290 research outputs found
Factors affecting the propensity of tsetse flies to enter houses and attack humans inside : increased risk of sleeping sickness in warmer climates
No full textBackground:
Sleeping sickness, or human African trypanosomiasis, is caused by two species of Trypanosoma brucei that are transmitted to humans by tsetse flies (Glossina spp.) when these insects take a bloodmeal. It is commonly assumed that humans must enter the normal woodland habitat of the flies to become infected, but recent studies found that tsetse frequently attack humans inside buildings. Factors affecting human/tsetse contact in buildings need identification.
Methodology/Principal Findings:
In Zimbabwe, tsetse were allowed access to a house via an open door. Those in the house at sunset, and those alighting on humans in the house during the day, were caught using hand-nets. Total catches were unaffected by: (i) the presence of humans in the house and at the door, (ii) wood smoke from a fire inside the house or just outside, (iii) open windows, and (iv) chemicals simulating the odor of cattle or of humans. Catches increased about 10-fold with rising ambient temperatures, and during the hottest months the proportion of the total catch that was taken from the humans increased from 5% to 13%. Of the tsetse caught from humans, 62% consisted of female G. morsitans morstans and both sexes of G. pallidipes, i.e., the group of tsetse that normally alight little on humans. Some of the tsetse caught were old enough to be effective vectors.
Conclusion/Significance:
Present results confirm previous suggestions that buildings provide a distinctive and important venue for transmission of sleeping sickness, especially since the normal repellence of humans and smoke seems poorly effective in such places. The importance of the venue would be increased in warmer climates
A Bayesian geostatistical Moran Curve model for estimating net changes of tsetse populations in Zambia
No full textFor the first time a Bayesian geostatistical version of the Moran Curve, a logarithmic form of the Ricker stock recruitment curve, is proposed that is able to give an estimate of net change in population demographic rates considering components such as fertility and density dependent and density independent mortalities. The method is applied to spatio-temporally referenced count data of tsetse flies obtained from fly-rounds. The model is a linear regression with three components: population rate of change estimated from the Moran curve, an explicit spatio-temporal covariance, and the observation error optimised within a Bayesian framework. The model was applied to the three main climate seasons of Zambia (rainy – January to April, cold-dry – May to August, and hot-dry – September to December) taking into account land surface temperature and (seasonally changing) cattle distribution. The model shows a maximum positive net change during the hot-dry season and a minimum between the rainy and cold-dry seasons. Density independent losses are correlated positively with day-time land surface temperature and negatively with night-time land surface temperature and cattle distribution. The inclusion of density dependent mortality increases considerably the goodness of fit of the model. Cross validation with an independent dataset taken from the same area resulted in a very accurate estimate of tsetse catches. In general, the overall framework provides an important tool for vector control and eradication by identifying vector population concentrations and local vector demographic rates. It can also be applied to the case of sustainable harvesting of natural population
Collateral benefits of restricted insecticide application for control of African trypanosomiasis on Theileria parva in cattle: a randomized controlled trial
No full textTick and tsetse-borne diseases (TTBDs) constrain livestock production in tropical and subtropical regions of the world. Of this community of endemic diseases, East coast fever (T.parva) is the most important tick-borne disease (TBD) accounting for 70% of all losses due to TBDS in this region where control efforts target either tsetse or TBDs and seldom both. In those instances where simultaneous pyrethroid insecticide TTBD control is implemented, collateral benefits of tsetse control on TBD control have not been quantified. In the interest of guiding future TTBD control efforts, the effect of restricting pyrethroid insecticides to the legs, belly and ears (RAP) of cattle for tsetse and trypanosomiasis control on T.parva prevalence in crop-livestock production systems in Tororo district, south-eastern Uganda was determined
Expression of procyclin mRNAs during cyclical transmission of <i>Trypanosoma brucei</i>
No full text<i>Trypanosoma brucei</i>, the parasite causing human sleeping sickness, relies on the tsetse fly for its transmission. In the insect, EP and GPEET procyclins are the major surface glycoproteins of procyclic (midgut) forms of the parasite, with GPEET predominating in the early procyclic form and two isoforms of EP in the late procyclic form. EP procyclins were previously detected on salivary gland trypanosomes, presumably epimastigotes, by immunoelectron microscopy. However, no procyclins could be detected by mass spectrometry when parasites were isolated from infected glands. We have used qualitative and quantitative RT-PCR to analyse the procyclin mRNAs expressed by trypanosomes in the tsetse midgut and salivary glands at different time points after infection. The coding regions of the three EP isoforms (EP1, EP2 and EP3) are extremely similar, but their 3′ untranslated regions contain unique sequences that make it possible to assign the cDNAs amplified by this technique. With the exception of EP2, we found that the spectrum of procyclin mRNAs expressed in the midgut mirrors the protein repertoire of early and established procyclic forms. Surprisingly, procyclin mRNAs, including that of GPEET, are present at relatively high levels in salivary gland trypanosomes, although the proteins are rarely detected by immunofluorescence. Additional experiments using transgenic trypanosomes expressing reporter genes or mutant forms of procyclin point to a mechanism of translational or post-translational control, involving the procyclin coding regions, in salivary gland trypanosomes. It is widely accepted that T. brucei always has a coat of either variant surface glycoprotein or procyclin. It has been known for many years that the epimastigote form does not have a variant surface glycoprotein coat. The finding that this life cycle stage is usually negative for procyclin as well is new, and means that the paradigm will need to be revis
Improvements on Restricted Insecticide Application Protocol for Control of Human and Animal African Trypanosomiasis in Eastern Uganda
No full textAfrican trypanosomes constrain livestock and human health in Sub-Saharan Africa, and aggravate poverty and hunger of these otherwise largely livestock-keeping communities. To solve this, there is need to develop and use effective and cheap tsetse control methods. To this end, we aimed at determining the smallest proportion of a cattle herd that needs to be sprayed on the legs, bellies and ears (RAP) for effective Human and Animal African Trypanosomiasis (HAT/AAT) control.Methodology/Principal finding: Cattle in 20 villages were ear-tagged and injected with two doses of diminazene diaceturate (DA) forty days apart, and randomly allocated to one of five treatment regimens namely; no treatment, 25%, 50%, 75% monthly RAP and every 3 month Albendazole drench. Cattle trypanosome re-infection rate was determined by molecular techniques. ArcMap V10.3 was used to map apparent tsetse density (FTD) from trap catches. The effect of graded RAP on incidence risk ratios and trypanosome prevalence was determined using Poisson and logistic random effect models in R and STATA V12.1 respectively. Incidence was estimated at 9.8/100 years in RAP regimens, significantly lower compared to 25.7/100 years in the non-RAP regimens (incidence rate ratio: 0.37; 95% CI: 0.22–0.65; P,0.001). Likewise, trypanosomeprevalence after one year of follow up was significantly lower in RAP animals than in non-RAP animals (4% vs 15%, OR: 0.20,95% CI: 0.08–0.44; P,0.001). Contrary to our expectation, level of protection did not increase with increasing proportion of animals treated.Conclusions/significance: Reduction in RAP coverage did not significantly affect efficacy of treatment. This is envisaged to improve RAP adaptability to low income livestock keepers but needs further evaluation in different tsetse challenge, HAT/ AAT transmission rates and management systems before adopting it for routine tsetse control programs
Tsetse control, agricultural expansion and environmental change in Nigeria
No full textA brief account of the history of government organised tsetse and trypanosomiasis control in Nigeria is presented, and major features of the tsetse eradication programme are summarised.The achievements are considered in the context of widespread environmental change, brought about by an increasing human population, and a long term process of agricultural expansion, which have resulted in an overall reduction in natural tsetse habitats and hosts, and led to a general decline in tsetse populations.A comparison of two areas, one within, and the other outside the tsetse eradication zone, showed that they had both experienced similar rates of change in land use, and available information indicated that human and cattle populations had also increased at similar rates. The present day distribution and abundance of tsetse and cattle in a region of the Nigerian sub-humid zone, not yet reached by the tsetse eradication programme, are described. In the virtual absence of wildlife, abundance of cattle, and concentration of the two riverine tsetse species at crossing points, it was concluded that tsetse were largely dependent on cattle and/or man for their survival.The low density of riverine tsetse populations, their restricted distribution and their low infection rates, combined with Fulani herd management practices, which limited the period of contact between tsetse and cattle, indicated that under the prevailing conditions, trypanosome challenge was likely to be very low. It is suggested that this situation was typical for many areas within the sub-humid zone, and that in the future, similar conditions are likely to become even more widespread.It is concluded that, whilst government trypanosomiasis control programmes must have contributed to the general decline of the disease which has taken place, the environmental context within which they were mounted, has changed significantly. Over the past fifty years human population has almost certainly increased three or four fold, and the extent and intensity of both farming and hunting have increased commensurately. This has resulted in an overall reduction in natural tsetse habitats and hosts, which has led to a decline in vector populations. It is argued that this, together with a trend for Fulani and their cattle to become more sedentarised, has brought about a fundamental change in the balance of relationships in the vector-host-disease complex, which has favoured the development of appropriate immune responses in Fulani cattle, and the selection of less pathogenic strains of trypanosome
<i>Trypanosoma brucei rhodesiense</i> transmitted by a single tsetse fly bite in vervet monkeys as a model of human African trypanosomiasis
No full textSleeping sickness is caused by a species of trypanosome blood parasite that is transmitted by tsetse flies. To understand better how infection with this parasite leads to disease, we provide here the most detailed description yet of the course of infection and disease onset in vervet monkeys. One infected tsetse fly was allowed to feed on each host individual, and in all cases infections were successful. The characteristics of infection and disease were similar in all hosts, but the rate of progression varied considerably. Parasites were first detected in the blood 4-10 days after infection, showing that migration of parasites from the site of fly bite was very rapid. Anaemia was a key feature of disease, with a reduction in the numbers and average size of red blood cells and associated decline in numbers of platelets and white blood cells. One to six weeks after infection, parasites were observed in the cerebrospinal fluid (CSF), indicating that they had moved from the blood into the brain; this was associated with a white cell infiltration. This study shows that fly-transmitted infection in vervets accurately mimics human disease and provides a robust model to understand better how sleeping sickness develops
Opportunity and Problem in Context (OPiC). A framework for environmental management in developing countries
No full textEnvironmental management is usually a complex issue that involves many scientific disciplines and many stakeholders. Environmental management is therefore much helped by schemes that can guide research, reports and discussions in a manner that makes the interconnections between the key elements of problems and solutions visible. OPiC is the name of such a scheme (‘framework’). It is applicable to any environmental problem but the thesis of David Tsetse focuses especially on developing countries. OPiC interconnects, for instance, the causal chains in the environment and their mirror chains of environmental standards, the functions of nature, the desires of society, the analysis of products and services over their entire life cycle, criteria for evaluation, the identification of options for solutions and principles of policy design. A framework such as OPiC is not only a tool for the effective scientific and technical analysis, but may serve as well as a common foundation for collaboration between governments, companies and citizens.LEI Universiteit LeidenConservation Biolog
Role of the chancre in induction of immunity to tsetse-transmitted Trypanosoma (Nannomonas) congolense in goats
No full textLocal skin reactions (chancres) developed in goats at the sites of deposition, by tsetse flies, of metacyclics of Trypanosoma congolense. The chancres developed much faster and were more pronounced when ten infected tsetse were allowed to feed on a spot as compared to only one fly per spot. The initial host cellular reaction in the chancre was predominantly polymorphonuclear, followed at the peak of development of the chancre by a predominantly lymphoblastic and plasmacytic reaction. Trypanosomes were found in various stages of division as well as degeneration in chancre biopsies taken at various days post-infection (p.i.). Most of the trypanosomes recovered from the chancre tissue fluid were found to bear the same variable surface glycoprotein (VSG) epitopes as the corresponding metacyclics for as long as 13 days p.i., as revealed by indirect immunofluorescence using mouse anti-metacyclic VSG hyperimmune sera and monoclonal antibodies. Immunization of goats with metacyclic trypanosomes, by exposure to infected tsetse bites followed by treatment of the infected goats on day 13 p.i., gave rise to the development of protection to homologous tsetse-transmitted challenge, whilst immunization by intravenous inoculation of the metacyclics did not induce such protection. Chancre formation would thus appear to be vital for the induction of comprehensive immune recognition of the metacyclic variable antigen repertoire deposited in the skin by infected tsetse, and hence development of protective immunity.LR: 20031114; PUBM: Print; JID: 8002006; 0 (Antibodies, Monoclonal); 0 (Antibodies, Protozoan); 0 (Antigens, Protozoan); ppublishSource type: Electronic(1
Impact of imperfect paratransgenic immunity, tsetse population composition, and tsetse remating on paratransgene effectiveness.
No full text<p>(A) Effect of an imperfect paratransgene that provides perfect immunity to trypanosomes for proportion of tsetse carrying the paratransgene and no immunity to the remaining of tsetse carrying the transgene. (B) Effect of multiple tsetse species inhabiting the target region. Only the target tsetse species is affected by the paratransgene. (C) Effect of remating by no female tsetse (“None”, the baseline, same as <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002374#pntd-0002374-g002" target="_blank">Figure 2A</a>), by all female tsetse (“All”), and by only female tsetse with incompatible sperm (“Incompatibles”). When remating was allowed, 38% of the eligible females mated a second time. Empirical values (<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002374#pntd-0002374-t002" target="_blank">Table 2</a>) were used for the other parameters. Paratransgene releases were 10% of the wild tsetse population.</p
- …
