Fly Belt Research Articles

In vitro trypanocidal potency and in vivo treatment efficacy of oligomeric ethylene glycol-tethered nitrofurantoin derivatives

African trypanosomiasis is a significant vector-borne disease of humans and animals in the tsetse fly belt of Africa, particularly affecting production animals such as cattle, and thus, hindering food security. Trypanosoma congolense (T. congolense), the causative agent of nagana, is livestock's most virulent trypanosome species. There is currently no vaccine against trypanosomiasis; its treatment relies solely on chemotherapy. However, pathogenic resistance has been established against trypanocidal agents in clinical use. This underscores the need to develop new therapeutics to curb trypanosomiasis. Many nitroheterocyclic drugs or compounds, including nitrofurantoin, possess antiparasitic activities in addition to their clinical use as antibiotics. The current study evaluated the in vitro trypanocidal potency and in vivo treatment efficacy of previously synthesized antileishmanial active oligomeric ethylene glycol derivatives of nitrofurantoin. The trypanocidal potency of analogues 2a-o varied among the trypanosome species; however, T. congolense strain IL3000 was more susceptible to these drug candidates than the other human and animal trypanosomes. The arylated analogues 2k (IC50 0.04 µM; SI >6365) and 2l (IC50 0.06 µM; SI 4133) featuring 4-chlorophenoxy and 4-nitrophenoxy moieties, respectively, were revealed as the most promising antitrypanosomal agents of all analogues against T. congolense strain IL3000 trypomastigotes with nanomolar activities. In a preliminary in vivo study involving T. congolense strain IL3000 infected BALB/c mice, the oral administration of 100 mg/kg/day of 2k caused prolonged survival up to 18 days post-infection relative to the infected but untreated control mice which survived 9 days post-infection. However, no cure was achieved due to its poor solubility in the in vivo testing medium, assumably leading to low oral bioavailability. These results confirm the importance of the physicochemical properties lipophilicity and water solubility in attaining not only in vitro trypanocidal potency but also in vivo treatment efficacy. Future work will focus on the chemical optimization of 2k through the investigation of analogues containing solubilizing groups at certain positions on the core structure to improve solubility in the in vivo testing medium which, in the current investigation, is the biggest stumbling block in successfully treating either animal or human Trypanosoma infections.

In Vitro and In Vivo Trypanocidal Efficacy of Nitrofuryl- and Nitrothienylazines.

African trypanosomiasis is a vector-borne disease of animals and humans in the tsetse fly belt of Africa. Trypanosoma congolense ("nagana") is the most pathogenic trypanosome in livestock and causes high morbidity and mortality rates among cattle. In the absence of effective preventative vaccines, the management of trypanosomiasis relies on chemoprophylaxis and/or -therapy. However, the trypanocides in clinical use exhibit poor oral bioavailability and toxicity, and therapeutic failures occur because of resistant strains. Because nitrofurantoin displayed, in addition to its clinical use, promising antiparasitic activity, the current study was conducted to evaluate the in vitro trypanocidal activity and preliminary in vivo treatment efficacy of previously synthesized nitrofuranylazines. The trypanocidal activity of these nitrofuran derivatives varied among the evaluated trypanosome species; however, T. congolense strain IL3000 was more susceptible than other animal and human trypanosomes. The nitrofurylazines 4a (IC50 0.04 μM; SI > 7761) and 7a (IC50 0.03 μM; SI > 9542) as well as the nitrothienylazine 8b (IC50 0.04 μM; SI 232), with nanomolar IC50 values, were revealed as early antitrypanosomal leads. Although these derivatives showed strong trypanocidal activity in vitro, no in vivo treatment efficacy was observed in T. congolense IL3000 infected mice after both oral and intraperitoneal administration in a preliminary study. This was attributed to the poor solubility of the test compounds in the in vivo testing media. Indeed, a challenge in drug discovery is finding a balance between the physicochemical properties of a drug candidate, particularly lipophilicity and water solubility, and maintaining adequate potency to provide an effective dose. Hence, future chemical modifications may be required to generate lead-like to lead-like nitrofuranylazines that possess optimal physicochemical and pharmacokinetic properties while retaining in vitro and, ultimately, in vivo trypanocidal efficacy.

Molecular characterization of pathogenic African trypanosomes in biting flies and camels in surra-endemic areas outside the tsetse fly belt in Kenya

African animal trypanosomosis (nagana) is becoming prevalent beyond its traditionally defined geographical boundaries in African tsetse belts. However, knowledge of clinically important trypanosomes and infection rate in non-tsetse hematophagous flies and domestic animals are limited. This study characterized the potential mechanical vectors, their host feeding patterns, and trypanosome infection in them and domestic animals outside the tsetse belt in northern Kenya. Field-trapped flies and blood from camels, cattle, donkeys, goats, and sheep were screened for trypanosome infection by microscopy and polymerase chain reaction (PCR) of the internal transcribed spacer 1 region. Blood-fed specimens were analysed using PCR-HRM and/or sequencing of 16S rRNA gene to identify vertebrate blood-meal host sources. Hippobosca camelina, Stomoxys calcitrans, Tabanus spp., and Pangonia rueppellii were identified as potential vectors of trypanosomes outside the tsetse belt in Marsabit County. The trypanosome species, Trypanosoma vivax, T. evansi, T. brucei, and T. congolense were recovered in biting flies as well as in camels (Camelus dromedarius). The diversity of parasites in the biting flies was similar to that detected in the tsetse fly Glossina pallidipes collected from the tsetse-infested Shimba Hills, in coastal Kenya, suggesting a wide geographic distribution of the trypanosomes in Kenya. The biting flies fed on camels, cattle, goats, and sheep. Furthermore, we identified diverse clinical outcomes based on PCV (anemia), heamorrhagia) associated with infection with disparate Trypanosoma species. Thus, infection of flies and camels by diverse Trypanosoma species could contribute to the complex epidemiology of observed trypanosomosis in camels.

Basic Biology of Trypanosoma brucei with Reference to the Development of Chemotherapies.

Trypanosoma brucei are protozoan parasites that cause the lethal human disease African sleeping sickness and the economically devastating disease of cattle, Nagana. African sleeping sickness, also known as Human African Trypanosomiasis (HAT), threatens 65 million people and animal trypanosomiasis makes large areas of farmland unusable. There is no vaccine and licensed therapies against the most severe, late-stage disease are toxic, impractical and ineffective. Trypanosomes are transmitted by tsetse flies, and HAT is therefore predominantly confined to the tsetse fly belt in sub-Saharan Africa. They are exclusively extracellular and they differentiate between at least seven developmental forms that are highly adapted to host and vector niches. In the mammalian (human) host they inhabit the blood, cerebrospinal fluid (late-stage disease), skin, and adipose fat. In the tsetse fly vector they travel from the tsetse midgut to the salivary glands via the ectoperitrophic space and proventriculus. Trypanosomes are evolutionarily divergent compared with most branches of eukaryotic life. Perhaps most famous for their extraordinary mechanisms of monoallelic gene expression and antigenic variation, they have also been investigated because much of their biology is either highly unconventional or extreme. Moreover, in addition to their importance as pathogens, many researchers have been attracted to the field because trypanosomes have some of the most advanced molecular genetic tools and database resources of any model system. The following will cover just some aspects of trypanosome biology and how its divergent biochemistry has been leveraged to develop drugs to treat African sleeping sickness. This is by no means intended to be a comprehensive survey of trypanosome features. Rather, I hope to present trypanosomes as one of the most fascinating and tractable systems to do discovery biology.

Effects of Human Settlements and Spatial Distribution of Wing Vein Length, Wing Fray Categories and Hunger Stages in Glossina morsitans morsitans (Diptera: Glossinidae) and Glossina pallidipes (Diptera: Glossinidae) in Areas Devoid of Cattle in North-Eastern Zambia.

The effect of human-associated habitat degradation on tsetse populations is well established. However, more insights are needed into how gradual human encroachment into tsetse fly belts affect tsetse populations. This study investigated how wing vein length, wing fray categories, and hunger stages, taken as indicators of body size, age, and levels of access to hosts, respectively, in Glossina morsitans morsitans Westwood (Diptera: Glossinidae) and Glossina pallidipes Austen (Diptera: Glossinidae), varied along a transect from the edge into inner parts of the tsetse belt, in sites that had human settlement either concentrated at the edge of belt or evenly distributed along transect line, in north-eastern Zambia. Black-screen fly round and Epsilon traps were used in a cross-sectional survey on tsetse flies at three sites, following a transect line marked by a road running from the edge into the inner parts of the tsetse belt, per site. Two sites had human settlement concentrated at or close to the edge of the tsetse belt, whereas the third had human settlement evenly distributed along the transect line. Where settlements were concentrated at the edge of tsetse belt, increase in distance from the settlements was associated with increase in wing vein length and a reduction in the proportion of older, and hungry, tsetse flies. Increase in distance from human settlements was associated with improved tsetse well-being, likely due to increase in habitat quality due to decrease in effects of human activities.

Blood of African Hedgehog Atelerix albiventris Contains 115-kDa Trypanolytic Protein that Kills Trypanosoma congolense.

Protozoan parasites of the Order Trypanosomatida infect a wide range of multicellular plants and animals, causing devastating and potentially fatal diseases. Trypanosomes are the most relevant members of the order in sub-Saharan Africa because of mortalities and morbidities caused to humans and livestock. There are growing concerns that trypanosomes are expanding their reservoirs among wild animals, which habours the parasites, withstand the infection, and from which tsetse flies transmit the parasites back to humans and livestock. This study was designed to investigate the potentials of the African hedgehog serving as reservoir for African animal trypanosomes. Five adult hedgehogs alongside five laboratory mice were intraperitoneally inoculated with 106 and 104 of Trypanosoma congolense cells, respectively, and monitored for parasitemia and survival. Serum from twenty hedgehogs was subjected to trypanocidal activity-guided fractionation by successive ion-exchange and gel-filtration chromatographies, followed by characterization with Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE). Hedgehogs were resistant to the infection as no parasite was detected and none died even after 60days, while all the mice died within 12days. Both the serum and plasma prepared from hedgehogs demonstrated trypanocidal activity- rapidly killed trypanosomes even when diluted 1000 times. The trypanolytic factor was identified to be proteinaceous with an estimated molecular weight of 115-kDa. For the first time, it is here demonstrated that hedgehog blood has significant trypanolytic activity against T. congolense. The potential application of the hedgehog protein for the breeding of trypanosomosis-resistant livestock in tsetse fly belt is discussed.

Phylogeography and population structure of the tsetse fly Glossina pallidipes in Kenya and the Serengeti ecosystem.

Glossina pallidipes is the main vector of animal African trypanosomiasis and a potential vector of human African trypanosomiasis in eastern Africa where it poses a large economic burden and public health threat. Vector control efforts have succeeded in reducing infection rates, but recent resurgence in tsetse fly population density raises concerns that vector control programs require improved strategic planning over larger geographic and temporal scales. Detailed knowledge of population structure and dispersal patterns can provide the required information to improve planning. To this end, we investigated the phylogeography and population structure of G. pallidipes over a large spatial scale in Kenya and northern Tanzania using 11 microsatellite loci genotyped in 600 individuals. Our results indicate distinct genetic clusters east and west of the Great Rift Valley, and less distinct clustering of the northwest separate from the southwest (Serengeti ecosystem). Estimates of genetic differentiation and first-generation migration indicated high genetic connectivity within genetic clusters even across large geographic distances of more than 300 km in the east, but only occasional migration among clusters. Patterns of connectivity suggest isolation by distance across genetic breaks but not within genetic clusters, and imply a major role for river basins in facilitating gene flow in G. pallidipes. Effective population size (Ne) estimates and results from Approximate Bayesian Computation further support that there has been recent G. pallidipes population size fluctuations in the Serengeti ecosystem and the northwest during the last century, but also suggest that the full extent of differences in genetic diversity and population dynamics between the east and the west was established over evolutionary time periods (tentatively on the order of millions of years). Findings provide further support that the Serengeti ecosystem and northwestern Kenya represent independent tsetse populations. Additionally, we present evidence that three previously recognized populations (the Mbeere-Meru, Central Kenya and Coastal “fly belts”) act as a single population and should be considered as a single unit in vector control.

Using genetic and phenetic markers to assess population isolation within the southernmost tsetse fly belt in Africa.

The effective control of tsetse flies (Diptera; Glossinidae), the biological vectors of trypanosome parasites that cause human African trypanosomosis and African animal trypanosomosis throughout sub-Saharan Africa, is crucial for the development of productive livestock systems. The degree of genetic isolation of the targeted populations, which indicate reinvasion potential from uncontrolled areas, will be critical to establish a control strategy. Molecular and morphometrics markers were used to assess the degree of genetic isolation between seemingly fragmented populations of Glossina brevipalpis Newstead and Glossina austeni Newstead present in South Africa. These populations were also compared with flies from adjacent areas in Mozambique and Eswatini. For the molecular markers, deoxyribonucleic acid was extracted, a r16S2 Polymerase chain reaction (PCR) was performed and the PCR product sequenced. Nine landmarks were used for the morphometrics study as defined by vein intersections in the right wings of female flies. Generalised Procrustes analyses and regression on centroid size were used to determine the Cartesian coordinates for comparison between populations. Both methods indicated an absence of significant barriers to gene flow between the G. brevipalpis and G. austeni populations of South Africa and southern Mozambique. Sustainable control can only be achieved if implemented following an area-wide management approach against the entire G. brevipalpis and G. austeni populations of South Africa and southern Mozambique. Limited gene flow detected between the G. austeni population from Eswatini and that of South Africa or Mozambique may imply that these two populations are in the proses of becoming isolated.

Bovine and small ruminant African animal trypanosomiasis in Nigeria - A review.

Despite extensive attempts over many decades to control African Animal Trypanosomiasis (AAT) across the tsetse fly belt of Nigeria, AAT persists as major animal health problem causing severe morbidity and mortality in livestock. The large agricultural losses in turn have severe adverse impacts on sustainable agricultural development. Despite this, in the past 50 years there have been no significant national control programs against AAT. This review explores the history of AAT control in Nigeria, examining the successes and failures in measures adopted in Nigeria to control AAT and the changing disease epidemiology.

East of Gaza

East of Gaza Phillip Parotti (bio) Broome? Yes, of course I know him. Served under him in Palestine from early 1917 until the end of the war. Ian Broome was one of Meinertzhagen’s subs during the East African campaign. Can’t recall the exact details; but, if I’m not mistaken, at some point in 1916, Meinertzhagen had a bout of fever and was sent home to recuperate. That’s when Broome took his place, coordinating intelligence for the East African Field Force. Meinertzhagen didn’t take long to recover, but when he did, rather than send him back into the East African fly belts, the War Office shipped him out to Palestine with a promotion; and, as soon as he took up his duties, he called for Broome, so Broome once more found himself serving as one of Meinertzhagen’s chief subordinates. Eventually, working that close to Meinertzhagen and Allenby, he must have caught Allenby’s eye, and that, I think, gave his career a boost. I read last week in the Times that he has been promoted to major general. Good man, Broome. Well done. Sent him a note of congratulation. Tall? Oh, yes, very. Six feet, four inches at least. High forehead, receding hairline that bristled along the back of his scalp, piercing, close-set blue eyes, and a sharp nose that protruded like a beak. That was Broome. The men, well out of his hearing, called him The Heron; and, in more ways than one, the description was apt. In the first place, setting aside mere appearance, he had the patience of Job; but, when he was on the hunt, he exhibited all of the determination of a heron stalking a trout, and then, when he did strike, he struck both fast and sure. And, if a man made the mistake of crossing him or not coming up to the mark in doing his duty, Broome had no hesitation about putting that beak right into the offender’s face with the implied threat that he might peck the man to death in half a second. Jolly unnerving, that. On the other [End Page 1] side, and this, I think, is something that appealed to Meinertzhagen, Broome was a man of swift apprehension and ready wit. He was in no way a joker, you will understand, but from time to time he would let something fall so dry and incisive as to cause me to double up until I could regain possession of myself. Me? Why I was the lowest of the low, the most junior second lieutenant in the section. I’d done my schooling at Winchester and then gone straight to Sandhurst, and when I passed out in March of 1917, someone at the War Office seems to have culled from my records a suggestion that I had been good at maths. How one automatically connects that discovery with intelligence work, I really can’t say; but, all at once, rather than joining my regiment as a platoon leader, and much against my will, I found myself shipped out to Cairo, and as soon as I landed, I found myself stuck in a tiny sweltering office correcting maps. It was mind-numbing, that work, the sort of thing that a well-trained ape might have been able to do, and I hated it; but, when Meinertzhagen showed up in June, he somehow found me out. “You’re wasted here,” he said to me, at the conclusion of our interview. “Pack your kit, and report to Advanced G.H.Q. at Dayr-al-Balah. That’s about two hundred miles up the coast from here, in case you haven’t already seen it on one of your maps. Report specifically to Captain Broome; he will have work for you.” That was a reprieve, I don’t mind telling you; and, as quickly as I could, I packed up and made the move. Sir Archibald Murray had been commanding on the Palestine front, but after two failed attacks on Gaza, he was on his way out, and the Bull, General Sir Edmund Allenby, was on the way in, already in transit somewhere between Italy and...

Spatial distribution of tsetse flies in the Blue Nile State, Sudan

The present study was carried out to spot the limit of tsetse fly belt in the Blue Nile State as the consecutive ecological changes tend to create significant modification in tsetse distribution. The survey was carried out for three weeks during March, 2011. Traps were placed in various vegetation types assumed to possibly harbor tsetse flies and were placed 200 m for three days at each site and harvested after 24 h. The sites where tsetse flies were encountered were marked using Global Positioning System (GPS) and the maps were generated. Tsetse geo-distribution generated map revealed that Glossina fuscipes fuscipes and Glossina morsitans submorsitans co-existed in Yabus District. Nevertheless our findings of G. m. submorsitans in the area far north is not surprising given that tsetse populations are known to recover from refugia following intervention or re-colonisation of a cleared zone from neighboring sources. However, G. f. fuscipes using biconical traps were only encountered in the river Khor Yabus extending to the East up to Platoma more than 35 linear Km west from the Ethiopian border. The apparent densities vary from 0.3 to 8 flies/trap/day, and tremendously decreased from east to west. The G. m. submorsitans flies using transect fly-round technique were caught north of its previously known limits which amounted to roughly 45 linear km north of River Khor Yabus to areas which had been assumed as devoid of the species Key words: Spatial-distribution, Glossina fuscipes fuscipes, G. morsitans submorsitans, Blue Nile State, Sudan.

A review of ecological factors associated with the epidemiology of wildlife trypanosomiasis in the luangwa and zambezi valley ecosystems of zambia.

Trypanosomiasis has been endemic in wildlife in Zambia for more than a century. The disease has been associated with neurological disorders in humans. Current conservation strategies by the Zambian government of turning all game reserves into state-protected National Parks (NPs) and game management areas (GMAs) have led to the expansion of the wildlife and tsetse population in the Luangwa and Zambezi valley ecosystem. This ecological niche lies in the common tsetse fly belt that harbors the highest tsetse population density in Southern Africa. Ecological factors such as climate, vegetation and rainfall found in this niche allow for a favorable interplay between wild reservoir hosts and vector tsetse flies. These ecological factors that influence the survival of a wide range of wildlife species provide adequate habitat for tsetse flies thereby supporting the coexistence of disease reservoir hosts and vector tsetse flies leading to prolonged persistence of trypanosomiasis in the area. On the other hand, increase in anthropogenic activities poses a significant threat of reducing the tsetse and wildlife habitat in the area. Herein, we demonstrate that while conservation of wildlife and biodiversity is an important preservation strategy of natural resources, it could serve as a long-term reservoir of wildlife trypanosomiasis.

Geospatial forecast model for tsetse-transmitted animal trypanosomosis in Ethiopia

The aims of this study were to develop a geographic information systems (GIS) forecast and risk assessment model for cyclically transmitted trypanosomosis in Ethiopia by matching features in the environment to available information on the preferences and limits of tolerance of the parasite and its vector, and validate and further develop the GIS model using data from current and historical prevalence survey data and habitat microenvironment studies from trypanosomosis endemic areas. Results indicate that GIS model developed for parasitic diseases based on growing degree day (GDD) concept can be applied to tsetse-transmitted trypanosomosis. GIS for animal trypanosomosis was created using Food and Agriculture Organization – Crop Production System Zones (FAO-CPSZ) database and Normalized Difference Vegetation Index (NDVI) and maximum temperature (Tmax) from the Global Land 1km dataset. The two datasets used to determine the risk of tsetse flies and consequently animal trypanosomosis in Ethiopia indicated the magnitude of the disease and possible expansion of the “fly belt” in the future. The GIS model indicated the distribution and importance of tsetse-transmitted trypanosomosis in Ethiopia. Spatial and statistical analysis verified the use of GDD concept and climate forecast system that was developed to determine the suitability of a given environment for the proliferation of a biotype, in this case tsetse and trypanosomes. Results presented here indicate the importance of GDD and the two climatic variables (NDVI and Tmax) in the development of forecast model for tsetse-transmitted trypanosomosis in Ethiopia. Key words/phrases: Ethiopia, GIS, NDVI, Tmax, trypanosomosis SINET: Ethiopian Journal of Science Vol.27(1) 2004: 1-8

Identification of trypanosomes in Glossina pallidipes and G. longipennis in Kenya

The polymerase chain reaction (PCR) was used to identify trypanosomes in Glossina pallidipes and G. longipennis caught in Kenya. Of 3826 flies dissected, 188 (4.9%) were parasitologically positive overall. The infection rate in G. pallidipes was 5.7% (187 of 3301 flies), but only one of 525 G. longipennis was infected (infection rate 0.2%). There was a higher infection rate in female G. pallidipes flies than male flies ( χ 2=18.5, P<0.001) and odds ratio=2.5 (95% 1.6, 3.7). The infected flies were analysed by PCR using 10 sets of primers specific for species and subgroups within the subgenera Nannomonas, Trypanozoon and Duttonella. Of 188 parasitologically positive samples, PCR identified 137 (72.9%), leaving 51 (27.1%) non-identified. We recorded infection rates of 47.2% for Trypanosoma congolense savannah, forest and kilifi subgroups, 20.9% for T. simiae/ T. simiae tsavo/ T. godfreyi, 14.9% for T. brucei ssp. and 13.8% for T. vivax. Thirty-nine (26.7%) flies had mixed infections, with a minor association between T. congolense savannah/ T. simiae tsavo/ T. godfreyi ( χ 2=6.93, d.f.=1, P<0.05). The relative proportion of each trypanosome species or subgroup varied between fly belts with T. congolense (all subgroups) being the most abundant and T. godfreyi the least. Statistical analysis showed that dissection method and PCR test classified infections independently ( χ 2=10.5, d.f.=1, P<0.05 and κ=0.38). This study shows that pathogenic trypanosomes are widespread in all sampled testes fly belts with G. pallidipes as the main vector. Further, PCR test is more reliable in detecting and identifying trypanosomes than dissection method.

Tsetse flies are attracted to the invasive plant Lantana camara

In tsetse both sexes feed exclusively on the blood of vertebrates for a few minutes every 2–3 days. Tsetse flies seek cover from high temperatures to conserve energy and plants provide shelter for tsetse in all the biotopes they occupy. Recently, tsetse have taken cover in plantations and under the invasive bush Lantana camara that has invaded large areas of the tsetse fly belt of Africa. Flies from such refugia are implicated in sleeping sickness epidemics. In a wind tunnel we show that both foliage and an extract of volatiles from foliage of L. camara attract three tsetse spp. from different habitats: Glossina fuscipes fuscipes (riverine), G. brevipalpis (sylvatic) and G. pallidipes (savannah). Gas chromatography analysis of volatiles extracted from leaves and flowers of L. camara coupled to electroantennograme recordings show that 1-octen-3-ol and β-caryophyllene are the major chemostimuli for the antennal receptor cells of the three tsetse spp. studied. A binary mixture of these products attracted these flies in the wind tunnel. The gas chromatography linked electroantennograme analysis of the L. camara extracts also show that the antennal receptor cells of the three tsetse spp. respond similarly to groups of volatiles derived from the major biosynthetic and catabolic pathways of plants, i.e. to mono- and sesquiterpenes, to lipoxidation products and to aromatics. Mixtures of these plant volatiles also attracted tsetse in the wind tunnel. These findings show that tsetse flies have conserved a strong sensitivity to volatile secondary products of plants, underlining the fundamental role of vegetation in tsetse survival.

An example of decision support for trypanosomiasis control using a geographical information system in eastern Zambia.

In many African countries where both Government resources and donor aid for the control of tsetse-transmitted trypanosomiasis are declining, there is an increasing need to identify areas where intervention is most likely to be technically, economically, socially and environmentally sustainable. Activities then can be focused so that the maximum benefits are obtained from limited resources. We describe a decision-support framework based on a geographical information system to identify areas of high priority for the control of tsetse and trypanosomiasis in the common fly belt of eastern Zambia. Digital coverages were generated for six environmental variables: (1) cattle density, (2) human density, (3) land designation, (4) relative arable potential, (5) crop-use intensity and (6) proximity to existing control operations. The distribution of tsetse in the area was predicted using a multivariate (maximum likelihood) analysis of areas of known presence and absence and a series of environmental data. Experienced Zambian veterinarians and biologists working in the region established criteria weights for the input variables and the data were integrated in a geographical information system (GIS), using weighted linear combinations to prioritize areas for trypanosomiasis control. The results of this exercise and estimates of the errors involved are discussed.

Genetic differentiation of some Glossina morsitans morsitans populations.

To study the population structure of Glossina morsitans morsitans Westwood (Diptera: Glossinidae), polymerase chain reaction (PCR) and singlestrand conformational polymorphism (SSCP) methods were used to estimate mitochondrial DNA diversity at four loci in six natural populations from Zambia, Zimbabwe and Mozambique, and in two laboratory cultures. The Zambian and Zimbabwean samples were from a single fly belt. Four alleles were recorded at 12S and 16S1, and five alleles at 16S2 and COI. Nucleotide sequencing confirmed their singularities. Chi-square contingency tests showed that allele frequencies differed significantly among populations. Mean allele diversities in populations averaged over loci varied from 0.14 to 0.61. Little loss in haplotype diversity was detected in the laboratory cultures thereby indicating little inbreeding. Wright's fixation index F(ST) in the natural populations was 0.088+/-0.016, the correlation of haplotypes within populations relative to correlations in the total. A function of its inverse allows an estimate of the mean equivalent number of females exchanged per population per generation, 5.2. No correlation was detected between pairwise genetic distance measures and geographical distances. Drift explains the high degree of differentiation.

Reproductive status, catch and age compositions of a natural population of Glossina morsitans submorsitans in Bahr El Arab fly belt, Sudan

Studies were conducted during the dry period February to May 1986 in River Shelliekha, Bahr EI Arab fly belt, Sudan, to obtain baseline data on catch and age compositions, reproductive status and trypanosome infection rates of trapped and fly round samples of Glossina morsilans submorsitans. The objective was to assess the tsetse situation before the establishment of trypanosomiasis treatment stations at the northern limits of the fly belt. Trapped tsetse included significantly higher proportions of teneral and non-teneral females and a lower male:female ratio. Inseminatipn rates were over 98% in both samples. In anyone group, the frequency of pregnancy with egg predominated, followed by the second, first and lastly the third instar larva. There were significant differences between the two groups of females in the proportions of nullipars and pregnancy with anyone of the larval instars. Abortion was the predominant reproductive abnormality and no relationship could be found between abortion rate and the sampling method, age or trypanosome infection rate of females. Age compositions were similar in the two samples, save for age categories 0 and 1 for females and two and four for males. Flies were infected with Trypanosoma vivax and T. congolense only, though T. brucei infections could also be diagnosed in livestock.

Trypanosome infection rate of Glossina morsitans submorsitans in Bahr El Arab, South Darfur Province, Sudan.

Trypanosome infection rate of Glossina morsitans submorsitans in Bahr El Arab fly belt, Sudan was investigated in four areas using fly rounds with screen and bait animals together with traps during the dry season February to May 1985. The overall infection rate of tests flies captured in the four areas was 5.1%. The infection rate of vivax group trypanosomes comprised 64.7% of total infections, congolense group 31.2% and brucei group trypanosomes 3.9%: 27.3% of the vivax and 31.3% of the congolense were immature trypanosome infections. Mixed trypanosome infections were encountered in a few flies. Trypanosome infection rate of flies differed with the sampling technique employed. A linear positive correlation existed between the physiological age of males and their trypanosome infection rates.

Genetics of two populations of Glossina morsitans centralis (Diptera: Glossinidae) from Zambia

Glossina morsitans centralis Machado was collected from the main fly belt west of Mumbwa Zambia and from the apparently isolated ‘Keembe pocket’ and 11 gene-enzyme systems were examined by polyacrylamide gel electrophoresis. There were no significant differences in allele frequencies among flies collected entering a vehicle, from fly-rounds, or from F3 traps in the main fly belt. Mean heterozygosity per locus is slightly higher in flies from the main fly belt than it is in flies from the ‘Keembe pocket’. Allele frequencies at loci for xanthine oxidase ( X o ), aldehyde oxidase ( A o ) and a thoracic esterase ( Est-2) were significantly different in the two populations and it is concluded that there is little gene flow between them.