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.

Study on the sequential tsetse-transmitted Trypanosoma congolense, T. brucei brucei and T. vivax infections to African buffalo, eland, waterbuck, N'Dama and Boran cattle.

Susceptibility of African buffalo, eland, waterbuck, N'Dama and Boran cattle to sequential Glossina morsitans centralis-transmitted infections of Trypanosoma congolense, T. brucei brucei and T. vivax was compared, and their possible role as reservoirs of these parasites for G. moristans centralis, G. pallidipes, G. austeni, G. brevipalpis and G. longipennis determined. The buffalo, eland, waterbuck and N'Dama controlled T. congolense parasitaemias and were able to prevent anaemia. By contrast, one Boran became severely anaemic whilst the other controlled parasitaemia and anaemia. When the above five species of Bovidae were rechallenged with T. brucei brucei they showed persistent parasitaemias but did not develop anaemia. The buffalo died of other causes. When the remaining four bovids were rechallenged with T. vivax they became infected with mixed T. vivax/T. b. brucei parasites. Eland, waterbuck and N'Dama controlled parasitaemias and anaemia whereas the Boran became anaemic. Cyclical development of T. congolense occurred in G. moristans centralis when fed on the bovid hosts, with buffalo being infective for tsetse flies for a much longer period. There was no relationship between the levels of T. congolense parasitaemia in the bovid hosts and the resultant infection rates in tsetse flies. Glossina m. centralis was more susceptible than G. pallidipes to T. brucei brucei whilst G. austeni the least; G. brevipalpis and G. longipennis were refractory to the mature infection. Again there was no relationship between T. brucei brucei parasitaemia levels in the hosts and infection rates in the flies. Glossina m. centralis and G. pallidipes showed mixed T. brucei brucei/T. vivax infections whilst G. austeni, G. brevipalpis and G. longipennis became infected with T. vivax alone. Tsetse flies showed higher T. vivax infection rates when fed on the hosts with high parasitaemias than thosewith low parasitaemias. Thus trypanotolerant African buffalo, eland, waterbuck, N'Dama as well as some trypanosusceptible Boran cattle can serve as reservoirs of single or mixed trypanosome infections for tsetse flies. This study has also shown that the Ag-ELISA on the sera from the five bovid hosts had low sensitivity and species-specificity. Examinations of thin wet blood films and buffy coats with a phase-contrast microscope were not sensitive enough to detect the parasites on all occasions. Xenodiagnosis using mice for T. brucei brucei and T. congolense infections, and tsetse flies for all the three trypanosome species were most sensitive for the detection of trypanosome infections in the bovid hosts.

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

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 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 study on the maturation of procyclic Trypanosoma brucei brucei in Glossina morsitans centralis and G. brevipalpis.

Teneral Glossina morsitans centralis and G. brevipalpis were fed in vitro upon medium containing procyclic Trypanosoma brucei brucei derived from the midguts of G. m. centralis or G. brevipalpis which had immature trypanosome infections. The tsetse were then maintained on rabbits and, on day 31, were dissected to determine the infection rates. In G. m. centralis the midgut and salivary gland infection rates by T. b. brucei were 46.0% and 27.0% with procyclic trypanosomes from G. m. centralis, and 45.4% and 24.7% with procyclic trypanosomes from G. brevipalpis, respectively. In G. brevipalpis the rates were 20.2% and 0.0% with procyclic trypanosomes from G. m. centralis, and 28.0% and 0.0% with procyclic trypanosomes from G. brevipalpis, respectively. Teneral G. m. centralis and G. brevipalpis were also fed similarly upon procyclic T. b. brucei derived from G. m. centralis or G. brevipalpis on day 31 of infection, the former tsetse species had mature infections while the latter were without infections in the salivary glands. In G. m. centralis the infection rates in the midgut and salivary glands were 48.9% and 17.0%, and 38.0% and 17.0% when fed on procyclic trypanosomes from G. m. centralis and G. brevipalpis, respectively. In G. brevipalpis the rates were 21.5% and 0.0%, and 10.7% and 0.0% with procyclic trypanosomes of G. m. centralis and G. brevipalpis origin, respectively. Thus, procyclic T. b. brucei from susceptible G. m. centralis could not complete cyclical development in refractory G. brevipalpis, whereas those from G. brevipalpis developed to metatrypanosomes in the salivary glands of G. m. centralis.(ABSTRACT TRUNCATED AT 250 WORDS)

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

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.

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.

Diagnosis of Rhodesian sleeping sickness in the Lambwe Valley (1980-1984).

In primary Rhodesian sleeping sickness patients, parasitological diagnosis was best performed by rodent inoculation of blood (98.5%+) followed by Giemsa-stained thick blood smears (93.3%+). Parasitological diagnosis in relapse patients was sometimes impossible and clinical diagnosis based on CSF examination was necessary. Early during a disease outbreak in 1980, 89% of the infections were detected by mobile field teams, but once established in the endemic area a stationary diagnostic facility detected most of the cases. A total number of 23,751 examinations for Rhodesian sleeping sickness and malaria were made by mobile field teams during 1980-1984; 102 primary cases (0.43%) and 25 (0.10%) relapse cases were diagnosed. A total of 9339 individuals (39%) had patent malaria infections. The IFAT was positive in 89% of the primary sleeping sickness patients and 77% of the relapse patients. Seventy-nine per cent of the primary patients were positive in a CFT test, and 77% of the relapse patients were considered positive.

An enzyme-linked immunosorbent assay for the detection of antibodies to Trypanosoma (T.) brucei evansi in camels (Camelus dromedarius) using peroxidase-conjugated protein A.

Serum samples from dromedary camels naturally and experimentally infected with Trypanosoma (T.) brucei evansi were examined by means of the ELISA, using either an anti-camel or a protein A conjugate. The protein A horseradish peroxidase conjugate was found to bind to camel IgG and thus to be a suitable alternative to the anti-camel conjugate. Results obtained from both tests showed that the respective values correlate significantly.

A complement fixation test for visceral leishmaniasis using homologous parasite antigen I.

The complement fixation test using homologous parasite antigen was evaluated in 60 individuals with confirmed visceral leishmaniasis and compared with the results obtained in individuals with other parasitic and infectious diseases; 88% of the confirmed cases of visceral leishmaniasis were positive whilst no positive reactions were observed in individuals with other infectious and parasitic diseases. The specificity was partially compromised by anticomplementary activity in 5%, limited to individuals with visceral leishmaniasis, and doubtful (2%) or sero-negative (7%) results.

A complement fixation test for visceral leishmaniasis using homologous parasite antigen II. Results in an endemic area in Kenya.

Further studies of the complement fixation test using homologous parasite antigen in an endemic area for visceral leishmaniasis have showed that 82% of individuals with proven visceral leishmaniasis were positive initially whilst 92% were positive at some stage during their illness. Titres fell slowly following effective treatment and anticomplementary activity, confined to confirmed visceral leishmaniasis, was usually lost during treatment. Individuals with alternative causes of hepatosplenomegaly from the same population were negative apart from those with a presumptive diagnosis of visceral leishmaniasis but without parasitological confirmation. Less than 1% of people in the same endemic area without visceral leishmaniasis were positive, suggesting that preliminary serodiagnostic investigation would limit the need for invasive investigation under field conditions.