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Nambala P, Musaya J, Hayashida K, Maganga E, Senga E, Kamoto K, Chisi J, Sugimoto C. Comparative evaluation of dry and liquid RIME LAMP in detecting trypanosomes in dead tsetse flies. ACTA ACUST UNITED AC 2018; 85:e1-e6. [PMID: 30326717 PMCID: PMC6324077 DOI: 10.4102/ojvr.v85i1.1543] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Revised: 07/23/2018] [Accepted: 07/25/2018] [Indexed: 11/06/2022]
Abstract
Xenomonitoring is an important approach in assessing the progress of trypanosomiasis control as well as in estimating the endemicity of trypanosomes in affected areas. One of the major challenges in this approach is the unavailability of sensitive and easy to use xenomonitoring tools that can be used in the remote areas where the disease occurs. One tool that has been used successfully in detecting the parasites in tsetse flies is the repetitive insertion mobile element loop-mediated isothermal amplification (RIME LAMP). This tool has recently been modified from the liquid form to dry form for use in remote areas; however, uptake for use in the field has been slow. Field-collected tsetse flies were used to evaluate the performance of dry RIME LAMP over the conventional liquid RIME LAMP. All the samples were also subjected to internal transcribed spacer 1 (ITS1) ribosomal deoxyribonucleic acid (DNA) polymerase chain reaction (PCR) as a standard. ITS1-PCR-positive samples were further sequenced for confirmation of the species. A total of 86 wild tsetse flies were left to dry at room temperature for 3 months and DNA was extracted subsequently. All 86 flies were Glossina morsitans morsitans. From these, dry RIME LAMP detected 16.3% while liquid RIME LAMP detected 11.6% as infected with trypanosomes. Ten positive samples on ITS1-PCR were sequenced and all were shown to be trypanosomes. The use of dry RIME LAMP in the field for xenomonitoring of trypanosomes in tsetse flies will greatly contribute towards control of this neglected tropical disease as it provides the cheapest, fastest and simplest way to estimate possible human infective trypanosome infection rates in the tsetse fly vectors.
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Affiliation(s)
- Peter Nambala
- Department of Basic Medical Sciences, University of Malawi.
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Ganyo EY, Boampong JN, Masiga DK, Villinger J, Turkson PK. Haematology of N'Dama and West African Shorthorn cattle herds under natural Trypanosoma vivax challenge in Ghana. F1000Res 2018; 7:314. [PMID: 30228875 PMCID: PMC6117849 DOI: 10.12688/f1000research.14032.2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 08/02/2018] [Indexed: 11/20/2022] Open
Abstract
Background: Animal trypanosomosis is a major cause of economic loss in livestock production in Africa. A suggested control measure is to use breeds with traits of trypanotolerance. The study examines the effect of natural
Trypanosoma vivax challenge on haematological parameters in two trypanotolerant cattle [N’Dama and West African Shorthorn (WASH)] herds. Methods: Trypanosoma vivax-specific primers were used to diagnose
T. vivax infection in an N’Dama herd at Cape Coast in southern Ghana and a WASH herd at Chegbani in northern Ghana from May to July 2011 in a cross-sectional study. Levels of haematological parameters comprising packed cell volume (PCV), haemoglobin (Hb) concentration and red blood cell (RBC) and total white blood cell (TWBC) counts; differential WBC counts (neutrophils, lymphocytes, eosinophils, monocytes and basophils); and RBC indices of mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were determined in blood samples and then compared between infected and uninfected cattle. Results: We found that haematological indices for infected and uninfected animals in both breeds were within the normal range. However, the mean PCV values for
T. vivax-infected WASH and N’Dama were lower in infected compared to uninfected animals. The difference was significant (
p< 0.05) in N’Dama but not in WASH. Conclusion: Despite the presence of infection by
T. vivax, N’Dama and WASH cattle maintained their haematological parameters within acceptable normal ranges, which confirms their trypanotolerant trait. This highlights the need for low-input traditional African farmers in medium, high and severe tsetse challenge areas to be educated on the advantages of N’Dama and WASH breeds to increase their utilization in integrated tsetse and trypanosomosis control programmes.
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Affiliation(s)
- Ebenezer Yaw Ganyo
- Department of Biomedical and Forensic Sciences, School of Biological Sciences, University of Cape Coast, Ghana
| | - Johnson N Boampong
- Department of Biomedical and Forensic Sciences, School of Biological Sciences, University of Cape Coast, Ghana
| | - Daniel K Masiga
- International Centre of Insect Physiology and Ecology (icipe), Nairobi, Kenya
| | - Jandouwe Villinger
- International Centre of Insect Physiology and Ecology (icipe), Nairobi, Kenya
| | - Paa Kobina Turkson
- Department of Animal Science, School of Agriculture, University of Cape Coast, Ghana
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Abstract
Trypanosomes (genus Trypanosoma) are parasites of humans, and wild and domestic mammals, in which they cause several economically and socially important diseases, including sleeping sickness in Africa and Chagas disease in the Americas. Despite the development of numerous molecular diagnostics and increasing awareness of the importance of these neglected parasites, there is currently no universal genetic barcoding marker available for trypanosomes. In this review we provide an overview of the methods used for trypanosome detection and identification, discuss the potential application of different barcoding techniques and examine the requirements of the 'ideal' trypanosome genetic barcode. In addition, we explore potential alternative genetic markers for barcoding Trypanosoma species, including an analysis of phylogenetically informative nucleotide changes along the length of the 18S rRNA gene.
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Onyekwelu KC, Ejezie FE, Eze AA, Ikekpeazu JE, Ezeh RC, Edeh GC. Prevalence of trypanosome infection in tsetse flies from Oji River and Emene axis of Enugu State, Nigeria: A preliminary report. Trop Parasitol 2017; 7:98-102. [PMID: 29114487 PMCID: PMC5652062 DOI: 10.4103/tp.tp_14_17] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2017] [Accepted: 09/25/2017] [Indexed: 11/30/2022] Open
Abstract
INTRODUCTION Trypanosomes are protozoan parasites of vertebrates transmitted by blood-sucking tsetse fly. Trypanosomes remain a constant threat to the lives of humans and animals throughout large regions of Africa. AIMS AND OBJECTIVES This study investigated the presence, prevalence, and species of trypanosome parasite in tsetse flies caught in two areas of no previous documented history of trypanosome infection. MATERIALS AND METHODS For this purpose, 63 and 77 nonterenal tsetse flies were collected from Oji River and Emene areas of Enugu State Nigeria, respectively. Genomic DNA was isolated from the whole tsetse fly using genomic DNA extraction kit. Identification and characterization of trypanosome were done using two approaches: the amplification of internal transcribed spacer 1 of ribosomal DNA and the use of primers specific to Trypanozoon. RESULTS In Oji River, of 63 tsetse flies collected, the identification of trypanosome parasite was done on 57 flies and 6 (10.71%) tsetse flies were infected with trypanosome parasite. Six flies were infected with Trypanosoma Congolense, 2 with Trypanosoma Vivax, and 1 with Trypanosoma brucei. Two mixed infections of T. vivax and T. congolense and 1 mixed infection of T. brucei and T. congolense was also identified. In Emene, of 77 tsetse flies collected, the identification of trypanosome parasite was done on 66 flies and 11 (16.6%) tsetse flies were infected with trypanosome parasite. Nine flies were infected with T. congolense, 2 with T. vivax, and 3 with T. brucei. Mixed infections identified include 2 mixed infections of T. brucei and T. congolense and 1 mixed infections of T. vivax and T. brucei. None of the subspecies of T. brucei were detected using species specific primers. DISCUSSION This study shows the parasitological evidence on the occurrence of animal African trypanosomiasis and also demonstrated that there is likely no active transmission of human African trypanosomiasis in the study areas. CONCLUSION This study shows that there is likely no active transmission of human African trypanosomiasis going on in these localities since no human infective form of the parasite was detected.
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Affiliation(s)
| | - Fidelis Ebele Ejezie
- Department of Medical Biochemistry, College of Medicine, University of Nigeria, Enugu Campus, Enugu State, Nigeria
| | - Anthonius Anayochukwu Eze
- Department of Medical Biochemistry, College of Medicine, University of Nigeria, Enugu Campus, Enugu State, Nigeria
| | - Joy Ebele Ikekpeazu
- Department of Medical Biochemistry, College of Medicine, University of Nigeria, Enugu Campus, Enugu State, Nigeria
| | - Richard Chukwunonye Ezeh
- Department of Medical Biochemistry, Faculty of Basic Medical Sciences, Enugu State University of Science and Technology College of Medicine, Parklane, Enugu State, Nigeria
| | - Godknows Chizurumoke Edeh
- Nigerian Institute for Trypanosomiasis Research, South East Zonal Office, Enugu, Enugu State, Nigeria
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Rediscovery of Trypanosoma (Pycnomonas) suis, a tsetse-transmitted trypanosome closely related to T. brucei. INFECTION GENETICS AND EVOLUTION 2015; 36:381-388. [PMID: 26477932 DOI: 10.1016/j.meegid.2015.10.018] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Revised: 10/13/2015] [Accepted: 10/14/2015] [Indexed: 11/19/2022]
Abstract
The African tsetse-transmitted trypanosomes are considered to be a well-known group of parasitic protozoa, but in 2008 a novel and distinctive trypanosome related to Trypanosoma brucei was discovered among tsetse isolates from Msubugwe in Tanzania. The host range, distribution and potential pathogenicity of this new trypanosome remain to be elucidated; such studies would be facilitated by a sensitive and specific identification method. Here, we identified two highly repetitive elements in the genome of the new trypanosome: a 177 bp repeat, which was located predominantly on the highly abundant minichromosomes, and a 138 bp repeat, which was widely dispersed in the genome. A PCR test based on each repeat was specific for the new trypanosome and sensitive to <0.1 trypanosome equivalent. These PCR tests were used to identify trypanosomes in archival pig blood smears from the 1950's, confirming the identity of the Msubugwe trypanosome as Trypanosoma (Pycnomonas) suis. We also present data on the molecular karyotype and spliced leader (SL, miniexon) repeat of the new trypanosome, both of which distinguish T. suis from other, better-known African tsetse-transmitted trypanosomes. The rediscovery of T. suis opens new lines of research into the evolution and biology of the African trypanosomes.
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Malele II, Ouma JO, Enyaru JCK, Matovu E, Alibu V, Auma JE, Onyoyo SG, Bateta R, Changasi RE, Mukiria PW, Ndung'u K, Gitonga PK, Mwaniki LM, Nyingilili HS, Lyaruu EA, Kapange LA, Kamau PK, Masiga DK. Comparative diagnostic and analytical performance of PCR and LAMP-based trypanosome detection methods estimated using pooled whole tsetse flies and midguts. Vet Parasitol 2013; 197:549-56. [PMID: 23796572 DOI: 10.1016/j.vetpar.2013.05.022] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Revised: 05/07/2013] [Accepted: 05/20/2013] [Indexed: 11/20/2022]
Abstract
Detection of trypanosomes that cause disease in human beings and livestock within their tsetse fly hosts is an essential component of vector and disease control programmes. Several molecular-based diagnostic tests have been developed for this purpose. Many of these tests, while sensitive, require analysis of trypanosome DNA extracted from single flies, or from pooled tsetse fly heads and amplified trypanosome DNA. In this study, we evaluated the relative analytical and diagnostic sensitivities of two PCR-based tests (ITS and TBR) and a Trypanozoon specific LAMP assay using pooled whole tsetse flies and midguts spiked with serially diluted procyclics of a laboratory strain of Trypanosoma brucei brucei (KETRI 3386). Test sensitivity was also evaluated using experimentally infected tsetse flies. The aim was to determine the most appropriate pooling strategy for whole tsetse and midguts. RIME-LAMP had the highest diagnostic sensitivity (100%) followed by TBR-PCR (95%) and ITS-PCR (50%) in detecting trypanosome DNA from pooled tsetse midguts. RIME-LAMP also had the best diagnostic specificity (75%) followed by ITS-PCR (68%) and TBR-PCR (50%). The relative detection limit determined by serial dilution of procyclics was below 10(-6) (equivalent to 1parasite/ml). Using TBR-PCR, ITS-PCR and RIME-LAMP, it was possible to detect trypanosome DNA in single flies or in pools of 2, 3, 4, 5, 10, or 15 flies/midguts. The proportion of positive pools declined by up to 60% when testing pools of 15 whole flies as opposed to testing pools of 5-10 flies. Additionally, it was possible to detect DNA in a single infected tsetse fly in the background of 4, 9, or 14 uninfected tsetse flies. Averaged across pool sizes and tsetse species, RIME-LAMP detected the highest proportion of positive pools in spiked whole tsetse and midguts (86.6% and 87.2%) followed by TBR-PCR (78. 6% and 79.2%) and ITS-PCR (34.3% and 40.2%). There were no significant differences between the proportions of positive pools detected in whole flies and midguts. We conclude that pooling of whole tsetse/midguts is an effective strategy to reduce hands-on-time and hence has potential application in large scale xenomonitoring to generate epidemiological data for decision making. RIME-LAMP offers the best diagnostic sensitivity and specificity on pooled tsetse midguts, thus demonstrating its superior diagnostic performance when compared with TBR-PCR and ITS-PCR. Using pools of whole tsetse or midguts as source of DNA does not have any significant effect on test results and is more representative of the field conditions where the proportion of flies with infected midguts tends to be higher than flies with infected salivary glands. Therefore to save time and minimize costs, pooling of whole tsetse flies is recommended.
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Affiliation(s)
- Imna I Malele
- Tsetse & Trypanosomiasis Research Institute, P.O. Box 1026, Tanga, Tanzania.
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Abd-Alla AMM, Bergoin M, Parker AG, Maniania NK, Vlak JM, Bourtzis K, Boucias DG, Aksoy S. Improving Sterile Insect Technique (SIT) for tsetse flies through research on their symbionts and pathogens. J Invertebr Pathol 2013; 112 Suppl:S2-10. [PMID: 22841636 PMCID: PMC4242710 DOI: 10.1016/j.jip.2012.07.009] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2012] [Revised: 05/10/2012] [Accepted: 05/12/2012] [Indexed: 11/23/2022]
Abstract
Tsetse flies (Diptera: Glossinidae) are the cyclical vectors of the trypanosomes, which cause human African trypanosomosis (HAT) or sleeping sickness in humans and African animal trypanosomosis (AAT) or nagana in animals. Due to the lack of effective vaccines and inexpensive drugs for HAT, and the development of resistance of the trypanosomes against the available trypanocidal drugs, vector control remains the most efficient strategy for sustainable management of these diseases. Among the control methods used for tsetse flies, Sterile Insect Technique (SIT), in the frame of area-wide integrated pest management (AW-IPM), represents an effective tactic to suppress and/or eradicate tsetse flies. One constraint in implementing SIT is the mass production of target species. Tsetse flies harbor obligate bacterial symbionts and salivary gland hypertrophy virus which modulate the fecundity of the infected flies. In support of the future expansion of the SIT for tsetse fly control, the Joint FAO/IAEA Programme of Nuclear Techniques in Food and Agriculture implemented a six year Coordinated Research Project (CRP) entitled "Improving SIT for Tsetse Flies through Research on their Symbionts and Pathogens". The consortium focused on the prevalence and the interaction between the bacterial symbionts and the virus, the development of strategies to manage virus infections in tsetse colonies, the use of entomopathogenic fungi to control tsetse flies in combination with SIT, and the development of symbiont-based strategies to control tsetse flies and trypanosomosis. The results of the CRP and the solutions envisaged to alleviate the constraints of the mass rearing of tsetse flies for SIT are presented in this special issue.
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Affiliation(s)
- Adly M M Abd-Alla
- Insect Pest Control Laboratory, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Vienna, Austria.
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Auty H, Anderson NE, Picozzi K, Lembo T, Mubanga J, Hoare R, Fyumagwa RD, Mable B, Hamill L, Cleaveland S, Welburn SC. Trypanosome diversity in wildlife species from the serengeti and Luangwa Valley ecosystems. PLoS Negl Trop Dis 2012; 6:e1828. [PMID: 23094115 PMCID: PMC3475651 DOI: 10.1371/journal.pntd.0001828] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Accepted: 08/08/2012] [Indexed: 12/02/2022] Open
Abstract
Background The importance of wildlife as reservoirs of African trypanosomes pathogenic to man and livestock is well recognised. While new species of trypanosomes and their variants have been identified in tsetse populations, our knowledge of trypanosome species that are circulating in wildlife populations and their genetic diversity is limited. Methodology/Principal Findings Molecular phylogenetic methods were used to examine the genetic diversity and species composition of trypanosomes circulating in wildlife from two ecosystems that exhibit high host species diversity: the Serengeti in Tanzania and the Luangwa Valley in Zambia. Phylogenetic relationships were assessed by alignment of partial 18S, 5.8S and 28S trypanosomal nuclear ribosomal DNA array sequences within the Trypanosomatidae and using ITS1, 5.8S and ITS2 for more detailed analysis of the T. vivax clade. In addition to Trypanosoma brucei, T. congolense, T. simiae, T. simiae (Tsavo), T. godfreyi and T. theileri, three variants of T. vivax were identified from three different wildlife species within one ecosystem, including sequences from trypanosomes from a giraffe and a waterbuck that differed from all published sequences and from each other, and did not amplify with conventional primers for T. vivax. Conclusions/Significance Wildlife carries a wide range of trypanosome species. The failure of the diverse T. vivax in this study to amplify with conventional primers suggests that T. vivax may have been under-diagnosed in Tanzania. Since conventional species-specific primers may not amplify all trypanosomes of interest, the use of ITS PCR primers followed by sequencing is a valuable approach to investigate diversity of trypanosome infections in wildlife; amplification of sequences outside the T. brucei clade raises concerns regarding ITS primer specificity for wildlife samples if sequence confirmation is not also undertaken. The trypanosomes include a number of species that cause disease in livestock. In recent years, several trypanosomes have been identified which do not fit into the classic trypanosome classification system. However, previous work has focused on trypanosomes identified in the tsetse vector, with little information available on trypanosomes found in their natural hosts, wildlife. We studied trypanosome sequences from wildlife in Serengeti National Park in Tanzania and the Luangwa Valley in Zambia and found a number of trypanosome species pathogenic to livestock were circulating in these areas. For Trypanosoma vivax, one of the causes of trypanosomiasis in cattle, variants were identified in giraffe and waterbuck that were different from all published sequences and from each other. These variants did not test positive with the molecular tests usually used to identify T. vivax suggesting that T. vivax may often be under-diagnosed in Tanzania. The trypanosome classification system is facing challenges as molecular data are incorporated into a system that historically was based on factors such as morphology, host range and geographical distribution.
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MESH Headings
- Animals
- Animals, Wild/parasitology
- Cluster Analysis
- DNA, Protozoan/chemistry
- DNA, Protozoan/genetics
- DNA, Ribosomal/chemistry
- DNA, Ribosomal/genetics
- DNA, Ribosomal Spacer/chemistry
- DNA, Ribosomal Spacer/genetics
- Ecosystem
- Genes, rRNA
- Genetic Variation
- Molecular Sequence Data
- Phylogeny
- RNA, Protozoan/genetics
- RNA, Ribosomal/genetics
- RNA, Ribosomal, 18S/genetics
- RNA, Ribosomal, 5.8S/genetics
- Sequence Analysis, DNA
- Tanzania
- Trypanosoma/classification
- Trypanosoma/genetics
- Trypanosoma/isolation & purification
- Zambia
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Affiliation(s)
- Harriet Auty
- Centre for Infectious Diseases, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, United Kingdom
- Institute for Biodiversity, Animal Health and Comparative Medicine, College of Medicine, Veterinary Medicine and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Neil E. Anderson
- Centre for Infectious Diseases, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, United Kingdom
| | - Kim Picozzi
- Centre for Infectious Diseases, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, United Kingdom
| | - Tiziana Lembo
- Centre for Infectious Diseases, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, United Kingdom
- Institute for Biodiversity, Animal Health and Comparative Medicine, College of Medicine, Veterinary Medicine and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Joseph Mubanga
- Centre for Infectious Diseases, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, United Kingdom
| | - Richard Hoare
- Tanzania Wildlife Research Institute - Messerli Foundation Wildlife Veterinary Programme, Arusha, Tanzania
| | - Robert D. Fyumagwa
- Tanzania Wildlife Research Institute - Serengeti Wildlife Research Centre, Arusha, Tanzania
| | - Barbara Mable
- Institute for Biodiversity, Animal Health and Comparative Medicine, College of Medicine, Veterinary Medicine and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Louise Hamill
- Centre for Infectious Diseases, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, United Kingdom
| | - Sarah Cleaveland
- Centre for Infectious Diseases, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, United Kingdom
- Institute for Biodiversity, Animal Health and Comparative Medicine, College of Medicine, Veterinary Medicine and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Susan C. Welburn
- Centre for Infectious Diseases, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, United Kingdom
- * E-mail:
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Auty HK, Picozzi K, Malele I, Torr SJ, Cleaveland S, Welburn S. Using molecular data for epidemiological inference: assessing the prevalence of Trypanosoma brucei rhodesiense in tsetse in Serengeti, Tanzania. PLoS Negl Trop Dis 2012; 6:e1501. [PMID: 22303496 PMCID: PMC3269424 DOI: 10.1371/journal.pntd.0001501] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2011] [Accepted: 12/12/2011] [Indexed: 11/19/2022] Open
Abstract
Background Measuring the prevalence of transmissible Trypanosoma brucei rhodesiense in tsetse populations is essential for understanding transmission dynamics, assessing human disease risk and monitoring spatio-temporal trends and the impact of control interventions. Although an important epidemiological variable, identifying flies which carry transmissible infections is difficult, with challenges including low prevalence, presence of other trypanosome species in the same fly, and concurrent detection of immature non-transmissible infections. Diagnostic tests to measure the prevalence of T. b. rhodesiense in tsetse are applied and interpreted inconsistently, and discrepancies between studies suggest this value is not consistently estimated even to within an order of magnitude. Methodology/Principal Findings Three approaches were used to estimate the prevalence of transmissible Trypanosoma brucei s.l. and T. b. rhodesiense in Glossina swynnertoni and G. pallidipes in Serengeti National Park, Tanzania: (i) dissection/microscopy; (ii) PCR on infected tsetse midguts; and (iii) inference from a mathematical model. Using dissection/microscopy the prevalence of transmissible T. brucei s.l. was 0% (95% CI 0–0.085) for G. swynnertoni and 0% (0–0.18) G. pallidipes; using PCR the prevalence of transmissible T. b. rhodesiense was 0.010% (0–0.054) and 0.0089% (0–0.059) respectively, and by model inference 0.0064% and 0.00085% respectively. Conclusions/Significance The zero prevalence result by dissection/microscopy (likely really greater than zero given the results of other approaches) is not unusual by this technique, often ascribed to poor sensitivity. The application of additional techniques confirmed the very low prevalence of T. brucei suggesting the zero prevalence result was attributable to insufficient sample size (despite examination of 6000 tsetse). Given the prohibitively high sample sizes required to obtain meaningful results by dissection/microscopy, PCR-based approaches offer the current best option for assessing trypanosome prevalence in tsetse but inconsistencies in relating PCR results to transmissibility highlight the need for a consensus approach to generate meaningful and comparable data. Human African trypanosomiasis is a fatal disease that is carried by a tsetse vector. Assessing the proportion of tsetse which carries human-infective trypanosomes is important in assessing human disease risk and understanding disease transmission dynamics. However, identifying flies which carry transmissible infections is difficult, due to potential presence of other trypanosome species in the same fly, and concurrent detection of immature infections which are not transmissible. We used three methods to estimate the proportion of flies carrying human-infective trypanosomes: dissection and microscopic examination of flies to visualise trypanosomes directly in the fly; PCR of fly midguts in which trypanosomes were observed by microscopy; and theoretical analysis using a mathematical model of disease transmission. All three methods found the prevalence to be extremely low. Given the low prevalence, dissection/microscopy requires prohibitively large sample sizes and therefore PCR-based approaches are likely to be of most value. However, interpretation of PCR data is not straightforward; whilst PCR identifies flies carrying pathogen genetic material it does not directly identify flies with transmissible infections. This study highlights the need for a consensus approach on the analysis and interpretation of PCR data to generate reliable and comparable measures of the proportion of flies which carry transmissible human-infective trypanosomes.
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Affiliation(s)
- Harriet K. Auty
- Division of Pathway Medicine and Centre for Infectious Diseases, School of Biomedical Sciences, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, United Kingdom
- Institute for Biodiversity, Animal Health and Comparative Medicine, College of Medicine, Veterinary Medicine and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Kim Picozzi
- Division of Pathway Medicine and Centre for Infectious Diseases, School of Biomedical Sciences, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, United Kingdom
| | - Imna Malele
- Tsetse and Trypanosomiasis Research Institute, Tanga, Tanzania
| | - Steve J. Torr
- Natural Resources Institute, University of Greenwich, Chatham Maritime, United Kingdom
| | - Sarah Cleaveland
- Institute for Biodiversity, Animal Health and Comparative Medicine, College of Medicine, Veterinary Medicine and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Sue Welburn
- Division of Pathway Medicine and Centre for Infectious Diseases, School of Biomedical Sciences, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, United Kingdom
- * E-mail:
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