PCR primer evaluation for the detection of trypanosome DNA in naturally infected goats

Dried Blood Spots technology for veterinary applications and biological investigations: technical aspects, retrospective analysis, ongoing status and future perspectives

Dried Blood Spots (DBS) technology has become a valuable tool in medical studies, however, in veterinary and biological research DBS technology applications are still limited. Up-to-date no review has comprehensively integrated all the evidence existing across the fields, technologies and animal species. In this paper we summarize the current applications of DBS technology in the mentioned areas, and provide a scope of different types of dried sample carriers (cellulose and non-cellulose), sampling devices, applicable methods for analyte extraction and detection. Mammals, birds, insects and other species are represented as the study objects. Besides the blood, the review considers a variety of specimens, such as milk, saliva, tissue samples and others. The main applications of dried samples highlighted in the review include epidemiological surveys and monitoring for infections agents or specific antibodies for disease/vaccination control in households and wildlife. Besides the genetic investigations, the paper describes detection of environmental contaminants, pregnancy diagnosis and many other useful applications of animal dried samples. The paper also analyses dried sample stability and storage conditions for antibodies, viruses and other substances. Finally, recent developments and future research for DBS technology in veterinary medicine and biological sciences are discussed.

Development of Cathepsin L-like Real-Time PCR Assays for the Detection of African Animal Trypanosomosis (AAT) in South Africa

African animal trypanosomosis (AAT), is an infectious parasitic disease of wildlife and livestock caused by multiple species and strains of Trypanosoma. In South Africa, it is restricted to northern KwaZulu-Natal (NKZN) and caused by Trypanosoma congolense and Trypanosoma vivax. A cross-sectional study was done to determine AAT prevalence in 384 goat samples and identify trypanosome species circulating in 60 cattle at dip tanks that are on the interface with the Hluhluwe-uMfolozi game reserve in NKZN. Both cattle and goat samples were analyzed using the buffy coat technique (BCT) and a polymerase chain reaction (PCR) assay targeting the internal transcribed spacer 1 (ITS) region. Cattle samples were further analyzed using an ITS quantitative real-time PCR (qPCR) assays designed for the detection of T. congolense, T. vivax, and T. brucei. None of the goat samples tested positive for Trypanosoma infections. The ITS qPCR assay detected Trypanosoma DNA in 30% of the cattle samples, while only 8.3% were positive with the ITS PCR and 11.7% were positive using BCT. Quantitative real-time PCR assays were designed to amplify a 98 bp, 137 bp, and 116 bp fragment of the cathepsin L-like (CATL) gene from T. brucei, T. theileri, and T. congolense, respectively. Each assay was shown to be efficient (>94%) and specific (10⁹ to 10²/10¹ copies/reaction) in the detection of Trypanosoma species. The CATL qPCR assays detected T. congolense and T. theileri infections in 33.3% of the cattle samples. The CATL qPCR assays also detected T. congolense infections in goats (23.1%) that were neither detected by BCT nor the ITS PCR. The CATL qPCR assays provide an additional, sensitive, and specific tool for Trypanosoma diagnostics. The presence of trypanosomes in goats suggests they might be potential reservoirs of infections to other livestock.

Global distribution, host range and prevalence of Trypanosoma vivax: a systematic review and meta-analysis

BACKGROUND

Trypanosomosis caused by Trypanosoma vivax is one of the diseases threatening the health and productivity of livestock in Africa and Latin America. Trypanosoma vivax is mainly transmitted by tsetse flies; however, the parasite has also acquired the ability to be transmitted mechanically by hematophagous dipterans. Understanding its distribution, host range and prevalence is a key step in local and global efforts to control the disease.

METHODS

The study was conducted according to the methodological recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist. A systematic literature search was conducted on three search engines, namely PubMed, Scopus and CAB Direct, to identify all publications reporting natural infection of T. vivax across the world. All the three search engines were screened using the search term Trypanosoma vivax without time and language restrictions. Publications on T. vivax that met our inclusion criteria were considered for systematic review and meta-analysis.

RESULT

The study provides a global database of T. vivax, consisting of 899 records from 245 peer-reviewed articles in 41 countries. A total of 232, 6277 tests were performed on 97 different mammalian hosts, including a wide range of wild animals. Natural infections of T. vivax were recorded in 39 different African and Latin American countries and 47 mammalian host species. All the 245 articles were included into the qualitative analysis, while information from 186 cross-sectional studies was used in the quantitative analysis mainly to estimate the pooled prevalence. Pooled prevalence estimates of T. vivax in domestic buffalo, cattle, dog, dromedary camel, equine, pig, small ruminant and wild animals were 30.6%, 6.4%, 2.6%, 8.4%, 3.7%, 5.5%, 3.8% and 12.9%, respectively. Stratified according to the diagnostic method, the highest pooled prevalences were found with serological techniques in domesticated buffalo (57.6%) followed by equine (50.0%) and wild animals (49.3%).

CONCLUSION

The study provides a comprehensive dataset on the geographical distribution and host range of T. vivax and demonstrates the potential of this parasite to invade other countries out of Africa and Latin America.

Trypanosomosis prevalence in natural field-based infection: insights into systematic review and meta-analysis of studies from 1980 to 2018 on The Gambian ruminants with special emphasis on cattle

Consistent quantification of trypanosomes, the parasite responsible for African animal trypanosomosis, is important for effective surveillance, control, and eradication strategies. Here, we used a rigorously predefined protocol to search and select eligible publications that utilized either microscopy, serology, or molecular methods to investigate prevalence of trypanosomosis based on the presence of any of three most common Trypanosoma spp. (T. congolense, T. vivax, and T. brucei) in the field-based naturally grazed Gambian cattle, sheep, and goats. To combine results of studies on cattle through meta-analysis, sensitivity and subgroup analyses were carried out with the random effects model, and prevalence estimates of each study with 95% confidence intervals (CI) were presented with a forest plot. All the eligible studies utilized the buffy coat technique (BCT) to detect trypanosomes in the blood samples, while the more sensitive serological and molecular detection methods are yet to be widely exploited. Heterogeneity among the studies on cattle was moderate (I² = 55%), and the pooled trypanosomosis prevalence based on the BCT was 5.2% (95% CI: 4.0-6.4). Meanwhile, estimated prevalence varied according to the trypanosome detection methods, study locations, types of publication, year, and length of observations. We could not pool the trypanosomosis prevalence in sheep and goats through meta-analysis due to small number of studies. The prevalence estimates based on the BCT ranged from 3.2 to 8.1% in goats and 2.8 to 10.6% in sheep. Even though there seems to be a slight decrease in trypanosomosis prevalence in cattle in one of the Gambian districts, there was no consistent trend across the years. It is thought that the literature search and formatting procedures presented in this study contribute to doing systematic reviews on the investigated subject and can be adapted for similar cases.

Detection of African animal trypanosomes: the haematocrit centrifugation technique compared to PCR with samples stored on filter paper or in DNA protecting buffer

The present study aimed at comparing the trypanosome specific 18S-PCR-RFLP using samples stored either on Whatman filter papers (PCR-RFLP-fp) or in a commercial cell lysis and DNA protecting buffer (PCR-RFLP-pb) with the haematocrit centrifugation technique (HCT), a method widely used for the diagnosis of African Animal Trypanosomosis. Out of 411 head of cattle, 49 (11.92%) (CI=8.95-15.45) scored positive for the presence of trypanosomes by HCT whereas 75 (18.25%) (CI=14.63-22.33) and 124 (30.17%) (CI=25.77-34.86) scored positive using PCR-RFLP-fp and PCR-RFLP-pb, respectively. Out of the 49 positives by HCT, 14 (28.57%) (CI=16.58-43.26) and 28 (57.14%) (CI=42.21-71.18) were concordant by PCR-RFLP-fp and PCR-RFLP-pb, respectively. None of the PCR techniques detected parasites from the Trypanozoon group. Although HCT detected more cases of Trypanosoma vivax (33), species identification using PCR-RFLP-fp and PCR-RFLP-pb were significantly different (p<0.001) from the HCT technique. The use of DNA protective buffer is thus recommended as the output of the PCR-RFLP-pb is improved and the risk of contamination between samples is reduced.

Low-dose intradermal infection with trypanosoma congolense leads to expansion of regulatory T cells and enhanced susceptibility to reinfection

BALB/c mice are highly susceptible to experimental intraperitoneal Trypanosoma congolense infection. However, a recent report showed that these mice are relatively resistant to primary intradermal low-dose infection. Paradoxically, repeated low-dose intradermal infections predispose mice to enhanced susceptibility to an otherwise noninfectious dose challenge. Here, we explored the mechanisms responsible for this low-dose-induced susceptibility to subsequent low-dose challenge infection. We found that akin to intraperitoneal infection, low-dose intradermal infection led to production of interleukin-10 (IL-10), IL-6, IL-12, tumor necrosis factor alpha (TNF-α), transforming growth factor β (TGF-β), and gamma interferon (IFN-γ) by spleen and draining lymph node cells. Interestingly, despite the absence of parasitemia, low-dose intradermal infection led to expansion of CD4+ CD25+ Foxp3+ cells (T regulatory cells [Tregs]) in both the spleens and lymph nodes draining the infection site. Depletion of Tregs by anti-CD25 monoclonal antibody (MAb) treatment during primary infection or before challenge infection following repeated low-dose infection completely abolished the low-dose-induced enhanced susceptibility. In addition, Treg depletion was associated with dramatic reduction in serum levels of TGF-β and IL-10. Collectively, these findings show that low-dose intradermal infection leads to rapid expansion of Tregs, and these cells mediate enhanced susceptibility to subsequent infection.

Trypanosoma evansi: detection of Trypanosoma evansi DNA in naturally and experimentally infected animals using TBR(1) & TBR(2) primers

A polymerase chain reaction (PCR-based) assay was evaluated for detection of Trypanosoma evansi DNA in experimentally infected mice and naturally infected camels, sheep and goats using the set of primers TBr(1) & TBr(2) that amplified 164 bp DNA fragment. The results revealed that PCR-based assay was able to detect T. evansi directly from the blood during both acute and chronic phase of infection in all tested animals and in the blood and tissues of intraperitoneally infected mice depending upon the level of infection in the test samples. PCR was more powerful than CATT/T. evansi and mouse inoculation tests, when detected the infection in mice (24 h) post infection. Present results show that sheep & goats probably play a role in transmission of T. evansi to camels and supported that PCR could be used as a diagnostic tool for epidemiological studies on T. evansi in Egypt.

Ghibe river basin in Ethiopia: present situation of trypanocidal drug resistance in Trypanosoma congolense using tests in mice and PCR-RFLP

A cross-sectional study was carried out in the Ghibe valley from August to October 2010. 411 head of cattle were sampled in eight villages for buffy coat examination (BCE) and blood spots were collected from each animal for trypanosomose diagnosis by 18S-PCR-RFLP and diminazene aceturate (DA) resistance by Ade2-PCR-RFLP. Three villages were selected in a zone where trypanosomosis control operations are currently on-going whereas the other 5 villages were located outside these control operations. Twenty-four samples (5.84%) were diagnosed positive for Trypanosoma congolense by BCE and injected in mice for further characterization. Twelve of those isolates successfully multiplied in mice and were tested by an in vivo mouse test for diminazene (DA) (10 and 20mg/kg B.W.) and isometamidium (ISM) (1mg/kg B.W.) resistance. All were shown to be resistant to both drugs at all doses. The use of the Ade2-PCR-RFLP on these isolates confirmed their DA-resistance profile. Seventy-three of the collected blood spots (17.8%) were diagnosed positive for T. congolense by 18S-PCR-RFLP of which 37 (50.7%) gave amplification products with the Ade2-PCR-RFLP. Here, 35 (94.6%) showed a resistant profile, 1 (2.7%) a sensitive profile and 1 (2.7%) a mixed profile. The data were analysed by logistic regression model and the relapsing time in mice tests was assessed using the Cox regression model. There was no significant intervention effect (P=0.83) with odds ratio equal to 1.21 when using the BCE data. 18S-PCR-RFLP test also showed no significant intervention effect (P=0.60) with odds ratio equal to 1.43. The hazard ratio of getting parasitaemic after treatment with DA at 20mg/kg B.W. compared to the control group was 0.38 which differs significantly from one (P<0.001). Relapsing time after treatment with DA 10mg/kg B.W. or ISM 1mg/kg B.W. was also significantly longer than the prepatent period of the control group. The situation of drug resistance in the Ghibe valley is further discussed.

The best practice for preparation of samples from FTA®cards for diagnosis of blood borne infections using African trypanosomes as a model system

Background

Diagnosis of blood borne infectious diseases relies primarily on the detection of the causative agent in the blood sample. Molecular techniques offer sensitive and specific tools for this although considerable difficulties exist when using these approaches in the field environment. In large scale epidemiological studies, FTA^®cards are becoming increasingly popular for the rapid collection and archiving of a large number of samples. However, there are some difficulties in the downstream processing of these cards which is essential for the accurate diagnosis of infection. Here we describe recommendations for the best practice approach for sample processing from FTA^®cards for the molecular diagnosis of trypanosomiasis using PCR.

Results

A comparison of five techniques was made. Detection from directly applied whole blood was less sensitive (35.6%) than whole blood which was subsequently eluted from the cards using Chelex^®100 (56.4%). Better apparent sensitivity was achieved when blood was lysed prior to application on the FTA cards (73.3%) although this was not significant. This did not improve with subsequent elution using Chelex^®100 (73.3%) and was not significantly different from direct DNA extraction from blood in the field (68.3%).

Conclusions

Based on these results, the degree of effort required for each of these techniques and the difficulty of DNA extraction under field conditions, we recommend that blood is transferred onto FTA cards whole followed by elution in Chelex^®100 as the best approach.

Trypanosomosis in Goats

Trypanosomosis is a major constraint on ruminant livestock production in Africa, Asia, and South America. The principal host species affected varies geographically, but buffalo, cattle, camels, and horses are particularly sensitive. Natural infections with Trypanosoma congolense, T. vivax, T. brucei, and T. evansi have been described in goats. Trypanosomosis in goats produces acute, subacute, chronic, or subclinical forms, being T. vivax, T. congolense, and T. evansi, the most invasive trypanosomes for goats. However, the role of goats in the epidemiology of trypanosomosis is largely discussed and not well understood. Thus, it has commonly been assumed that trypanosomosis presents a subclinical course and that goats do not play an important role in the epidemiology of the disease. This can partially be due to parasitemia caused by trypanosomes which has been considered low in goats. However, this assumption is currently undergoing a critical reappraisal because of goats may also serve as a reservoir of trypanosome infection for other species, including the human beings in the case of T. brucei rhodesiense. The present article describes the current status of trypanosomosis in goats in Africa, Asia, and South America. Pathogenesis, clinical features, diagnosis, and treatment of the different trypanosomes are also described. The possible role in the epidemiology of the disease in the different areas is also discussed.

Trypanosomes, fleas and field voles: ecological dynamics of a host-vector--parasite interaction

To investigate the prevalence of a flea-borne protozoan (Trypanosoma (Herpetosoma) microti) in its field vole (Microtus agrestis) host, we monitored over a 2-year period a range of intrinsic and extrinsic parameters pertaining to host demographics, infection status and vector (flea) prevalence. Generalized Linear Mixed Modelling was used to analyse patterns of both flea and trypanosome occurrence. Overall, males of all sizes and ages were more likely to be infested with fleas than their female counterparts. Flea prevalence also showed direct density dependence during the winter, but patterns of density dependence varied amongst body mass (age) classes during the summer. Trypanosome prevalence did not vary between the sexes but was positively related to past flea prevalence with a lag of 3 months, with the highest levels occurring during the autumn season. A convex age-prevalence distribution was observed, suggesting that individuals develop a degree of immunity to trypanosome infection with age and exposure. An interaction between age and whether the individual was new or recaptured suggested that infected animals are less likely to become territory holders than their uninfected counterparts.

Variable Surface Glycoprotein RoTat 1.2 PCR as a specific diagnostic tool for the detection of Trypanosoma evansi infections

Background

Based on the recently sequenced gene coding for the Trypanosoma evansi (T. evansi) RoTat 1.2 Variable Surface Glycoprotein (VSG), a primer pair was designed targeting the DNA region lacking homology to other known VSG genes. A total of 39 different trypanosome stocks were tested using the RoTat 1.2 based Polymerase Chain Reaction (PCR).

Results

This PCR yielded a 205 bp product in all T. evansi and in seven out of nine T. equiperdum strains tested. This product was not detected in the DNA from T. b. brucei, T. b. gambiense, T. b. rhodesiense, T. congolense, T. vivax and T. theileri parasites. The Rotat 1.2 PCR detects as few as 10 trypanosomes per reaction with purified DNA from blood samples, i.e. 50 trypanosomes/ml.

Conclusion

PCR amplification of the RoTat 1.2 VSG gene is a specific marker for T. evansi strains, except T. evansi type B, and is especially useful in dyskinetoplastic strains where kDNA based markers may fail to amplify. Furthermore, our data support previous suggestions that some T. evansi stocks have been previously misclassified as T. equiperdum.

Applications of PCR-based tools for detection and identification of animal trypanosomes: a review and perspectives

This paper aims to review the applications of the polymerase chain reaction (PCR) for the detection and identification of trypanosomes in animals. The diagnosis of trypanosomes, initially based on microscopic observations and the host range of the parasites, has been improved, since the 1980s, by DNA-based identification. These diagnostic techniques evolved successively through DNA probing, PCR associated to DNA probing, and currently to PCR alone. Several DNA sequences have been investigated as possible targets for diagnosis, especially multi-copy genes such as mini-exon, kinetoplastid mini-circles, etc., but the most favoured target is the nuclear satellite DNA of mini-chromosomes, which presents the advantages, and the drawbacks, of highly repetitive short sequences (120-600 bp). Several levels of specificity have been achieved from sub-genus to species, sub-species and even types. Random priming of trypanosome DNA has even allowed "isolate specific" identification. Other work based on microsatellite sequences has provided markers for population genetic studies. For regular diagnosis, the sensitivity of PCR has increased with the advancement of technologies for sample preparation, to reach a level of 1 trypanosome/ml of blood, which has brought to field samples a sensitivity two to three times higher than microscopic observation of the buffy coat. Similarly, PCR has allowed an increase in the specificity and sensitivity of diagnosis in vectors such as tsetse flies. However, because of the diversity of Trypanosoma species potentially present in a single host, PCR diagnosis carried out on host material requires several PCR reactions; for example, in cattle, up to five reactions per sample may be required. Research is now focusing on a diagnosis based on the amplification of the internal transcribed spacer-1 (ITS-1) of ribosomal DNA which presents the advantages of being a multi-copy locus (100-200), having a small size (300-800 bp), which varies from one taxon to another but is conserved in size in a given taxon. This may lead to the development of a multi-species-specific diagnostic protocol using a single PCR. By reducing the cost of the PCR diagnosis, this technique would allow a greater number of field samples to be tested in epidemiological studies and/or would increase the variety of Trypanosoma species that could be detected. Further investigations are required to develop and optimise multi-species-specific diagnostic tools for trypanosomes, which could also serve as a model for such tools in other pathogens.

Prevalence and incidence of trypanosomosis in horses and donkeys in the Gambia

In a study of the prevalence and incidence of trypanosomosis in horses and donkeys in two regions of the Gambia, surveys were carried out at Niamina east and Bansang south with a high and low to moderate tsetse challenge, respectively. Eleven horses and 67 donkeys were sampled monthly from August 1997 to September 1998. Blood samples were examined for trypanosomes using the buffy-coat (BC) method and polymerase chain reaction (PCR). Three primer sets were used, specific for either Trypanosoma vivax (TVW), Trypanosoma congolense (GOL) or Trypanosoma brucei (ORPHON5J). The BC results showed that the prevalence (August 1997) and the average monthly incidence (September 1997-1998) of trypanosome infections in horses (45.5 and 16%, respectively) were significantly higher than in donkeys (6.2 and 9%, respectively). Using PCR, the number of detected cases was seven times higher than using the BC. T. congolense was the most frequently observed species, followed by T. vivax and T. brucei. This study confirms earlier observations by other authors that donkeys, which are exposed to a similar tsetse challenge as horses, are significantly less infected with trypanosomes than the latter.

Trypanosoma vivax: characterization of the spliced-leader gene of a Brazilian stock and species-specific detection by PCR amplification of an intergenic spacer sequence

The sequence of the spliced-leader gene repeat of a Brazilian Trypanosoma vivax stock from cattle showed high similarity to sequences of West African T. vivax in both intron and intergenic sequences. This is the first evidence based on DNA sequences of close-relatedness between Brazilian and West African T. vivax stocks. A T. vivax-specific diagnostic PCR assay based on spliced-leader gene intergenic sequences was able to amplify DNA from T. vivax stocks from South America (Brazil, Bolivia, and Colombia) and West Africa. Species-specificity of this method was confirmed by results obtained by testing 15 other trypanosomes, including other species and subspecies that can also infect cattle. The PCR assay developed presented high sensitivity, detecting the DNA content of only one parasite and also revealing T. vivax infection in asymptomatic animals without detectable parasitemia by microhematocrit or in Giemsa-stained blood smears. Use of crude preparations from field-blood samples collected on both filter paper and glass slides as DNA template suggested that this method could be useful for the diagnosis of T. vivax in large epidemiological studies.

Methods for the rapid appraisal of African animal trypanosomosis in the Gambia

A technique for the rapid field assessment of African animal trypanosomosis (AAT) was developed during studies in the Gambia. This involved gathering indigenous information from rapid-appraisal questionnaires addressed to local informants, the results of single tsetse surveys and evaluations of the prevalence of trypanosome infections in village cattle. Local informants included livestock owners and herdsmen and trained personnel such as livestock assistants. The answers to the questionnaires were weighted in order to translate them into semi-quantitative ranked estimates (zero, low, medium, high or very severe) of the severity of AAT problems. A similar ranking was also defined for tsetse and prevalence data in the Gambia. The three assessment methods generally gave complementary results leading to similar conclusions about the severity of tsetse-trypanosomosis problems in a survey area; inconsistencies usually suggested that additional information was needed. The rankings of AAT intensity were used to develop management guidelines for minimising the impact of AAT at different levels through control interventions or improved livestock management. The methodology was designed to provide reliable, up-to-date and cost-effective assessments of AAT problems. Emphasis was placed on the importance of the involvement, priorities and perceptions of village livestock owners and herdsmen in making these assessments.