein RoTat 1.2 gene marker revealed some heterogeneity at this gene locus. To our knowledge, this is the first molecular analysis of T. evansi in Egypt.

Iron metabolism in trypanosomatids, and its crucial role in infection

Iron is almost ubiquitous in living organisms due to the utility of its redox chemistry. It is also dangerous as it can catalyse the formation of reactive free radicals - a classical double-edged sword. In this review, we examine the uptake and usage of iron by trypanosomatids and discuss how modulation of host iron metabolism plays an important role in the protective response. Trypanosomatids require iron for crucial processes including DNA replication, antioxidant defence, mitochondrial respiration, synthesis of the modified base J and, in African trypanosomes, the alternative oxidase. The source of iron varies between species. Bloodstream-form African trypanosomes acquire iron from their host by uptake of transferrin, and Leishmania amazonensis expresses a ZIP family cation transporter in the plasma membrane. In other trypanosomatids, iron uptake has been poorly characterized. Iron-withholding responses by the host can be a major determinant of disease outcome. Their role in trypanosomatid infections is becoming apparent. For example, the cytosolic sequestration properties of NRAMP1, confer resistance against leishmaniasis. Conversely, cytoplasmic sequestration of iron may be favourable rather than detrimental to Trypanosoma cruzi. The central role of iron in both parasite metabolism and the host response is attracting interest as a possible point of therapeutic intervention.

Isolation and analysis of the genetic diversity of repertoires of VSG expression site containing telomeres from Trypanosoma brucei gambiense, T. b. brucei and T. equiperdum

Background

African trypanosomes (including Trypanosoma brucei) are unicellular parasites which multiply in the mammalian bloodstream. T. brucei has about twenty telomeric bloodstream form Variant Surface Glycoprotein (VSG) expression sites (BESs), of which one is expressed at a time in a mutually exclusive fashion. BESs are polycistronic transcription units, containing a variety of families of expression site associated genes (ESAGs) in addition to the telomeric VSG. These polymorphic ESAG families are thought to play a role in parasite-host adaptation, and it has been proposed that ESAG diversity might be related to host range. Analysis of the genetic diversity of these telomeric gene families has been confounded by the underrepresentation of telomeric sequences in standard libraries. We have previously developed a method to selectively isolate sets of trypanosome BES containing telomeres using Transformation associated recombination (TAR) cloning in yeast.

Results

Here we describe the isolation of repertoires of BES containing telomeres from three trypanosome subspecies: Trypanosoma brucei gambiense DAL 972 (causative agent of West-African trypanosomiasis), T. b. brucei EATRO 2340 (a nonhuman infective strain) and T. equiperdum STIB 818 (which causes a sexually transmitted disease in equines). We have sequenced and analysed the genetic diversity at four BES loci (BES promoter region, ESAG6, ESAG5 and ESAG2) from these three trypanosome BES repertoires.

Conclusion

With the exception of ESAG2, the BES sequence repertoires derived from T. b. gambiense are both less diverse than and nearly reciprocally monophyletic relative to those from T. b. brucei and T. equiperdum. Furthermore, although we find evidence for adaptive evolution in all three ESAG repertoires in T. b. brucei and T. equiperdum, only ESAG2 appears to be under diversifying selection in T. b. gambiense. This low level of variation in the T. b. gambiense BES sequence repertoires is consistent both with the relatively narrow host range of this subspecies and its apparent long-term clonality. However, our data does not show a clear correlation between size of trypanosome host range and either number of BESs or extent of ESAG genetic diversity.

Genetic diversity of Trypanosoma evansi in buffalo based on internal transcribed spacer (ITS) regions

The nucleotide sequences of 18S rDNA and internal transcribed spacer (ITS) regions were used for studying the relationships of Trypanosoma evansi isolate from a buffalo. The sequences were analyzed and compared to 18S rDNA and the ITS regions of the other Trypanosoma spp. Maximum likelihood phylogenetic trees were constructed using Leishmania major as the outgroup. The tree of 18S rDNA indicated that T. evansi (buffalo B18) isolate was closely related to those of Taiwan and T. brucei stock. The ITS tree showed the genetic diversity among 32 clones of T. evansi (B18) within a single host. This data will be useful for epidemiological and dynamic studies for designing the rational control programs of the disease.

Trypanosoma equiperdum: master of disguise or historical mistake?

After 100 years of research, only a small number of laboratory strains of Trypanosoma equiperdum exists, and the history of most of the strains is unknown. No definitive diagnosis of dourine can be made at the serological or molecular level. Only clinical signs are pathognomonic and international screening relies on an outdated cross-reactive serological test (the complement-fixation test) from 1915, resulting in serious consequences at the practical level. Despite many characterization attempts, no clear picture has emerged of the position of T. equiperdum within the Trypanozoon group. In this article, we highlight the controversies that exist regarding T. equiperdum, and the overlap that occurs with Trypanosoma evansi and Trypanosoma brucei brucei. By revisiting the published data, from the early decades of discovery to the recent serological- and molecular-characterization studies, a new hypothesis arises in which T. equiperdum no longer exists as a separate species and in which current strains can be divided into T. evansi (the historical mistake) and Trypanosoma brucei equiperdum (the master of disguise). Hence, dourine is a disease caused by specific host immune responses to a T. b. equiperdum or T. evansi infection.