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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.

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.

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.

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.

Twenty-five goats were randomly allocated to five groups of five animals each and infected with Trypanosoma congolense IL 3274 via the bites of infected Glossina morsitans centralis. At intervals of 1, 4, 8, 12 or 19 days following infection, each group of five animals was treated intramuscularly with diminazene aceturate at a dose of 7.0 mg kg-1 body weight (b.w.). While treatment on Day 1 eliminated infections in all five goats, treatment on Day 19 did not cure any of the animals; in groups treated 4, 8 or 12 days following infection, two of five goats in each group were cured. Since the alteration in apparent resistance of T. congolense IL 3274 between Day 1 and Day 19 could have been due to alteration in expression of drug resistance by trypanosomes as the population expanded, the experiment was repeated using trypanosomes that reappeared in the animals that had been treated with diminazene aceturate on Day 19. On Day 36, when all five animals were parasitaemic, five groups of teneral G. m. centralis, each containing 160 flies, were fed on one occasion on each of the five goats (one group of testse flies per goat). Thereafter, each group of tsetse flies was maintained on clean rabbits. When infective, five flies from each group were allowed to feed on two naive goats each (i.e. two goats per group of tsetse flies). One animal in each pair was treated 24 h after infection with diminazene aceturate at a dose of 7.0 mg kg-1 b.w., the other was treated on Day 19, when parasitaemic, with the same drug dosage. As before, treatment 24 h following infection eliminated infections in all animals, but when treatment was delayed until Day 19, trypanosomes in all animals were refractory to treatment. Thus, although tsetse flies were infected with trypanosomes that had arisen in infected goats following treatment with diminazene aceturate at a dose of 7.0 mg kg-1 b.w., when the same flies were allowed to feed on clean goats, the resultant infections were sensitive to treatment with the same drug dosage when administered 24 h following infection. These data therefore indicate that there is a significant alteration in diminazene sensitivity of IL 3274 between Day 1 and Day 19 and that this is associated with an alteration in the resistance phenotype of the trypanosomes.

SUMMARYThe midgut epithelium ofGlossina morsitans centralis, G. austeni, G. pallidipes, G. palpalis palpalis, G. p. gambiensis, G. fuscipes fuscipes, G. tachinoidesandG. brevipalpisfrom ILRAD-bred colonies was examined, by electron microscopy, for the presence and distribution of Rickettsia-like organisms (RLOs). RLOs were present in the midgut epithelial cells of all non-teneral tsetse. InG. m. centralis, G. pallidipesand, to a much lesser extent,G. brevipalpis, RLOs were numerous and were present in all the specimens examined. RLOs were present in fewer numbers in the epithelial cells of tenerals of these three tsetse species. In contrast, RLOs occurred in very much lower numbers within the midgut cells of nonteneralG. austeni, G. p. palpalis, G. p. gambiensis, G. f. fuscipesandG. tachinoides; were not seen in every specimen, and were rarely observed in the midgut cells of teneral tsetse. The RLOs were typical rod-shaped bacteria with an inner and outer membrane, which occurred free within the host cell cytoplasm and appeared to cause no obvious pathology. The micro-organisms divided by binary fission and at least two distinct morphological forms plus a range of intermediate forms were seen in the midgut cells. A comparison of the presence and numbers of RLOs within the midgut cells and the midgut infection rates of bothTrypanosoma congolenseandT. b. brucei, both betweenGlossinaspecies and also within the same stock of tsetse, clearly indicates that the ability of trypanosomes to establish and develop to mature infections is unlikely to be correlated solely with the presence of RLOs within the tsetse midgut.

Investigations were conducted on the sensitivity to isometamidium chloride (Samorin R ) and diminazene aceturate (Berenil R ) of derivatives of three of the Trypanosoma congolense stocks isolated between 1978 and 1983 from Zebu cattle in the Bobo-Dioulasso region of Burkina Faso. Boran cattle were used in the drug-sensitivity tests and were infected using Glossina morsitans centralis . The results showed that T. congolense stock IL 2466 isolated in 1978 was sensitive to the standard therapeutic dose of isometamidium chloride (0.25 mg kg −1 ) and of diminazene aceturate (a.i. 3.5 mg kg −1 ). However, T. congolense stock IL 2468 isolated in 1982 was resistant to both the prophylactic (0.5 and 1.0 mg kg −1 ) as well as the therapeutic doses of isometamidium chloride (up to 1.0 mg kg −1 ) although the sensitivity to the theapeutic dose of diminazene aceturate (3.5 mg kg −1 ) was not affected. The T. congolense stock IL 2856 isolated in 1983 was highly resistant to the therapeutic action of diminazene aceturate (up to 10.5 mg kg −1 ), as well as to the prophylactic (up to 1.0 mg kg −1 ) and therapeutic action of isometamidium chloride (up to 2.0 mg kg −1 ). The infection rates of the drug-resistant stocks of T. congolense in G.m. centralis , when goats were used as reservoir hosts, were as high (range, 22.3–56.3%) as of the drug sensitive stock (49.5%). The resistance trait in the two stocks remained stable after their cyclical development in the tsetse vectors. The rate of transmission of the drug-resistant stocks to mice by the infected tsetse was also high (mean 81.3%).

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.

A black rhinoceros (Diceros bicornis) moved from a tsetse-free to a tsetse-infested area in Kenya was monitored for two months following translocation. The animal acquired a Trypanosoma vivax infection from natural tsetse challenge, but survived without requiring treatment with trypanocides. The infection was characterised by moderately high parasitaemia, with symptoms of anaemia, leukopaenia and thrombocytopaenia. Although confirmed to be T. vivax through deoxyribonucleic acid hybridisation and parasite development in tsetse in the proboscis only, the parasite had unusual morphology and motility. It also failed to infect normally susceptible hosts such as cows and goats, and produced unusually low infection rates in Glossina morsitans centralis and G. brevipalpis.

Diminazene aceturate is one of a limited number of compounds currently marketed for treatment of trypanosomiasis in cattle, sheep and goats. The pharmacokinetics of the compound in goats suggest that double treatment with diminazene aceturate might enhance the compound's therapeutic activity. A study was therefore conducted in goats using two clones of Trypanosoma congolense, IL 3274 and IL 1180, which were previously shown to be resistant and sensitive, respectively, to single treatment with diminazene aceturate. The results indicated that, as compared to single treatment, double treatment with diminazene aceturate at a dose of 7.2 mg kg-1 bodyweight, at either eight or 24 hour intervals, did not greatly enhance the therapeutic activity of the drug. Furthermore, treatment with the same drug dose eliminated infections with T congolense IL 3274 when treatment was administered 24 hours after infected Glossina morsitans centralis had fed, but failed to do so if treatment was delayed until after goats were detected to be parasitaemic. This suggests that failure of T congolense IL 3274 to respond to treatment with diminazene may not be due to drug resistance per se.

Glossina brevipalpis Newstead, G.longipennis Corti, and G.pallidipes Austen maintained at ILRAD, Nairobi, Kenya, were examined for genetic variation of fourteen enzyme loci, using polyacrylamide gel electrophoresis. G.brevipalpis had six polymorphic loci, an average of 1.46 effective alleles per locus and a mean heterozygosity per locus of 20.0 +/- 7.1%. The figures for the same parameters in G.longipennis were 3, 1.16 and 8.2 +/- 4.9%, and for G.pallidipes the figures were 7, 1.40 and 22.3 +/- 6.3%. Seven rare alleles were lost from the G.brevipalpis colony during a 1-year period, but no statistically significant changes were observed in the genetics of the colony during this period. Using allele frequency data for ten of the enzymes studied, and frequencies for these enzymes in other taxa, a phenogram was constructed that indicated that the subgenus Austenina (i.e. the fusca group) is the oldest of the three subgenera within the genus Glossina, and that the subgenus Glossina s.str. (i.e. the morsitans group) may be paraphyletic.

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.

In a follow-up survey of sleeping sickness in the Ikoma-Serengeti region of Tanzania, carried out in May and June 1972, 11,060 G. swynnertoni and 95 G. pallidipes were collected, triturated mainly in batches of 50, and the supernate of each batch was inoculated into cyclophosphamide-treated mice. Nine strains of brucei-subgroup were isolated from G. swynnertoni, which indicated the vector ro1e of the local tsetses in the transmission cycle of infection in this endemic region. All the 9 brucei-subgroup isolates gave consistently negative results by the Blood Incubation Infectivity Test (BIIT) whereas the respective controls gave positive results. However, T. (T.) brucei and particularly T. (T.) rhodesiense standards which were tested simultaneously with the test strains gave inconsistent results. It would seem therefore that the BII test in its present form is not reliable for differentiating between the above two trypanosome species, and so the 9 brucei-subgroup isolates could not be classified further. In the Ikoma-Serengeti region there are no restricted foci of Rhodesian sleeping sickness but rather the various components comprising zoonosis interact sporadically throughout this part of Tanzania. The biocenosis of infection favours intense circulation of the parasites, mainly via the tsetse vectors, among game animals some of which function as natural reservoirs; in this ecological zone man is only an incidental host.

SUMMARYInvestigations were conducted on the infection rates and transmission charecteristics of sterile male Glossina morsitans morsitans for Trypanosoma vivax, T. congolense and T. brucei. Pupae were irradiated after the first flush of female emergences with 7, 10 or 13 krad. in a 137caesium radiation source under ambient conditions. The emergent males were fed on a T. viuax-infected goat at peak parasitaemia. They were subsequently mated at 8 days old with 3-day-old normal, virgin females. A batch of sexually fertile males which had been infected as tenerals on the goat at the same time were similarly mated to serve as controls. All the tsetse were maintained on rabbits' ears; the survival and reproductive performance were monitored for seven age-group periods of 9 days each. The sterility rates of the males were 73, 91 and 98% for the 7, 10 and 13 krad. doses of radiation; the percentage of T. vivax infection rates were 78·3, 82·3 and 74·4, respectively. For the control males, the fecundity of the mated females was 90% and the infection rate was 75·7%. In all other experiments, the 10 krad. dose was selected since both the survival and the sterility of the irradiated males were good. The T. vivax-challenged cows and goats died with symptoms of anaemia. There was no difference in the transmission characteristics between sterile and fertile vectors. There was also no significant difference between the sterile and normal males in the infection rates and the transmission frequency of T. congolense and T. brucei to cattle, goats and mice. These results indicate that release of sterile male tsetse in tsetse control programmes will potentially increase the trypanosomiasis risk in the affected area. Consideration must therefore be given to integrating adequate surveillance and chemotherapeutic measures for protection of man and his domestic livestock in the region during the period of such tsetse control campaigns.

Twenty-four Boran cattle were injected with isometamidium chloride (1 mg/kg bodyweight) to investigate the duration of drug-induced prophylaxis against infection by metacyclic forms of Trypanosoma congolense and to determine if specific antibody responses to the organism were mounted by animals under chemoprophylactic cover. Complete protection against either single challenge by five tsetse flies infected with T congolense, or repeated challenge at monthly intervals by five tsetse flies, lasted for five months. Six months after treatment, two-thirds of the cattle were resistant to challenge, irrespective of whether subjected to single or multiple challenge with trypanosome-infected tsetse flies, or titrated doses of in vitro-cultured metacyclic forms of T congolense (5 X 10(2) to 5 X 10(5) organisms), inoculated intradermally. No animal which resisted infection developed detectable skin reactions at the site of deposition of metacyclic trypanosomes or produced trypanosome-specific antibodies. It was concluded that drug residues effectively limited trypanosome multiplication at the site of deposition in the skin, thus preventing subsequent parasitaemia or priming of the host's immune response.

Investigations were conducted on the infection rates of a West African stock of Trypanosoma vivax in Glossina morsitans morsitans and G. m. centralis. The mature infection rate, as revealed by the warm-slide probe, was only 9·4% in contrast to 67·7% by the dissection method. The infection rates determined by the latter technique varied between 46·;7 and 100%, and there were no significant differences in the rates between tenerals and non-tenerals, males and females, the two sub-species, the different age of the vectors or the different peaks of parasitaemia in the goats at the time of the infective meal. In some tsetse the number of parasites in the hypopharynx was markedly high, and there was no significant difference in the frequency of such vectors between the sexes. The mean infection rates in G. m. morsitans increased with increase of the parasitaemia in the host goats. The overall results are discussed in terms of the field situation.

The development and distribution of Trypanosoma congolense, T vivax and T brucei in the skin of goats was examined after the animals were bitten by infected Glossina morsitans centralis. Following the tsetse bite, the trypanosomes in the skin multiplied, reaching maximum numbers when the skin reaction (chancre) of the host attained its maximum size. In goats infected with T vivax and T brucei, trypanosomes were observed circulating in the blood before the peak of the chancre, while in T congolense-infected goats microscopically detectable parasites were found in blood only during the decline of the chancre. In contrast to T vivax, large numbers of T congolense and T brucei parasites were found in the skin following tsetse-transmitted infection. Ultrastructural differences were observed in T congolense and T brucei indicating an intracutaneous transformation from metacyclic to blood stream forms. T congolense forms in the skin reactions had a well developed secretory reticulum, small mitochondria and lacked large lipid inclusions compared to metacyclic and blood stream forms. The intracutaneous forms of T brucei had smaller mitochondria, the glycosomes were of more uniform size and the rough endoplasmic reticulum was less developed than in metacyclic or blood stream forms.

SUMMARYThe feeding behaviour ofGlossina morsitans morsitansinfected withTrypanosoma vivax, T. congolenseorT. bruceiwas studied and compared with that of uninfected control tsetse. The following parameters were measured. (1) Mean number of feeds taken in 20 consecutive days; (2) mean rate of blood meal intake in μg/sec of the total days fed; (3) mean weight of blood meal intake/day of the total days fed; (4) mean total blood meal engorgement in 20 days; (5) mean number of probes/day of the days fed; (6) mean frequency of the multiple probe feeds and (7) mean number of pre-feeding probes of the multiple probe feeds. Evidence was found to suggest that the rosettes ofT. vivaxandT. congolensein the proboscis, and colonies ofT. bruceiparasites in the salivary glands, did not significantly alter the feeding behaviour of the vector.

SUMMARYTo determine if, as is the case withTrypanosoma bruceiandT. congolense, serodemes ofT. vivaxcould be distinguished on the basis of immunity to the metacyclic stages of the parasite, attempts were made to immunize goats by infection with infected tsetse, followed by chemotherapy or eventual ‘self-cure’. Thirty goats were infected by tsetse with either clones or stocks ofT. vivaxfrom East or West Africa. Twenty-four goats were treated with diminazene aceturate (Berenil, Hoechst A.G.) 2–6 weeks after infection and 6 goats were allowed to self-cure. Infection, followed by treatment, induced immunity to a first homologous challenge by infected tsetse in only 2 of 24 goats (one immune to the East African stock, and the other to a clone of the West African stock). Immunity to a clone of the East African stock was induced in 3 or 4 animals after a second infection and treatment and in the fourth animal of the group following a third infection and treatment. One of 2 goats infected with the clone of the East African stock was immune to challenge at 16 weeks, following self-cure without treatment, and 1 of 4 goats infected with the parent stock was similarly immune when challenged at 40 weeks post-infection. Goats susceptible to infection with East AfricanT. vivaxshowed evidence of partial immunity by delayed pre-patent periods and depressed parasitaemias after challenge. Goats infected with the relatively more virulent West AfricanT. vivaxwere, however, completely susceptible to infection after homologous challenge, and showed only a slight delay in pre-patent period. A similar result was obtained in a further 8 goats primed and challenged by large numbers of tsetse (20 or 100 infected tsetse/goat) with the West AfricanT. vivax. In further experiments using a very short treatment interval, infections following challenge were clearly shown to be the result of a lack of immunity rather than relapse following treatment. Lytic antibody activity to cultured metacyclic trypanosomes could not be detected during infection but such activity against bloodstream forms was detected after 2 weeks of infection. It is suggested that the primary reason for the erratic induction of immunity toT. vivaxemploying this methodology is the low number of metacyclics transmitted by infected tsetse, and thus poor antigenic stimulus encountered by goats upon tsetse challenge.

Ten Boran steers were infected with Trypanosoma vivax, transmitted by Glossina morsitans centralis; five steers with a T vivax clone from Nigeria and five with a T vivax clone from Kenya. Eleven days after infection all 10 animals were treated with 0.5 mg kg-1 isometamidium chloride. Four steers infected with the Nigerian T vivax and all five infected with the Kenyan T vivax were completely cured. When different steers received a single prophylactic dose of 0.5 mg kg-1 isometamidium chloride and subjected to monthly tsetse-transmitted challenge with the same T vivax clones, complete protection was afforded for at least two months against challenge with the Nigerian T vivax, but for less than one month against the Kenyan T vivax. The findings indicate that the level of sensitivity of a T vivax population to the prophylactic activity of isometamidium chloride cannot be concluded from sensitivity studies based on the therapeutic action of the drug.

Local skin reactions were elicited in goats by tsetse infected with either T. (N.) congolense of T. (D.) vivax. For the former trypanosomes, the skin reaction was detected initially 7 days after challenge and was maximal 3 days later. Histologically, the cellular response involved an initial influx of polymorphonuclear leucocytes (PMN) which was followed by a substantial infiltration of lymphocytes and macrophages. Large numbers of plasma cells remained in the skin reaction during its decline. Moderate numbers of parasites were observed in lesion at the height of the reaction. T. (D.) vivax provoked a small nodular skin reaction which became apparent 7 days after challenge. The cellular response, which peaked on day 9, contained large numbers of lymphocytes and macrophages and only a small contribution from PMN. Only small numbers of trypanosomes were observed in the chancre. The skin reaction elicited in goats by T. (N.) congolense, T. (D.) vivax or T. (T.) brucei were mutually distinct in their morphological appearance and size at the peak of the response, and in the interval required after challenge to attain maximum dimensions.

A comparison was made of the susceptibility of buffaloes, cattle and goats to infection with Trypanosoma vivax transmitted either by Glossina morsitans centralis or by syringe inoculation. Three different isolates of T vivax (two from East Africa, one from West Africa) were used to compare skin reactions, parasitaemia, anaemia and the development of trypanosome-specific antibodies in buffaloes, cattle and goats. African buffaloes reared in captivity in an area free from trypanosomiasis proved to be highly resistant to infection with the three stocks of T vivax tested, irrespective of whether infection was by tsetse transmitted metacyclic forms or by intradermal or intravenous inoculation of bloodstream forms of the parasite. The bites of 19 tsetse infected with a West African T vivax stock did not cause local skin reactions, detectable bloodstream infections or antibody responses in two buffaloes. Following the bites of 120 tsetse flies infected with the same stock, two different buffaloes showed no local skin reactions, but had detectable bloodstream infections without showing signs of anaemia. Cattle and goats infected in a similar way showed severe local inflammatory skin reactions, high levels of parasitaemia and severe anaemia. The two East African stocks of T vivax caused no local skin reactions and only a transient parasitaemia in buffaloes following tsetse-transmitted infection or intradermal inoculation of bloodstream forms. On the other hand, cattle and goats infected with the East African stocks showed high parasitaemias but local skin reactions only occurred in the goats.(ABSTRACT TRUNCATED AT 250 WORDS)

Following tsetse-transmitted infection with Trypanosoma congolense, major differences in development of localised skin reactions, the ability to control parasitaemia, the degree of anaemia and in antibody response to trypanosomes were found between the reputedly trypanotolerant breeds of cattle (N'Dama, N'Dama/Baoule crosses, Baoule) and the trypanosusceptible West African Zebu. The local skin reactions that developed in the Zebu were large and severe while those that occurred in the other breeds were smaller and less severe or mild. The timing of appearance of parasitaemia and the height of the first peaks were similar in all the animals, but the Zebu were less able to control subsequent waves of parasitaemia. Possibly reflecting these events, it was only in the Zebu that significant anaemia developed. Neutralizing antibody against homologous metacyclic trypanosomes developed between 14 to 18 days after infection in all breeds of cattle; however, marked differences were found when antibody to trypanosomes derived from first peak parasitaemias were tested in the Zebu and Baoule. Neutralizing antibody against these parasites appeared in the Baoule on day 24 but were not detected in Zebu until day 51. Furthermore, the antibody titres were 3 log2 higher in the Baoule. It was concluded that the trypanotolerance exhibited by the West African taurine cattle might be related to a) their ability to control trypanosome numbers in the skin and in the bloodstream, an outcome that was possibly brought about by the earlier and superior immune response and b) failure to develop anaemia which might be associated with their capacity to control parasitaemia.

Exposure of 2 day old virgin females of Glossina fuscipes fuscipes, G. pallidipes, G. brevipalpis, and G. morsitans centralis to carbon dioxide anaesthesia for 15 sec has the effect of suppressing their subsequent insemination frequency. This insemination-inhibitory effect of the gas is more pronounced in G. f. fuscipes and G. pallidipes than in G. brevipalpis and G. m. centralis. In G.f. fuscipes the adverse effect on insemination persists, albeit to a lesser degree, at least up to 72 hr. Carbon dioxide anaesthesia also reduces the insemination capability of G.f. fuscipes males; this effect, however, is less marked than in females. Exposure of wild non-teneral G.f. fuscipes, G. pallidipes, G. brevipalpis, and 3 day old G.m. centralis to the gas for 30 min causes some mortality during anaesthesia, which increases with increasing exposure period. G. m. centralis is most tolerant to the lethal effect of the gas within the 10-90 min exposure periods. Wild females of G.f. fuscipes and G. pallidipes seem to be more sensitive to carbon dioxide in this report than males. In view of these adverse effects produced by carbon dioxide anaesthesia, its use on tsetse is not to be recommended.

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.

The drug sensitivity of seven Trypanosoma vivax-isolates from Kenya and Somalia was examined. With the exception of diminazene aceturate all commercially available trypanocidal drugs failed to effect a cure. The results suggest the existence of multiple drug resistance of T. vivax-strains, geographically widely distributed along the East African Coast. The isolates were resistant to the recommended dose rates of isometamidium, homidium and quinapyramine. Isometamidium showed no prophylactic properties when tested against one of the isolates. All were sensitive to diminazene aceturate.

Five hundred and sixty teneral male Glossina morsitans centralis were fed, at the height of parasitaemia, on a goat infected with Trypanosoma brucei brucei. Thereafter, the tsetse were divided into 4 equal groups. Group I was fed in vitro once weekly for 4 weeks and Group II twice weekly for 4 weeks on fresh defibrinated ox blood containing 2 mg/ml purified monoclonal antibody against T. b. brucei procyclics, while Group III was fed twice a week for 4 weeks on blood containing 2 mg/ml anti-T. vivax monoclonal antibody. The last group was fed on a rabbit. The tsetse were dissected on day 31 and the percent salivary gland infection rates observed were 18.2, 18.6, 39.8 and 40.8, respectively. In another experiment, 2 groups of tsetse, 120 per group, were fed on fresh defibrinated ox blood containing 2 mg/ml anti-T. b. brucei (test group) or anti-T. vivax (control group), on days 3, 6 and 9 following the infected feed. Dissection of the tsetse on day 31 revealed salivary gland infection rates of 0% in the test group and 6.5% in the control group. Thus the monoclonal antibody had a marked, specific suppression of the cyclical development of T. b. brucei in the tsetse vector.

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.

Following injection of U-14C threonine into the haemolymph of adult female Glossina morsitans during late pregnancy, radioactivity was detected in the postparturient female and in its offspring, in threonine, lipids, and a range of non-essential amino acids. The level of radioactivity recovered from the larva was higher than that remaining in the injected adult, and the radioactivity recovered was considerably higher in the amino acid than in the lipid fraction. Administration of labelled threonine into maternal haemolymph on each of the first 8 days of the 9-10 day long pregnancy cycle was followed 24 h later by measurement of radioactivity in the developing oöcyte and in the intra-uterine progeny. The patterns of nutrient uptake are discussed in relation to vitellogenesis in the oöcyte and to growth of the larva. Analysis of the expired carbon dioxide and excreta was carried out 24 h after maternal injection of labelled threonine on the first or eighth day of pregnancy. Carbon dioxide and excreta from females in early pregnancy showed significantly higher radioactivity than those from females in late pregnancy. In both cases, radioactivity in the amino acid fraction from the excreta was extremely small and about 95% of the total activity was in uric acid. These results are discussed in terms of the utilization of threonine in relation to the metabolic demands for various nutriments by the pregnant female.

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.

Significant suppression in the incidence of cyclical development ofTrypanosonia congolense, T. vivaxandT. bruceioccurred inGlossina morsitans centralismaintained on goats immunized within vitro-propagated uncoated forms ofT. congolense, T. vivaxandT. brucei, respectively. This was observed when tsetse given aT. congolense-infected feed were subsequently maintained on uninfected immunized goats and also when uninfected tsetse were fed on immunized goats infected withT. congolense, T. vivaxandT. brucei. Suppression of infection rates in tsetse was trypanosome species specific, but was independent of the trypanosome stock used for immunization of goats. These findings were reflected in antibody responses to uncoated trypanosomes, as measured by immunofluorescence and the solid-phase immuno radiometric binding assay. Thus, antibody from goats immunized with uncoated trypano somes of one species exhibited minimal reactivity with uncoated forms of other species of trypanosomes, but showed high levels of activity with uncoated forms of the same or unrelated stocks of the same species. However, in view of the range of hosts upon which tsetse feed, it is open to question whether the use of a vaccine which suppresses trypanosome infection rates in tsetse would have any significant effect in the field.

Sequential biopsies of the skin reaction elicited in goats by Glossina morsitans morsitans infected with Trypanosoma (Trypanozoon) brucei were examined histologically to identify and to quantify the cellular populations involved in the reaction. The peak of the tissue response occurred 7-8 days after challenge with infected tsetse and preceded the initial detection of parasitaemia by 4-5 days. Microscopically, the cellular reaction was characterized initially by a marked infiltration of polymorphonuclear leucocytes (PMN) which were replaced by lymphoid cells. Plasma cells and macrophages were numerous during the decline of the skin reaction. Marked enlargement of, and germinal centre formation in the regional lymph node accompanied the development and regression of the chancre. The results suggest that the formation of a chancre is dependent on the skin thickness of the host at the site of tsetse challenge.

An apparatus for the artificial feeding of tsetse has been described. Fresh defibrinated blood at 36 °C is circulated with a peristaltic pump through feeding capsules. The efficiency of the method has been compared with that of the Cockings' method and with the live host feeding. The flies exposed to feeding on this apparatus showed significantly higher feeding frequency than those allowed to feed on the Cockings' apparatus. Compared with the live host feeding, the feeding frequency for circulating blood method was slightly lower but the difference was not significant. Once the fly is induced to feed, it would in most cases complete engorgement unless disturbed. The rate of crop emptying in flies fed by the Cockings' method was abnormally slower as compared to those fed on the circulating blood. The present study indicates that for the successful artificial feeding of tsetse, it is essential to circulate the blood and regulate the temperature of the medium and the feeding surface to approximately 36 °C.I wish to thank Mr S. B. Kutuza for technical help, and the Director of E.A.T.R.O. for permission to publish this work.

In a survey of animal trypanosomiasis in Musoma District, carried out in October and November 1970, 6344G. swynnertoniwere collected from six different localities of the Ikoma-Serengeti area and 623G. pallidipesfrom Ikoma. These were dissected and examined for trypanosome infections. The mean infection rates ofvivax-type inG. swynnertoniandG. pallidipeswere 12.6% and 7.5%, respectively. Thecongolensegroup infection rates were 2.0% inG. swynnertoniand 1.8% inG. pallidipes. No salivary gland infection was encountered. The incidence of vivax- and congolense-type infections in general increased with age of both the tsetse species, suggesting that the latter can become infected with these trypanosome types at all ages. The infection rate among female tsetse was higher than among males in the six wing-fray categories. This was due to the slower rate of fraying of the wings with age of the former, so that at each wing-fray category the females were generally older than the males.Vivax-type greatly exceededcongolense-type infection rate in bothG. swynnertoniandG. pallidipes. It is suggested that this probably reflects the known greater infectivity of the former group of trypanosomes toGlossina. It is concluded that in Ikoma, where game functions as the reservoir of animal trypanosomiasis and where infected tsetse are abundant, the domestic animals are exposed to a continuous trypanosome challenge.