The tsetse fly Glossina palpalis palpalis is composed of several genetically differentiated small populations in the sleeping sickness focus of Bonon,Côte d’Ivoire

Glossina palpalis is the main vector of human African trypanosomosis (HAT, or sleeping sickness) that dramatically affects human health in sub-Saharan Africa. Because of the implications of genetic structuring of vector populations for the design and efficacy of control campaigns, G. palpalis palpalis in the most active focus of sleeping sickness in Côte d’Ivoire was studied to determine whether this taxon is genetically structured. High and statistically significant levels of within population heterozygote deficiencies were found at each of the five microsatellite loci in two temporally separated samples. Neither null alleles, short allele dominance, nor trap locations could fully explain these deviations from random mating, but a clustering within each of the two samples into different genetic sub-populations (Wahlund effect) was strongly suggested. These different genetic groups, which could display differences in infection rates and trypanosome identity, were composed of small numbers of individuals that were captured together, leading to the observed Wahlund effect. Implications of this population structure on tsetse control are discussed.     

Population genetics of Glossina palpalis palpalis in sleeping sickness foci of Côte d’Ivoire before and after vector control

Glossina palpalis palpalis remains the major vector of sleeping sickness in Côte d'Ivoire. The disease is still active at low endemic levels in Bonon and Sinfra foci in the western-central part of the country. In this study, we investigated the impact of a control campaign on G. p. palpalis population structure in Bonon and Sinfra foci in order to adapt control strategies. Genetic variation at microsatellite loci was used to examine the population structure of different G. p. palpalis cohorts before and after control campaigns. Isolation by distance was observed in our sampling sites. Before control, effective population size was high (239 individuals) with dispersal at rather short distance (731 m per generation). We found some evidence that some of the flies captured after treatment come from surrounding sites, which increased the genetic variance. One Locus, GPCAG, displayed a 1000% increase of subdivision measure after control while other loci only exhibited a substantial increase in variance of subdivision. Our data suggested a possible trap avoidance behaviour in G. p. palpalis. It is important to take into account and better understand the possible reinvasion from neighboring sites and trap avoidance for the sake of sustainability of control campaigns effects.     

Reactivation of an old sleeping sickness focus in Mamfe (Cameroon): epidemiological, immunological and parasitological findings

We report the reactivation of an old sleeping sickness focus in Mamfe (Cameroon). Screening of 9827 people using the Testryp CATT (card agglutination test for trypanosomiasis) gave a total of 137 positive cases (1.4%). The prevalence of CATT positivity was significantly linked to sex, age, place of residence and type of occupation of the people. 26 of these immunological suspects were later confirmed as sleeping sickness patients, giving a morbidity index of 0.26%. Only 44% of 16 sera from these confirmed patients were CATT positive on serum while only 31% of the sera had a positive Indirect Immunofluorescent Antibody Test (IFAT) reaction, supporting the hypothesis of the existence of a new T.b gambiense serodeme in this region. The reasons for the reactivation of this old sleeping sickness focus are discussed.     

Characterization of Trypanozoon stocks from the South Nyanza sleeping sickness focus in Western Kenya

220 Trypanosoma (Trypanozoon) brucei sp. stocks isolated between 1969 and 1983 from the Lambwe valley sleeping sickness focus in South Nyanza, Western Kenya, were characterized by isoenzyme electrophoresis using 12 enzymes. 12 different zymodemes of T. (T.) b. rhodesiense were isolated from patients during the 13-year period and identical stocks were also found in cattle, reedbuck (Redunca redunca) and tsetse (Glossina pallidipes). Cattle may have played an important role in maintaining and increasing peridomestic transmission of trypanosomes during the 1980 outbreak of sleeping sickness in the valley, even though they themselves suffered heavy mortality. Sleeping sickness in Lambwe valley is unlikely to have been introduced from elsewhere, since T. (T.) b. rhodesiense stocks isolated from the valley were different from those from neighbouring epidemic areas. Alternatively, the recent outbreak may have been caused by the increased transmission associated with an expanding tsetse population. The possibility that genetic exchange contributed to the biochemical diversity of the trypanosomes examined is discussed.     

First isolation of Enterobacter,Enterococcus, and Acinetobacter spp. as inhabitants of the tsetse fly (Glossina palpalis palpalis) midgut

This paper reports the first evidence of the presence of bacteria, other than the three previously described as symbionts, Wigglesworthia glossinidia, Wolbachia, and Sodalis glossinidius, in the midgut of Glossina palpalis palpalis, the tsetse fly, a vector of the chronic form of human African trypanosomiasis in sub-Saharan African countries. Based on the morphological, nutritional, physiological, and phylogenetic results, we identified Enterobacter, Enterococcus, and Acinetobacter spp. as inhabitants of the midgut of the tsetse fly from Angola. Enterobacter spp. was the most frequently isolated. The role of these bacteria in the gut, in terms of vector competence of the tsetse fly, is discussed, as is the possibility of using these bacteria to produce in situ trypanolytic molecules.     

Monitoring the pleomorphism of Trypanosoma brucei gambiense isolates in mouse: Impact on its transmissibility to Glossina palpalis gambiensis

Substantial differences have been observed between the cyclical transmission of three Trypanosoma brucei gambiense field isolates in Glossina palpalis gambiensis (Ravel et al., 2006). Differences in the pleomorphism of these isolates in rodent used to provide the infective feed to Glossina, could explain such results, since stumpy forms are preadapted for differentiation to procyclic forms when taken up in a tsetse bloodmeal. To assess this possibility, mice were immunosuppressed and inoculated intraperitoneally with the three isolates (six mice for each trypanosome isolate); then parasitaemia and pleomorphism were determined daily for each mouse. The three T. b. gambiense isolates induced different infection patterns in mouse. The parasitaemia peak was rapidly reached for all the isolates and maintained until mice death for two isolates, while the third isolate rapidly showed a falling phase followed by a second parasitaemia plateau. The proportion of the stumpy forms varied from 15% to 70% over the duration of the experiment and according to the isolate. One isolate, which displayed the highest proportion of stumpy forms and reached the stumpy peak at the onset of the falling phase of parasitaemia, was used to study the relationship between the proportion of stumpy forms and transmissibility to tsetse fly. The results indicated that the transmissibility of trypanosomes was not correlated to the proportion of non-dividing stumpy forms.     

New concepts in the epidemiology of Rhodesian sleeping sickness

The results from recent studies of a number of outbreaks of T. rhodesiense sleeping sickness have enabled workers in this field to reconsider the epidemiology of the disease.     

Population genetics of Trypanosoma brucei gambiense in sleeping sickness patients with treatment failures in the focus of Mbuji-Mayi,Democratic Republic of the Congo

Human African trypanosomiasis (HAT) in the Democratic Republic of the Congo (DRC) is caused by the protozoan Trypanosoma brucei gambiense. Until recently, all patients in the second or neurological stage of the disease were treated with melarsoprol. At the end of the past and the beginning of the present century, alarmingly high relapse rates in patients treated with melarsoprol were reported in isolated HAT foci. In the Mbuji-Mayi focus of DRC, a particular mutation that confers cross resistance for pentamidine and melarsoprol was recently found for all strains studied. Nevertheless, treatment successfully cured a significant proportion of patients. To check for the existence of other possible genetic factors of the parasites, we genotyped trypanosomes isolated from patients before and after treatment (relapsing patients) with eight microsatellite markers. We found no evidence of any genetic correlation between parasite genotype and treatment outcome and we concluded that relapse or cure probably depend more on patients’ factors such as disease progression, nutritional or immunological status or co-infections with other pathogens. The existence of a melarsoprol and pentamidine resistance associated mutation at such high rates highlights an increasing problem, even for other drugs, especially those using the same transporters as melarsoprol and pentamidine.     

Further progress in the control of sleeping sickness in Nigeria

Three types of sleeping sickness are described as occurring in Nigeria— the mild type, the toxic and the nervous. The great majority of the cases found at sleeping sickness surveys belong to the first group. Patients suffer from occasional attacks of headache and fever and from some weakness, very little else. It is their increased susceptibility to intercurrent diseases which often caused the depopulation found in some of the more heavily infected areas. In the second group, which is much more rare, toxaemia is the salient feature. In the third, there are signs of progressive nervous involvement. The proportion of patients suffering from the three types varies. Even in the more virulent epidemics the mild form is common.In Northern Nigeria there is a striking correlation between the areas of infection and the lines of communication, railways, roads, and mining areas. The main zone is confined to the central part of the country. Peripheral areas, though heavily infested with tsetse-fly, are still practically free from infection.Nigerian policy is to establish convenient permanent treatment centres once a full survey of the whole population has been followed by mass treatment. The information obtained at the survey makes the planning of effective protective measures possible. The work of the sleeping sickness teams, dispensaries and the control of mines labour is described.From 1931 to 1943 a total of 3,148,069 people were examined in new areas and 306,322 cases found, an infection rate of 9·7 per cent. In the worst areas 913,718 people were re-examined and an infection rate of 2·2 per cent. found. During the first 5 years of this period the disease was still increasing. The average infection rate was 13·6 per cent. In the next 5 years the spread had been stopped though the infection rate was still high in the remaining new areas. From 1941 onwards the new areas discovered had a low infection rate. The rate for resurveys of what were formerly some of the worst areas was 2·5 per cent. Taking Northern Nigeria as a whole, it is doubtful if there is much more than a tenth of the old amount of infection.The sleeping sickness dispensary system has been expanded during the last few years. Some 80,704 cases of sleeping sickness have been treated. Practically all were voluntary attendances. The general medical and health work also has been improved.With the 43,674 cases treated at general medical stations, a total of 450,451 cases have been treated in the last 13 years. Of these about 400,000 were new cases, the remainder relapses. 'The control of the disease by communal clearing campaigns is described. So far about 240,400 people have been protected from any serious risk of contracting sleeping sickness.A brief account is also given of the Zaria sleeping sickness settlement scheme. So much attention has been paid to all aspects of rural planning and development in the settlement area that it has come to be regarded as a model of rural development.The changes in population figures, particularly in Zaria Emirate, give a striking indication of what has been accomplished. In the period 1923–1933, when the disease was increasing, the population fell by about 12 per cent. At the survey of the whole Emirate 78,000 cases were diagnosed and treated, an infection rate of 20 per cent. There was direct evidence of correlation between infection rates and mortality. With the decrease in sleeping sickness consequent on treatment and control, depopulation stopped. Since 1933 the total population has increased about 24 per cent. It is not claimed that results of treatment have been as valuable in the milder area where there was no sign of the disease causing immediate loss of population.The general position is much more satisfactory throughout the country though constant vigilance is necessary if this relative improvement is to be maintained.     

A history of Rhodesian sleeping sickness in the Lambwe Valley

The main events in the spread of Rhodesian sleeping sickness around the eastern shores of Lake Victoria during the 1930s and 1940s are summarized and the history of the disease in the Lambwe Valley area of western Kenya is described since its appearance there in 1959. The area was very receptive to the introduction and dispersal of T. rhodesiense on account of a close association between human communities and their domestic livestock, a large tsetse (Glossina pallidipes) population, and game animals. The possible origins of the first Lambwe Valley disease focus and the epidemiological significance of the main elements of the Lambwe environment (man, tsetse, game animals) are discussed in relation to the consolidation and spread of the disease throughout the area.     

The epidemiology of human sleeping sickness in the Lambwe Valley, South Nyanza, Kenya

Human infection with Trypanosoma rhodesiense in the Lambwe Valley area of South Nyanza, Kenya, was first reported in 1959 although T. gambiense sleeping sickness had been the present there since the turn of the century. The two forms of the disease are associated with the presence of the tsetse Glossina fuscipes, which is plentiful and widespread throughout the hinterland, including part of the study area, and G. fuscipes in the thickets near the shores of Lake Victoria and along some of the river systems. Fairly successful attempts have been made to eliminate tsetse by control operations around the lake shore and by aerial spraying of insecticide in the Lambwe Valley. The incidence and geographical distribution of cases of T. rhodesiense sleeping sickness in the Lambwe Valley are described in this report. Eight survey areas were studied between June 1968 and August 1970. Three types of survey procedure were adopted and blood samples were taken for examination. The most reliable method of demonstrating trypanosomes was by direct microscopy of stained blood films. Cases were treated with either suramin or melarsoprol, the latter being preferred for long-standing infections, but a course of suramin was given first. Although there were localized foci of infection in the study area, cases occurred sporadically, usually in April, i.e., in the early part of the long rainy season. It is suggested that, for diagnosis, survey teams should be replaced by a few fixed diagnostic microscopy centres.     

Identification of Trypanosoma brucei circulating in a sleeping sickness focus in C?te d'Ivoire: assessment of genotype selection by the isolation method.

Genetic studies of Trypanosoma brucei have been mainly based on rodent inoculation (RI) for isolation of trypanosome strains. However, Trypanosoma brucei gambiense is difficult to grow in rodents. The development and use of the Kit for In Vitro Isolation (KIVI) of trypanosomes has led to a better isolation success. However, some authors report a genetic monomorphism in T. b. gambiense, and the extensive use of the KIVI was suspected as being responsible for this low genetic diversity. In the present work, trypanosome stocks were isolated from both humans and pigs in an active sleeping sickness focus in C?te d'Ivoire. Two methods were simultaneously used for this purpose: KIVI and rodent inoculation. None of the human stocks grew in rodents. Some of the stocks originating from pigs could be isolated with both methods. Each of these stocks (from the same pig) showed a different isoenzymatic pattern according to the isolation method used. All the human stocks identified belonged to the major zymodeme 3 of T. b. gambiense group 1, whereas the stocks isolated from pigs belonged to a new group of zymodemes even if they were genetically closely related. These observations may have significant implications when analysing the population structure of T. brucei, and also raise again the question of the importance of the animal reservoir in Human African Trypanosomiasis (HAT).     

The hosts and trypanosome infection rates of Glossina pallidipes in the Lambwe and Roo valleys

Several thousand Glossina pallidipes flies were dissected to determine trypanosome infection rates in the Lambwe Valley and to collect information on the hosts of this tsetse. A total of 1 450 (19.3%) flies had mature trypanosome infections but the rate varied between 9.6% and 30.9% in the Lambwe Valley. In the Roo Valley the rate was 19.7-28.6%. Blood-meal squashes from tsetse collected in the Roo Valley and Obaluanda areas and in the Ruma, Otuok, and Rari thickets showed that the important hosts were bushbuck and bushpig. Analyses showed that T. brucei subgroup infection rates in the Roo Valley near two small dams (3.7% and 4.0%) were higher than might have been expected; in another part of the Roo Valley the rate was only 0.8%. To account for such a large difference it is concluded that the dissecting techniques were probably at fault, leading to an overestimation of T. brucei subgroup infection rates in the Roo Valley tsetse. In the main Lambwe Valley there was a tendency for the tsetse trypanosome infection rates to increase towards the southern part of the valley where game animals were numerous and readily available to tsetse in the favourable thicket habitats.     

Estimating the burden of rhodesiense sleeping sickness during an outbreak in Serere,eastern Uganda

Background  

Zoonotic sleeping sickness, or HAT (Human African Trypanosomiasis), caused by infection with Trypanosoma brucei rhodesiense, is an under-reported and neglected tropical disease. Previous assessments of the disease burden expressed as Disability-Adjusted Life Years (DALYs) for this infection have not distinguished T.b. rhodesiense from infection with the related, but clinically distinct Trypanosoma brucei gambiense form. T.b. rhodesiense occurs focally, and it is important to assess the burden at the scale at which resource-allocation decisions are made.