Lessons learned from the emergence of a new Trypanosoma brucei rhodesiense sleeping sickness focus in Uganda

Livestock Network Analysis for Rhodesiense Human African Trypanosomiasis Control in Uganda

Background: Infected cattle sourced from districts with established foci for Trypanosoma brucei rhodesiense human African trypanosomiasis (rHAT) migrating to previously unaffected districts, have resulted in a significant expansion of the disease in Uganda. This study explores livestock movement data to describe cattle trade network topology and assess the effects of disease control interventions on the transmission of rHAT infectiousness. Methods: Network analysis was used to generate a cattle trade network with livestock data which was collected from cattle traders (n = 197) and validated using random graph methods. Additionally, the cattle trade network was combined with a susceptible, infected, recovered (SIR) compartmental model to simulate spread of rHAT (R o 1.287), hence regarded as "slow" pathogen, and evaluate the effects of disease interventions. Results: The cattle trade network exhibited a low clustering coefficient (0.5) with most cattle markets being weakly connected and a few being highly connected. Also, analysis of the cattle movement data revealed a core group comprising of cattle markets from both eastern (rHAT endemic) and northwest regions (rHAT unaffected area). Presence of a core group may result in rHAT spread to unaffected districts and occurrence of super spreader cattle market or markets in case of an outbreak. The key cattle markets that may be targeted for routine rHAT surveillance and control included Namutumba, Soroti, and Molo, all of which were in southeast Uganda. Using effective trypanosomiasis such as integrated cattle injection with trypanocides and spraying can sufficiently slow the spread of rHAT in the network. Conclusion: Cattle trade network analysis indicated a pathway along which T. b. rhodesiense could spread northward from eastern Uganda. Targeted T. b. rhodesiense surveillance and control in eastern Uganda, through enhanced public-private partnerships, would serve to limit its spread.

Salivarian Trypanosomes Have Adopted Intricate Host-Pathogen Interaction Mechanisms That Ensure Survival in Plain Sight of the Adaptive Immune System

Salivarian trypanosomes are extracellular parasites affecting humans, livestock and game animals. Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense are human infective sub-species of T. brucei causing human African trypanosomiasis (HAT—sleeping sickness). The related T. b. brucei parasite lacks the resistance to survive in human serum, and only inflicts animal infections. Animal trypanosomiasis (AT) is not restricted to Africa, but is present on all continents. T. congolense and T. vivax are the most widespread pathogenic trypanosomes in sub-Saharan Africa. Through mechanical transmission, T. vivax has also been introduced into South America. T. evansi is a unique animal trypanosome that is found in vast territories around the world and can cause atypical human trypanosomiasis (aHT). All salivarian trypanosomes are well adapted to survival inside the host’s immune system. This is not a hostile environment for these parasites, but the place where they thrive. Here we provide an overview of the latest insights into the host-parasite interaction and the unique survival strategies that allow trypanosomes to outsmart the immune system. In addition, we review new developments in treatment and diagnosis as well as the issues that have hampered the development of field-applicable anti-trypanosome vaccines for the implementation of sustainable disease control.

Haemoparasitic Infections in Cattle from a Trypanosoma brucei Rhodesiense Sleeping Sickness Endemic District of Eastern Uganda

We carried out a baseline survey of cattle in Kaberamaido district, in the context of controlling the domestic animal reservoir of Trypanosoma brucei rhodesiense human African trypanosomiasis (rHAT) towards elimination. Cattle blood was subjected to capillary tube centrifugation followed by measurement of the packed cell volume (PCV) and examination of the buffy coat area for motile trypanosomes. Trypanosomes were detected in 561 (21.4%) out of 2621 cattle screened by microscopy. These 561 in addition to 724 apparently trypanosome negative samples with low PCVs (≤25%) were transported to the laboratory and tested by PCR targeting the trypanosomal Internal Transcribed Spacer (ITS-1) as well as suspect Tick-Borne Diseases (TBDs) including Anaplasmamosis, Babesiosis, and Theileriosis. PCR for Anaplasma sp yielded the highest number of positive animals (45.2%), followed by Trypanosoma sp (44%), Theileria sp (42.4%) and Babesia (26.3%); multiple infections were a common occurrence. Interestingly, 373 (29%) of these cattle with low PCVs were negative by PCR, pointing to other possible causes of aneamia, such as helminthiasis. Among the trypanosome infections classified as T. brucei by ITS-PCR, 5.5% were positive by SRA PCR, and were, therefore, confirmed as T. b. rhodesiense. Efforts against HAT should therefore consider packages that address a range of conditions. This may enhance acceptability and participation of livestock keepers in programs to eliminate this important but neglected tropical disease. In addition, we demonstrated that cattle remain an eminent reservoir for T. b. rhodesiense in eastern Uganda, which must be addressed to sustain HAT elimination.

A spatial genetics approach to inform vector control of tsetse flies (Glossina fuscipes fuscipes) in Northern Uganda

Tsetse flies (genus Glossina) are the only vector for the parasitic trypanosomes responsible for sleeping sickness and nagana across sub-Saharan Africa. In Uganda, the tsetse fly Glossina fuscipes fuscipes is responsible for transmission of the parasite in 90% of sleeping sickness cases, and co-occurrence of both forms of human-infective trypanosomes makes vector control a priority. We use population genetic data from 38 samples from northern Uganda in a novel methodological pipeline that integrates genetic data, remotely sensed environmental data, and hundreds of field-survey observations. This methodological pipeline identifies isolated habitat by first identifying environmental parameters correlated with genetic differentiation, second, predicting spatial connectivity using field-survey observations and the most predictive environmental parameter(s), and third, overlaying the connectivity surface onto a habitat suitability map. Results from this pipeline indicated that net photosynthesis was the strongest predictor of genetic differentiation in G. f. fuscipes in northern Uganda. The resulting connectivity surface identified a large area of well-connected habitat in northwestern Uganda, and twenty-four isolated patches on the northeastern margin of the G. f. fuscipes distribution. We tested this novel methodological pipeline by completing an ad hoc sample and genetic screen of G. f. fuscipes samples from a model-predicted isolated patch, and evaluated whether the ad hoc sample was in fact as genetically isolated as predicted. Results indicated that genetic isolation of the ad hoc sample was as genetically isolated as predicted, with differentiation well above estimates made in samples from within well-connected habitat separated by similar geographic distances. This work has important practical implications for the control of tsetse and other disease vectors, because it provides a way to identify isolated populations where it will be safer and easier to implement vector control and that should be prioritized as study sites during the development and improvement of vector control methods.

Genetic diversity and population structure of the tsetse fly Glossina fuscipes fuscipes (Diptera: Glossinidae) in Northern Uganda: Implications for vector control

Uganda is the only country where the chronic and acute forms of human African Trypanosomiasis (HAT) or sleeping sickness both occur and are separated by < 100 km in areas north of Lake Kyoga. In Uganda, Glossina fuscipes fuscipes is the main vector of the Trypanosoma parasites responsible for these diseases as well for the animal African Trypanosomiasis (AAT), or Nagana. We used highly polymorphic microsatellite loci and a mitochondrial DNA (mtDNA) marker to provide fine scale spatial resolution of genetic structure of G. f. fuscipes from 42 sampling sites from the northern region of Uganda where a merger of the two disease belts is feared. Based on microsatellite analyses, we found that G. f. fuscipes in northern Uganda are structured into three distinct genetic clusters with varying degrees of interconnectivity among them. Based on genetic assignment and spatial location, we grouped the sampling sites into four genetic units corresponding to northwestern Uganda in the Albert Nile drainage, northeastern Uganda in the Lake Kyoga drainage, western Uganda in the Victoria Nile drainage, and a transition zone between the two northern genetic clusters characterized by high level of genetic admixture. An analysis using HYBRIDLAB supported a hybrid swarm model as most consistent with tsetse genotypes in these admixed samples. Results of mtDNA analyses revealed the presence of 30 haplotypes representing three main haplogroups, whose location broadly overlaps with the microsatellite defined clusters. Migration analyses based on microsatellites point to moderate migration among the northern units located in the Albert Nile, Achwa River, Okole River, and Lake Kyoga drainages, but not between the northern units and the Victoria Nile drainage in the west. Effective population size estimates were variable with low to moderate sizes in most populations and with evidence of recent population bottlenecks, especially in the northeast unit of the Lake Kyoga drainage. Our microsatellite and mtDNA based analyses indicate that G. f. fuscipes movement along the Achwa and Okole rivers may facilitate northwest expansion of the Rhodesiense disease belt in Uganda. We identified tsetse migration corridors and recommend a rolling carpet approach from south of Lake Kyoga northward to minimize disease dispersal and prevent vector re-colonization. Additionally, our findings highlight the need for continuing tsetse monitoring efforts during and after control.

Northern Uganda is an epidemiologically important region affected by human African trypanosomiasis (HAT) because it harbors both forms of the HAT disease (T. b. gambiense and T. b. rhodesiense). The geographic location of this region creates the risk that these distinct foci could merge, which would complicate diagnosis and treatment, and may result in recombination between the two parasite strains with as yet unknown consequences. Both strains require a tsetse fly vector for transmission, and in Uganda, G. f. fuscipes is the major vector of HAT. Controlling the vector remains one of the most effective strategies for controlling trypanosome parasites. However, vector control efforts may not be sustainable in terms of long term reduction in G. f. fuscipes populations due to population rebounds. Population genetics data can allow us to determine the likely source of population rebounds and to establish a more robust control strategy. In this study, we build on a previous broad spatial survey of G. f. fuscipes genetic structure in Uganda by adding more than 30 novel sampling sites that are strategically spaced across a region of northern Uganda that, for historical and political reasons, was severely understudied and faces particularly high disease risk. We identify natural population breaks, migration corridors and a hybrid zone with evidence of free interbreeding of G. f. fuscipes across the geographic region that spans the two HAT disease foci. We also find evidence of low effective population sizes and population bottlenecks in some areas that have been subjects of past control but remain regions of high tsetse density, which stresses the risk of population rebounds if monitoring is not explicitly incorporated into the control strategy. We use these results to make suggestions that will enhance the design and implementation of control activities in northern Uganda.

Evidence of temporal stability in allelic and mitochondrial haplotype diversity in populations of Glossina fuscipes fuscipes (Diptera: Glossinidae) in northern Uganda

BACKGROUND

Glossina fuscipes fuscipes is a tsetse species of high economic importance in Uganda where it is responsible for transmitting animal African trypanosomiasis (AAT) and both the chronic and acute forms of human African trypanosomiasis (HAT). We used genotype data from 17 microsatellites and a mitochondrial DNA marker to assess temporal changes in gene frequency for samples collected between the periods ranging from 2008 to 2014 in nine localities spanning regions known to harbor the two forms of HAT in northern Uganda.

RESULTS

Our findings suggest that the majority of the studied populations in both HAT foci are genetically stable across the time span sampled. Pairwise estimates of differentiation using standardized FST and Jost's DEST between time points sampled for each site were generally low and ranged between 0.0019 and 0.1312 for both sets of indices. We observed the highest values of FST and DEST between time points sampled from Kitgum (KT), Karuma (KR), Moyo (MY) and Pader (PD), and the possible reasons for this are discussed. Effective population size (Ne) estimates using Waple's temporal method ranged from 103 (95% CI: 73-138) in Kitgum to 962 (95% CI: 669-1309) in Oculoi (OC). Additionally, evidence of a bottleneck event was detected in only one population at one time point sampled; Aminakwach (AM-27) from December 2014 (P < 0.03889).

CONCLUSION

Findings suggest general temporal stability of tsetse vectors in foci of both forms of HAT in northern Uganda. Genetic stability and the moderate effective population sizes imply that a re-emergence of vectors from local residual populations missed by control efforts is an important risk. This underscores the need for more sensitive sampling and monitoring to detect residual populations following control activities.

Clinical profiles, disease outcome and co-morbidities among T. b. rhodesiense sleeping sickness patients in Uganda

BACKGROUND

The acute form of Human African Trypanosomiasis (HAT, also known as Sleeping sickness) caused by Trypanosoma brucei rhodesiense has been shown to have a wide spectrum of focus specific clinical presentation and severity in East and Southern Africa. Indeed HAT occurs in regions endemic for other tropical diseases, however data on how these co-morbidities might complicate the clinical picture and affect disease outcome remains largely scanty. We here describe the clinical presentation, presence of co-infections, and how the latter impact on HAT prognosis.

METHODS AND FINDINGS

We carried out a retrospective analysis of clinical data from 258 sleeping sickness patients reporting to Lwala hospital between 2005 and 2012. The mean patient age was 28.6 years with a significant number of cases below 18 years (p< 0.0001). About 93.4% of the cases were diagnosed as late stage (p< 0.0001). The case fatality rate was 10.5% with post treatment reactive encephalopathys reported in 7.9% of the cases, of whom 36.8% eventually died. Fever was significantly (p = 0.045) higher in patients under 18 years. Of the early stage patients, 26.7% and 6.7% presented with late stage signs of sleep disorder and mental confusion respectively. Among the co-infections, malaria was significantly more prevalent (28.9%; p< 0.0001) followed by urinary tract infections (4.2%). Co-infections were present in 14.3% of in-hospital deaths, 38.5% of which were recorded as Malaria. Malaria was significantly more common in patients under 18 years (45.5%; p< 0.02), and was reported in 60% of the fatal cases in this age group.

CONCLUSIONS

We show a wide spectrum of sleeping sickness clinical presentation and disease outcome that was apparently not significantly influenced by concurrent infections. It would thus be interesting to determine the host and/or parasite factors that might be responsible for the observed diverse clinical presentation.

Quantifying the association between bovine and human trypanosomiasis in newly affected sleeping sickness areas of Uganda

BACKGROUND

Uganda has active foci of both chronic and acute HAT with the acute zoonotic form of disease classically considered to be restricted to southeast Uganda, while the focus of the chronic form of HAT was confined to the northwest of the country. Acute HAT has however been migrating from its traditional disease focus, spreading rapidly to new districts, a spread linked to movement of infected cattle following restocking. Cattle act as long-term reservoirs of human infective T. b. rhodesiense showing few signs of morbidity, yet posing a significant risk to human health. It is important to understand the relationship between infected cattle and infected individuals so that an appropriate response can be made to the risk posed to the community from animals infected with human pathogens in a village setting.

METHODOLOGY/PRINCIPAL FINDINGS

This paper examines the relationship between human T. b. rhodesiense infection and human infective and non-human T. brucei s.l. circulating in cattle at village level in Kaberamaido and Dokolo Districts, Uganda. The study was undertaken in villages that had reported a case of sleeping sickness in the six months prior to sample collection and those villages that had never reported a case of sleeping sickness.

CONCLUSIONS AND SIGNIFICANCE

The sleeping sickness status of the villages had a significant effect with higher odds of infection in cattle from case than from non-case villages for T. brucei s.l. (OR: 2.94, 95%CI: 1.38-6.24). Cattle age had a significant effect (p<0.001) on the likelihood of T. brucei s.l. infection within cattle: cattle between 18-36 months (OR: 3.51, 95%CI: 1.63-7.51) and cattle over 36 months (OR: 4.20, 95%CI: 2.08-8.67) had significantly higher odds of T. brucei s. l. infection than cattle under 18 months of age. Furthermore, village human sleeping sickness status had a significant effect (p<0.05) on the detection of T. b. rhodesiense in the village cattle herd, with significantly higher likelihood of T. b. rhodesiense in the village cattle of case villages (OR: 25, 95%CI: 1.2-520.71). Overall a higher than average T. brucei s.l. prevalence (>16.3%) in a village herd over was associated with significantly higher likelihood of T. b. rhodesiense being detected in a herd (OR: 25, 95%CI: 1.2-520.71).

Outcome of acute East African trypanosomiasis in a Polish traveller treated with pentamidine

Background

African trypanosomiasis is a parasitic infection sporadically imported to Europe by tourists or immigrants returning from endemic areas. We present the first and an unusual case of East African trypanosomiasis imported to Poland by a patient returning from a tourist trip to Uganda and Rwanda, which was successfully treated with pentamidine.

Case presentation

A 61-year-old Polish man was admitted to the Department because of high-grade fever and multi-organ dysfunction after a tourist trip to East Africa. He experienced a single tsetse fly bite during a safari trip to the Queen Elizabeth National Park in Uganda. On admission, his clinical status was severe, with high fever of 41ºC, preceded by chills, bleeding from the gums and oral mucosa, haemorrhages at the sites of venipuncture, numerous ecchymoses, fine-spotted skin rash, tachycardia, hepatosplenomegaly, dehydration, jaundice, dyspnoea, hypoxaemia, generalised oedema and oliguria. There was a typical non-painful trypanosomal chancre with central necrosis and peripheral erythema on his left arm. Laboratory investigations showed leucopenia, thrombocytopenia, haemolytic anaemia, hyperbilirubinaemia, hypoglycaemia, elevated creatinine and urea, high activity of aminotransferases, elevated levels of inflammatory markers, hypoproteinaemia, proteinuria, abnormal clotting and bleeding times, low fibrinogen level, metabolic acidosis, and electrolyte disturbances. A peripheral blood smear showed numerous Trypanosoma brucei trypomastigotes with a massive parasitaemia of 100,000/μl. T. brucei rhodesiense subspecies was finally identified on the basis of the characteristic serum resistance-associated gene using a polymerase chain reaction, and a seroconversion of specific immunoglobulin M and G antibodies in the peripheral blood by enzyme-linked immunosorbent assay. Serological tests for T. brucei gambiense subspecies were negative. A severe clinical course of acute rhodesiense trypanosomiasis with renal failure, respiratory distress, disseminated intravascular coagulation syndrome, haemolysis, liver insufficiency and myocarditis was confirmed. Intensive anti-parasitic and symptomatic treatment was immediately instituted, including intravenous pentamidine, plasmaphereses, oxygen therapy, blood transfusion, catecholamine administration, and fluid infusions, as well as haemostatic, hepatoprotective, anti-inflammatory, antipyretic and diuretic drugs. The final outcome was a full recovery with no late sequelae.

Conclusion

Sleeping sickness should always be considered in the differential diagnosis of fever in people returning from safari trips to the national parks or nature reserves of sub-Saharan Africa.

DNA vaccines against tropical parasitic diseases

Parasitic diseases caused by protozoan and helminth parasites are among the leading causes of morbidity and mortality in tropical and subtropical regions of the world. Unfortunately, at present, there is no vaccine against any human parasitic disease. Conventional vaccine methods have largely failed against parasitic infections. This is due, in part, to the complexity of the parasite life cycle, the ability of the parasite to evade the immune system, and difficulties in identifying and eliciting the desired protective immune responses. The discovery of DNA vaccines has renewed hope for vaccine development against parasites. In the last decade, DNA vaccines were successful in inducing at least partial protection against several parasitic diseases. This review discusses the latest developments in DNA vaccines against tropical parasitic diseases.

Potential risk of regional disease spread in West Africa through cross-border cattle trade

BACKGROUND

Transboundary animal movements facilitate the spread of pathogens across large distances. Cross-border cattle trade is of economic and cultural importance in West Africa. This study explores the potential disease risk resulting from large-scale, cross-border cattle trade between Togo, Burkina Faso, Ghana, Benin, and Nigeria for the first time.

METHODS AND PRINCIPAL FINDINGS

A questionnaire-based survey of livestock movements of 226 cattle traders was conducted in the 9 biggest cattle markets of northern Togo in February-March 2012. More than half of the traders (53.5%) operated in at least one other country. Animal flows were stochastically simulated based on reported movements and the risk of regional disease spread assessed. More than three quarters (79.2%, range: 78.1-80.0%) of cattle flowing into the market system originated from other countries. Through the cattle market system of northern Togo, non-neighbouring countries were connected via potential routes for disease spread. Even for diseases with low transmissibility and low prevalence in a given country, there was a high risk of disease introduction into other countries.

CONCLUSIONS

By stochastically simulating data collected by interviewing cattle traders in northern Togo, this study identifies potential risks for regional disease spread in West Africa through cross-border cattle trade. The findings highlight that surveillance for emerging infectious diseases as well as control activities targeting endemic diseases in West Africa are likely to be ineffective if only conducted at a national level. A regional approach to disease surveillance, prevention and control is essential.

Polyandry is a common event in wild populations of the Tsetse fly Glossina fuscipes fuscipes and may impact population reduction measures

BACKGROUND

Glossina fuscipes fuscipes is the main vector of human and animal trypanosomiasis in Africa, particularly in Uganda. Attempts to control/eradicate this species using biological methods require knowledge of its reproductive biology. An important aspect is the number of times a female mates in the wild as this influences the effective population size and may constitute a critical factor in determining the success of control methods. To date, polyandry in G.f. fuscipes has not been investigated in the laboratory or in the wild. Interest in assessing the presence of remating in Ugandan populations is driven by the fact that eradication of this species is at the planning stage in this country.

METHODOLOGY/PRINCIPAL FINDINGS

Two well established populations, Kabukanga in the West and Buvuma Island in Lake Victoria, were sampled to assess the presence and frequency of female remating. Six informative microsatellite loci were used to estimate the number of matings per female by genotyping sperm preserved in the female spermathecae. The direct count of the minimum number of males that transferred sperm to the spermathecae was compared to Maximum Likelihood and Bayesian probability estimates. The three estimates provided evidence that remating is common in the populations but the frequency is substantially different: 57% in Kabukanga and 33% in Buvuma.

CONCLUSIONS/SIGNIFICANCE

The presence of remating, with females maintaining sperm from different mates, may constitute a critical factor in cases of re-infestation of cleared areas and/or of residual populations. Remating may enhance the reproductive potential of re-invading propagules in terms of their effective population size. We suggest that population age structure may influence remating frequency. Considering the seasonal demographic changes that this fly undergoes during the dry and wet seasons, control programmes based on SIT should release large numbers of sterile males, even in residual surviving target populations, in the dry season.

Importance of nonenteric protozoan infections in immunocompromised people

There are many neglected nonenteric protozoa able to cause serious morbidity and mortality in humans, particularly in the developing world. Diseases caused by certain protozoa are often more severe in the presence of HIV. While information regarding neglected tropical diseases caused by trypanosomatids and Plasmodium is abundant, these protozoa are often not a first consideration in Western countries where they are not endemic. As such, diagnostics may not be available in these regions. Due to global travel and immigration, this has become an increasing problem. Inversely, in certain parts of the world (particularly sub-Saharan Africa), the HIV problem is so severe that diseases like microsporidiosis and toxoplasmosis are common. In Western countries, due to the availability of highly active antiretroviral therapy (HAART), these diseases are infrequently encountered. While free-living amoebae are rarely encountered in a clinical setting, when infections do occur, they are often fatal. Rapid diagnosis and treatment are essential to the survival of patients infected with these organisms. This paper reviews information on the diagnosis and treatment of nonenteric protozoal diseases in immunocompromised people, with a focus on patients infected with HIV. The nonenteric microsporidia, some trypanosomatids, Toxoplasma spp., Neospora spp., some free-living amoebae, Plasmodium spp., and Babesia spp. are discussed.

A geographical approach to identify sleeping sickness risk factors in a mangrove ecosystem

OBJECTIVES

To provide a better understanding of sleeping sickness transmission and spread in mangrove areas to optimize its control.

METHODS

In the Forecariah mangrove area, Guinea, 19 sleeping sickness cases and 19 matched controls were followed up in their living areas (at home, in fields and at water points). All occupational sites and pathways were mapped and then placed in their environmental context.

RESULTS

The sleeping sickness cases displayed a significantly broader and more diverse spatial occupation than the controls. They covered double the daily walking distances of controls and had on average two more occupational sites, most of which were located in mangrove forests. Activities with a higher transmission risk (rice culture, attendance of pirogue jetties) were identified as well as high-risk areas and pathways.

CONCLUSIONS

An entomological control strategy targeting transmission risk areas is proposed. Its implementation in a control programme would reduce by 86% the efforts needed for a classical vector control programme throughout the area. Medical surveys set up at specific locations, such as pirogue jetties and high-risk paths, should also enable better targeting of the population at highest risk.

Sleeping sickness in Uganda: revisiting current and historical distributions

BACKGROUND

Sleeping sickness is a parasitic, vector-borne disease, carried by the tsetse fly and prevalent in sub-Saharan Africa. The disease continues to pose a public health burden in Uganda, which experienced a widespread outbreak in 1900-1920, and a more recent outbreak in 1976-1989. The disease continues to spread to uninfected districts.

OBJECTIVES

This paper compares the spatial distributions of sleeping in Uganda for the 1900-1920 outbreak period with current disease foci, and discusses information gaps and implications arising for future research, prevention and control.

METHODS

Population census records for 1911 and sleeping sickness records from Medical and Sanitary Reports of the Ugandan Protectorate for 1905-1936 were extracted from the Uganda Archives. Current sleeping sickness distribution data were provided by the Ministry of Health, Uganda. These were used to develop sleeping sickness distribution maps for comparison between the early 1900s and the early 2000s.

RESULTS

The distribution of sleeping sickness from 1905-1920 shows notable differences compared to the current distribution of disease. In particular, archival cases were recorded in south-west and central Uganda, areas currently free of disease. The disease focus has moved from lakeshore Buganda (1905-1920) to the Busoga and south-east districts.

CONCLUSIONS

Archival sleeping sickness distributions indicate the potential for a much wider area of disease risk than indicated by current disease foci. This is compounded by an absence of tsetse distribution data, continued political instability in north-central Uganda, continued spread of disease into new districts, and evidence of the role of livestock movements in spreading the parasite. These results support concerns as to the potential mergence of the two disease foci in the south-east and north-west of the country.

High levels of genetic differentiation between Ugandan Glossina fuscipes fuscipes populations separated by Lake Kyoga

Background

Glossina fuscipes fuscipes is the major vector of human African trypanosomiasis, commonly referred to as sleeping sickness, in Uganda. In western and eastern Africa, the disease has distinct clinical manifestations and is caused by two different parasites: Trypanosoma brucei rhodesiense and T. b. gambiense. Uganda is exceptional in that it harbors both parasites, which are separated by a narrow 160-km belt. This separation is puzzling considering there are no restrictions on the movement of people and animals across this region.

Methodology and Results

We investigated whether genetic heterogeneity of G. f. fuscipes vector populations can provide an explanation for this disjunct distribution of the Trypanosoma parasites. Therefore, we examined genetic structuring of G. f. fuscipes populations across Uganda using newly developed microsatellite markers, as well as mtDNA. Our data show that G. f. fuscipes populations are highly structured, with two clearly defined clusters that are separated by Lake Kyoga, located in central Uganda. Interestingly, we did not find a correlation between genetic heterogeneity and the type of Trypanosoma parasite transmitted.

Conclusions

The lack of a correlation between genetic structuring of G. f. fuscipes populations and the distribution of T. b. gambiense and T. b. rhodesiense indicates that it is unlikely that genetic heterogeneity of G. f. fuscipes populations explains the disjunct distribution of the parasites. These results have important epidemiological implications, suggesting that a fusion of the two disease distributions is unlikely to be prevented by an incompatibility between vector populations and parasite.

The two types of sleeping sickness in West and East Africa are markedly distinct, require different treatments, and are caused by different parasites. The only country where both parasites are present is Uganda, where they are separated by a narrow 160 km disease-free belt. Because there is no restriction on the movement of humans and animals between the two disease zones, this separation is puzzling. We asked whether this disjunct distribution can be explained by variation within the tsetse fly that is largely responsible for transmitting both diseases in Uganda, Glossina fuscipes fuscipes. We therefore examined whether this tsetse subspecies is genetically uniform across Uganda. Our results indicate that G. f. fusicipes is not genetically different between the two disease zones, but there are clear genetic differences between northern and southern populations, which are separated by Lake Kyoga. Therefore, it is unlikely that variation in the tsetse fly determines the distribution of the two parasites. This implies that the two diseases may fuse in the near future, which would greatly complicate diagnosis and treatment of sleeping sickness in any potential area of overlap.

Surveillance of arthropod vector-borne infectious diseases using remote sensing techniques: a review

Epidemiologists are adopting new remote sensing techniques to study a variety of vector-borne diseases. Associations between satellite-derived environmental variables such as temperature, humidity, and land cover type and vector density are used to identify and characterize vector habitats. The convergence of factors such as the availability of multi-temporal satellite data and georeferenced epidemiological data, collaboration between remote sensing scientists and biologists, and the availability of sophisticated, statistical geographic information system and image processing algorithms in a desktop environment creates a fertile research environment. The use of remote sensing techniques to map vector-borne diseases has evolved significantly over the past 25 years. In this paper, we review the status of remote sensing studies of arthropod vector-borne diseases due to mosquitoes, ticks, blackflies, tsetse flies, and sandflies, which are responsible for the majority of vector-borne diseases in the world. Examples of simple image classification techniques that associate land use and land cover types with vector habitats, as well as complex statistical models that link satellite-derived multi-temporal meteorological observations with vector biology and abundance, are discussed here. Future improvements in remote sensing applications in epidemiology are also discussed.

Civil conflict and sleeping sickness in Africa in general and Uganda in particular

Conflict and war have long been recognized as determinants of infectious disease risk. Re-emergence of epidemic sleeping sickness in sub-Saharan Africa since the 1970s has coincided with extensive civil conflict in affected regions. Sleeping sickness incidence has placed increasing pressure on the health resources of countries already burdened by malaria, HIV/AIDS, and tuberculosis. In areas of Sudan, the Democratic Republic of the Congo, and Angola, sleeping sickness occurs in epidemic proportions, and is the first or second greatest cause of mortality in some areas, ahead of HIV/AIDS. In Uganda, there is evidence of increasing spread and establishment of new foci in central districts. Conflict is an important determinant of sleeping sickness outbreaks, and has contributed to disease resurgence. This paper presents a review and characterization of the processes by which conflict has contributed to the occurrence of sleeping sickness in Africa. Conflict contributes to disease risk by affecting the transmission potential of sleeping sickness via economic impacts, degradation of health systems and services, internal displacement of populations, regional insecurity, and reduced access for humanitarian support. Particular focus is given to the case of sleeping sickness in south-eastern Uganda, where incidence increase is expected to continue. Disease intervention is constrained in regions with high insecurity; in these areas, political stabilization, localized deployment of health resources, increased administrative integration and national capacity are required to mitigate incidence. Conflict-related variables should be explicitly integrated into risk mapping and prioritization of targeted sleeping sickness research and mitigation initiatives.

Experimental therapy of African trypanosomiasis with a nanobody-conjugated human trypanolytic factor

High systemic drug toxicity and increasing prevalence of drug resistance hampers efficient treatment of human African trypanosomiasis (HAT). Hence, development of new highly specific trypanocidal drugs is necessary. Normal human serum (NHS) contains apolipoprotein L-I (apoL-I), which lyses African trypanosomes except resistant forms such as Trypanosoma brucei rhodesiense. T. b. rhodesiense expresses the apoL-I-neutralizing serum resistance-associated (SRA) protein, endowing this parasite with the ability to infect humans and cause HAT. A truncated apoL-I (Tr-apoL-I) has been engineered by deleting its SRA-interacting domain, which makes it lytic for T. b. rhodesiense. Here, we conjugated Tr-apoL-I with a single-domain antibody (nanobody) that efficiently targets conserved cryptic epitopes of the variant surface glycoprotein (VSG) of trypanosomes to generate a new manmade type of immunotoxin with potential for trypanosomiasis therapy. Treatment with this engineered conjugate resulted in clear curative and alleviating effects on acute and chronic infections of mice with both NHS-resistant and NHS-sensitive trypanosomes.

Sleeping sickness in Uganda: a thin line between two fatal diseases

OBJECTIVE

To determine, through the use of molecular diagnostic tools, whether the two species of parasite that cause human African trypanosomiasis have become sympatric.

DESIGN

Blood sampling of all available patients between June 2001 and June 2005 in central Uganda and between July and September 2003 in northwest Uganda and analysis of subcounty sleeping sickness records in Uganda between 1985 and 2005.

SETTING

Sleeping sickness treatment centres in central and northwest Uganda and in south Sudan.

PARTICIPANTS

Patients presenting at the treatment centres and diagnosed as having sleeping sickness.

MAIN OUTCOME MEASURE

Classification of parasites from patients from each disease focus as either Trypanosoma brucei rhodesiense (acute form) or T b gambiense (chronic form).

RESULTS

Blood from 231 patients with sleeping sickness in central Uganda and from 91 patients with sleeping sickness in northwest Uganda and south Sudan were screened for T b rhodesiense (detection of SRA gene) and T b gambiense (detection of TgsGP gene). All samples from central Uganda were classified as T b rhodesiense, and all samples from northwest Uganda and south Sudan were identified as T b gambiense.

CONCLUSIONS

The two focuses of human African trypanosomiasis remain discrete, but the area of Uganda affected by the acute form of human sleeping sickness has increased 2.5-fold since 1985, spreading to three new districts within the past five years through movement of infected livestock. Without preventive action targeted at the livestock reservoir of this zoonotic disease, it is likely that the two disease focuses will converge. This will have a major impact on diagnosis and treatment of this neglected disease. Real time monitoring is recommended, using molecular diagnostic tools (at a regional surveillance centre, for example) targeted at both livestock and human patients.

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.

A burgeoning epidemic of sleeping sickness in Uganda

The epidemic of Trypanosoma brucei rhodesiense sleeping sickness in eastern Uganda, which began in 1998 as a result of movements of the livestock reservoir of the parasite, has continued to spread. An additional 133 000 people have been put at risk of infection in Kaberamaido, another newly affected district. The few resources committed to control interventions in Soroti district have failed to contain the epidemic. The high prevalence of the parasite in cattle presents a significant risk for transmission to human beings and further spread of this neglected zoonotic disease. Targeted interventions are urgently needed to control epidemics and reduce the high mortality resulting from sleeping sickness.

African trypanosomiasis: Changing epidemiology and consequences

Human African trypanosomiasis has re-emerged as a serious public health threat after near-elimination because of diminished investment in previously successful control programs. The continued, occasional importation of African trypanosomiasis to the United States can be expected as tourists and immigrants travel from high-risk areas. No vaccine or chemoprophylaxis is available for this disease, and travelers to affected areas should be counseled on tsetse fly avoidance. New diagnostic and staging tests are promising but have not replaced the classical method of examining body fluids for trypanosomes. Prompt diagnosis and staging is essential because if untreated, East African and West African sleeping sickness are fatal. Drug regimens are toxic and cumbersome, and short-term prospects for therapeutic advances are limited.

Options for field diagnosis of human african trypanosomiasis

Human African trypanosomiasis (HAT) due to Trypanosoma brucei gambiense or T. b. rhodesiense remains highly prevalent in several rural areas of sub-Saharan Africa and is lethal if left untreated. Therefore, accurate tools are absolutely required for field diagnosis. For T. b. gambiense HAT, highly sensitive tests are available for serological screening but the sensitivity of parasitological confirmatory tests remains insufficient and needs to be improved. Screening for T. b. rhodesiense infection still relies on clinical features in the absence of serological tests available for field use. Ongoing research is opening perspectives for a new generation of field diagnostics. Also essential for both forms of HAT is accurate determination of the disease stage because of the high toxicity of melarsoprol, the drug most widely used during the neurological stage of the illness. Recent studies have confirmed the high accuracy of raised immunoglobulin M levels in the cerebrospinal fluid for the staging of T. b. gambiense HAT, and a promising simple assay (LATEX/IgM) is being tested in the field. Apart from the urgent need for better tools for the field diagnosis of this neglected disease, improved access to diagnosis and treatment for the population at risk remains the greatest challenge for the coming years.

Candidate protein selection for diagnostic markers of African trypanosomiasis

The ability to accurately diagnose the presence of an infective micro-organism is not only important for individual human and animal health and wellbeing, but is also central to surveillance programmes. Effective and sustainable control of many diseases in the developing world depends on the availability of field applicable diagnostics that are cheap, reliable, simple in design and application, and which provide immediate results. This review examines how the genome sequences can be used in the selection of potential candidate proteins for developing new serodiagnostics for African trypanosomiasis.

Emerging parasitic infections

Parasitic infections are felt by most individuals to have little impact on the health and well being of most inhabitants of Canada, Western Europe, and the United States. As the authors show in this article, parasites are always "emerging" somewhere and have a significant impact on those areas of the world. Moreover, as we are becoming an ever-smaller global village, catastrophes and instability in the Third World affect control of parasitic diseases endemic to those areas, ensuring greater chances of transmission to visitors there. The foundation of successful limitation of parasitic diseases in both developing and developed regions is still accurate and rapid diagnosis.

Bovine trypanosomiasis in south-western Uganda: packed-cell volumes and prevalences of infection in the cattle

Following confirmed cases of trypanosomiasis ('nagana') and reports of trypanosome-attributable deaths among local cattle, a cross-sectional study was undertaken to determine the prevalence of bovine infection with trypanosomes in south-western Uganda. Cattle from 10 different localities were checked by the microscopical examination of wet bloodsmears and thin, stained bloodsmears, and by blood centrifugation followed by the examination of the resultant buffy coats. Of the 1309 cattle investigated, 6.42% (5.56% and 7.26% of those from the Mbarara and Mubende districts, respectively) were found to be infected. Of the positive animals, 71 (84.5%), 11 (13.1%) and two (2.4%) appeared to be infected with Trypanosoma vivax only, T. congolense only and both T. vivax and T. congolense, respectively. The prevalence of infection with T. vivax was significantly higher than that with T. congolense (P<0.001). The mean packed-cell volumes (PCV) for the trypanosome-positive animals were lower than those for the trypanosome-negative, whether the cattle considered were all those investigated (22.3% v. 29.0%; P<0.001) or just those from the Mbarara (22.8% v. 28.2%) or Mubende (21.5% v. 29.7%) districts. South-western Uganda has been relatively free of both human and bovine trypanosomiasis for the past three decades. The factors leading to the current resurgence of bovine trypanosomiasis need further investigation.

Trypanosome microtubule-associated protein p15 as a vaccine for the prevention of African sleeping sickness

Trypanosomes cause African sleeping sickness, affecting millions of humans and animals. We tested trypanosome microtubule-associate protein (MAP p15) as a vaccine in mice, and show that p15 (native or recombinant) generated up to 100% protection from an otherwise lethal challenge of a heterologous strain of Trypanosoma brucei. We also tested the adenovirus as a vaccine delivery system and show that both adenoviral vector containing p15 gene or control adenovirus containing lacZ gene generated a protective response and exhibited strong CD8+ T-cell proliferation. These results suggest that the p15 protein itself is an effective vaccine and that the adenovirus may be used to mount a non-specific cellular immune response.