Morphological and taxonomic studies on mammalian trypanosomes: VIII. Revision of Trypanosoma evansi

The Occurrence of Malignancy in Trypanosoma brucei brucei by Rapid Passage in Mice

Pleomorphic Trypanosoma brucei are best known for their tightly controlled cell growth and developmental program, which ensures their transmissibility and host fitness between the mammalian host and insect vector. However, after long-term adaptation in the laboratory or by natural evolution, monomorphic parasites can be derived. The origin of these monomorphic forms is currently unclear. Here, we produced a series of monomorphic trypanosome stocks by artificially syringe-passage in mice, creating snapshots of the transition from pleomorphism to monomorphism. We then compared these artificial monomorphic trypanosomes, alongside several naturally monomorphic T. evansi and T. equiperdum strains, with the pleomorphic T. brucei. In addition to failing to generate stumpy forms in animal bloodstream, we found that monomorphic trypanosomes from laboratory and nature exhibited distinct differentiation patterns, which are reflected by their distinct differentiation potential and transcriptional changes. Lab-adapted monomorphic trypanosomes could still be induced to differentiate, and showed only minor transcriptional differences to that of the pleomorphic slender forms but some accumulated differences were observed as the passages progress. All naturally monomorphic strains completely fail to differentiate, corresponding to their impaired differentiation regulation. We propose that the natural phenomenon of trypanosomal monomorphism is actually a malignant manifestation of protozoal cells. From a disease epidemiological and evolutionary perspective, our results provide evidence for a new way of thinking about the origin of these naturally monomorphic strains, the malignant evolution of trypanosomes may raise some concerns. Additionally, these monomorphic trypanosomes may reflect the quantitative and qualitative changes in the malignant evolution of T. brucei, suggesting that single-celled protozoa may also provide the most primitive model of cellular malignancy, which could be a primitive and inherent biological phenomenon of eukaryotic organisms from protozoans to mammals.

ABA. Study Iron Homeostasis of Infected and Non-Infected Iraqi Camels with Trypanosomiasis

Trypanosomiasis is one of the common parasitic diseases, which infects the dromedary camels and decreases the numbers of these animals in Iraq. To get the best knowledge of the changes of iron status in camels infected with trypanosomiasis, in an attempt to take advantage of these variables as markers for infection, we designed this study. The current study conducted in blood sample collection from155 dromedary camels, 33 were infected (21.29%), according to the status of infection with Trypanosoma evansi that depends on blood smear examination as a golden test. Results denote significant differences of infection ratio by sex and age, from total of 132 male tested, 29 (21.96%) infected, distributed into 12 (%41.37) of age ≤ 2 years and 17 (58.62) of ≥ 2 years. From 23 female tested, 4 (17.39%) were infected at age ≤ 2 years. Furthermore, the results of this study demonstrated significant (p˂0.05) decrease in total serum iron, transferrin saturation, ferritin, whereas increased in total iron binding capacity and unsaturated iron binding capacity in the infected male and female camels with different age. Analyzed data of iron status parameters denoted that the cutoff point test between sensitivity (97) and specificity (100) for serum iron is (≤67.26), for transferrin saturation is (≤17.23) between the sensitivity and specificity (100) and (≥378.66), for total iron binding capacity between the sensitivity and specificity (93.9 and 96.7) respectively. Also, the cutoff point test between the sensitivity (100) and specificity (96.7) for unsaturated iron binding capacity is (≥301.27) and ferritin concentration has a cutoff point is (≤ 249.88) for the sensitivity (100) and specificity (99.2). It could be concluded from what was stated in the results of the current study, that the measurement of the concentration of serum ferritin could be considered as a good marker for the T. evansi infection

Mitochondrial DNA is critical for longevity and metabolism of transmission stage Trypanosoma brucei

The sleeping sickness parasite Trypanosoma brucei has a complex life cycle, alternating between a mammalian host and the tsetse fly vector. A tightly controlled developmental programme ensures parasite transmission between hosts as well as survival within them and involves strict regulation of mitochondrial activities. In the glucose-rich bloodstream, the replicative 'slender' stage is thought to produce ATP exclusively via glycolysis and uses the mitochondrial F1FO-ATP synthase as an ATP hydrolysis-driven proton pump to generate the mitochondrial membrane potential (ΔΨm). The 'procyclic' stage in the glucose-poor tsetse midgut depends on mitochondrial catabolism of amino acids for energy production, which involves oxidative phosphorylation with ATP production via the F1FO-ATP synthase. Both modes of the F1FO enzyme critically depend on FO subunit a, which is encoded in the parasite's mitochondrial DNA (kinetoplast or kDNA). Comparatively little is known about mitochondrial function and the role of kDNA in non-replicative 'stumpy' bloodstream forms, a developmental stage essential for disease transmission. Here we show that the L262P mutation in the nuclear-encoded F1 subunit γ that permits survival of 'slender' bloodstream forms lacking kDNA ('akinetoplastic' forms), via FO-independent generation of ΔΨm, also permits their differentiation into stumpy forms. However, these akinetoplastic stumpy cells lack a ΔΨm and have a reduced lifespan in vitro and in mice, which significantly alters the within-host dynamics of the parasite. We further show that generation of ΔΨm in stumpy parasites and their ability to use α-ketoglutarate to sustain viability depend on F1-ATPase activity. Surprisingly, however, loss of ΔΨm does not reduce stumpy life span. We conclude that the L262P γ subunit mutation does not enable FO-independent generation of ΔΨm in stumpy cells, most likely as a consequence of mitochondrial ATP production in these cells. In addition, kDNA-encoded genes other than FO subunit a are important for stumpy form viability.

Biology of Trypanosoma (Trypanozoon) evansi in experimental heterologous mammalian hosts

Trypanosoma (Trypanozoon) evansi is a causative agent of the dreadful mammalian disease trypanosomiasis or 'Surra' and carried as a latent parasite in domestic cattle but occasionally proves fatal when transmitted to horses and camel. Sporadic outbreak of 'Surra' to different animals (beside their natural hosts) reminds that T. evansi may be zoonotic, as their close relative cause sleeping sickness to human being. This haemoflagellate is mechanically transmitted by horse fly and its effect on different host varies depending on certain factors including the effectiveness of transmission by mechanical vector, the suitability and susceptibility of the host as well as most importantly the ability of the disease establishment of parasite to adapt itself to the host's resistance, etc. The course of the disease caused by T. evansi is similar to that of human sleeping sickness caused by T. (T.) brucei gambiense. The target organs and symptoms show close similarity. T. evansi can successfully be transmitted among unnatural hosts i.e., other classes of vertebrates, like chicken. In transmission experiments, the unnatural hosts may sometimes induce profound changes in the biology of trypanosomes. Hence, in present study the observations are the biology of different morphological changes of T. evansi as well as its ability of disease formation within some heterologous mammal viz., albino rat, guineapig, bandicoot, mongoose, domestic cat and common monkey. Blood smears of infected albino rats, bandicoot, and mongoose revealed only monomorphic form. Interestingly, blood smears of infected cat and monkey, T. evansi shows slender trypomastigote form and short intermediate form whereas organ smears shows other two forms of haemoflagellate viz., sphaeromastigote and amastigote form. The haemoflagellate maintains a common reproductive cycle in all the experimental heterologous hosts whereas disease symptoms differ. T. evansi infected cat and monkey shows nervous symptoms. Infected monkey expresses some symptoms similar to that of human sleeping sickness disease. Thus the paper highlights zoonotic potentialities of T. evansi.

VSG 117 gene is conservatively present and early expressed in Trypanosma evansi YNB stock

African trypanosomes, including Trypanosoma brucei and the closely related species Trypanosoma evansi, are flagellated unicellular parasites that proliferate extracellularly in the mammalian bloodstream and tissue spaces. They evade host immune system by periodically switching their variant surface glycoprotein (VSG) coat. Each trypanosome possesses a vast archive of VSGs with distinct sequence identity and different strains contain different archive of VSGs. VSG 117 was reported as a widespread VSG detected in the genomes of all the T. brucei strains. In this study, the presence and expression of VSG 117 gene was observed in T. evansi YNB stock by RT-PCR with VSG-specific primers. We further confirmed that this VSG tends to be expressed in the early stage of T. evansi infections (on day 12-15) by immuno-screening the previously isolated infected blood samples. It is possible that the VSG 117 gene evolved and spread through the African trypanosome population via genetic exchange, before T. evansi lost its ability to infect tsetse fly. Our finding provided an evidence of the close evolutionary relationship between T. evansi and T. brucei, in the terms of VSG genes.

Host restriction, morphology and isoenzymes among trypanosomes of some British freshwater fishes

Trypanosomes were studied from the blood of 6 species of small British fish caught in the River Lee. Morphologically the trypanosomes from the blood ofNemacheilus barbatulusL.,Phoxinus phoxinusL.,Cottus gobioL.,Gobio gobioL.,Gasterosteus aculeatusandPungitus pungitusL. were indistinguishable. Cross-transmission experiments using syringe passage of culture forms and also the leech vectorHemiclepsis marginatashowed that the trypanosomes were not host specific. The isoenzyme patterns of culture forms fromN. barbatulusandP. phoxinuswere identical for 11 enzymes studied. The trypanosomes from the 6 species of fish previously classified as separate species are, on the basis of these results, regarded as a single species,Trypanosoma cobitis(Mitrophanow, 1883).

A morphological and biometrical study of the blood forms ofTrypanosoma suisOchmann, 1905

The status ofTrypanosoma suiswas held in doubt from the time it was first seen in 1905 until it was re-discovered and carefully studied in the Belgian Congo in 1954.

A description is given of the morphology of single and dividing forms ofT. suisas seen in stained thin films made from the blood of infected pigs, and a selection of these is illustrated by line drawings. Briefly this trypanosome is short and stumpy with a free flagellum.

A biometrical study was made on 200 organisms, showing a normal length distribution with a range from 8·5 to 18·5μ, and mean = 14·43μ.

The monomorphism of the trypanosome is verified, and—because of its development in the salivary glands ofGlossina—its systematic position as a monomorphic subgroup of theBruceigroup is confirmed.

I am much indebted to Dr C. A. Hoare, F.R.S., for the loan of the blood films used in this study and for his interest in the work. I am also grateful to Professor P. C. C. Garnham for providing me with accommodation and equipment at the London School of Hygiene and Tropical Medicine.

Trypanosoma evansi: a convenient model for studying intracellular Ca(2+) homeostasis using fluorometric ratio imaging from single parasites

The aim of this work was to measure, for the first time, the basal cytosolic Ca(2+) levels of Trypanosoma evansi and to explore the possibility of observing changes in the intracellular Ca(2+) concentration ([Ca(2+)](i)) using fluorescence ratio imaging techniques in single isolated parasites of this species. Under appropriate loading conditions, the high intracellular levels of the Ca(2+) fluorescence probe Fura-2 permits resolution, in real time, of single parasite [Ca(2+)](i) signals. Measurements of the basal [Ca(2+)](i) indicate that homeostatic mechanisms maintain [Ca(2+)](i) at 106 +/- 38 (n = 32) nM in the presence of 2 mM extracellular calcium. The resting [Ca(2+)](i) was unaffected by changes in extracellular Ca(2+) in the range from 0 to 10 mM. The Ca(2+) ionophore A23187 induced a large increase in [Ca(2+)](i) which (i) reached a steady state value even in the simultaneous presence of both external calcium and ionophore and (ii) returned to base line upon removal of extracellular Ca(2+). A dose-response curve of the protonophore nigericin shows that T. evansi contains an important pH-sensitive intracellular pool which may be released by this drug with a K(1/2) of 8 microM. These data demonstrate that this parasite contains highly efficient systems to control [Ca(2+)](i). Finally, our results, with the use of sera as source of an antibody-complement to induce Ca(2+) entry, demonstrate that it is possible to resolve fast [Ca(2+)](i) signals in single parasites from T. evansi.

Biological and biochemical characterization of isolates of Trypanosoma evansi from Pantanal of Matogrosso--Brazil

Ten isolates of Trypanosoma evansi from the Pantanal region of Brazil, recently derived from coati (Nasua nasua, carnivora, Procyonidae), horses and dogs, were characterized on the basis of biological (experimental infections in Wistar rats) and biochemical (multilocus enzyme eletrophoresis) data. Biological data were analyzed by Nested analysis of variance and Kruskal-Wallis. Marked heterogeneity in virulence was observed in the isolates. Some of the isolates showed an undulating parasitaemia, typical for African trypanosomes. This biological heterogeneity did not correspond with the biochemical homogeneity observed in the T. evansi isolates. T. evansi has one of the widest distributions and greatest range of mammalian hosts and is widely recognized to have evolved from Trypanosoma brucei. Adaptability of T. evansi was not reflected in the variability of biochemical and molecular parameters studied to date. The variability in virulence was very significant, but not correlated with the host from which it was derived. These data suggested that, in the region studied, T. evansi is transmitted among both domestic and sylvatic animals in one single transmission cycle.

Studies of infectivity and pathogenicity of an isolate of Trypanosoma evansi in Yankasa sheep

The course of experimental infection and pathogenicity of an isolate of Trypanosoma evansi were investigated using eight infected and six uninfected control Yankasa sheep. The sheep were each infected intravenously via the jugular vein with approximately 2.0 x 10(6) T. evansi parasites. The effects of the parasite on body temperature, packed cell volume (PCV), haemoglobin, erythrocytes, total protein, were monitored three times a week for approximately 9 weeks. Body weights were determined once every week for the duration of the experiment. The results showed that all the infected sheep were positive for the parasite. The prepatent period varied between 3 and 6 days. T. evansi produced parasitaemic waves at an average of 8.3 days interval. Two distinct forms of the disease were produced namely, acute (4-14 days postinfection), and chronic (43-59 days postinfection). Anaemia was a distinct feature of the disease. While the mean rectal temperatures were significantly elevated (P < 0.05), the mean values of the haematological parameters of the infected sheep dropped significantly (P < 0.05) compared to the preinfection levels. Observed clinical signs included pale mucous membrane, epiphora, loss of appetite, emaciation, dullness and rough hair coat together with fluctuating pyrexia which in most cases coincided with rise in parasitaemia. It is suggested that the isolate of T. evansi is pathogenic for Yankasa sheep.

Trypanosoma evansi and T. equiperdum: distribution, biology, treatment and phylogenetic relationship (a review)

Trypanosoma evansi and T. equiperdum were compared regarding their ultrastructure, their mammalian hosts, way of transmission, pathogenicity, diagnosis and treatment, and biochemical and molecular characteristics. Electron microscopic investigation revealed no ultrastructural differences between the two species except that there were more coated vesicles in the flagellar pocket of T. equiperdum. Biological, biochemical and molecular studies were reviewed and exhibited many similarities between T. evansi and T. equiperdum. The most prominent differences between the two species are the presence of maxicircles in T. equiperdum, which are missing in T. evansi, and the route of transmission. While T. evansi is transmitted by biting flies, T. equiperdum is transmitted from one equine host to another during copulation when mucous membranes come into contact. Otherwise the two species are remarkably similar. The phylogenetic relationship between the two species and T. b. brucei is being discussed, and the hypothesis is proposed that T. evansi arose from a clone of T. equiperdum which lost its maxicircles.

Outbreak of trypanosomosis due to Trypanosoma evansi in horses of Pantanal Mato-grossense, Brazil

This paper reports an outbreak of trypanosomosis due to Trypanosoma evansi in horses of the Pantanal Mato-grossense region of Brazil. Forty-eight horses died (51% mortality) and abortion in one mare was recorded. The clinical signs observed were fever, anemia, conjunctivitis, edema of the legs and lower parts of the body, progressive weakness, loss of condition, and loss of appetite. The diagnosis was confirmed by morphological and biometrical studies.

The isoenzyme characteristics of Trypanosoma evansi and Trypanosoma equiperdum isolated from domestic stocks in China

Twelve stocks of Trypanosoma evansi and one of Trypanosoma equiperdum isolated from domestic animals in China were examined for 16 enzymes using cellulose acetate and thin-layer starch gel electrophoresis. Differences were seen between stocks in only two of the enzymes, MDH and ALAT. Three of the T. evansi stocks, isolated from buffalo, and the T. equiperdum stock had the unusual pattern MDH-3, while all the other Chinese stocks had the common MDH-1. Two other stocks of T. evansi and again the T. equiperdum, all from equines, showed a new pattern ALAT-14. Otherwise the Chinese stocks had the same enzyme profile as T. evansi from elsewhere.

The effects of the methylating agent 1,2-bis(methylsulfonyl)-1-methylhydrazine on morphology, DNA content and mitochondrial function of Trypanosoma brucei subspecies

Repeated exposure of trypanosomes in vitro or in vivo to low concentrations of the methylating agent 1,2-bis(methylsulfonyl)-1-methylhydrazine induces a series of moderately synchronous morphological and biochemical changes. Cell division halts and the long-slender bloodstream forms transform to short-stumpy forms via larger intermediate-stage cells which contain approximately double the normal G2 content of DNA. In common with naturally occurring short-stumpy trypanosomes, drug-induced short-stumpy forms do not infect rodents and when transferred to Cunningham's medium, transform to and replicate as procyclics. Furthermore, these short-stumpy forms exhibit alpha-ketoglutarate supported motility and oxygen consumption, acquire the ability to reduce nitroblue tetrazolium (NADH diaphorase positivity) and appear to be in the G1 or G0 stage of the cell cycle based upon DNA content.

Trypanosoma b. brucei: a culture medium reverting a monomorphic to a pleomorphic strain

A monomorphic strain of Trypanosoma b. brucei cultured for 5 days at 37 degrees C in Eagle's Minimum Essential Medium (with or without feeder cells) supplemented with Nu-Serum became pleomorphic after inoculation into mice. Dividing stumpy forms were still seen in blood after the third mouse passage. The strain remained monomorphic when cultured in the medium supplemented with foetal calf serum. This supports the hypothesis that some slender forms, under certain conditions, have the genetic capability of transforming into stumpy forms which can multiply by binary fission in the mammalian host.

Species differentiation in the genus Leishmania by morphometric studies with the electron microscope

Morphometric comparison of some ultrastructural features of leishmanial amastigotes demonstrated species-characteristic differences. These occurred in parameters relating to size, such as diameter and microtubule number; statistical analysis resolved four groups from the seven isolates studied. The results were not inconsistent with previous measurements, mostly with the light microscope, by other workers. The unqualified assertion that Leishmania species are morphologically identical is therefore no longer valid.