Extrachromosomal inheritance of susceptibility to trypanosome infection in tsetse flies. II. Susceptibility of selected lines of Glossina morsitans morsitans to different stocks and species of trypanosome

Evidence of the absence of human African trypanosomiasis in two northern districts of Uganda: Analyses of cattle, pigs and tsetse flies for the presence of Trypanosoma brucei gambiense

BACKGROUND

Large-scale control of sleeping sickness has led to a decline in the number of cases of Gambian human African trypanosomiasis (g-HAT) to <2000/year. However, achieving complete and lasting interruption of transmission may be difficult because animals may act as reservoir hosts for T. b. gambiense. Our study aims to update our understanding of T. b. gambiense in local vectors and domestic animals of N.W. Uganda.

METHODS

We collected blood from 2896 cattle and 400 pigs and In addition, 6664 tsetse underwent microscopical examination for the presence of trypanosomes. Trypanosoma species were identified in tsetse from a subsample of 2184 using PCR. Primers specific for T. brucei s.l. and for T. brucei sub-species were used to screen cattle, pig and tsetse samples.

RESULTS

In total, 39/2,088 (1.9%; 95% CI = 1.9-2.5) cattle, 25/400 (6.3%; 95% CI = 4.1-9.1) pigs and 40/2,184 (1.8%; 95% CI = 1.3-2.5) tsetse, were positive for T. brucei s.l.. Of these samples 24 cattle (61.5%), 15 pig (60%) and 25 tsetse (62.5%) samples had sufficient DNA to be screened using the T. brucei sub-species PCR. Further analysis found no cattle or pigs positive for T. b. gambiense, however, 17/40 of the tsetse samples produced a band suggestive of T. b. gambiense. When three of these 17 PCR products were sequenced the sequences were markedly different to T. b. gambiense, indicating that these flies were not infected with T. b. gambiense.

CONCLUSION

The lack of T. b. gambiense positives in cattle, pigs and tsetse accords with the low prevalence of g-HAT in the human population. We found no evidence that livestock are acting as reservoir hosts. However, this study highlights the limitations of current methods of detecting and identifying T. b. gambiense which relies on a single copy-gene to discriminate between the different sub-species of T. brucei s.l.

Sustainable Elimination (Zero Cases) of Sleeping Sickness: How Far Are We from Achieving This Goal?

The recent massive reduction in the numbers of fresh Human African Trypanosomiasis (HAT) infection has presented an opportunity for the global elimination of this disease. To prevent a possible resurgence, as was the case after the reduced transmission of the 1960s, surveillance needs to be sustained and the necessary tools for detection and treatment of cases need to be made available at the points of care. In this review, we examine the available resources and make recommendations for improvement to ensure the sustenance of the already achieved gains to keep the trend moving towards elimination.

Tsetse fly evolution, genetics and the trypanosomiases - A review

This reviews work published since 2007. Relative efforts devoted to the agents of African trypanosomiasis and their tsetse fly vectors are given by the numbers of PubMed accessions. In the last 10 years PubMed citations number 3457 for Trypanosoma brucei and 769 for Glossina. The development of simple sequence repeats and single nucleotide polymorphisms afford much higher resolution of Glossina and Trypanosoma population structures than heretofore. Even greater resolution is offered by partial and whole genome sequencing. Reproduction in T. brucei sensu lato is principally clonal although genetic recombination in tsetse salivary glands has been demonstrated in T. b. brucei and T. b. rhodesiense but not in T. b. gambiense. In the past decade most genetic attention was given to the chief human African trypanosomiasis vectors in subgenus Nemorhina e.g., Glossina f. fuscipes, G. p. palpalis, and G. p. gambiense. The chief interest in Nemorhina population genetics seemed to be finding vector populations sufficiently isolated to enable efficient and long-lasting suppression. To this end estimates were made of gene flow, derived from F_ST and its analogues, and Ne, the size of a hypothetical population equivalent to that under study. Genetic drift was greater, gene flow and Ne typically lesser in savannah inhabiting tsetse (subgenus Glossina) than in riverine forms (Nemorhina). Population stabilities were examined by sequential sampling and genotypic analysis of nuclear and mitochondrial genomes in both groups and found to be stable. Gene frequencies estimated in sequential samplings differed by drift and allowed estimates of effective population numbers that were greater for Nemorhina spp than Glossina spp. Prospects are examined of genetic methods of vector control. The tsetse long generation time (c. 50 d) is a major contraindication to any suggested genetic method of tsetse population manipulation. Ecological and modelling research convincingly show that conventional methods of targeted insecticide applications and traps/targets can achieve cost-effective reduction in tsetse densities.

Beyond Tsetse--Implications for Research and Control of Human African Trypanosomiasis Epidemics

Epidemics of both forms of human African trypanosomiasis (HAT) are confined to spatially stable foci in Sub-Saharan Africa while tsetse distribution is widespread. Infection rates of Trypanosoma brucei gambiense in tsetse are extremely low and cannot account for the catastrophic epidemics of Gambian HAT (gHAT) seen over the past century. Here we examine the origins of gHAT epidemics and evidence implicating human genetics in HAT epidemiology. We discuss the role of stress causing breakdown of heritable tolerance in silent disease carriers generating gHAT outbreaks and see how peculiarities in the epidemiologies of gHAT and Rhodesian HAT (rHAT) impact on strategies for disease control.

Flying tryps: survival and maturation of trypanosomes in tsetse flies

Survival in and colonization of the tsetse fly midgut are essential steps in the transmission of many species of African trypanosomes. In the fly, bloodstream trypanosomes transform into the procyclic stage within the gut lumen and later migrate to the ectoperitrophic space, where they multiply, establishing an infection. Progression of the parasite infection in the fly depends on factors inherent to the biology of trypanosomes, tsetse, and the bloodmeal. Flies usually eradicate infection early on with both pre-existing and inducible factors. Parasites, in contrast, respond to these stimuli by undergoing developmental changes, allowing a few to both survive and migrate within the tsetse. Here we discuss parasite and fly factors determining trypanosome colonization of the tsetse, focusing mainly on the midgut.

Priorities for the elimination of sleeping sickness

Sleeping sickness describes two diseases, both fatal if left untreated: (i) Gambian sleeping sickness caused by Trypanosoma brucei gambiense, a chronic disease with average infection lasting around 3 years, and (ii) Rhodesian sleeping sickness caused by T. b. rhodesiense, an acute disease with death occurring within weeks of infection. Control of Gambian sleeping sickness is based on case detection and treatment involving serological screening, followed by diagnostic confirmation and staging. In stage I, patients can remain asymptomatic as trypanosomes multiply in tissues and body fluids; in stage II, trypanosomes cross the blood-brain barrier, enter the central nervous system and, if left untreated, death follows. Staging is crucial as it defines the treatment that is prescribed; for both forms of disease, stage II involves the use of the highly toxic drug melarsoprol or, in the case of Gambian sleeping sickness, the use of complex and very expensive drug regimes. Case detection of T. b. gambiense sleeping sickness is known to be inefficient but could be improved by the identification of parasites using molecular tools that are, as yet, rarely used in the field. Diagnostics are not such a problem in relation to T. b. rhodesiense sleeping sickness, but the high level of under-reporting of this disease suggests that current strategies, reliant on self-reporting, are inefficient. Sleeping sickness is one of the 'neglected tropical diseases' that attracts little attention from donors or policymakers. Proper quantification of the burden of sleeping sickness matters, as the primary reason for its 'neglect' is that the true impact of the disease is unknown, largely as a result of under-reporting. Certainly, elimination will not be achieved without vast improvements in field diagnostics for both forms of sleeping sickness especially if there is a hidden reservoir of 'chronic carriers'. Mass screening would be a desirable aim for Gambian sleeping sickness and could be handled on a national scale in the endemic countries - perhaps by piggybacking on programmes committed to other diseases. As well as improved diagnostics, the search for non-toxic drugs for stage II treatment should remain a research priority. There is good evidence that thorough active case finding is sufficient to control T. b. gambiense sleeping sickness, as there is no significant animal reservoir. Trypanosoma brucei rhodesiense sleeping sickness is a zoonosis and control involves interrupting the fly-animal-human cycle, so some form of tsetse control and chemotherapy of the animal reservoir must be involved. The restricted application of insecticide to cattle is the most promising, affordable and sustainable technique to have emerged for tsetse control. Animal health providers can aid disease control by treating cattle and, when allied with innovative methods of funding (e.g. public-private partnerships) not reliant on the public purse, this approach may prove more sustainable. Sleeping sickness incidence for the 36 endemic countries has shown a steady decline in recent years and we should take advantage of the apparent lull in incidence and aim for elimination. This is feasible in some sleeping sickness foci but must be planned and paid for increasingly by the endemic countries themselves. The control and elimination of T. b. gambiense sleeping sickness may be seen as a public good, as appropriate strategies depend on local health services for surveillance and treatment, but public-private funding mechanisms should not be excluded. It is timely to take up the tools available and invest in new tools - including novel financial instruments - to eliminate this disease from Africa.

Estimation of tsetse challenge and its relationship with trypanosomosis incidence in cattle kept under pastoral production systems in Kenya

In an on-farm trial conducted amongst the Maasai pastoralists in Nkuruman and Nkineji areas of Kenya between April 2004 and August 2005 designed to evaluate the effectiveness of a synthetic tsetse repellent technology, we assessed the relationship between tsetse challenge and trypanosomosis incidence in cattle. Six villages were used in each area. Each of these villages had a sentinel cattle herd that was screened for trypanosomosis on monthly basis using buffy coat technique. Animals found infected at each sampling were treated with diminazene aceturate at 7 mg kg(-1) body weight. Treatments administered by the owners over the sampling intervals were recorded as well. Tsetse flies were trapped at the time of sampling using baited stationary traps and apparent tsetse density estimated as flies per trap per day (FTD). A fixed proportion (10%) of the flies was dissected and their infection status determined through microscopy. Blood meals were also collected from some of the flies and their sources identified using enzyme-linked immunosorbent assay (ELISA). Tsetse challenge was obtained as a product of tsetse density, trypanosome prevalence and the proportion of blood meals obtained from cattle. This variable was transformed using logarithmic function and fitted as an independent factor in a Poisson model that had trypanosomosis incidence in the sentinel cattle as the outcome of interest. The mean trypanosomosis incidence in the sentinel group of cattle was 7.2 and 10.2% in Nkuruman and Nkineji, respectively. Glossina pallidipes was the most prevalent tsetse species in Nkuruman while G. swynnertoni was prevalent in Nkineji. The proportions of tsetse that had mature infections in the respective areas were 0.6 and 4.2%. Most tsetse (28%) sampled in Nkuruman had blood meals from warthogs while most of those sampled in Nkineji (30%) had blood meals from cattle. A statistically significant association between tsetse challenge and trypanosomosis incidence was obtained only in Nkuruman when data was pooled and analyzed at the area but not at the village-level. In the later scenario, lagging tsetse challenge by 1 month improved the strength but not the significance of the association. These findings show that when the spatial unit of analysis in observational studies or on-farm trials is small, for instance a village, it may not be possible to demonstrate a statistically significant association between tsetse challenge and trypanosomosis incidence in livestock so as to effectively control for tsetse challenge.

Cyclical transmission of Trypanosoma brucei gambiense in Glossina palpalis gambiensis displays great differences among field isolates

Six sets of teneral Glossina palpalis gambiensis (Diptera: Glossinidae) were fed on mice infected with six different isolates of Trypanosoma brucei gambiense (each mouse was infected with one of the isolates), previously isolated from patients in the sleeping sickness focus of Bonon, Côte d'Ivoire and in Makoua, Congo. All the tsetse flies were dissected 42 days post-infection and midgut and salivary glands were examined for trypanosomes by microscopical examination. No infection was observed with the reference stock whereas each of the five recently isolated trypanosome isolates was able to infect tsetse flies, with rates of infection varying between 9.7 and 18.2% depending on the isolate. Three isolates displayed only immature infections with 9.7, 17.3 and 18% of the flies showing trypanosomes in their midgut. One isolate gave both immature (12.1%) and mature infections (6.1%). Finally, the last isolate involved only mature infections in 9.7% of the Glossina species examined. These substantial differences in the cyclical transmission of T. b. gambiense in the same fly species could have important implications for the epidemiology of the transmission of Human African Trypanosomiasis.

Comparison of the transmissibility ofTrypanosoma congolensestrains, isolated in a trypanosomiasis endemic area of eastern Zambia, byGlossina morsitans morsitans

Transmission experiments were conducted to compare the transmissibility of genetically differentTrypanosoma congolense(Savannah subgroup) strains isolated from cattle in a trypanosomiasis endemic area of eastern Zambia. A total of 17 strains were compared. Three strains were extremely virulent with a short pre-patent period, high parasitaemia and a short median survival time (between 5 and 9 days) in mice. The remainder of the strains belonged to the moderate (6 strains) or low (8 strains) virulence categories with median survival times between 10 and 30 days and >30 days, respectively. Batches of 40 teneralGlossina morsitans morsitans(Diptera: Glossinidae) were offered a single bloodmeal on mice infected with one of those strains. Flies were dissected to determine their infection status 21 days later. The proportion of flies with procyclic and metacyclic infections differed significantly between trypanosome strains and were significantly higher in flies infected with extremely virulent strains (P=0·033 andP=0·016 for the differences in the procyclic infection rate of strains with moderate and low virulence, respectively andP=0·005 andP=0·019 for the differences in the metacyclic infection rate of strains with moderate and low virulence, respectively). On the other hand, moderately virulent strains had, in general, higher procyclic and metacyclic infection rates compared to low virulent strains. But the differences were not significant (P>0·05). The outcome of those experiments shows clear differences in transmissibility of trypanosome strains associated with their virulence. This observation confirms the theory for the evolution and maintenance of virulence in a parasite population and may explain the persistence of virulent trypanosome strains in a susceptible host population.

Two Tsetse fly species, Glossina palpalis gambiensis and Glossina morsitans morsitans, carry genetically distinct populations of the secondary symbiont Sodalis glossinidius

Genetic diversity among Sodalis glossinidius populations was investigated using amplified fragment length polymorphism markers. Strains collected from Glossina palpalis gambiensis and Glossina morsitans morsitans flies group into separate clusters, being differentially structured. This differential structuring may reflect different host-related selection pressures and may be related to the different vector competences of Glossina spp.

Monitoring the developmental status of Trypanosoma brucei gambiense in the tsetse fly by means of PCR analysis of anal and saliva drops

Teneral Glossina palpalis gambiensis (Diptera: Glossinidae) were infected with a culture of procyclic forms of Trypanosoma brucei gambiense using a single-bloodmeal membrane feeding technique. The infection was monitored by analysing the saliva (mature infection) and anal drop (midgut infection) of each fly at different post-infection times both by microscopic observation and polymerase chain reaction (PCR). Amplification revealed many more positive anal drops than microscopy. The monitoring showed that the installation of T. b. gambiense in Glossina took place at least 11 days after the infection and that maturation occurred after 29 days. It also reflected precisely the parasitic status of each tsetse fly as determined by the dissection, microscopic examination and PCR amplification of the midguts and salivary glands 47 days post-infection. Twice as many tsetse flies with mature salivary glands infection were revealed by PCR than by microscopic examination, but the two techniques gave exactly the same results regarding the proportion of flies with midgut infection. This study also demonstrated the ability of natural non-infective procyclic forms of T. b. gambiense, to colonise the midgut and subsequently establish in the salivary glands of G. p. gambiensis.

Genetic variation in arthropod vectors of disease-causing organisms: obstacles and opportunities

An overview of the genetic variation in arthropods that transmit pathogens to vertebrates is presented, emphasizing the genetics of vector-pathogen relationships and the biochemical genetics of vectors. Vector-pathogen interactions are reviewed briefly as a prelude to a discussion of the genetics of susceptibility and refractoriness in vectors. Susceptibility to pathogens is controlled by maternally inherited factors, sex-linked dominant alleles, and dominant and recessive autosomal genes. There is widespread interpopulation (including intercolony) and temporal variation in susceptibility to pathogens. The amount of biochemical genetic variation in vectors is similar to that found in other invertebrates. However, the amount varies widely among species, among populations within species, and temporally within populations. Biochemical genetic studies show that there is considerable genetic structuring of many vectors at the local, regional, and global levels. It is argued that genetic variation in vectors is critical in understanding vector-pathogen interactions and that genetic variation in vectors creates both obstacles to and opportunities for application of genetic techniques to the control of vectors.

A comparison of Glossina morsitans centralis originating from Tanzania and Zambia, with respect to vectorial competence for pathogenic Trypanosoma species, genetic variation and inter-colony fertility

Two laboratory strains of Glossina morsitans centralis originating from different fly-belts (one from Singida, in Tanzania, and the other from Mumbwa, in Zambia) were compared with respect to vectorial competence for pathogenic Trypanosoma species, genetic variation and inter-colony fertility. The vectorial competence of G.m.centralis of Tanzanian origin for Trypanosma vivax and T. congolense is similar to, whereas for T.brucei brucei it is lower than the colony of Zambian origin. Nevertheless, these two laboratory strains of G.m.centralis showed levels of susceptibility to the three pathogenic Trypanosoma species which were much greater than previously observed in laboratory colonies of other Glossina species. Electrophoresis of fifteen enzymes revealed that the two colonies differ significantly in allele frequencies at only three loci that are relatively close together on one of the autosomes. Hybridization experiments revealed that G.m.centralis from the two fly-belts are consubspecific.

Rickettsia-like organisms and chitinase production in relation to transmission of trypanosomes by tsetse flies

Rickettsia-like organisms (RLO) from testse midguts and mosquito cell cultures showed high levels of endochitinase activity. A line of Glossina morsitans morsitans highly susceptible to midgut trypanosome infection and with high incidence of RLO infection showed significantly greater chitinolytic activity than G. austeni which had low RLO incidence and were correspondingly refractory to midgut infection. Midgut infection rates of Trypanosoma brucei rhodesiense in G. m. morsitans showed a dose-related increase when flies were fed N-acetyl-D-glucosamine (GlcNAc) in the infective meal and for 4 subsequent days. A model is proposed for susceptibility to trypanosome infection based on the generation of GlcNAc by RLO endochitinase activity in tsetse pupae inhibiting midgut lectin in teneral flies.

The influence of host blood on infection rates in Glossina morsitans sspp. infected with Trypanosoma congolense, T. brucei and T. simiae

Trypanosoma congolense, T. brucei and T. simiae isolated from wild-caught Glossina pallidipes were fed to laboratory-reared G. morsitans centralis and G.m. morsitans to determine the effect of host blood at the time of the infective feed on infection rates. Bloodstream forms of trypanosomes were membrane-fed to flies either neat, or mixed with blood from cows, goats, pigs, buffalo, eland, waterbuck and oryx. The use of different bloods for the infective feed resulted in differences in infection rates that were repeatable for both tsetse subspecies and most parasite stocks. Goat, and to a lesser extent, pig blood facilitated infection, producing high infection rates at low parasitaemias. Blood from cows and the wildlife species produced low infection rates, with eland blood producing the lowest. Addition of D(+)-glucosamine (an inhibitor of tsetse midgut lectin) increased infection rates in most cases. These results indicate the presence of species-specific factors in blood that affect trypanosome survival in tsetse. In certain hosts, factors actually appear to promote infection. The nature of these factors and how they might interact with midgut lectins and proteases are discussed.

The nature of the teneral state in Glossina and its role in the acquisition of trypanosome infection in tsetse

Teneral Glossina morsitans morsitans from outbred and susceptible stocks infected with Trypanosoma (Nannomonas) congolense developed, respectively, three and six times higher midgut infection rates than flies of the same stock which had previously taken a bloodmeal. Non-teneral G. m. morsitans remained relatively refractory to infection when infected at subsequent feeds. Differences in susceptibility to midgut infection between teneral flies from susceptible and outbred lines of G. m. morsitans disappeared in non-teneral flies, showing that maternally inherited susceptibility to midgut infection is a phenomenon restricted to the teneral state of the fly. Laboratory reared G. m. morsitans were found to have become significantly more susceptible to trypanosome infection than wild flies from the population from which the colony was derived. The likely role of rickettsia-like organisms (RLO) in potentiating teneral susceptibility to midgut infection is discussed. The addition of the specific midgut lectin inhibitor D-glucosamine to the infective feed of non-teneral flies increased midgut infection rates to levels comparable with those achieved in teneral flies. It is concluded that the peritrophic membrane does not act as a barrier preventing non-teneral flies becoming infected. The relative refractoriness of non-teneral flies suggests that they do not play a significant part in the epidemiology of Trypanozoon or T. congolense infections.

Infection rates in Glossina morsitans morsitans fed on waterbuck and Boran cattle infected with Trypanosoma congolense

Teneral Glossina morsitans morsitans were fed on waterbuck (Kobus defassa) and Boran cattle (Bos indicus) infected experimentally with Trypanosoma congolense clone IL2895. Infection rates in tsetse varied from 9 to 31% when fed on cattle, and from 2 to 59% when fed on waterbuck. In waterbuck, infections were often detected through the development of parasites in tsetse at times when parasitaemia could not be detected through microscopic examination of blood. Male and female, and 1- and 2-day-old flies were equally susceptible to infection on both hosts. Infection in tsetse was associated with a 14% absolute reduction in survival during the month following the infective feed.

Rickettsia-like organisms, puparial temperature and susceptibility to trypanosome infection in Glossina morsitans

Maintaining the puparial stage of successive generations of a population of tsetse 3 degrees C lower than normal reduced the numbers of rickettsia-like organisms (RLO) carried by emerging flies. The susceptibility of these flies to midgut infection with Trypanosoma congolense was also significantly reduced compared with control flies held at normal temperature. These results support the view that the relationship between RLO and susceptibility is quantitative-teneral flies with heavier RLO infections being more susceptible to trypanosome infection.

The Tsetse Research Laboratory

The Tsetse Research Laboratory in Bristol was opened in December 1962, with the initial objective of developing techniques for rearing tsetse flies on a large scale outside Africa. Its work has, however, extended greatly since then. This article highlights the research undertaken at the Laboratory, not only on the breeding of tsetse flies but also on various aspects of their biology and control.

Identification of midgut trypanolysin and trypanoagglutinin in Glossina palpalis sspp. (Diptera: Glossinidae)

A midgut trypanolysin and an agglutinin from Glossina palpalis subspecies were isolated and partially characterized using anion-exchange chromatography and polyacrylamide gel electrophoresis. FPLC fractions of midgut extracts of Glossina palpalis palpalis caused agglutination and lysis of two trypanosome species (Trypanosoma congolense and Trypanosoma brucei brucei), although Glossina palpalis gambiensis caused only agglutination. The trypanolysin and agglutinin were active only in the posterior midguts, were heat labile above 50 degrees C, had a periodic cycle of 'activity' in response to bloodmeal intake and were not affected by protease inhibitors or trypsin but were inactivated by pronase. The lytic substance contained two proteins with approximate molecular weights (Mr) of 12,000 and 10,000 Da respectively. The agglutinin had an approximate Mr of 67,000 Da. Gamma-irradiation of the two subspecies caused a temporary inhibition of trypanolytic and agglutinin activities in midgut extracts.

Salivary gland infection: a sex-linked recessive character in tsetse?

Male tsetse, when infected in the laboratory with trypanosomes of the subgenus Trypanozoon, usually produce greater salivary gland infection rates than females of the same species. We show that a single sex-linked gene model can be fitted to most recently published data for salivary gland infection rates in tsetse. The maturation of Trypanosoma congolense infections is shown to be independent of fly sex. The possible effects of genetic control of maturation of Trypanozoon infections in tsetse populations on the transmission of sleeping sickness are considered.

The possible role of Rickettsia-like organisms in trypanosomiasis epidemiology

A simple model of human and animal trypanosomiasis is proposed in which the Ross equation for disease transmission is supplemented by a differential equation describing the inheritance of susceptibility in the vector. The model predicts an equilibrium state of balanced polymorphism for the fraction, theta, of susceptible tsetse and the occurrence of periodic epidemics at roughly the observed intervals. A loss of infectivity to tsetse of mechanically transmitted strains of trypanosome would seem to be a good evolutionary strategy for the trypanosome. The main implication for disease control is that measures initially reducing trypanosomiasis incidence could trigger off subsequent epidemics. Since theta leads incidence, monitoring theta could give several years advance warning of major epidemics. The model leads to oscillations in prevalence which are only lightly damped. Other mechanisms producing periodic epidemics would interact with this mechanism, and result in only one sequence of recurrent epidemics. With typical random variation of tsetse numbers about the seasonal norm the model shows the behaviour of a narrow-band system excited by broad-band noise, i.e. predicted trypanosomiasis incidence exhibits an undamped series of oscillations of variable amplitude and phase, similar to what is actually observed.

Cloning of a repetitive DNA from the rickettsia-like organisms of tsetse flies (Glossina spp.)

Three DNA fragments from the genome of the rickettsia-like organism (RLO) symbiotic in tsetse flies (Glossina spp.) have been cloned. One of these fragments represents a family of highly conserved repeats, which occurs in RLO from all species of tsetse examined and has been amplified in the original RLO culture from which the DNA is cloned. This fragment serves as a highly sensitive and specific probe for the detection of RLO in tsetse midguts. As few as 30 organisms were unequivocally identified by dot blot hybridization of homogenized midgut preparations. Since the presence of RLO within tsetse midguts is associated with susceptibility to trypanosome infection, this technique provides a rapid and reliable method of assessing the potential susceptibility of a tsetse population to Trypanosoma brucei s.l. and T. congolense infections.

Comparative study on the infection rates of different Glossina species for East and West African Trypanosoma vivax stocks

Teneral male Glossina morsitans centralis, G. austeni, G. palpalis palpalis, G. p. gambiensis, G. fuscipes fuscipes, G. tachinoides and G. brevipalpis were fed on the flanks of Boran calves infected with Trypanosoma vivax stock ILRAD 2241 isolated from a cow in Likoni, Kenya; stock ILRAD 2337 isolated from a cow in Galana, Kenya; stock ILRAD 1392 isolated from a cow in Nigeria; or, stock EATRO 1721 isolated from G. m. submorsitans in Nigeria. The tsetse were fed on the infected hosts for 24 days and were then dissected to determine the infection rates. In G. m. centralis and G. brevipalpis, the mature infection rates of T. vivax from Kenya were 61.1%, and 75.3% for ILRAD 2241, and 36.2% and 58.2% for ILRAD 2337, respectively. In G. austeni and in the four palpalis group of tsetse, the rates for these two stocks were very low and ranged from 0% in G. p. palpalis to 1.8% in G. austeni for ILRAD 2241 and from 0% in G. f. fuscipes to 5% in G. tachinoides for ILRAD 2337. In contrast, the hypopharyngeal infection rates of T. vivax from Nigeria were quite high in all the 7 tsetse species and sub-species. They ranged from 55.5% in G. austeni to 91.9% in G. p. gambiensis for ILRAD 1392, and from 71.4% in G. austenei to 97.1% in G. brevipalpis for EATRO 1721.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro cultivation of rickettsia-like-organisms from Glossina spp

A method is described for the in vitro cultivation of the rickettsia-like-organisms (RLO) from Glossina spp. which are believed to be associated with susceptibility to trypanosome infection. Cultures of RLO were established by infecting a mosquito cell line (Aedes albopictus) with haemolymph taken from teneral flies. RLO from nine species of Glossina have been isolated and maintained in continuous culture using this technique.