Fifty years of Tsetse control in Tanzania: challenges and prospects for the future

Tsetse flies are the vectors of trypanosomes, the causative organisms of trypanosomiasis, nagana, in animals and sleeping sickness in man. In Tanzania, tsetse transmitted trypanosomiasis is one of the most important disease affecting both animals and humans. About 40% of land suitable for grazing and areas with high agricultural potential are currently tsetse infested. It is estimated that about 4.4 million livestock and 4 million people are at risk of contracting tsetse borne trypanosomiasis. African animal trypanosomiasis (AAT) causes loss in animals due to mortality and reduced milk yield, which is estimated at US$ 7.98 million annually. Even after 50 years of independence, Human African Trypanosomiasis (HAT) or Sleeping Sickness is still one of the major public health problems with about 300 cases being reported annually. Tsetse control has been sporadic and uncoordinated hence no tangible results have been accrued since independence despite the fact that technologies which have facilitated tsetse control in other places are available. Fifty years of independence have seen shrinkage of tsetse belt to 43% in 16 surveyed regions. Opportunities for future are wide open if tsetse control will involve all stakeholders, who are directly or indirectly affected by the tsetse problem; if tsetse and trypanosomiasis eradication will adopt an area wide and participatory approach with emphasis on environmentally and user friendly techniques for expanded livestock sector; improved food security and livelihood in affected communities, for achievement of the millennium development goals

Major Disease Vectors in Tanzania: Distribution, Control and Challenges

Disease vectors remain a major public health challenge in spite of efforts done to control across Tanzania. Different disease vectors have been controlled and efforts are on to eradicate them but challenges are still emerging and managed. In spite of all these success, different disease vectors have been observed to have developed resistance to all classes of insecticides used in public health practices in Tanzania.Resistance reports to main different vectors have been coming throughout Tanzania. The resistance of vectors to insecticides has been of different mechanisms depending on species, insecticides and mechanisms of action of the pesticides. Social economic factors and housing style still a major factor for the distribution and foci of vector abundance. The impact of public health intervention has been observed but still disease vector existence is noticed. Careful monitoring of the public health priorities for disease vectors control should be rethought to keep the elimination track live. Different tools such as insecticides use, understanding control measures, vector distribution and human lifestyle can lead to reduced burden caused by disease vectors. This chapter has described mosquitoes, tsetse flies, soft ticks, blackflies, and houseflies in terms of distribution, abundance, control and challenges of eradication in Tanzania

Development of Loop-Mediated Isothermal Amplification (LAMP) Assays for Rapid Detection of Ehrlichia ruminantium

<p>Abstract</p> <p>Background</p> <p>The rickettsial bacterium <it>Ehrlichia ruminantium </it>is the causative agent of heartwater, a potential zoonotic disease of ruminants transmitted by ticks of the genus <it>Amblyomma</it>. The disease is distributed in nearly all of sub-Saharan Africa and some islands of the Caribbean, from where it threatens the American mainland. This report describes the development of two different loop-mediated isothermal amplification (LAMP) assays for sensitive and specific detection of <it>E. ruminantium</it>.</p> <p>Results</p> <p>Two sets of LAMP primers were designed from the pCS20 and <it>sodB </it>genes. The detection limits for each assay were 10 copies for pCS20 and 5 copies for <it>sodB</it>, which is at least 10 times higher than that of the conventional pCS20 PCR assay. DNA amplification was completed within 60 min. The assays detected 16 different isolates of <it>E. ruminantium </it>from geographically distinct countries as well as two attenuated vaccine isolates. No cross-reaction was observed with genetically related Rickettsiales, including zoonotic <it>Ehrlichia </it>species from the USA. LAMP detected more positive samples than conventional PCR but less than real-time PCR, when tested with field samples collected in sub-Saharan countries.</p> <p>Conclusions</p> <p>Due to its simplicity and specificity, LAMP has the potential for use in resource-poor settings and also for active screening of <it>E. ruminantium</it> in both heartwater-endemic areas and regions that are at risk of contracting the disease.</p

Using molecular data for epidemiological inference: assessing the prevalence of Trypanosoma brucei rhodesiense in Tsetse in Serengeti, Tanzania

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

Multiple Trypanosoma infections are common amongst Glossina species in the new farming areas of Rufiji district, Tanzania

<p>Abstract</p> <p>Background</p> <p>Tsetse flies and trypanosomiasis are among several factors that constrain livestock development in Tanzania. Over the years Rufiji District was excluded from livestock production owing to tsetse fly infestation, however, a few years ago there was an influx of livestock following evictions aimed at conserving the Usangu wetlands.</p> <p>Methods</p> <p>A study was conducted to determine the efficiency of available traps for catching tsetse flies, <it>Glossina </it>species infesting the area, their infection rates and <it>Trypanosoma </it>species circulating in the area. Trapping was conducted during the semi dry season for a total of 30 days (ten days each month) during the onset of the dry season of May - July 2009. Harvested flies after every 24 hours were dissected and examined under a light microscope for trypanosome infections and whole fly DNA was extracted from 82 flies and analyzed for trypanosomes by polymerase chain reaction (PCR) using different sets of primers.</p> <p>Results</p> <p>The proportions of total tsetse catches per trap were in the following decreasing order S3 (33%), H-Trap (27%), Pyramidal (19%), sticky panel (11%) and biconical trap (10%). Of the 1200 trapped flies, 75.6% were identified as <it>Glossina pallidipes</it>, 11.7% <it>as G. brevipalpis</it>, 9.6% as <it>G. austeni </it>and 3.0% <it>G. morsitans morsitans</it>. Dissections revealed the overall infection rate of 6.6% (13/197). Whole DNA was extracted from 82 tsetse flies and the prevalence of trypanosomes circulating in the area in descending order was 92.7% (76/82) for <it>T. simiae</it>; 70.7% (58/82) for <it>T. brucei </it>types; 48.8% (40/82) for the <it>T. vivax </it>types and 32.9% (27/82) for the <it>T. congolense </it>types as determined by PCR. All trypanosome types were found in all tsetse species analysed except for the <it>T. congolense </it>types, which were absent in <it>G. m. morsitans</it>. None of the <it>T. brucei </it>positive samples contained human infective trypanosomes by SRA - PCR test</p> <p>Conclusion</p> <p>All tsetse species found in Rufiji are biologically important in the transmission of animal trypanosomiasis and the absence of <it>T. congolense </it>in <it>G. m. morsitans </it>could be a matter of chance only. Therefore, plans for control should consider all tsetse species.</p

Tracking the Feeding Patterns of Tsetse Flies (Glossina Genus) by Analysis of Bloodmeals Using Mitochondrial Cytochromes Genes

Tsetse flies are notoriously difficult to observe in nature, particularly when populations densities are low. It is therefore difficult to observe them on their hosts in nature; hence their vertebrate species can very often only be determined indirectly by analysis of their gut contents. This knowledge is a critical component of the information on which control tactics can be developed. The objective of this study was to determine the sources of tsetse bloodmeals, hence investigate their feeding preferences. We used mitochondrial cytochrome c oxidase 1 (COI) and cytochrome b (cytb) gene sequences for identification of tsetse fly blood meals, in order to provide a foundation for rational decisions to guide control of trypanosomiasis, and their vectors. Glossina swynnertoni were sampled from Serengeti (Tanzania) and G. pallidipes from Kenya (Nguruman and Busia), and Uganda. Sequences were used to query public databases, and the percentage identities obtained used to identify hosts. An initial assay showed that the feeds were from single sources. Hosts identified from blood fed flies collected in Serengeti ecosystem, included buffaloes (25/40), giraffes (8/40), warthogs (3/40), elephants (3/40) and one spotted hyena. In Nguruman, where G. pallidipes flies were analyzed, the feeds were from elephants (6/13) and warthogs (5/13), while buffaloes and baboons accounted for one bloodmeal each. Only cattle blood was detected in flies caught in Busia and Uganda. Out of four flies tested in Mbita Point, Suba District in western Kenya, one had fed on cattle, the other three on the Nile monitor lizard. These results demonstrate that cattle will form an integral part of a control strategy for trypanosomiasis in Busia and Uganda, while different approaches are required for Serengeti and Nguruman ecosystems, where wildlife abound and are the major component of the tsetse fly food source

Genome sequence of the tsetse fly (Glossina morsitans):Vector of African trypanosomiasis

Tsetse flies are the sole vectors of human African trypanosomiasis throughout sub-Saharan Africa. Both sexes of adult tsetse feed exclusively on blood and contribute to disease transmission. Notable differences between tsetse and other disease vectors include obligate microbial symbioses, viviparous reproduction, and lactation. Here, we describe the sequence and annotation of the 366-megabase Glossina morsitans morsitans genome. Analysis of the genome and the 12,308 predicted protein-encoding genes led to multiple discoveries, including chromosomal integrations of bacterial (Wolbachia) genome sequences, a family of lactation-specific proteins, reduced complement of host pathogen recognition proteins, and reduced olfaction/chemosensory associated genes. These genome data provide a foundation for research into trypanosomiasis prevention and yield important insights with broad implications for multiple aspects of tsetse biology.IS

Quantifying Heterogeneity in Host-Vector Contact: Tsetse (Glossina swynnertoni and G. pallidipes) Host Choice in Serengeti National Park, Tanzania

Identifying hosts of blood-feeding insect vectors is crucial in understanding their role in disease transmission. Rhodesian human African trypanosomiasis (r-HAT or ‘sleeping sickness’) caused by Trypanosoma brucei rhodesiense and transmitted by tsetse flies, is commonly associated with wilderness areas of east and southern Africa. Such areas hold a diverse range of species which form communities of hosts for disease maintenance. The relative importance of different wildlife hosts remains unclear. This study quantified tsetse feeding preferences in a wilderness area of great host species richness, Serengeti National Park, Tanzania, assessing tsetse feeding and host density contemporaneously. Glossina swynnertoni and G.pallidipes were collected from six study sites. Bloodmeal sources were identified through matching Cytochrome B sequences amplified from bloodmeals from fed flies to published sequences. Densities of large mammal species in each site were quantified, and feeding indices calculated to assess the relative selection or avoidance of each host species by tsetse. The host species most commonly identified in G. swynnertoni bloodmeals, warthog (94/220), buffalo (48/220) and giraffe (46/220), were found at relatively low densities (3-11/km2) and fed on up to 15 times more frequently than expected by their relative density. Wildebeest, zebra, impala and Thomson’s gazelle, found at the highest densities, were never identified in bloodmeals. Commonly identified hosts for G. pallidipes were buffalo (26/46), giraffe (9/46) and elephant (5/46). This study is the first to quantify tsetse host range by molecular analysis of tsetse diet with simultaneous assessment of host density in a wilderness area. Although G.swynnertoni and G.pallidipes can feed on a range of species, they are highly selective. Many host species are rarely fed on, despite being present in areas where tsetse are abundant. These feeding patterns, along with the ability of key host species to maintain and transmit T.b.rhodesiense, drive the epidemiology of r-HAT in wilderness areas

Occurrence of haemoparasites in cattle in Monduli district, northern Tanzania

Haemoparasite infections are among the most economically important cattle diseases in sub-Saharan Africa. The present study investigated the occurrence of haemoparasites in 295 indigenous cattle from five villages (Mswakini, Lake Manyara, Naitolia, Makuyuni and Nanja) of the Monduli district, a wildlife-domestic animal-human interface area in northern Tanzania. The data showed that the overall occurrence of haemoparasites in the sampled cattle was 12.5% (95% CI: 8.7% – 16.3%), involving single and mixed infections with Theileria parva, Anaplasma marginale, Babesia bovis, Trypanosoma vivax and Trypanosoma brucei. The highest haemoparasite occurrence was recorded in Lake Manyara (18.3%; 95% CI: 8.5% – 28.1%), and the lowest was recorded in Nanja (6.5%; 95% CI: 0.4% – 12.6%). This preliminary study, furthermore, provided evidence of the possible arthropod vectors (ticks and tsetse flies) that may be involved in the transmission of haemoparasites to cattle in the Monduli district. It is envisaged that this survey will stimulate more studies to determine the prevalence of haemoparasites in livestock by using more sensitive molecular techniques