Trypanosoma congolense infected tsetse were fed on the flanks of goats at sites drained by the prefemoral lymph node. The efferent lymphatic of this lymph node was surgically cannulated and the lymph was collected daily and examined for appearance of parasites, lymph flow and cells. Trypanosomes were detected in the lymph 4 days after infection, which was 2 days prior to the appearance of the local skin reaction or the presence of parasites in the blood. Once the animal became parasitaemic, trypanosomes were found to recirculate in the lymphatic system, appearing in the lymph of the contralateral lymph node 11 days after infection. In goats infected with T. congolense and superinfected 12 or 13 days later with a different tsetse-transmitted T. congolense serodeme, parasites belonging to the second serodeme were apparently delayed in their development in the skin and appeared up to 7 days later in the efferent lymph when compared to control animals. This delay in development might have implications for field situations where superinfections frequently occur; it might result in limiting the number of serodemes of T. congolense an animal can be infected with at any one time.

Ten Boran (Bos indicus) cows were studied over 64 oestrous cycles. Alterations in sexual behaviour and of the ovaries palpated per rectum were related to the plasma progesterone profiles detemined using an extracted double antibody radioimmunoassay. The mean cycle length in the cows was 23 ± 0 · 4 days. Oestrus detection efficiency using standing to be mounted, was 27 percent. Restlessness, where observed, reliably indicated that a cow was in the period of basal progesterone concentration. Mounting, sniffing, head-butting, being sniffed, being mounted with avoidance behaviour, although shown by 50 percent of cows during the basal progesterone period were not confined solely to this part of the cycle. Use of Kamar heat-mount detectors in conjunction with standing to be mounted identified 44 percent of oestrous animals. However, the occurrence of false positives during the rest of the cycle precluded their use as sole indicators of oestrus. Accuracy of palpation of corpora lutea was 61 percent during periods of elevated and 98 percent in periods of basal progesterone concentrations.

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.

Relapse of infection after trypanocidal drug treatment of trypanosome infections is normally attributed to drug resistance on the part of the parasite, under-dosage of the drug, or reinfection of the host. We have demonstrated relapse infections in goats arising from none of these. Fourteen goats infected withTrypanosoma bruceisuffered severe illness and 3 died within 45 days. Despite treatment with the trypanocidal drug Berenil, a 4th goat died 2 days later. Recovery of the remainder followed chemotherapy, and in 2 goats, necropsiecl 45 days after treatment, no trypanosomes or abnormalities were detected. However 2–3 months after Berenil chemotherapy, despite trypanosomes being undetectable in the blood during the intervening period, infections in 4 of the remaining 8 animals relapsed. At all stages of the primary and relapse infections, trypanosomes isolated from the blood of the goats were completely susceptible to Berenil when tested in mice, as were parasites isolated from cerebrospinal fluid and brain tissue at necropsy. At the time of treatment, only minimal cellular infiltration was found in the central nervous system (CNS), but death from the relapse infection was associated with a very severe meningoencephalitis. We conclude that the relapse infections were caused by the re-emergence of trypanosornes from the CNS, where sequestered parasites were inaccessible to the trypanocidal effects of the drug.

Significant suppression in the incidence of cyclical development of Trypanosonia congolense, T. vivax and T. brucei occurred in Glossina morsitans centralis maintained on goats immunized with in vitro -propagated uncoated forms of T. congolense, T. vivax and T. brucei , respectively. This was observed when tsetse given a T. congolense -infected feed were subsequently maintained on uninfected immunized goats and also when uninfected tsetse were fed on immunized goats infected with T. congolense, T. vivax and T. 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.

Administration of the immunostimulants Corynebacterium parvum, Bacillus Calmette-Guérin (BCG) or Bordetella pertussis prior to, or at the same time as, challenge with Trypanosoma congolense significantly increased survival times in mice, both of trypano-susceptible (A/J) and trypano-resistant (C57Bl) strains. The increased survival time was associated with significant alterations in parasitaemia, which included lengthening of the pre-patent period, a delay in the time taken to reach the first peak of parasitaemia and a reduction in the level of parasitaemia. Similar results were obtained when these strains of mice were challenged with Trypanosoma brucei following pre-treatment with C. parvum. Thus, by the use of immunostimulants it was possible to reduce the susceptibility of mice to trypanosomiasis and the hope is that this can also be achieved with domestic livestock.