Feeding behaviour of Glossina pallidipes and g. morsitans centralis on Boran cattle infected with trypanosoma congolense or T. vivax under laboratory conditions

In field studies, tsetse flies (Diptera: Glossinidae) feed more successfully on cattle infected with Trypanosoma congolense Broden (Kinetoplastida: Trypanosomatidae) than on cattle infected with T. vivax Ziemann or uninfected cattle. Here we describe the first laboratory investigation of this phenomenon. In the first experiment, caged Glossina pallidipes Austen were fed for 1 and 5 min on a Boran steer infected with T. congolense clone IL 1180 and on an uninfected steer. Feeding success was recorded in this way five times over several weeks. The same protocol was subsequently used in three additional experiments with the following combinations: G. pallidipes and a steer infected with T. vivax stock IL 3913, G. morsitans centralis Machado and a steer infected with T. congolense, and G. morsitans centralis and a steer infected with T. vivax. The four experiments were replicated once, making eight experiments in total. In three experiments there was increased tsetse feeding success, measured at 1 min, after a steer became infected (T. congolense, two experiments and T. vivax, one experiment). Analysis of all data combined found no significant differences in tsetse feeding success on the different groups of cattle prior to infection, but after infection tsetse feeding success was significantly greater on the infected cattle (P< 0.001). Trypanosoma congolense infection led to a greater increase in tsetse feeding success than T. vivax infection. The increase in feeding success was not related to changes in the level of anaemia, skin surface temperature or parasitaemia. A possible explanation is the effects of trypanosome infection on cutaneous vasodilation and/or blood clotting in infected cattle. When allowed to feed for 5 min, nearly all tsetse engorged successfully and effects of cattle infection on feeding success were not found.     

Trypanosoma congolense: susceptibility of cattle to cyclical challenge

Cattle primed by cyclical infection with Glossina morsitans morsitans infected with cloned derivatives of Trypanosoma congolense and treated with the trypanocidal drug Berenil after 3 or 4 weeks were immune to cyclical challenge with homologous clones 3 to 5 weeks later. In these animals, localized skin reactions (chancres) and parasitemia did not develop. The same results were obtained in cattle given a homologous superinfection without prior treatment. On the other hand, cattle subjected to a cyclical challenge with heterologous clones were completely susceptible as demonstrated by the development of chancres. Immunity to homologous challenge was achieved irrespective of the bloodstream variable antigenic types used to infect the tsetse. It was concluded that for a given serodeme the variable antigen composition of the metacyclic population which develops in the tsetse is constant and characteristic. Immunity to cyclical challenge was also obtained with uncloned stocks, providing the same stock was used for challenge. On the other hand, cattle immune to homologous cyclical challenge with cloned material were not always immune to cyclical challenge with parent stock, indicating that certain stocks consist of more than one serodeme. On the basis of these findings, it may be possible to use the chancre as a marker for serodeme analysis.     

Comparative study on the infection rates of different laboratory strains of Glossina species by Trypanosoma congolense

Teneral Glossina morsitans centralis Machado, G.austeni Newstead, G.palpalis palpalis Robineau-Desvoidy, G.p.gambiensis Vanderplank, G.fuscipes fuscipes Newstead, G.tachinoides Westwood and G.brevipalpis Newstead, from laboratory-bred colonies, were fed at the same time on the flanks of ten goats infected with Trypanosoma congolense Broden isolated in Tanzania or in Nigeria. The seven tsetse species were infected over the range 0.3-49.2%. Survival of both T.congolense isolates was best in G.m.centralis, poorest in G.austeni and the four palpalis group tsetse, with G.brevipalpis intermediate. It is suggested that there are differences in the gut of different laboratory-bred cultures of Glossina Westwood species and subspecies such that T.congolense parasites can survive better in the gut of some than in others and undergo cyclical development to metacyclics in the hypopharynx.     

Comparison of the susceptibility of different Glossina species to simple and mixed infections with Trypanosoma (Nannomonas) congolense savannah and riverine forest types

Abstract Teneral Glossina morsitans mositans, G.m.submorsitans, G.palpalis gambiensis and G.tachinoides were allowed to feed on rabbits infected with Trypanosoma congolense savannah type or on mice infected with T.congolense riverine-forest type. The four tsetse species and subspecies were also infected simultaneously in vitro on the blood of mice infected with the two clones of T.congolense via a silicone membrane. The infected tsetse were maintained on rabbits and from the day 25 after the infective feed, the surviving tsetse were dissected in order to determine the infection rates.
Results showed higher mature infection rates in morsitans-gwup tsetse flies than in palpalis-group tsetse flies when infected with the savannah type of T.congolense. In contrast, infection rates with the riverine-forest type of T.congolense were lower, and fewer flies showed full development cycle. The intrinsec vectorial capacity of G.m.submorsitans for the two T.congolense types was the highest, whereas the intrinsic vectorial capacity of G.p.gambiensis for the Savannah type and G.m.morsitans for the riverine-forest type were the lowest. Among all tsetse which were infected simultaneously with the two types of T.congolense , the polymerase chain reaction detected only five flies which had both trypanosome taxa in the midgut and the proboscis. All the other infections were attributable to the savannah type.
The differences in the gut of different Glossina species and subspecies allowing these two sub-groups of T.congolense to survive better and undergo the complete developmental cycle more readily in some species than other are discussed.     

The effect of starvation on the susceptibility of teneral and non-teneral tsetse flies to trypanosome infection

Transmission of vector-borne diseases depends largely on the ability of the insect vector to become infected with the parasite. In tsetse flies, newly emerged or teneral flies are considered the most likely to develop a mature, infective trypanosome infection. This was confirmed during experimental infections where laboratory-reared Glossina morsitans morsitans Westwood (Diptera: Glossinidae) were infected with Trypanosoma congolense or T. brucei brucei. The ability of mature adult tsetse flies to become infected with trypanosomes was significantly lower than that of newly emerged flies for both parasites. However, the nutritional status of the tsetse at the time of the infective bloodmeal affected its ability to acquire either a T. congolense or T. b. brucei infection. Indeed, an extreme period of starvation (3-4 days for teneral flies, 7 days for adult flies) lowers the developmental barrier for a trypanosome infection, especially at the midgut level of the tsetse fly. Adult G. m. morsitans became at least as susceptible as newly emerged flies to infection with T. congolense. Moreover, the susceptibility of adult flies, starved for 7 days, to an infection with T. b. brucei was also significantly increased, but only at the level of maturation of an established midgut infection to a salivary gland infection. The outcome of these experimental infections clearly suggests that, under natural conditions, nutritional stress in adult tsetse flies could contribute substantially to the epidemiology of tsetse-transmitted trypanosomiasis.     

Trypanosoma vivax in Glossina palpalis gambiensis do not appear to affect feeding behaviour, longevity or reproductive performance of the vector

Feeding behaviour of Glossina palpalis gambiensis Vanderplank infected with Trypanosoma vivax Ziemann was studied and compared with that of uninfected control tsetse. The parameters measured were: total number of probes into the ear-skin of rabbits; rate of bloodmeal engorgement; weight of freshly ingested blood; survival; and mean weight of pupae. The results showed that the rosettes of T.vivax parasites in the labrum did not interfere with the feeding behaviour of the vectors. Furthermore, mean survival of T. vivax-infected males was significantly higher (82.2 +/- 4.2 days) compared with that of uninfected ones (70.5 +/- 3.1 days). However, with the female tsetse, mean survival of those infected was lower (98.8 +/- 4.0 days) compared to the uninfected controls (102.2 +/- 5.6 days), but the difference was not significant. A few infected males and females lived a little longer than the uninfected ones. Fecundity of the female tsetse remained unaffected by the infection, and furthermore the mean weight of pupae from the infected females was not significantly different from that of pupae from the uninfected control group. Thus the physiology of pregnant female tsetse in terms of nourishment of intra-uterine larva was unaffected by T.vivax infection. Two successive probes into the skin of two different goats followed by feeding on a third goat by each of four infected tsetse resulted in successful transmission of the infection to eleven out of twelve goats. Thus probing alone into the skin of this host can result in the transmission of T.vivax infection.     

Effect of puparia incubation temperature: increased infection rates of Trypanosoma congolense in Glossina morsitans centralis, G.fuscipes fuscipes and G.brevipalpis

Puparia of Glossina morsitans centralis (Machado), G.fuscipes fuscipes (Newstead) and G.brevipalpis (Newstead) were incubated at 25 +/- 1 degrees C, 28 +/- 1:25 +/- 1 degrees C, day:night or 29 +/- 1 degrees C throughout the puparial period, and maintained at 70-80% relative humidity. Puparial mortality was higher at 29 than at 25 degrees C (optimum temperature) in all three species, particularly in G.f.fuscipes and G.brevipalpis. Adults of G.m.centralis from puparia incubated at 29 degrees C, and those of this subspecies, G.f.fuscipes and G.brevipalpis from puparia incubated at 28:25 degrees C, day:night or 25 degrees C throughout, were infected as tenerals (27 h old) by feeding them at the same time on goats infected with Trypanosoma congolense (Broden) IL 1180 after the parasites were detected in the wet blood film. Infection rates on day 25 post-infected feed were higher in G.m.centralis from puparia incubated at 29 degrees C and in adults of the three different tsetse species from puparia incubated at 28:25 degrees C, day:night, than in those from puparia incubated at 25 degrees C. However, in G.f.fuscipes the labral and hypopharyngeal infection rates were not significantly different from those of the tsetse produced by puparia kept at 25 degrees C.     

Comparative study on the susceptibility of different laboratory strains of Glossina species to Trypanosoma simiae

Abstract. Teneral tsetse of four Glossina species from laboratory-reared colonies were fed on four Large White pigs infected with three different stocks of Trypanosoma simiae isolated in Coast Province, Kenya. Thereafter the tsetse were maintained on goats and dissected on day 28 to determine the trypanosome infection rates. Glossina brevipalpis was as susceptible as G.pallidipes whilst G.palpalis gambiensis was not susceptible to T.simiae CP 11 a stock causing acute infection, which was isolated from a wild G.austeni. Glossina brevipalpis was as susceptible as G.pallidipes to another stock causing acute infection, T.simiae CP 813 isolated from a wild G.pallidipes. Glossina morsitans centralis was also as susceptible as G.brevipalpis and G.pallidipes whilst G.p.gambiensis was not susceptible to this T.simiae stock. Glossina m.centralis showed very low susceptibility to a stock causing chronic infection, T.simiae CP 1896 isolated from a bushpig, whilst G.brevipalpis, G.p.gambiensis and G.pallidipes could not be infected by this T.simiae stock. Male Glossina were generally more susceptible than females to the three T.simiae stocks.     

Selection of susceptible and refractory lines of Glossina morsitans centralis for Trypanosoma congolense infection and their susceptibility to different pathogenic Trypanosoma species

Abstract .In a single generation of selection, two lines of Glossina morsitans centralis were established that differed significantly in susceptibility to Trypanosoma congolense clone IL 1180. Reciprocal crosses demonstrated that susceptibility was a maternally inherited trait. Differences between the lines, to all phases of the trypanosome infection, were maintained for eight generations, whereas differences in susceptibility to midgut infections were maintained for twenty-eight generations. Thereafter, the lines did not differ in susceptibility to Trypanosoma congolense IL 1180. Susceptibility to infections with Trypanosoma congolense IL 1180 was only a weak predictor of susceptibility to T. congolense clones IL 13-E3 and K60/1, as well as clone T. brucei brucei STIB 247-L. However, the susceptible and refractory lines displayed these phenotypes when tested with Trypanosoma vivax, indicating that the factors that affect susceptibility to trypanosomes are expressed both within and outside the midgut.     

A comparison of African buffalo, N''Dama and Boran cattle as reservoirs of Trypanosoma congolense for different Glossina species

Teneral Glossina morsitans centralis Machado were fed on the flanks of the African buffalo (Syncerus caffer Sparrman), N'Dama (Bos taurus L.) or Boran (Bos indicus L.) cattle infected with Trypanosoma congolense Broden. The infected tsetse were maintained on rabbits and on day 30 after the infected feed, the surviving tsetse were dissected to determine the infection rates. The mean infection rates (% +/- SE) in the midgut of tsetse fed on buffalo, N'Damas and Borans were 23.5 +/- 3.3, 31.6 +/- 2.7 and 33.7 +/- 4.6, respectively. The differences were not significant. However, the mean mature infection rate in tsetse fed on the buffalo (13.2 +/- 2.1%) was significantly lower compared to the rates in tsetse fed on the N'Dama (20.4 +/- 1.4) or the Boran cattle (21.4 +/- 1.1). When groups of teneral G.m.centralis, G.pallidipes Austen, G.p.gambiensis Vanderplank, G.f.fuscipes Newstead, G.brevipalpis Newstead and G.longipennis Corti were fed simultaneously on either an infected buffalo, an N'Dama or a Boran steer, the mature infection rates ranged from 0 to 16.1%. Irrespective of the host species used, the T.congolense infection rate was highest in G.m.centralis, lowest in the palpalis and fusca group tsetse, with G.pallidipes being intermediate. Nevertheless, the trypanoresistant African buffalo and N'Dama may serve as reservoirs of T.congolense as can trypanosusceptible Boran cattle.     

Trypanosoma vivax: sequence of antigenic variants in mice and goats

Three populations composed of different variable antigen types were derived from a clone of the recently isolated mouse-infective Trypanosoma vivax stock Zaria Y486. The antigenic composition of the trypanosome populations which appeared following infection of mice and goats with these populations was compared using the immune lysis test. Significant differences were observed in the antigenic composition of both the initial and relapse populations obtained from goats and mice. These observations suggest that there may be selective growth of different variable antigen types in different hosts with the result that the antigenic composition of a goat-derived population may be greatly altered following subinoculation into normal mice. This can be somewhat reduced however if goat derived populations are subinoculated into lethally irradiated mice. Two antigenically different T. vivax populations were also cyclically transmitted to individual goats in a preliminary study of the effect of tsetse transmission on the antigenic composition of the ingested populations. It was observed that the composition of the first detectable populations in the infected goats was similar but different from that ingested by the tsetse flies.     

A comparison of susceptibility of two allopatric populations of Glossina pallidipes for stocks of Trypanosoma congolense

Abstract. A colony of Glossina pallidipes Austen which originated from Nguruman, Rift Valley Province, Kenya, was significantly more susceptible to infection (19.3%) with a stock of Trypanosoma congolense Broden isolated from G. pallidipes in Nguruman than a colony of the same species which originated from Shimba Hills, Coast Province, Kenya (5.6%). Male G. pallidipes from Nguruman were significantly more susceptible than females to this T. congolense stock whilst the susceptibility of both sexes of G. pallidipes from Shimba Hills did not differ significantly. All six goats on which six infected G. pallidipes fed singly (three tsetse per colony) became infected. Similarly, the G. pallidipes colony of Nguruman origin was significantly more susceptible to infection (16.4%) with a stock of T. congolense isolated from G. pallidipes in Shimba Hills than the colony of Shimba Hills origin (4.9%). The susceptibility of the sexes of G. pallidipes from both the colonies to this stock of T. congolense did not differ significantly. Again, all six goats on which six infected G. pallidipes fed singly (three tsetse per colony) became infected. If the observed differences in susceptibility of the two G. pallidipes colonies reflect transmission of trypanosomes by the two allopatric populations of tsetse in the field, then the epidemiology of congolense-trypanosomiasis in livestock must differ between these two areas of Kenya endemic for trypanosomiasis.     

Suppressive action of Samorin on the cyclical development of pathogenic trypanosomes in Glossina morsitans centralis

Male Glossina sexually sterilized by gamma-irradiation are as efficient vectors of trypanosomiasis as fertile males. An attempt was made, using isometamidium chloride (Samorin), to interfere with the cyclical development of trypanosomes in sterile males, destined for use in the sterile insect release (SIR) method of tsetse eradication. The infection rate with mature Trypanosoma congolense Broden was effectively reduced in sterile male Glossina morsitans centralis Machado, when the flies were fed on an infected goat 2 days after they were fed as tenerals on an in vitro bloodmeal containing 8 micrograms Samorin/ml blood. The infection rates with mature T.vivax Ziemann and T.brucei brucei Plimmer & Bradford were completely suppressed at this drug dose. Whensterile teneral males were fed on a bloodmeal containing 12 micrograms/ml Samorin and given the infected bloodmeal 10 days later, infections by mature T.vivax, T.congolense and T.b.brucei were completely suppressed. Hence in the management of a tsetse eradication programme utilizing the SIR method, it is recommended that the sterile teneral male tsetse should, prior to release, be given a bloodmeal containing Samorin at 12-15 micrograms/ml blood. This will effectively suppress future disease transmission.     

Comparison of the infection rate of tsetse, Glossina morsitans morsitans, fed in vitro or in vivo

Studies were made of infection rates of trypanosomes in the tsetse fly Glossina morsitans morsitans Westwood (Diptera: Glossinidae) when maintained in vivo (rabbits) or in vitro on high quality, gamma-irradiated, sterile defibrinated bovine blood, obtained from the Entomology Unit of the International Atomic Energy Agency (IAEA). For both Trypanosoma congolense Broden and T. b. brucei Plimmer & Bradford, in vitro maintenance significantly reduced the proportion of flies that developed mature metacyclic trypanosome infections.     

New epidemiological features on animal trypanosomiasis by molecular analysis in the pastoral zone of Sideradougou, Burkina Faso

A multidisciplinary work was undertaken in the agropastoral zone of Sidéradougou, Burkina Faso to try to elucidate the key factors determining the presence of tsetse flies. In this study the PCR was used to characterize trypanosomes infecting the vector ( Glossina tachinoides and Glossina palpalis gambiensis ) and the host, i.e. cattle. A 2-year survey involved dissecting 2211 tsetse of the two Glossina species. A total of 298 parasitologically infected tsetse were analysed by PCR. Trypanosoma vivax was the most frequently identified trypanosome followed by the savannah type of T. congolense and, to a lesser extent, the riverine forest type of T. congolense , and by T. brucei . No cases of T. simiae were found. From the 107 identified infections in cattle, the taxa were the same, but T. congolense savannah type was more frequent, whereas T. vivax and T. congolense riverine forest types were found less frequently. A correlation was found between midgut infection rates of tsetse, nonidentified infections and reptile bloodmeals. These rates were higher in G.p. gambiensis , and in the western part of the study area. T. vivax infections were related to cattle bloodmeals, and were more frequent in G. tachinoides and in the eastern study area. The PCR results combined with bloodmeal analysis helped us to establish the relationships between the vector and the host, to assess the trypanosome challenge in the two parts of the area, to elucidate the differences between the two types of T. congolense , and to suspect that most midgut infections were originating from reptilian trypanosomes.     

Effects of an experimental Trypanosoma congolense infection on the reproductive performance of West African Dwarf goats

Thirty-six West African Dwarf (WAD) goats were used to assess the effects of an experimental Trypanosoma congolense infection on their reproductive system. Estrous cycles were synchronised and when confirmed pregnant (n = 31), the does were randomly allocated into control and trypanosome-infected groups. After infection, the animals were carefully observed till parturition. Trypanosome infection caused an increase of rectal temperature, a significant drop in PCV (infected: 23.3 +/- 0.3%; control: 28.5 +/- 0.4%; P < 0.0001) and abortions in 27.8% of the infected does. Kids born from infected does had a lower birth weight than kids born from control goats (0.9 +/- 0.1 kg versus 1.6 +/- 0.1 kg; P < 0.0001). Eight out of 13 kids (61.5%) that were born alive from infected does died during their first week of life. Plasma pregnancy-associated glycoprotein (PAG) and progesterone concentrations were lower in the infected animals than in the controls. In general, PAG concentration in does which aborted dropped before abortion. Our results revealed that artificial T. congolense infection affected reproductive performance of WAD goats with abortions, premature births and perinatal losses being observed. Neither transplacental transmission of T. congolense nor histopathological lesions of the placenta could be demonstrated.     

Studies on the transmission of a West African stock of Trypanosoma vivax to rabbits,rats, mice and goats by Glossina morsitans morsitans and G. m. centralis

The cyclical transmission of a West African stock of Trypanosoma vivax by Glossina morsitans morsitans and G. m. centralis was studied. It was possible to transmit this parasite amongst rabbits, rats, mice and goats. Whereas goats and mice succumbed to the disease very rapidly, rats and rabbits showed scant and transient parasitaemia and frequently suppressed the infection. A trypanosome challenge using single infected tsetse showed that goats became infected much more readily than mice. The infected vector can transmit the infection throughout its life but not at every feed.     

A comparison of susceptibility to stocks of Trypanosoma simiae of Glossina pallidipes originating from allopatric populations in Kenya

Abstract. A colony of Glossina pallidipes which originated from Nguruman, Rift Valley Province, Kenya, was significantly more susceptible than a colony of the same species which originated from Shimba Hills, Coast Province, Kenya, to infection with a stock of Trypanosoma simiae CP 11 isolated from wild G. austeni in Coast Province, Kenya, irrespective of whether pigs or goats were used as infecting hosts. Male G. pallidipes from both the colonies were more susceptible than females to this T. simiae stock. Similarly, a G. pallidipes colony of Nguruman origin was significantly more susceptible than the colony of Shimba Hills origin to infection with another stock of T. simiae CP 813 isolated from wild G. pallidipes in Coast Province, Kenya, again irrespective of whether pigs or goats were used as infecting hosts. The susceptibility of the sexes of G. pallidipes from both the colonies to T. simiae CP 813 did not differ significantly when pigs were used as infecting hosts, but male G. pallidipes from both the colonies were significantly more susceptible than female tsetse to this T. simiae stock when goats were used as infecting hosts. Nevertheless, if the observed differences in susceptibility of the two G. pallidipes colonies reflect transmission of trypanosomes by the two allopatric populations of tsetse in the field, then the epidemiology of simiae- trypanosomiasis probably differs between these two areas of Kenya.