A species-specific antigen of Trypanosoma (Duttonella) vivax detectable in the course of infection is encoded by a differentially expressed tandemly reiterated gene

Eco-epidemiology of porcine trypanosomosis in Karim Lamido, Nigeria: prevalence, seasonal distribution, tsetse density and infection rates

Background

Animal trypanosomosis is a major economic disease in Nigeria causing considerable morbidity and mortality in livestock. Despite reports in other animals, the disease is under reported in pigs.

Methods

We conducted a community based epidemiological study on African animal trypanosomosis in Karim Lamido area of Taraba State, Nigeria using species-specific PCR on 712 pigs and 706 of the 2822 captured tsetse flies. Data were analysed using Chi-square, odds ratio and multivariate analysis at 95 % confidence interval.

Results

Overall prevalence of porcine trypanosomosis was 16.6 % and ranged between 2.0 and 8.8 % across Trypanosoma species. Seasonal distribution of porcine trypanosomosis varied significantly (χ² = 16.62, df = 3, P = 0.0008) ranging between 7.9 and 23.6 % across seasons. Mixed infections involving T. b. brucei, T. congolense forest and T. congolense savannah recorded infection rates ranging between 2.5 and 9.3 %. There were significant variations between the trypanosome infection rates in relation to age (χ² = 7.629, df = 1, P = 0.0057, OR = 1.932, 95 % CI = 1.203–3.100), sex (χ² = 10.09, df = 1, P = 0.0015, OR = 2.085, 95 % CI = 1.315–3.304) and body condition (χ² = 22.10, df = 2, P < 0.0001) of pigs ranging between 10.4 and 30.3 %. Tsetse infection rates were 11.2 % (79/706) for Glossina palpalis and 6.8 % (48/706) for G. tachinoides yielding an overall infection rate of 18.0 %.

Conclusion

Trypanosoma species are prevalent in the study area with similar distribution patterns in both pigs and tsetse flies. Late rainy season, adults, females and pigs with poor body condition recorded higher trypanosome infection rates. Of the three Trypanosoma spp. identified, T. b. brucei showed predominance.

A comparative evaluation of PCR- based methods for species- specific determination of African animal trypanosomes in Ugandan cattle

Background

In recent years, PCR has been become widely applied for the detection of trypanosomes overcoming many of the constraints of parasitological and serological techniques, being highly sensitive and specific for trypanosome detection. Individual species-specific multi-copy trypanosome DNA sequences can be targeted to identify parasites. Highly conserved ribosomal RNA (rRNA) genes are also useful for comparisons between closely related species. The internal transcribed spacer regions (ITS) in particular are relatively small, show variability among related species and are flanked by highly conserved segments to which PCR primers can be designed. Individual variations in inter-species length makes the ITS region a useful marker for identification of multiple trypanosome species within a sample.

Methods

Six hundred blood samples from cattle collected in Uganda on FTA cards were screened using individual species-specific primers for Trypanosoma congolense, Trypanosoma brucei and Trypanosoma vivax and compared to a modified (using eluate extracted using chelex) ITS-PCR reaction.

Results

The comparative analysis showed that the species-specific primer sets showed poor agreement with the ITS primer set. Using species-specific PCR for Trypanozoon, a prevalence of 10.5% was observed as compared to 0.2% using ITS PCR (Kappa = 0.03). For Trypanosoma congolense, the species-specific PCR reaction indicated a prevalence of 0% compared to 2.2% using ITS PCR (Kappa = 0). For T. vivax, species-specific PCR detected prevalence of 5.7% compared to 2.8% for ITS PCR (Kappa = 0.29).

Conclusions

When selecting PCR based tools to apply to epidemiological surveys for generation of prevalence data for animal trypanosomiasis, it is recommended that species-specific primers are used, being the most sensitive diagnostic tool for screening samples to identify members of Trypanozoon (T. b. brucei s.l). While ITS primers are useful for studying the prevalence of trypanosomes causing nagana (in this study the species-specific primers did not detect the presence of T. congolense) there were discrepancies between both the species-specific primers and ITS for the detection of T. vivax.

Species-specific probes for the identification of the African tsetse-transmitted trypanosomes

The first step in studying the epidemiology of a disease is the accurate identification of the pathogen. Traditional reliance on morphological identification has given way to the use of molecular methods for the detection and identification of pathogens, greatly improving our understanding of epidemiology. For the African tsetse-transmitted trypanosomes, the growth of PCR methods for identification of trypanosomes has led to increased appreciation of trypanosome genetic diversity and discovery of hitherto unknown trypanosome species, as well as greater knowledge about the number and type of trypanosome infections circulating in mammalian hosts and vectors. Sequence data and phylogenetic analysis have provided quantitative information on the relatedness of different trypanosome species and allowed the new trypanosome genotypes discovered through the use of species identification methods in the field to be accurately placed in the phylogenetic tree.

A PCR based assay for detection and differentiation of African trypanosome species in blood

Direct PCR analysis of trypanosome infected blood samples in the quantities required for large scale epidemiological study has always been problematic. Current methods for identifying and differentiating trypanosomes typically require several species-specific reactions, many of which rely on mouse passaged samples to obtain quality concentrated genomic DNA. As a consequence important epidemiological information may be lost during the sample preparation stage. Here, we report a PCR methodology that reduces processing and improves on the sensitivity of present screening methods. The PCR technique targets the gene encoding the small ribosomal subunit in order to identify and differentiate all clinically important African trypanosome species and some subspecies. The method is more economical, simple, and sensitive than current screening methods, and yields more detailed information, thereby making it a viable tool for large-scale epidemiological studies.

Evaluation of a polymerase chain reaction assay for the diagnosis of bovine trypanosomiasis and epidemiological surveillance in Bolivia

Background

Sporadic outbreaks of bovine trypanosomiasis have been reported in Bolivia since 1996 when T. vivax and T. evansi were identified for the first time by parasitological means. However, comprehensive epidemiological information concerning T. vivax and T. evansi in the country is lacking. Current parasitological and serological diagnostic methods for trypanosomiasis have important limitations either in their sensitivity or specificity, which can result in unreliable data when applied in epidemiological studies. PCR assays are a recently developed procedure that might help to overcome the constraints of parasitological and serological assays. Therefore, the objective of this study was to evaluate PCR assays as a diagnostic tool for epidemiological studies in Bolivia.

Results

PCR assays for diagnosis of trypanosome infection in cattle were evaluated for their ability to detect trypanosome DNA in blood spots samples collected from cattle in four different provinces from the Bolivian lowlands and the results compared with those obtained with standard parasitological Micro Haematocrit Centrifugation Technique (MHCT) and stained smears and serological methods (Card Agglutination Test for T. evansi (CATT), and Antibody ELISAs for T. vivax and T. congolense). Kappa agreement analysis showed a significant agreement between PCR assays and results from parasitological methods but there was no agreement when PCR was compared with serological assays. Some samples from T. vivax smear positive animals were negative by PCR, therefore modifications to the PCR assay conditions were undertaken to try to improve agreement between PCR and parasitological assays. Changes in the template DNA concentration or the use of an alternative primer set resulted in improvements in the PCR detection rate, but not all the parasitologically positive samples were detected by PCR. Results from PCR assays for T. vivax and T. evansi were combined with results from parasitological and serological assays to provide information on prevalence rates for the four provinces from where the samples were obtained.

Conclusion

The present study established evidence of the usefulness of PCR as diagnostic tool for epidemiological studies and confirmed that cattle trypanosomiasis appears to be endemic in several regions of the Bolivian lowlands.

New molecular marker for Trypanosoma (Duttonella) vivax identification

Trypanosoma vivax is a widespread hemoparasite in tropical areas and is pathogenic to ruminant domestic livestock as well as wild ruminants. The accurate identification of parasites in both hosts and vectors is crucial for epidemiological studies and disease control programs. We describe here the development of molecular markers specific for T. vivax identification. These markers were used to identify mouthpart infections in field-collected tsetse flies from Cameroon. The markers target the genomic sequence of a species-specific antigen from the bloodstream stages. No cross amplification with other trypanosome species was observed, which makes the markers a reliable tool to detect T. vivax infections, both in hosts and vectors. The PCR-amplified sequence contains a (CA)(n) microsatellite repeat for which 11 different alleles were identified. This microsatellite, which showed high polymorphism, provides a suitable marker for population genetic studies.

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.

Genetic exchange in the trypanosomatidae

The only trypanosomatid so far proved to undergo genetic exchange is Trypanosoma brucei, for which hybrid production after co-transmission of different parental strains through the tsetse fly vector has been demonstrated experimentally. Analogous mating experiments have been attempted with other Trypanosoma and Leishmania species, so far without success. However, natural Leishmania hybrids, with a combination of the molecular characters of two sympatric species, have been described amongst both New and Old World isolates. Typical homozygotic and heterozygotic banding patterns for isoenzyme and deoxyribonucleic acid markers have also been demonstrated amongst naturally-occurring T. cruzi isolates. The mechanism of genetic exchange in T. brucei remains unclear, although it appears to be a true sexual process involving meiosis. However, no haploid stage has been observed, and intermediates in the process are still a matter for conjecture. The frequency of sex in trypanosomes in nature is also a matter for speculation and controversy, with conflicting results arising from population genetics analysis. Experimental findings for T. brucei are discussed in the first section of this review, together with laboratory evidence of genetic exchange in other species. The second section covers population genetics analysis of the large body of data from field isolates of Leishmania and Trypanosoma species. The final discussion attempts to put the evidence from experimental and population genetics into its biological context.

Study of the effect of gamma-irradiation on bovine serum samples on the ability of monoclonal antibodies to detect invariant antigens of Trypanosoma congolense, T. vivax and T. brucei in enzyme-linked immunosorbent assays

Samples of bovine serum from uninfected and African trypanosomes-infected animals were tested before and after gamma-irradiation, using three sandwich enzyme-linked immunosorbent assays (ELISA). Each test system utilized a different monoclonal antibody, reputedly allowing the specific detection of conserved-invariant cytoplasmic antigens of trypanonosomes, T. congolense, T. vivax, and T. brucei, respectively. Results have identified two groups of samples. The first contained samples where there were unequivocal ELISA results indicating positivity and negativity, for non-irradiated samples. In this group, irradiation had no effect on the diagnostic sensitivity of the assays. All samples shown to be positive before irradiation remained positive and those shown to be negative, remained negative. There was, however, a statistically significant reduction in signal in each of the ELISAs following irradiation. The second group contained samples identified before irradiation as flanking the diagnostic negative/positive threshold of OD > or =0.05. These showed a negative bias after irradiation of the order of OD -0.01, which was shown to be statistically significant by paired t-statistics. Without correction of the given diagnostic negative/positive threshold, bovine sera with OD values around the threshold were expected to deliver more false negative test results upon irradiation. This was confirmed when serological data were compared with parasitological findings; where three times more false negative test results were found from irradiated serum samples. Consequently, for this group of irradiated bovine samples tested by ELISA, the re-adjustment of the diagnostic negative/positive threshold of the ELISAs using defined irradiated serum samples is recommended; otherwise, the frequency of false negative results might be increased.

Sensitive and specific detection of Trypanosoma vivax using the polymerase chain reaction

The nucleic acid probes that are currently in use detect and distinguish Trypanosoma vivax parasites according to their geographic origin. To eliminate the need for using multiple DNA probes, a study was conducted to evaluate the suitability of a tandemly reiterated sequence which encodes a T. vivax diagnostic antigen as a single probe for detection of this parasite. The antigen is recognized by monoclonal antibody Tv27 currently employed in antigen detection ELISA (Ag-ELISA). A genomic clone which contained a tetramer of the 832-bp cDNA sequence was isolated and shown to be more sensitive than the monomer. Oligonucleotide primers were designed based on the nucleotide sequence of the 832-bp cDNA insert and used in amplifying DNA sequences from the blood of cattle infected with T. vivax isolates from West Africa, Kenya, and South America. The polymerase chain reaction (PCR) product of approximately 400 bp was obtained by amplification of DNA from all the isolates studied. The oligonucleotide primers also amplified DNA sequences in T. vivax-infected tsetse flies. Subsequently, PCR was evaluated for its capacity to detect T. vivax DNA in the blood of three animals experimentally infected with the parasite. T. vivax DNA was detectable in the blood of infected animals as early as 5 days post-infection. Blood and serum samples from the three cattle and from six other infected animals were also examined for the presence of trypanosomes and T. vivax-specific diagnostic antigen. Trypanosomes appeared in the blood 7-12 days post-challenge, while the antigenemia was evident on Days 5-20 of infection. Analysis of the data obtained in the three animals during the course of infection revealed that the buffy coat technique, Ag-ELISA, and PCR revealed infection in 42, 55, and 75% of the blood samples, respectively. PCR amplification of genomic DNA of T. vivax is thus superior to the Ag-ELISA in the detection of T. vivax. More importantly, both the T. vivax diagnostic antigen and the gene encoding it are detectable in all the T. vivax isolates examined from diverse areas of Africa and South America.