Hosts of Glossina fuscipes fuscipes and G. pallidipes in areas of western Kenya with endemic sleeping sickness, as determined using an egg-yolk (IgY) ELISA

Bloodmeal sources of Glossina fuscipes fuscipes and G. pallidipes, from the western Kenyan foci of human African trypanosomiasis (HAT) on Mageta Island and in Busia district, were identified using an ELISA based on chicken egg-yolk (IgY) antibodies. After absorption with cross-reacting antigens, the antibodies, which were produced against representatives of eight families of vertebrate host, were capable of differentiating serum from the different families. With the ELISA, it was possible to identify the family of host for 100% of laboratory-fed flies tested up to 48 h post-bloodmeal but only for 12% of such flies tested 96 h post-feed. Subsequently, attempts were made to identify the family of host that was the source of the (most recent) bloodmeal for each of 223 wild-caught flies, and these attempts were successful for 142 (63.7%) of the samples. Among the flies with identified bloodmeals, most (81.9%) of the G. f. fuscipes caught on Mageta Island had last fed on reptiles whereas most of the G. f. fuscipes (70.4%) and G. pallidipes (57.1%) caught in Busia had last fed on bovids. Bloodmeals of human origin accounted for <2% of the bloodmeals identified, perhaps indicating that, in the presence of alternative hosts, humans are not attractive hosts for tsetse in the study areas. This finding may account for the low reported incidence of HAT, despite the presence of circulating human-infective trypanosomes. In Busia at least, the use of animals, especially cattle, covered in insecticide would probably be an effective method of controlling the tsetse vectors of the trypanosomes that cause human and 'animal' trypanosomiases.     

Survey on bovine trypanosomosis and its vector in Metekel and Awi zones of Northwest Ethiopia

A cross-sectional study was conducted between November 2009 and December 2009 in the riverbank of Abay river tributaries, located in three districts of Awi and Metekel zones, Northwest Ethiopia. The prevalence of bovine trypanosomosis, associated risk factors and distribution as well as vector identification in the study area were considered. Blood samples were collected from 540 randomly selected local (zebu) breed of cattle in nine peasant associations of three districts and the assumed risk factors were recorded. The collected samples were examined using hematological and parasitological techniques. In this study, sixty-seven animals (12.42%) were infected with different species of trypanosomes. Most of the infections were due to T. congolense (77.6%) followed by T. vivax (14.9%), T. brucei (6.0%) and mixed infection of T. congolense and T. vivax (1.5%). There was no statistical significance (p > 0.05) between sex, age and coat color of skin, but significant differences were observed in body condition, altitude and districts (p < 0.05). Mean PCV value of infected (19.42%) and non-infected (24.13%) group of animals had significant variation; and mean PCV value of poor body condition was significantly different (p < 0.001) from good body condition. A total of 3072 tsetse flies of riverine species or palpalis group (Glossina tachinoides) and biting flies were caught, of these 2792 (90.9%) were tsetse flies and the remaining were Stomoxys and Tabanus. The overall apparent densities of tsetse and biting flies were 6.49 and 0.65 flies/trap/day, respectively and the difference was significant (p < 0.05). The study revealed that bovine trypanosomosis is more prevalent in low land and in poor body condition animals in the study area. Tsetse distribution also coincides with altitude, where there was high tsetse catch in low land, but none in mid land. Therefore, prompt control strategy has to be designed and implemented in the area to minimize the distribution of tsetse as well as trypanosomosis prevalence.     

Nutritional stress of adult female tsetse flies (Diptera: Glossinidae) affects the susceptibility of their offspring to trypanosomal infections

The epidemiology of tsetse-transmitted trypanosomiasis depends, among other factors, on the proportion of infected flies in a tsetse population. A wide range of intrinsic and extrinsic factors seem to determine the ability of a tsetse fly to become infected and to transmit the parasite. In this paper, we investigated the effect of nutritional stress of reproducing female Glossina morsitans morsitans on the susceptibility of their offspring to trypanosomal infections. Adult female flies that were nutritionally stressed by feeding only once a week, produced pupae with a significant lower weight and offspring with a significant lower fat content as well as a lower baseline immune peptide gene expression. Moreover, infection experiments showed that the emerging teneral flies were significantly more susceptible to a Trypanosoma congolense or Trypanosoma brucei brucei infection than flies emerging from non-starved adult females. These findings suggest that in the field, substantial nutritional stress of adult tsetse flies, as is often experienced during the hot dry season, can increase significantly the vectorial capacity of the emerging teneral flies and thus result in an increased infection rate of the tsetse population.     

Trypanosome infections in Glossina spp. inhabiting peridomestic agroecosystems in Nsukka area, Anambra State, Nigeria

Trypanosome infections in Glossina spp. inhabiting three peridomestic agroecosystems in Nsukka area were studied by dissection from April 1984 to July 1985. Approximately 0.65% of 4620 G. tachinoides and none of 17 G. palpalis were found with maturing or mature trypanosome infections. Of these infections, 20% were due to the Trypanosoma brucei group, 40% to the T. congolense group, and 40% to a mixture of the T. brucei and T. congolense groups. Trypanosome infection rates did not differ significantly with seasons or sex of fly, but they differed significantly with location. An apparent difference was observed in the frequency with which male and female G. tachinoides were infected by the various trypanosome species. Also there was a difference in the variety of trypanosome species encountered in the three locations. In infective flies, while the salivary gland, labrum and midgut were scantily to very heavily infected, the hypopharynx was never heavily infected. Dependence of tsetse flies on domestic pigs as the major source of blood meals, commercial activities in the area, the inherently limited vectorial capacity of palpalis group tsetse, and the fact that most flies apparently obtained their first blood meal when two to four days old, were identified as some of the factors responsible for the observed infection rates. The epizootiological and epidemiological implications of these findings are discussed.     

A study of host preference in tsetse flies using a modified heteroduplex PCR-based method

A study of host preference in tsetse flies using a modified heteroduplex PCR-based method is described. Domestic and wild animal blood samples were collected to extract the corresponding reference DNAs. In Campo (south Cameroon), tsetse flies (mainly Glossina palpalis palpalis) were trapped and 41 bloodmeals were collected. All reference DNAs and 37 bloodmeal DNAs (90.7%) were successfully amplified and hybridised. Twelve bloodmeals (32.4%) were of human origin, 13 (35.4%) were from Sitatunga (Tragelaphus spekei) (an antelope) while 12 (32.4%) were not identified using our set of reference DNAs. The results confirmed the occurrence of frequent contacts between wild animals and this population of tsetse flies.     

Infection rates in sterile males of morsitans, palpalis and fusca groups Glossina for pathogenic Trypanosoma species from East and West Africa

Infection rates in sterile male Glossina morsitans centralis, G. austeni, G. palpalis palpalis, G.p. gambiensis, G. fuscipes fuscipes, G. tachinoides and G. brevipalpis for Trypanosoma vivax, T. congolense and T. brucei isolated from East and West Africa, were studied. Five groups of the sterile males, together with the five groups of sexually fertile males, of each of the respective species and subspecies were allowed to feed for 24 days on a Boran calf or goats infected with T. vivax or T. congolense, or with T. brucei for 34 days, after which they were dissected. The results showed that the infection of the pathogenic Trypanosoma species became better established in some tsetse species than in others. Also, the infection rates of T. vivax, T. congolense and T. brucei for sterile and sexually fertile males of any of the above Glossina did not differ significantly. These results indicate that releases of sterile male tsetse in the tsetse control programme will potentially increase the risk of trypanosomiasis during the period of tsetse releases in the affected areas, unless in the areas with low tsetse density the sterile male tsetse are rendered refractory to trypanosome infection prior to their releases while in the areas with medium to high tsetse densities, the resident tsetse populations are initially reduced with insecticides, traps and/or targets.     

Studies on Trypanosoma (nannomonas) congolense II. Observations on the cyclical transmission of three field isolates by Glossina morsitans morsitans.

Teneral flies of Glossina morsitans morsitans were fed on mice infected with cloned and uncloned derivatives of three recent field isolates of Trypanosoma (Nannomonas) congolense. Flies with mature infections were identified by the warm-slide probe method and phase-contrast microscopy. High infection rates were achieved when such flies were fed on mice at peak parasitaemia. The infection rates were low when flies were fed on mice prior to or late after peak parasitaemia. The duration of the developmental cycle of T. congolense in the tsetse fly varied from 7 to 40 days: in 45% of the infective flies the developmental cycle was completed within 12 days; and in 76%, within 18 days.     

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.     

Description of a mono-screen trap for Glossina fuscipes fuscipes Newstead in Uganda.

A low-cost mono-screen trap for Glossina fuscipes fuscipes suitable for use by a rural community in Uganda is described. The trap has a single blue/black screen and a cone made from mosquito netting. The supporting framework is made from indigenous plant materials. The differences in trap catches between the mono-screen, biconical, pyramidal and vavoua traps were highly significant (P less than 0.001). Taking the standard biconical trap as control, the mono-screen trap was 1.25 times as efficient and the pyramidal trap was 0.04 times as efficient. The cost of one mono-screen trap is estimated as 1800 Uganda shillings (= U.S. $4.7), about half the cost of a pyramidal trap and one-quarter the cost of a biconical trap. The prospects for the use of the mono-screen trap by the community are discussed.     

Comparative sensitivity of dot-ELISA, PCR and dissection method for the detection of trypanosome infections in tsetse flies (Diptera: glossinidae)

A visually read dot-enzyme linked immunosorbent assay (dot-ELISA) developed for the detection of trypanosomes in tsetse flies (Glossina spp.) was evaluated in the laboratory and under field conditions. In the evaluation, the fly dissection method was used as a standard technique and compared to the polymerase chain reaction (PCR). In laboratory studies, 133 and 126 tsetse flies were experimentally infected with different stocks of Trypanosoma brucei and T. congolense, respectively. Twenty-five days after infection, the flies were dissected and tested for the presence of trypanosomes using dot-ELISA and PCR. Dot-ELISA detected 98.4% of T. brucei and 94% of T. congolense infections in tsetse midguts, while PCR detected 97.6% of T. brucei and 96% of T. congolense tsetse midgut samples. For field evaluation of dot-ELISA, 700 tsetse flies were caught and screened for trypanosome infections by dissection. Seven of these (1%) had trypomastigotes in the midgut, 23 (3.3%) in the proboscis and none had trypanosomes in the salivary glands. All the flies with midgut infections also had trypanosomes in their proboscides. Five of the seven flies (71.4%) with midgut infections revealed by dissection, were also positive for T. congolense by the dot-ELISA and PCR techniques. Dot-ELISA detected T. congolense infections in an additional 86 (12.4%) of the 700 flies dissected. Of the 23 infections in the proboscis, 16 were T. vivax. Dot-ELISA detected 13 of the 16 (81%) while PCR detected 15 of 16 (94%) T. vivax infections. No T. brucei infection was detected by any of the methods in all the 700 tsetse flies examined. The results obtained from both the laboratory and field studies indicate that the dot-ELISA and PCR techniques are sensitive and species-specific in revealing trypanosome infections in tsetse flies. While dot-ELISA required a single test to detect T. congolense, several primer pairs were needed for PCR. The potential use of dot-ELISA as a tool for studying the epidemiology of trypanosomosis, while considering its field applicability and relatively lower cost is discussed.     

Effects of Ethidium (homidium bromide) on female reproductive performance of laboratory-reared tsetse flies, Glossina morsitans morsitans Westwood (Diptera: Glossinidae)

Ethidium^® (homidium bromide) is a trypanocide likely to be encountered as a violative residue in blood collected from abattoirs for feeding laboratory tsetse flies. We investigated its effect on female reproduction of Glossina morsitans morsitans. One-milligram homidium per kilogram body weight was intra-muscularly administered to four steers and blood aseptically collected from them between 15 and 30 min post-treatment, analysed for homidium levels and processed for tsetse feeding. Two hundred teneral female flies were fed on homidium-treated diet while a control group of similar number was given untreated diet and the reproductive performance of the two groups statistically compared. Ethidium^®, at 266.15 ng homidium/ml blood diet, halved A-class portion of F₁-pupae, highly reduced decline of F₁-progeny quality associated with aging parents, but had no significant effect on the pupae viability, fecundity and abortion rate of the flies. We therefore concluded that Ethidium^® has beneficial effect on laboratory tsetse attributable to clearance of unfavourable microbes mediated by the drug, and could be used as a tsetse diet additive.     

Trypanosoma brucei rhodesiense: enhancement of infection rates in the tsetse fly, Glossina morsitans, by feeding artificial bloodmeal mixtures

Low mature salivary gland (SG) infection rates (6%) in less than 24-hour-old flies fed on blood containing bloodform trypanosomes can be significantly enhanced by feeding flies an artificial mixture containing procyclic forms in a red cell: culture medium mixture (procyclic mixture, SG rate = 21.0%). However, enhancement is not solely a function of the use of procyclic forms since blood forms fed to flies in the same red cell: culture medium mixture produce SG rates (15.4%) intermediate to those of blood forms in blood and procyclic mixtures. Use of these artificial mixtures produces a similar result in 24- to 48-hour-old flies and also tends to equalize their infection rates with those found in less than 24-hour-old flies. The possible relationships between the different infection rates observed and digestive proteinases in the tsetse fly are discussed.     

Heterogeneity in the trypanosomosis incidence in Zebu cattle of different ages and sex on the plateau of eastern Zambia

On the plateau of eastern Zambia, trypanosomosis is endemic. Glossina morsitans morsitans Westwood (Diptera: Glossinidae), the only tsetse species present, is almost entirely dependent on livestock as its source of food with cattle being the most preferred host. To determine if tsetse challenge is distributed equally over the various age categories and sexes within a cattle herd, a longitudinal study of trypanosomosis incidence was conducted during the rainy season. A total of 354 head of cattle consisting of 40% oxen, 30% cows, 15% young stock, 13% calves and 2% bulls were sampled for three consecutive months and their infection statuses determined using the PCR-RFLP technique as diagnostic method. Results indicated that there were significant differences (P<0.001) in the proportion of infected animals between the various categories. In oxen, the risk of infection was 5.6 times higher than in calves. Those results suggest heterogeneity in the challenge by tsetse flies and are in line with entomological observations on the feeding preference of tsetse on cattle. The implications of these results for the control of trypanosomosis in Eastern Province and other epidemiologically related areas are discussed.     

Detection of Trypanosoma brucei in field-captured tsetse flies and identification of host species fed on by the infected flies

The prevalence of trypanosome infections in tsetse flies in the Chiawa area of Lower Zambezi in Zambia, with endemic trypanosomosis, was determined by a polymerase chain reaction (PCR) method that allowed the detection of trypanosome DNA and determination of the type of animal host fed on by the tsetse fly Glossina pallidipes, using tsetse-derived DNA extracts as templates. Ninety G. pallidipes (82 females and 8 males; 18.3%) of the 492 flies captured by baited biconical traps tested positive for the presence of Trypanosoma brucei species genomic DNA. Of the 90 T. brucei-positive flies, 47 (52.2%) also tested positive for vertebrate mitochondrial DNA. Sequence analysis of the vertebrate mitochondrial DNA amplicons established that they originated from 8 different vertebrate species, namely, human (Homo sapiens), African elephant (Loxodonta cyclotis), African buffalo (Syncerus caffer), waterbuck (Kobus ellipsiprymnus), roan antelope (Hippotragus equinus), greater kudu (Tragelaphus strepsiceros), warthog (Phacochoerus africanus), and goat (Capra hircus). Furthermore, to investigate the prevalence of trypanosome infections in domestic goats in the same area where trypanosomes had been detected in tsetse files, a total of 86 goats were randomly selected from 6 different herds. Among the selected goats, 36 (41.9%) were found to be positive for T. brucei species. This combined detection method would be an ideal approach not only for mass screening for infection prevalence in tsetse populations, but also for the prediction of natural reservoirs in areas endemic for trypanosomosis.     

Isolation of Borrelia burgdorferi from Neotoma fuscipes, Peromyscus maniculatus, Peromyscus boylii, and Ixodes pacificus in Oregon.

The number of Lyme disease cases in Oregon has increased in recent years despite the fact that the pathogen, Borrelia burgdorferi, has never been isolated in the state. Rodent and tick surveys were undertaken in 1997 to isolate and characterize strains of B. burgdorferi from Oregon and to identify potential reservoirs and vectors of Lyme disease. Borrelia burgdorferi was isolated from Neotoma fuscipes, Peromyscus maniculatus, P. boylii, and Ixodes pacificus. Both N. fuscipes and P. maniculatus were infested with I. pacificus and I. spinipalpis. Although I. pacificus infested P. boylii, I. spinipalpis was not found on this rodent, and only 4% of the P. boylii were infected with B. burgdorferi compared with the 19% and 18% infection rates found in N. fuscipes and P. maniculatus, respectively. Variation in the molecular weights of the outer surface proteins A and B were found in these first confirmed isolates of B. burgdorferi from Oregon, as well as truncated forms of outer surface protein B.     

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, C?te 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.     

Trypanosomiasis 'risk' or 'challenge': a review

Definitions of the term 'challenge' as applied to the African trypanosomiases are reviewed. Data from one West and one East African site show simple linear relationships between the incidence of trypanosomiasis in both humans and animals, and either the amount of man-tsetse contact, or the Apparent Density of flies. Data from a number of East African sites are analysed and show a linear relationship between the mean Berenil Index of cattle and the logarithm of the challenge, where challenge is the simple product of Apparent Density and mean fly infection rate. Apparent Density is a more variable element of total challenge than is infection rate. The results of field studies are analysed to show that Berenil has a short prophylactic effect, lasting for about 22 days in cattle. When allowance is made for this effect there is a direct, apparently linear relationship between the daily probability of infection of cattle and total challenge, the latter varying over almost three orders of magnitude. Variations in tsetse fly density account for about 50% of the variability of Apparent Density. Hence the latter is a crude estimate of the former. Seasonal and density-related changes in the availability of flies to human catchers could account for the inadequacies of the fly-round technique in assessing fly density and/or challenge. Evidence at present available suggests that trypanotolerant cattle are more likely to be an economic alternative to drug-treated zebu at higher rather than lower challenge levels. Whether either type of animal could profitably be raised in areas of the highest challenge and without some form of tsetse control remains an open question.     

Vector competence of Glossina pallidipes and G. morsitans centralis for Trypanosoma vivax, T. congolense and T. b. brucei.

Vector competence of Glossina pallidipes for pathogenic Trypanosoma species was compared to that of G. morsitans centralis. Cattle or goats were the hosts used to infect teneral tsetse, rabbits were used to maintain tsetse which were dissected on day 30. Mean infection rates of G. pallidipes and G. m. centralis by T. vivax isolated from a cow in Kenya were respectively 39.5 +/- 8.9% and 32.1 +/- 10.3% whilst for T. vivax isolated from a cow in Nigeria, they were 30.0 +/- 7.5% and 19.8 +/- 4.3%. Differences were not significant. Differences in infection rates between the sexes of flies were also not significant. Transmission capability to goats by either tsetse species was good for the two T. vivax isolates. Mean infection rates by T. congolense isolated from a lion in Tanzania were significantly lower in G. pallidipes (8.5 +/- 1.8%) than in G. m. centralis (22.5 +/- 2.0%). Males of either tsetse were more susceptible than females. Transmission rates to goats and mice by both tsetse species was 100%. G. pallidipes (3.5%) was less susceptible than G. m. centralis (25.1%) to T. congolense isolated from a cow in Nigeria, but transmission rates to goats and mice by either tsetse was 100%. Also, G. pallidipes (2.7 +/- 0.4%) was significantly less susceptible than G. m. centralis (18.4 +/- 1.1%) to T. b. brucei isolated from a hartebeest in Tanzania. Males of either tsetse species were more susceptible than females. Transmission rates to goats and mice by either tsetse was 100%. G. pallidipes (0%) was not susceptible to T. b. brucei isolated from a pig in Nigeria whilst G. m. centralis showed infection rate of 9.3%. When male G. pallidipes and G. m. centralis were fed every day for 27 days on a goat infected with this T. b. brucei from Nigeria, the infection rates were 8.7% and 20.2%, respectively. Transmission rates to mice by either tsetse species was 100%. In conclusion, G. pallidipes has a vector competence equal to that of G. m. centralis for T. vivax, whilst G. pallidipes has lower vector competence than G. m. centralis for T. congolense and T. b. brucei.     

Tsetse fly blood meal modification and trypanosome identification in two sleeping sickness foci in the forest of southern Cameroon

The blood meal origins of 222 tsetse flies (213 Glossina palpalis palpalis, 7 Glossina pallicera pallicera, one Glossina nigrofusca and one Glossina caliginea) caught in 2008 in two Human African trypanosomiasis foci (Bipindi and Campo) of south Cameroon were investigated. 88.7% of tsetse flies blood meals were identified using the heteroduplex method and the origin of the remaining blood meals (11.3%) was identified by sequencing the cytochrome B gene. Most of the meals were from humans (45.9%) and pigs (37.4%), 16.7% from wild animals. Interestingly, new tsetse fly hosts including turtle (Trionyx and Kinixys) and snake (Python sebae) were identified. Significant differences were recorded between Bipindi where the blood meals from pigs were predominant (66.7% vs 23.5% from humans) and Campo where blood meals from humans were predominant (62.9% vs 22.7% from pigs). Comparison with the data recorded in 2004 in the same foci (and with the same molecular approach) demonstrated significant modifications of the feeding patterns: increase in blood meals from pigs in Bipindi (66.7% in 2008 vs 44.8% in 2004) and in Campo (20.5% in 2008 vs 6.8% in 2004), decrease in that from human (significant in Bipindi only). 12.6%, 8.1% and 2.7% of the flies were, respectively, Trypanosoma congolense forest type, Trypanosoma congolense savannah type and Trypanosoma brucei gambiense infected. These results demonstrate that tsetse fly feeding patterns can be specific of a given area and can evolve rapidly with time. They show an active circulation of a variety of trypanosomes in sleeping sickness foci of southern Cameroon.