16 research outputs found
Spatial distribution of Tsetse (Diptera: Glossinidae) within the Trypanosoma brucei rhodesiense focus of Uganda.
One of the greatest problems for sub-Saharan Africa is shortage of
epidemiological data to support planning for provision of adequate public
and animal health services. The overriding challenge is to provide the
necessary resources to facilitate the process of regular data collection in
support of disease surveillance and vector monitoring across target regions.
Due to such circumstances, there is currently an increasing interest towards
devising cheaper but yet significantly reliable means for availing the needed
epidemiological and vector data for planning purpose. This study comes as a
contribution towards solving such challenges.
The study has three research components starting with a review of past
Uganda national tsetse and trypanosomiasis control efforts as a means
towards appreciating the dynamics of controlling the vector and disease.
This is an analysis of what was applied, what worked, what didn't, and why
it didnât as linked to the broader vector and disease control system.
Secondly through the use of remote sensing, geographical information
systems and global positioning technologies tsetse species were sampled
within Lake Victoria Basin. Only two species of tsetse were trapped, G. f. fG.
f. fuscipes which was widely distributed across the surveyed area, and G.
Pallidipes which was detected in a few isolated locations close to the border
with Kenya in Eastern Uganda. The analysis of land cover with tsetse
findings showed an important association between G. f. fuscipes and
particular vegetation mosaics. Unfortunately, while the results are highly
informative, approaches for data collection such as this one are costly and
unlikely to be sustained by the already over-burdened health systems in the
low developed countries of Africa.
The third and main part of this study investigates, demonstrates and delivers
the possibilities of applying spatial epidemiological modelling techniques to
produce both tsetse distribution and abundance maps. Four spatial and non-spatial
regression models (Logistic, Autologistic, Negative binomial and
Auto-negative binomial), were constructed and used to predict tsetse fly
presence and tsetse fly abundance for the study area. The product is an
improved understanding of association between environmental variables
and tsetse fly distribution/abundance and maps providing continuous
representations of the probability of tsetse occurrence and predicted tsetse
abundance across the study area.
The results indicate that tsetse presence and abundance are influenced
differently. Tsetse abundance is highly determined by river systems while
tsetse presence is majorly influenced by forested landscapes. Therefore,
efforts to control trypanosomiasis through vector control in the Lake Victoria
basin will call for delineation of such clearly identified high tsetse
accumulation zones for targeted tsetse control operations. This will ensure
optimum utilization of the scarce resources and above all contribute to the
protection of humans and animals against trypanosomiasis infection
Tsetse Fly (G.f. fuscipes) Distribution in the Lake Victoria Basin of Uganda
Tsetse flies transmit trypanosomes, the causative agent of human and animal African trypanosomiasis. The tsetse vector is extensively distributed across sub-Saharan Africa. Trypanosomiasis maintenance is determined by the interrelationship of three elements: vertebrate host, parasite and the vector responsible for transmission. Mapping the distribution and abundance of tsetse flies assists in predicting trypanosomiasis distributions and developing rational strategies for disease and vector control. Given scarce resources to carry out regular full scale field tsetse surveys to up-date existing tsetse maps, there is a need to devise inexpensive means for regularly obtaining dependable area-wide tsetse data to guide control activities. In this study we used spatial epidemiological modelling techniques (logistic regression) involving 5000 field-based tsetse-data (G. f. fuscipes) points over an area of 40,000 km2, with satellite-derived environmental surrogates composed of precipitation, temperature, land cover, normalised difference vegetation index (NDVI) and elevation at the sub-national level. We used these extensive tsetse data to analyse the relationships between presence of tsetse (G. f. fuscipes) and environmental variables. The strength of the results was enhanced through the application of a spatial autologistic regression model (SARM). Using the SARM we showed that the probability of tsetse presence increased with proportion of forest cover and riverine vegetation. The key outputs are a predictive tsetse distribution map for the Lake Victoria basin of Uganda and an improved understanding of the association between tsetse presence and environmental variables. The predicted spatial distribution of tsetse in the Lake Victoria basin of Uganda will provide significant new information to assist with the spatial targeting of tsetse and trypanosomiasis control
Gambian human African trypanosomiasis in North West Uganda. Are we on course for the 2020 target?
In 1994, combined active and passive screening reported 1469 cases from the historic Gambian Human African Trypanosomiasis (gHAT) foci of West Nile, Uganda. Since 2011 systematic active screening has stopped and there has been reliance on passive screening. During 2014, passive screening alone detected just nine cases. In the same year a tsetse control intervention was expanded to cover the main gHAT foci in West Nile to curtail transmission of gHAT contributing to the elimination of gHAT as a public health problem in the area. It is known that sole reliance on passive screening is slow to detect cases and can underestimate the actual true number. We therefore undertook an active screening programme designed to test the efficacy of these interventions against gHAT transmission and clarify disease status. Screening was conducted in 28 randomly selected villages throughout the study area, aiming to sample all residents. Whole blood from 10,963 participants was analysed using CATT and 97 CATT suspects (0.9%) were evaluated with microscopy and trypanolysis. No confirmed cases were found providing evidence that the gHAT prevention programmes in West Nile have been effective. Results confirm gHAT prevalence in the study area of West Nile is below the elimination threshold (1 new case / 10,000 population), making elimination on course across this study area if status is maintained. The findings of this study can be used to guide future HAT and tsetse management in other gHAT foci, where reduced caseloads necessitate a shift from active to passive screening
Estimating the impact of Tiny Targets in reducing the incidence of Gambian sleeping sickness in the North-west Uganda focus
Background
Riverine species of tsetse (Glossina) transmit Trypanosoma brucei gambiense, which causes Gambian human African trypanosomiasis (gHAT), a neglected tropical disease. Uganda aims to eliminate gHAT as a public health problem through detection and treatment of human cases and vector control. The latter is being achieved through the deployment of âTiny Targetsâ, insecticide-impregnated panels of material which attract and kill tsetse. We analysed the spatial and temporal distribution of cases of gHAT in Uganda during the period 2010â2019 to assess whether Tiny Targets have had an impact on disease incidence.
Methods
To quantify the deployment of Tiny Targets, we mapped the rivers and their associated watersheds in the intervention area. We then categorised each of these on a scale of 0â3 according to whether Tiny Targets were absent (0), present only in neighbouring watersheds (1), present in the watersheds but not all neighbours (2), or present in the watershed and all neighbours (3). We overlaid all cases that were diagnosed between 2000 and 2020 and assessed whether the probability of finding cases in a watershed changed following the deployment of targets. We also estimated the number of cases averted through tsetse control.
Results
We found that following the deployment of Tiny Targets in a watershed, there were fewer cases of HAT, with a sampled error probability of 0.007. We estimate that during the intervention period 2012â2019 we should have expected 48 cases (95% confidence intervalsâ=â40â57) compared to the 36 cases observed. The results are robust to a range of sensitivity analyses.
Conclusions
Tiny Targets have reduced the incidence of gHAT by 25% in north-western Uganda
Tick-borne pathogens of zoonotic and veterinary importance in Nigerian cattle
Additional file 1: Multiple infections by tick-borne pathogens according
to age classes and overall number of animals. (PDF 19 kb)BACKGROUND : Ticks and tick-borne diseases undermine cattle fitness and productivity in the whole of sub-Saharan
Africa, including Nigeria. In this West African country, cattle are challenged by numerous tick species, especially during
the wet season. Consequently, several TBDs are known to be endemic in Nigerian cattle, including anaplasmosis,
babesiosis, cowdriosis and theilerioris (by Theileria mutans and Theileria velifera). To date, all investigations on cattle
TBDs in Nigeria have been based on cytological examinations and/or on serological methods. This study aimed to
ascertain the occurrence of tick-borne pathogens of veterinary and zoonotic importance in cattle in Nigeria using
molecular approaches.
METHODS : In October 2008, 704 whole blood samples were collected from indigenous cattle in the Plateau State,
Nigeria. Analysis for tick-borne pathogens was conducted by means of PCR-based reverse line blotting (RLB) and
sequencing targeting a panel of five genera of microorganisms (i.e. Babesia, Theileria, Anaplasma, Ehrlichia and
Rickettsia spp.).
RESULTS : In total, 561/704 (82.6 %) animals were found infected, with 465 (69.6 %) of them being infected by two
or more microorganisms, with up to 77 possible combinations of pathogens detected. Theileria mutans was the
most prevalent microorganism (66.3 %), followed by Theileria velifera (52.4 %), Theileria taurotragi (39.5 %),
Anaplasma marginale (39.1 %), Anaplasma sp. (Omatjenne) (34.7 %), Babesia bigemina (7.9 %), Anaplasma centrale
(6.3 %), Anaplasma platys (3.9 %), Rickettsia massiliae (3.5 %), Babesia bovis (2.0 %) and Ehrlichia ruminantium
(1.1 %). Calves were found significantly less infected than juvenile and adult cattle.
CONCLUSIONS : This study provides updated, molecular-based information on cattle TBDs in Nigeria. The molecular
approach employed allowed the diagnosis of numerous positive cases including carrier statuses, multiple infections
and novel pathogen detections within the indigenous cattle population. Moreover, the RLB method here described
enabled the detection of veterinary agents not only pertaining to bovine health, including also those of zoonotic
importance.
The high prevalence recorded for T. mutans, T. velifera, A. marginale, T. taurotragi and Anaplasma sp. (Omatjenne),
suggests they may be endemically established in Nigeria, whereas the lower prevalence recorded for other
microorganisms (i.e. A. centrale and B. bovis) highlights a less stable epidemiological scenario, requiring further
investigations.The UKâs Biotechnology and Biological Sciences
Research Council (BBSRC) under the âCombating Infectious Diseases in
Livestock for International Developmentâ (CIDLID) scheme, and the European
Unionâs Seventh Framework Program (FP7/2007â2013) under grant
agreement n° 221948, Integrated Control of Neglected Zoonoses (ICONZ).http://www.parasitesandvectors.comam2016Veterinary Tropical Disease
Harnessing technology and portability to conduct molecular epidemiology of endemic pathogens in resource-limited settings
Improvements in genetic and genomic technology have enabled field-deployable molecular laboratories and these have been deployed in a variety of epidemics that capture headlines. In this editorial, we highlight the importance of building physical and personnel capacity in low and middle income countries to deploy these technologies to improve diagnostics, understand transmission dynamics and provide feedback to endemic communities on actionable timelines. We describe our experiences with molecular field research on schistosomiasis, trypanosomiasis and rabies and urge the wider tropical medicine community to embrace these methods and help build capacity to benefit communities affected by endemic infectious diseases
Autologistic regression model statistics.
<p>Autologistic regression model statistics.</p
Covariates used in the analyses of tsetse fly distribution and abundance including their observed maximum and minimum values in the training dataset.
<p>Covariates used in the analyses of tsetse fly distribution and abundance including their observed maximum and minimum values in the training dataset.</p
Binary map of tsetse presence and absence, illustrating the extensive nature of the field survey.
<p>It shows the tsetse survey outcome categorised as âpresentâ and âabsentâ. All tsetse traps which had tsetse flies where categorised as âpresentâ while those without tsetse flies where categorised as âabsentâ. G.f.fuscipes were captured in only 28.8% of the sampling sites (âpresentâ). This implies that 71.2% of the trapping sites registered zero catches (âabsentâ). A total of 14,899 G.f.fuscipes flies (females = 7138, males = 7271 and 108 unidentified sex) were caught during the survey.</p