Trypanosoma caninum, a new parasite described in dogs in Brazil: aspects of natural infection

Phylogenetic evidence for a clade of tick-associated trypanosomes

BACKGROUND

Trypanosomes are protozoan parasites of vertebrates that are of medical and veterinary concern. A variety of blood-feeding invertebrates have been identified as vectors, but the role of ticks in trypanosome transmission remains unclear.

METHODS

In this study, we undertook extensive molecular screening for the presence and genetic diversity of trypanosomes in field ticks.

RESULTS

Examination of 1089 specimens belonging to 28 tick species from Europe and South America led to the identification of two new trypanosome strains. The prevalence may be as high as 4% in tick species such as the castor bean tick Ixodes ricinus, but we found no evidence of transovarial transmission. Further phylogenetic analyses based on 18S rRNA, EF1-α, hsp60 and hsp85 gene sequences revealed that different tick species, originating from different continents, often harbour phylogenetically related trypanosome strains and species. Most tick-associated trypanosomes cluster in a monophyletic clade, the Trypanosoma pestanai clade, distinct from clades of trypanosomes associated with transmission by other blood-feeding invertebrates.

CONCLUSIONS

These observations suggest that ticks may be specific arthropod hosts for trypanosomes of the T. pestanai clade. Phylogenetic analyses provide further evidence that ticks may transmit these trypanosomes to a diversity of mammal species (including placental and marsupial species) on most continents.

Molecular detection of vector-borne pathogens in semen from dogs in southeastern Brazil

Vector-borne pathogens (VBPs) are primarily transmitted by arthropod vectors, but secondary ways of transmission have been described, including via venereal route. Nonetheless, there is still limited research on possible sexual transmission of VBPs in dogs. We molecularly investigated the presence of vector-borne pathogens in semen from dogs living in an area where these agents are endemic. Upon PCR testing, seven out of 22 (31.8%) semen samples tested positive for at least one VBP, whereas simultaneous positivity to two or more pathogens was detected in three (13.6%) dogs. Among pathogens detected in semen, Trypanosoma cruzi (n = 1) and Leishmania infantum (n = 3) were identified to species level by restriction fragment length polymorphism analysis. Attempts to sequence PCR products from other pathogens were unsuccessful, but coupled epidemiological and molecular data suggest the presence of Anaplasma platys (n = 5), Babesia vogeli (n = 1) and Ehrlichia canis (n = 1) in semen from dogs. Further experimental studies would be needed to confirm the sexual transmission hypothesis for these VBPs and also the possible implications of these findings for canine reproduction.

Aflagellar Epimastigote of Trypanosoma caninum: Biological and Ultrastructural Study of this Atypical Evolutionary Form

PURPOSE

Trypanosoma caninum exhibits atypical epimastigote forms under axenic conditions. This study aimed to analyze this evolutionary form under different cultivation conditions and provide more information about this evolutionary form.

METHODS

We selected a T. caninum isolate with a high percentage of aflagellar epimastigote forms in axenic cultures. Two separate growth curves were generated for T. caninum cultured in Schneider axenic medium and co-cultured with the DH82 cell line, followed by analysis and quantification of evolutionary forms using bright field microscopy. In addition, ultrastructural analysis of T. caninum was performed under both cultivation conditions.

RESULTS

The growth curves of T. caninum under axenic and co-cultivation conditions exhibited similar profiles. However, in the axenic culture, the number of parasites was three times higher at the peak of the exponential phase than in the co-culture. In contrast to that in the axenic culture, in which only the epimastigote forms were observed along the entire curve, during co-cultivation with the DH82 cell line, differentiation was observed for the trypomastigote and spheromastigote forms in low proportions. These results demonstrated that when cultured alone, the T. caninum isolate preserved the aflagellar epimastigote form, but in the presence of DH82 canine macrophages, they differentiated into evolutionary forms, particularly trypomastigote forms. Moreover, this study is the first to describe the presence of lipid bodies, structure described as the parasite's nutritional reserve, throughout the body of T. caninum.

CONCLUSIONS

These findings describe biological and ultrastructural aspects of epimastigote aflagellar and suggest that this evolutionary form may be involved in the biological cycle of T. caninum, still unknown.

How relevant are in vitro culture models for study of tick-pathogen interactions?

Although tick-borne infectious diseases threaten human and animal health worldwide, with constantly increasing incidence, little knowledge is available regarding vector-pathogen interactions and pathogen transmission. In vivo laboratory study of these subjects using live, intact ticks is expensive, labor-intensive, and challenging from the points of view of biosafety and ethics. Several in vitro models have been developed, including over 70 continuous cell lines derived from multiple tick species and a variety of tick organ culture systems, facilitating many research activities. However, some limitations have to be considered in the translation of the results from the in vitro environment to the in vivo situation of live, intact ticks, and vertebrate hosts. In this review, we describe the available in vitro models and selected results from their application to the study of tick-borne viruses, bacteria, and protozoa, where possible comparing these results to studies in live, intact ticks. Finally, we highlight the strengths and weaknesses of in vitro tick culture models and their essential role in tick-borne pathogen research.

Isolation and partial characterisation of a novel Trypanosoma from the tick Ixodes ricinus

Trypanosomes have long been recognised as being amongst the most important protozoan parasites of vertebrates, from both medical and veterinary perspectives. Whilst numerous insect species have been identified as vectors, the role of ticks is less well understood. Here we report the isolation and partial molecular characterisation of a novel trypanosome from questing Ixodes ricinus ticks collected in Slovakia. The trypanosome was isolated in tick cell culture and then partially characterised by microscopy and amplification of fragments of the 18S rRNA and 24Sα rDNA genes. Analysis of the resultant sequences suggests that the trypanosome designated as Trypanosoma sp. Bratislava1 may be a new species closely related to several species or strains of trypanosomes isolated from, or detected in, ticks in South America and Asia, and to Trypanosoma caninum isolated from dogs in Brazil. This study highlights the potential involvement of ixodid ticks in the epidemiology of trypanosomes, as well as the use of tick cell lines for isolation of such tick-borne protozoa. Further studies are required to investigate the epidemiology, transmission and life cycle of this putative novel species.

Clinical-dermatological, histological abnormalities and prevalence of Trypanosoma caninum and Leishmania infantum in dogs from Midwest region of Brazil

Leishmania infantum is a trypanosomatid that causes parasitic dermatopathy in dogs. Trypanosoma caninum is another trypanosomatid, which infects the skin of dogs, although cutaneous abnormalities are absent. This study aimed to investigate the occurrence of T. caninum infection and its associated cutaneous and histological changes and compare it with the occurrence of L. infantum infection in dogs. The study included 150 dogs, of which T. caninum infection was identified in 3 (2%) and L. infantum infection in 15 (10%) of them, with no association (p>0.05) of these infections with the breed, gender, age, or cutaneous abnormalities. The cutaneous abnormalities were based on 1 (4.8%) and 12 (57.1%) dogs infected by T. caninum and L. infantum, respectively. The dermatohistopathological abnormalities in the dogs infected with T. caninum included mild perivascular lymphohistioplasmacytic infiltrates in the clinically asymptomatic ones, while in those with dermatological abnormalities, acanthosis, epidermal orthokeratotic hyperkeratosis, melanomacrophages, and co-infection with Microsporum sp. and Trichophyton sp. were observed. InL. infantum infected, the histopathological findings included chronic granulomatous inflammatory infiltrates and structures compatible with amastigotes. Despite the low frequency of T. caninum infection, our findings suggest that this trypanosomatid, unlike L. infantum, does not cause any macroscopic skin abnormalities.

Trypanosomatids in Small Mammals of an Agroecosystem in Central Brazil: Another Piece in the Puzzle of Parasite Transmission in an Anthropogenic Landscape

We surveyed infection by Trypanosoma spp. and Leishmania spp. in small wild mammals from Cumari, Goiás State aiming to investigate the diversity of trypanosomatid in a modified landscape of the Brazilian Cerrado (and possible infection overlapping with canids from the same area). Blood, skin, spleen, and liver samples were collected for parasitological, serological, and molecular assays. Gracilinanus agilis was the most abundant species (N = 70; 48.6%) and it was the only one with patent parasitemia. Characterization by mini-exon and 18SrDNA targets were achieved in 7/10 hemocultures with positive fresh blood examination, which confirmed the T. cruzi infection by Discrete Typing Units (DTU) TcI in single (N = 2) and mixed infections with other DTUs (N = 5). T. rangeli and T. dionisii were detected in skin fragments from Didelphis albiventris and Oecomys cleberi, respectively. G. agilis were found to be infected by L. braziliensis and L. guyanensis, while Leishmania sp. DNA was detected in the liver of Oligoryzomys nigripes and Calomys expulsus. Subpatent infection by T. cruzi and Leishmania sp. was serologically detected in 15% and 9% of the small mammal fauna, respectively. Small mammals from Cumari are included in T. cruzi and Leshmania spp. transmission cycles, showing a higher diversity of trypanosomatid species and/or genotypes than that observed in canids of the same agroecosystem.

Evaluation of DPP® and SNAP® Rapid Tests for diagnosis of Leishmania infantum canine infections

INTRODUCTION

Visceral leishmaniasis is a disease that affects humans, wildlife, and domestic species. Since dogs play a key role in urban Leishmania spp. transmission, the Brazilian government maintains the Monitoring and Control Program of Visceral Leishmaniasis (VLMCP) in endemic regions, which promotes awareness campaigns aiming to enhance the control of the infection. The VLMCP recommends the Dual Path Platform (DPP®) canine visceral leishmaniasis test (Bio-Manguinhos, Brazil) for screening and enzyme-linked immunosorbent assay to confirm the infection. The DPP® test is produced and distributed by the Health Ministry to the Municipal Health Centers responsible for the local VLMCP. The test is not available to all the clinics, forcing some veterinarians to use other rapid tests for screening and diagnosis of this disease in their daily routine.

METHODS

The present study was conducted to compare the performance of the DPP® and SNAP® tests using sera from the dogs with confirmed infections of L. infantum and from the dogs with no previous testing, residing in areas with a low Leishmania infection.

RESULTS

There was 97.0% agreement between the two tests. Sensitivity and specificity of the SNAP® test were 96.3% and 100%, respectively. Agreement between both the antibody tests and the parasitological detection methods was 96.8%. The DPP® test had 95.8% sensitivity and 100% specificity.

CONCLUSIONS

The SNAP® and the DPP® tests were virtually equivalent in terms of detection of canine antibodies against L. infantum, and both the tests demonstrated high and similar levels of sensitivity and specificity.

Biological study of Trypanosoma caninum under co-culture with different feeder layer cells

Trypanosoma caninum is a parasite isolated from domestic dogs, of which several biological aspects remain unknown, including evolutive forms found in vertebrate hosts. The objective of this study was to evaluate co-cultures of T. caninum with different cell lines as feeder layers to monitor the differentiation process and investigate infective potential. The study was performed using DH-82, MDCK, and Lulo cell lines. T. caninum from axenic culture was added to the cultured adherent cells. At intervals over 30 days, aliquots of the supernatant were collected for quantification and assessment of differentiation. Infectivity assays were performed on the aforementioned cell lines seeded on glass coverslips and evaluated after 6, 24, and 72 h. In the supernatant of the feeder layer, T. caninum presented similar growth profiles, with epimastigote and trypomastigote forms in binary and multiple divisions. During co-culture with DH-82 and MDCK cells, a higher level of differentiation to trypomastigotes was observed. This study shows that the differentiation process of this parasite can vary according to culture conditions and that DH-82 and MDCK lineages could be applied to the study of trypomastigote forms. All forms of T. caninum described until now (aflagellar epimastigotes, typical epimastigotes, or trypomastigotes) were unable to infect the cell line Finally, this study provides additional data about morphobiological aspects. Although the biological cycle of T. caninum has not been established, the present data suggest the importance of feeder layers in promoting the growth and differentiation of this new parasite.

Efficacy of Recombinase Polymerase Amplification to Diagnose Trypanosoma cruzi Infection in Dogs with Cardiac Alterations from an Endemic Area of Mexico

Chagas disease is a lingering Public Health problem in Latin America with ∼5.7 million people infected with Trypanosoma cruzi. Transmission is still taking place in most countries of the Americas, including the United States. Dogs are frequently infected with T. cruzi and its high infection prevalence is associated with increased risk of Chagas disease in humans. The city of Mérida in the Yucatan peninsula is endemic for Chagas disease and canines are frequently infected with T. cruzi. The objective of this study was to evaluate the performance of a qualitative point of care (POC) molecular test (RPA-LF, recombinase polymerase amplification-lateral flow) developed in our laboratory for identifying infected dogs. We used retrospective samples of dogs that came for consultation because of cardiac alterations and proved to be infected with T. cruzi as determined by enzyme-linked immunosorbent assay (ELISA), Western blot, and quantitative PCR (qPCR). The analytical sensitivity indicated that RPA-LF amplified T. cruzi DNA in samples containing almost equal to one to two parasites per reaction. Serial twofold dilutions of T. cruzi epimastigotes showed that the test had 95% (19/20) repeatability at concentrations of two parasites per reaction. The test showed no cross reactivity with human DNA or other protozoan parasites (Trypanosoma rangeli, Leishmania spp., and Plasmodium spp.). RPA-LF had the capacity to amplify all discrete typing units (DTUs I-VI) of T. cruzi that circulate in domestic or extradomestic environments. The RPA-LF had 93.2% (95% confidence interval 87.2-98.1) sensitivity and excellent agreement with qPCR used as gold standard (Cohen's Kappa test = 0.963). ELISA was positive in 96.6% (85/88) of dogs, which together with the molecular tests confirmed the frequent contact with infected triatomine bugs in the city of Mérida. These preliminary results on the diagnostic efficacy of the RPA-LF deserve further large-scale field testing of this POC test for T. cruzi infection in endemic areas.

Barros JH, Bell-Sakyi L, Fonseca AH. Trypanosoma amblyommi sp. nov. (Protozoa: Kinetoplastida) isolated from Amblyomma brasiliense (Acari: Ixodidae) ticks in Rio de Janeiro, Brazil

Parasites of the genus Trypanosoma are microorganisms that display wide morphological, biological and genetic variability. Here we present the first description of an isolate of the genus Trypanosoma naturally infecting the tick Amblyomma brasiliense. The ticks were collected from a specimen of Tayassu pecari (Queixada, white-lipped peccary) from the Itatiaia National Park, Itatiaia, Rio de Janeiro, Brazil. The isolate was characterised by molecular, morphometric and biological analyses. A Trypanosoma culture was isolated from crushed nymphal and adult ticks, propagated in the tick cell line IDE8 and maintained in L15B culture medium, incubated at 32 °C. The isolate grew well in L15B medium at 30 °C, 32 °C and 34 °C but not at lower or higher temperatures. The culture remained stable in axenic L15B medium at 30 °C. Cryopreserved cultures retained viability after cryopreservation in liquid nitrogen. Growth in axenic medium and developmental forms of the trypanosomes were analysed. Analysis of the 18S rDNA region confirmed the authenticity of this new species and the nucleotide sequence was deposited in Genbank. The species was named Trypanosoma amblyommi sp. nov. strain C1RJ. Characteristics related to pathogenicity, involvement with vertebrate hosts, epidemiology, developmental cycle and transmission mechanisms are still unknown. Therefore, further studies are necessary to understand aspects of the biological cycle of Trypanosoma amblyommi sp. nov.

Molecular study of Trypanosoma caninum isolates based on different genetic markers

Trypanosoma caninum is a parasite recently described in dogs, whose life cycle is rather unknown. Here, we performed a genetic study with T. caninum samples obtained in different Brazilian regions. The study was based on PCR assays target to small and large subunit ribosomal DNA (rDNA) (18S rDNA and 24Sα rDNA), cytochrome B (Cyt b), and internal transcribed spacer 1 rDNA (ITS1 rDNA) following by the sequence analysis. Additionally, we used primers for the variable regions of kinetoplast DNA (kDNA) minicircles and endonucleases restriction in the ITS1 rDNA amplification product. T. caninum samples displayed the same patterns. Tree construction confirmed the close relationship between T. caninum samples, regardless of the molecular target used and endonuclease restriction digestion revealed that all samples have the same restriction profile. Therefore, T. caninum seems to be a genetically homogeneous specie. In the kDNA assay, T. caninum possessed a different molecular size profile with respect to others trypanosomes, 330 and 350 bp. This study provides nucleotide sequences from different regions of the genome of T. caninum that certainly facilitate future studies.