Adaptation of Trypanosoma (NANNOMONAS) Congolense broden 1904 types to different hosts and transmission by Glossina species

Abstract

The influence of host bLood on midgut infection, maturation rates in Glossina species, transmission and virulence to mice of Trypanosoma congolense DNA types was investigated. The study was also coiKiucted to identify an optimum technique for isolating Nannomonas stocks from the field. Trypanosoma congolense parasites used in this study were identified by the Polymerase Chain Reaction Technique. Zebra and goat blood supported higher midgut and labral infection rates of T. congolense in Glossina morsitans centralis than pig, donkey, black rhinoceros, Thomson's gazelle and eland blood. Of these hosts, zebra supported the h^est metacyclic loads in the hypopharynx. The proportion of midgut infections maturing (transmission index) was generally high for most blood types. It ranged from about 58.0% for tsetse infected with eland blood to 97.0% for tsetse infected with zebra blood. From a practical view point, this study suggests that areas with many goats should have higher infection rates of some T. congolense genotypes. Zebra being a less favoured host probably has a lesser inpact on the infection rates. The pattern of T. congolense Savannah, Kilifi and Riverine / Forest infection rates in G. m. centralis infect«l with goat, black rhinoceros and Boran cow blood was similar during the first 10 days of infection. Rates were highest (up to 90%) on day 3, and dropped 1^ day 5 to reach constant values (ranging from 5% to 45%) by day 10. The 10th day midgut infection rates did not differ significantly from those on day 21 in fifes infected with pig, zebra, goat and eland blood. Carbohydrate binding proteins (lectins) and otter factors are considered to play a role in controlling trypanosoma establishment and maturation. Male G. m. centralis infected with zebra and eland blood matured significantly more gut infections than females. A higher proportion of mice became infected with T. congolense when the infection was initiated by the bite of male tsetse (56.0%) than when the infection was initiated by the bite of a female tsetse (33.0%). This firming was interpreted to suggest an inportant impact on the application of the Sterile Male Technique (SMT) for controlling tsetse flies. Kilifi T. congolense took a significantly shorter tin« to infect mice (13 days) than the Savannah DNA type (18 days). The Kilifi type of T. congolense (K60/1) killed a higher proportion of mice than the Savannah type within 45 days after infection. It also showed earlier parasitaemic peaks than the Savannah type, thus suggesting that the former (Kilifi T. congolense) used in this investigation is nwre virulent than the latter (Savannah T. congolense). Studies on parasite diversity have implications on trypanosomiasis control because they can provide clues to questions on factors that maintain trypanosomes at endemic or factors that can encourage trypanosomes to go into epidemic levels. Trypanosoma congolense (Kilifi type) was detected earlier in mice when the transmitting tsetse was fed on infective goat blood (mean =11 days) than When they were fed on infective eland blood (mean = 14 days). Transmission rates of Kilifi and Savannah types of T. congolense to mice were similar and were not influenced by the host blood type used to infect the transmitting fly. Therefore, the study suggests that host blood can exert host-specific effects on metacyclic devetopment in the tsetse fly that can be subsequently observed when the animal are transmitted with the trypanosomes. Isolation and cloning of trypanosomes by mouse isolation were more effective in Balb/c than Swiss mice. Isolation of T. congolense through gut-form transfer fi-om one tsetse species to another (procyclic expansion technique) was most effective in laboratory reared G. m. centralis and not effective in G. pallidipes and G. m. morsitans. Tsetse passaged with procyclics suspended in fresh goat blood generally survived well during the observation period (survival rates ranged from 58% to 95%). Cholesterol and D(+)-glucosamine added to the goat infective bloodmeal increased infection rates of son» but not all stocks of procyclics. Double cholesterol feeds supported significantly higter midgut infection rates than single cholesterol feeds. Tsetse fed on cholesterol-trypanosome-blood mixtures survived well (survival rates ranged from about 60% to 80%). D(+)-glucosamine facilitated infection rates of procyclics in G. m. centralis but also caused mortality. Pocyclics incubated in different blood mixtures, including cow and goat serum, reconstituted goat red blood cells, heated or unheated, retailed viability for a day at room temperature (25°C.). This suggested that the media used for cryopreserving procyclics was not a critical factor. This study suggests that it is feasible to isolate T. congolense types of trypanosomes by feeding laboratory - reared G. m. centralis tsetse on fresh goat blood and chemical additives such as cholesterol, but maintaining the flies on a rabbit. This finding is discussed in relation to other methods such as the use of G. m. morsitans fed on synthestic diets or the combined use of culture and laboratory reared tsetse flies to isolate T. congolense from wild hosts.