In vitro antiplasmodial, antitrypanosomal and antileishmanial activities of selected medicinal plants from Ugandan flora: Refocusing into multi-component potentials

ETHNOPHARMACOLOGICAL RELEVANCE

Seven medicinal plants from Ugandan flora, namely Entada abyssinica, Khaya anthotheca, Vernonia amygdalina, Baccharoides adoensis, Schkuhria pinnata, Entandropragma utile and Momordica foetida, were selected in this study. They are used to treat conditions and infections ranging from inflammations, pains and fevers to viruses, bacteria, protozoans and parasites. Two of the plants, V. amygdalina and M. foetida, are also used as human food or relish, while others are important in ethnoveterinary practices and in zoopharmacognosy in the wild. The aim of this study was to evaluate the in vitro antiplasmodial, antitrypanosomal and antileishmanial activities, along with cytotoxicity of the multi-component extracts of these plants.

MATERIALS AND METHODS

Different parts of the plants were prepared and serially extracted with hexane, petroleum ether, dichloromethane, ethyl acetate, methanol and double distilled water. Solvent free extracts were assayed for in vitro inhibition against four reference parasite strains, Plasmodium falciparum (K1), Trypanosoma brucei rhodesiense (STIB 900), Trypanosoma cruzi (Talahuen C2C4) and Leishmania donovani (MHOM-ET-67/L82) using standard methods. Toxicity was assessed against L6 skeletal fibroblast and mouse peritoneal macrophage (J774) cells and selectivity indices (SIs) calculated for the most active extracts.

RESULTS

The strongest activities, demonstrating median inhibitory concentration (IC₅₀) values ≤ 2 μg/ml, were observed for the dichloromethane and petroleum ether extracts of K. anthotheca, B. adoensis and S. pinnata. Overall, IC₅₀ values ranged from < 1 μg/ml to > 90 μg/ml. Out of 22 extracts demonstrating IC_50s < 20 μg/ml, seven were against T. b. rhodesiense (IC₅₀: 1.6-16.2 μg/ml), six against T. cruzi (IC₅₀: 2.1-18.57 μg/ml), none against L. donovani (IC₅₀: falling > 3.3 and >10 μg/ml), and nine against P. falciparum (IC₅₀: 0.96 μg/ml to 4.69 μg/ml). Selectivity indices (SI) calculated for the most active extracts ranged from <1.00 to 94.24. However, the B. adoensis leaf dichloromethane extract (a) was equipotent (IC₅₀ = 3.3 μg/ml) against L. donovani and L6 cells respectively, indicating non-specific selection. Trypanosome and Plasmodium parasites were comparatively more sensitive to the test extracts.

CONCLUSIONS

The benefits achieved from the seven tested plant species as traditional ethnomedicinal and ethnoveterinary therapies or in zoopharmacognosy against infections and conditions of animals in the wild are strongly supported by results of this study. The synergy of plant extracts, so achieved by concerted actions of the ligands, produces adequate perturbation of targets in the four parasite genera, resulting in the strong potencies exhibited by low IC₅₀ values. The total inhibitory effect, achieved as a sum of perturbations contributed by each participating compound in the extract, minimises toxic effects of the compounds as seen in the high SI's obtained with some extracts. Those extracts demonstrating SI ≥ 4 form promising candidates for further cell-based and system pharmacology studies.

Spatial variation of tick abundance and seroconversion rates of indigenous cattle to Anaplasma marginale, Babesia bigemina and Theileria parva infections in Uganda

Tick abundance and seroconversion rates of 640 indigenous cattle in a mixed crop-livestock system in Uganda were investigated in a 14 months longitudinal study. Up to 100% of the cattle in Buyimini, Kubo, Nanjeho, Ojilai and Sitengo villages (high tick challenge zone) were consistently infested with Rhipicephalus appendiculatus, whereas on average 50% of the cattle in Bunghaji, Hitunga and Magoje villages (low tick challenge zone) were inconsistently infested. Likewise, up to 50% of the cattle in Buyimini, Kubo, Nanjeho, Ojilai and Sitengo villages were consistently infested with R. (Boophilus) decoloratus ticks, while on average 30% of the cattle in Bunghaji, Hitunga and Magoje were inconsistently infested. Seroconversion rates of cattle to Anaplasma marginale infection under low tick challenge were higher than those under high tick challenge, but the reverse was true for Babesia bigemina infection. For Theileria parva infection, seroconversion rates of cattle older than 6 months under low tick challenge were significantly higher than those under high tick challenge (P < 0.05). However, the likelihood of occurrence of theileriosis cases among calves (0-6 m) under high tick challenge was 6 times (Odds ratio = 5.82 [1.30-36.37]) higher than under low tick challenge. The high density of anti-tick plants Lantana camara and Ocimum suave that were widespread in villages with low tick challenge, among other factors, was probably the cause for unfavourable tick survival.

Serotype specificity of antibodies against foot-and-mouth disease virus in cattle in selected districts in Uganda

Uganda had an unusually large number of foot-and-mouth disease (FMD) outbreaks in 2006, and all clinical reports were in cattle. A serological investigation was carried out to confirm circulating antibodies against foot-and-mouth disease virus (FMDV) by ELISA for antibodies against non-structural proteins and structural proteins. Three hundred and forty-nine cattle sera were collected from seven districts in Uganda, and 65% of these were found positive for antibodies against the non-structural proteins of FMDV. A subset of these samples were analysed for serotype specificity of the identified antibodies. High prevalences of antibodies against non-structural proteins and structural proteins of FMDV serotype O were demonstrated in herds with typical visible clinical signs of FMD, while prevalences were low in herds without clinical signs of FMD. Antibody titres were higher against serotype O than against serotypes SAT 1, SAT 2 and SAT 3 in the sera investigated for serotype-specific antibodies. Only FMDV serotype O virus was isolated from one probang sample. This study shows that the majority of the FMD outbreaks in 2006 in the region studied were caused by FMDV serotype O; however, there was also evidence of antibodies to both SAT 1 and SAT 3 in one outbreak in a herd inside Queen Elizabeth national park area.

Glossina fuscipes fuscipes in the trypanosomiasis endemic areas of south eastern Uganda: apparent density, trypanosome infection rates and host feeding preferences

A study was undertaken in three districts in south eastern Uganda endemic for human and animal trypanosomiasis, to investigate the status of the vector tsetse fly population. Apparent density (AD) of tsetse was between 2 and 21 flies/trap/day across the three districts, with Glossinia fuscipes fuscipes identified as the predominant species. Trypanosomes were observed in G.f. fuscipes with an infection rate, as determined by microscopy, of 1.55% across the three studied areas. However, trypanosome infections were only identified in female flies giving an infection rate of 2.39% for the female tsetse when this sex was considered in isolation; no male flies were found to be infected. Bloodmeal analysis highlighted 3 principal vertebrate hosts, namely cattle, pigs and monitor lizards (Varanus niloticus). The implication of this, in relation to the cycle of transmission for human infective trypanosomes between domestic animals and man, is discussed.

Glossina fuscipes fuscipes in the trypanosomiasis endemic areas of south eastern Uganda: apparent density, trypanosome infection rates and host feeding preferences

A study was undertaken in three districts in south eastern Uganda endemic for human and animal trypanosomiasis, to investigate the status of the vector tsetse fly population. Apparent density (AD) of tsetse was between 2 and 21 flies/trap/day across the three districts, with Glossinia fuscipes fuscipes identified as the predominant species. Trypanosomes were observed in G.f. fuscipes with an infection rate, as determined by microscopy, of 1.55% across the three studied areas. However, trypanosome infections were only identified in female flies giving an infection rate of 2.39% for the female tsetse when this sex was considered in isolation; no male flies were found to be infected. Bloodmeal analysis highlighted 3 principal vertebrate hosts, namely cattle, pigs and monitor lizards (Varanus niloticus). The implication of this, in relation to the cycle of transmission for human infective trypanosomes between domestic animals and man, is discussed.

Knowledge and attitudes of cattle owners regarding trypanosomosis control in tsetse-infested areas of Uganda

A pilot survey using a structured questionnaire was conducted in Tororo and Busia districts of Uganda on the knowledge and attitudes of cattle owners regarding tsetse fly and trypanosomosis control, in order to understand factors that hindered their full participation. A total of 81 cattle owners was randomly selected and interviewed, of which 92.5% were aware of tsetse flies and trypanosomosis and 87.6% recognised animal trypanosomosis as a problem in the area. Most cattle owners were aware of tsetse fly trapping (76.5%), isometamidium chloride use (55.5%), diminazene aceturate use (48%) and pour-on applications (18.5%). However, knowledge did not coincide with the application of control measures. Despite the widespread awareness, tsetse fly trapping and pour-on applications were used by only a small percentage of cattle owners (7.5% applied tsetse fly trapping while 76.5% were aware of it; 1.2% applied pour-on insecticides while 18.5% were aware of them). Differences between awareness and application were highly significant for tsetse fly trapping (chi2 = 67.8, d.f. = 1, P < 0.001) and pour-on applications (chi2 = 10.8, d.f. = 1, P < 0.05), but not for isometamidium chloride use (chi2 = 0.08, d.f. = 1, P = 0.77) and diminazene aceturate use (chi2 = 0.00, d.f. = 1, P = 1.00). Most cattle owners (97.5%) were willing to participate in future control programmes, but preferred participating on a group basis (85.2%) rather than individually (14.8%). The 4 most favoured control options in order of importance were: fly traps supplied by the government and maintained by cattle owners; contribution of labour by cattle owners for trap deployment; self-financing of trypanocidal drugs and self-financing of pour-on insecticide. The control options that should be selected in order to elicit full participation by cattle owners are discussed.

Effect of strategic deworming of village cattle in Uganda with moxidectin pour-on on faecal egg count and pasture larval counts

Strategic application of moxidectin pour-on (Cydectin) was evaluated in Uganda for its effect on pasture larval counts and gastrointestinal nematode faecal egg counts in village cattle kept under tethering (semi-intensive) grazing management. The strategic deworming schedule involved treating cattle twice at an interval of 2 months, at the end of the 1st wet season and during the 2nd wet season. Two groups of 30 cattle, each consisting of a treated and a control group, were examined for nematode infections every 4 weeks from June 1999 to January 2000. The treated group had significantly lower mean faecal egg counts than the untreated groups (t-value = 2.47, P < 0.05). Generally, the pasture larval counts on treated farms were lower than on untreated ones, but not significantly so (t-value = 2.22, P = 0.068). Pasture larval counts with different nematode species on treated farms were lower than on untreated ones, but the differences were not significant for Haemonchus spp. (t-value = 1.68, P = 0.145), Oesophagostomum spp. (t-value = 1.87, P = 0.111), Trichostrongylus spp. (t-value = 1.93, P = 0.102), Dictyocaulus spp. (t-value = -0.74, P = 0.485) and Cooperia spp. (t-value = -1.00, P = 0.356). Treated farms did, however, have significantly lower pasture larval counts of Bunostomum spp. (t-value = 4.64, P < 0.05). This study has revealed that the application of moxidectin pour-on on cattle has an effect on faecal egg count and pasture contamination under the tethering grazing system. Moxidectin pour-on and the strategic deworming schedule evaluated here could be used for the control of gastrointestinal nematode infections in cattle by small-scale farmers who practise tethering or semi-intensive grazing management in Uganda and other tropical countries, especially where there is a bimodal rainfall pattern.

Immunogenicity of a Locally Produced Newcastle Disease I-2 Thermostable Vaccine in Chickens in Uganda

A locally-produced Newcastle disease (ND) I-2 thermostable vaccine of embryo-infective dose (EID50) 10(8.5) per ml was administered to 100 laboratory chickens in four test groups, each of 25 birds. It was given by the eye-drop method, in drinking water, in drinking water freshly medicated with levamisole, or using millet grains as a vaccine carrier. A fifth control group consisting of 25 birds received the heat-sensitive La Sota vaccine (EID50 10(9) per ml) by the eye-drop method. The immunological responses were monitored by the enzyme-linked immunosorbent assay (ELISA) ND antibody technique using serum samples collected from 18 birds in each group at 3-week intervals for 3 months. The overall mean ND antibody log(10) titres and percentage positivities were 3.1, 88%; 2.9, 70%; 3.0, 83%; 3.2, 87% and 3.3, 87%, respectively. The use of water alone or medicated with levamisole for vaccine administration produced significantly lower ND antibody titres only in the first 3 weeks. The immunogenicity shown by the I-2 vaccine as a potential vaccine is discussed in relation to free-range poultry management conditions in Uganda.

Implications of the re-invasion of Southeast Uganda by Glossina pallidipes on the epidemiology of bovine trypanosomosis

A study to assess the influence of re-invasion of Glossina pallidipes on the epidemiology of bovine trypanosomosis was conducted in Southeast Uganda. A total of 1,992 cattle were screened in villages, with (949) and without G. pallidipes (1043) for trypanosomosis using a combination of the BCT and HCT methods. The prevalence of trypanosomosis (15.5%), Trypanosoma brucei infection (1.4%), T. congolense infection (7.2%), T. vivax infection (5.3%) and mixed infection (1.6%) in cattle in villages with was significantly higher than in those without G. pallidipes: trypanosomosis (7.1%), T. brucei infection (0.6%), T. congolense infection (2.0%), T. vivax infection (3.3%) and mixed infection (1.2%) (overall trypanosome infection, chi2=35.5, d.f.=1, P<0.05; T. brucei infection, chi2=8.06, d.f.=1, P<0.05; T. congolense infection, chi2=22.8, d.f.=1, P<0.05 and T. vivax infection, chi2=6.4, d.f.=1, P<0.05). Infections of Trypanosoma congolense were predominant in cattle in villages with G. pallidipes, while T. vivax infections were predominant in cattle in villages without. In all villages, T. brucei infections were fewer than either T. congolense or T. vivax infections. The risk of transmission of T. brucei, T. congolense and T. vivax infections was 3, 2.7 and 1.6 times, respectively, higher in villages with G. pallidipes than in those without, despite the presence of G. f. fuscipes in either set of villages. The mean PCV (28.27+/-0.41, 95% CI) and mean herd size (3+/-0.46) of cattle in villages with G. pallidipes were significantly (P<0.05) lower than in those in villages without (mean PCV, 29.48+/-0.34; mean herd size, 4+/-0.72). It is evident that presence of G. pallidipes brings about an increase in the prevalence of T. congolense, which causes a more severe disease in cattle than other species of trypanosomes. This is a rare case of a re-invasion of a tsetse species whose disease transmission capability calls for refocusing of the traditional national tsetse and trypanosomosis control strategies to contain it.

A comparative study on the clinical, parasitological and molecular diagnosis of bovine trypanosomosis in Uganda

The clinical, parasitological and molecular diagnosis of bovine trypanosomosis were compared using samples from 250 zebu cattle exposed to natural trypanosome challenge in Uganda. Clinical examination, molecular and parasitological diagnoses detected 184 (73.6%), 96 (38.4%) and 36 (14.4%) as diseased, respectively. The sensitivity and specificity of clinical examination were 87.5% and 35%, and 78 % and 27 % based on molecular and parasitological diagnoses, as gold standards, respectively. Of the 33, 3, 13 and 12 parasitological-positive cattle that had Trypanosoma brucei, Trypanosoma congolense, Trypanosoma vivax or mixed infections, 78 %, 33 %, 84 % and 100 % respectively manifested clinical signs. Of the 24, 89, 12, 3, 6 and 27 cattle detected by molecular diagnosis to have mixed infections, T. brucei, T. vivax, T. congolense forest-, Savannah- and Tsavo-type, 100%, 83%, 91%, 100%, 67% and 81 % had clinical signs, respectively. In conclusion, treatment of cattle based on clinical examination may clear up to 87.5 % or 78 % of the cases that would be positive by either molecular or parasitological diagnosis, respectively. Under field conditions, in the absence of simple and portable diagnostic tools or access to laboratory facilities, veterinarians could rely on clinical diagnosis to screen and treat cases of bovine trypanosomosis presented by farmers before confirmatory diagnosis in diagnostic centres for few unclear cases is sought.

Domestic animals as reservoirs for sleeping sickness in three endemic foci in south-eastern Uganda

The persistence of sleeping sickness (human African trypanosomiasis) in some areas of south-eastern Uganda has necessitated further investigations, focusing mainly on domestic animals as reservoirs of this disease in three agro-ecological zones. The inter-zone differences in the prevalences of trypanosome infection among cattle (P < 0.001) and pigs (P < 0.001) were significant. Overall, 5.0% of the cattle, 13.9% of the pigs and 0.4% of the small ruminants investigated were found to be infected with parasites of the Trypanosoma brucei subgroup. The results of blood incubation infectivity tests (BIIT) indicated that all of the T. brucei-subgroup isolates from cattle in Kamuli district (zone I) were human-serum-sensitive. Of the zone-I pigs found infected, however, almost all (82.5%) were considered to be infected with T. brucei and many (30.2%) carried human-serum-resistant T. brucei. Pig-tsetse-human appears to be a major transmission cycle in zone I. In Mukono district (zone II), 10.5% and 26.1% of the T. brucei isolates from cattle and pigs, respectively, were human-serum-resistant, indicating that cattle-tsetse-human and pig-tsetse-human are major transmission cycles in zone II. In Tororo district (zone III), 47.3% of the T. brucei isolates from cattle were human-serum-resistant but there were no T. brucei isolates from pigs, indicating that cattle-tsetse-human is the major transmission cycle. Interestingly, as the only T. brucei isolate from sheep in zone III was human-serum-resistant, there may also be a sheep-tsetse-human cycle. In south-eastern Uganda, control efforts must be designed to eliminate the parasites not only from cattle but also from pigs and small ruminants.

Evidence for the occurrence of Trypanosoma brucei rhodesiense sleeping sickness outside the traditional focus in south-eastern Uganda

The occurrence of Trypanosoma brucei rhodesiense west of the River Nile, in Masindi district in the mid-western part of Uganda, is confirmed. Masindi borders the traditional belt of T. b. gambiense infection in the north-west, Gulu in the north and the Democratic Republic of Congo in the west. Of the 702 persons tested for sleeping sickness in Masindi, 113 (16%) were positive by the card agglutination test for trypanosomiasis (CATT). Trypanosomes were observed in samples of cerebrospinal fluid (CSF) from two (0.3%) of the subjects: a 7-year-old girl, who had been ill for 2 weeks and yet was in good general condition, with three white blood cells (WBC)/microliter CSF; and a 47-year-old woman who had been ill for 8 months, looked sickly, had seven WBC/microliter CSF, but was still able to dig in her gardens. Rats and mice inoculated with blood from the two parasitologically confirmed cases became parasitaemic on day 3 post-inoculation, indicating that the parasites were T. b. rhodesiense. Isoenzyme analysis revealed that the parasites isolated from one of these confirmed cases belonged to a zymodeme (449) which has not been previously observed among isolates from south-eastern or north-western Uganda. Although the isolate shared PGM2 and ICD3 patterns with T. b. gambiense and T. b. rhodesiense, respectively, it did not have the SOD3:5 pattern characteristic of T. b. gambiense. The spread of T. b. rhodesiense beyond its traditional focus and the development of areas where this subspecies and T. b. gambiense are co-endemic will complicate the control of sleeping sickness in Uganda; although the CATT is very useful for the mass screening of populations for T. b. gambiense area, it is not applicable in the detection of T. b. rhodesiense.

Trypanosomosis agglutination card test for Trypanosoma brucei rhodesiense sleeping sickness

OBJECTIVE

To develop a simple field test for diagnosis of Trypanosoma brucei rhodesiense in man.

DESIGN

Trypanosomosis Agglutination Card Test (TACT) was developed for the diagnosis of sleeping sickness due to Trypanosoma brucei rhodesiense infection, based on stabilised procyclic forms derived from Utat 4.1. Procyclics were fixed in buffered formalin at 4 degrees for 24 hours and further stabilised in acid/alcohol mixture for 30 minutes. The fixed antigen was stained with Coomassie blue and suspended in 0.1 M PBS/sodium azide buffer pH 7.2 at a concentration of 1 x 10(8) trypanosomes/ml and kept at room temperature. This antigen was used to screen 100 sera from rabbits infected with T. b. rhodesiense, eight from normal rabbits, and 220 only sera 60 of which were from sleeping sickness patients, 50 from normal persons and 110 from other parasitic infections.

SETTING

Laboratory testing of the antigen types against the rabbit and human sera infected with cloned variable antigen types of T. b. rhodesiense, was routinely carried on test cards under room temperature.

SUBJECTS/PARTICIPANTS

Serum samples from normal and infected rabbits and human subjects.

RESULTS

All sera from infected rabbits and 59 from sleeping sickness patients reacted strongly with the antigen showing agglutination reaction which ranged from 1:4 to 1:1024 serum dilution. There was minimal cross reaction with other parasitic infections as follows: one out of 20 malaria patients none of the 20 hookworm patients, one out of 30 for schistosomiasis patients, none of the 10 amoebiasis patients and one out of 20 for filariasis patients. Agglutination titres from all these non-sleeping sickness patients were below 1:16. Based on rabbit positive and negative sera, TACT gave a sensitivity and specificity of 100% and 80% while for human sera a sensitivity of 98.3% and specificity of 96% were observed.

CONCLUSION

These preliminary results show that TACT could be a promising screening field test for T. b. rhodesiense sleeping sickness.

Changes in classical pathway complement activity in dromedary camels experimentally infected with Trypanosoma evansi

The complement system is known to have important effector functions in immune responses. However, its role in camel trypanosomosis has not been determined. The present study was undertaken to evaluate haemolytic complement activity in Trypanosoma evansi-infected and uninfected camels. Five dromedary camels were experimentally infected with T. evansi and classical pathway haemolytic complement activity was assayed. Parasitaemia and packed cell volume were also monitored. Following infection, classical pathway haemolytic complement showed a slight initial increase (7%) in all the camels. The amounts later dropped as the infection progressed and correlated negatively with parasitaemia. Haemolytic complement recovered following elimination of trypanosomes by treatment with melarsomine. Treatment of uninfected camels had no effect on complement. This study has demonstrated that complement concentration increases in the initial phase of infection followed by a drop as the infection progresses towards chronicity. In addition, the study has shown that activation of the classical complement pathway occurs in camels infected with T. evansi. Complement could therefore be involved in the in vivo control of parasitaemia in dromedary camels infected with T. evansi. Decreased complement levels in this species could lead to immunosuppression, widely reported in animal trypanosomosis.

Studies on the haemolytic complement of the dromedary camel (Camelus dromedarius). II. Alternate complement pathway haemolytic activity in serum

Fresh camel serum caused lysis of unsensitised red blood cells (RBC) of chicken, rabbit and guinea pig. Homologous RBC were resistant to lysis. There was only minimal lysis of goat, sheep, rat and cattle RBC. Lysis of heterologous RBC was attributed to the presence of alternate complement activity (ACP) in the serum as adsorption with respective RBC and addition of 10 mM ethylene glycol-bistetraacetate (EGTA) in the SVBS diluent did not abrogate the haemolytic activity. Guinea pig RBC were the most sensitive to lysis, giving a mean ACP activity of 41.5 +/- 1.8 CH50 units ml-1. Clotting, followed by storing of blood between 0 and 37 degrees C for 1 h did not significantly affect ACP activity. However, considerable activity was lost when blood was clotted and stored at 44 degrees C for 1 h, or when serum was kept at 4 degrees C for 24 h. Treatment with zymosan, or incubation at 56 degrees C for 30 min inhibited ACP activity. Maximum ACP activity occurred in the presence of 8 mM Mg2+ in the SVBS-EGTA diluent, at pH 7.3 and incubation time of 2 h at 37 degrees C. Levels of ACP activity were determined in 79 healthy camels of different age groups, ranging from 3 months to 15 years. Calves between 3 months and 1 year of age had higher ACP activity than camels in the age group of 5 years and above. Highest mean ACP activity of 89 +/- 7.9 CH50 units ml-1 were recorded in 1-5 year old camels (P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the haemolytic complement of the dromedary camel (Camelus dromedarius). I. Classical pathway haemolytic activity in serum

Classical pathway haemolytic complement (CPHC) of the dromedary was assayed under standardised conditions. A total of 14 indicator systems of red blood cells (RBC) and haemolysins were investigated. Highest CH50 titre was obtained with rabbit RBC sensitised with goat haemolysin. Among the factors investigated were: ionic strength, Mg2+, Ca2+, ethylenediaminetetraacetic acid (EDTA) concentration, pH, incubation time and temperature. The standard system of titrating the HC levels consisted of rabbit RBC sensitised with goat haemolysin, sucrose veronal buffer (SVBS) pH 7.4, ionic strength 0.14 M and Ca2+ and Mg2+ concentrations of 4.0 x 10(-4) M and 1 x 10(-3) M, respectively. Incubation at 37 degrees C for 120 min gave the highest HC activity. Using these standardised conditions HC levels were determined in 79 camels aged between 3 months and 15 years. Highest mean HC value of 873 +/- 26.6 CH50 units ml-1 were recorded in the age group of 1-5 year old camels and the lowest mean HC value of 598 +/- 120.8 CH50 units ml-1 in the age group of 10-15 year old camels. Adult males in the age group 5-10 years had significantly higher mean HC levels than their female counterparts (P < 0.0001).

Immunoassay of circulating trypanosomal antigens in sleeping sickness patients undergoing treatment

Sera from 99 patients infected with Trypanosoma brucei rhodesiense and undergoing treatment, were analyzed for circulating trypanosomal antigens using a sandwich antigen-trapping enzyme-linked immunosorbent assay (ELISA). Trypanosomal antigens were detected in 83 (84%) of the patients. Post-treatment antigen profile in 67 patients showed five distinct patterns: in 48% of the patients antigen levels remained elevated throughout the time of hospitalisation and follow-up; in 31%, antigens dropped to the negative value by the second month; in 7.5%, antigens dropped to the negative level and became elevated afterwards; in 7.5%, antigen levels were negative initially, but later, became elevated and remained so throughout the observation period; in 6%, antigen levels remained below the negative value throughout. All patients who relapsed on follow-up had earlier shown evidence of elevated antigen profile. There were no cases of relapses among 21 patients whose antigen levels dropped subsequent to treatment. This ELISA trypanosome antigen detection test could be useful in evaluating treatment success, when used together with parasitological diagnostic techniques.

Evaluation of the in vitro transformation technique to distinguish Trypanosoma evansi from cyclically transmitted Trypanozoon stocks

In order to initiate transformation into procyclic forms, bloodstream trypanosomes, were transferred to semi-defined medium at 27 degrees C. All stocks previously classified as Trypanosoma brucei rhodesiense, T.b. gambiense and T.b. brucei transformed into procyclic forms. None of the 31 characterized T. evansi stocks transformed into procyclic forms, but died between day 4 and day 6 in culture. On the other hand, 3 out of 64 stocks of monomorphic brucei subgroup field isolates from camels transformed into procyclic forms, confirming the existence of T.b. brucei infection in camels kept close to tsetse belts.

Comparison of antibody- and antigen-detection enzyme immunoassays for the diagnosis of Trypanosoma evansi infections in camels

A total of 183 camels from Kenya were examined for circulating trypanosomal antigens by four methods: (1) a monoclonal antigen-detection enzyme-linked immunosorbent assay (Ag-ELISA) and circulating anti-trypanosomal antibodies; (2) antibody-detection enzyme-linked immunosorbent assay (Ab-ELISA); (3) buffy-coat examination (BCE); (4) mouse subinoculation (MI). Thirty-seven camels (20%) were parasite-positive by BCE and 60 camels (33%) were parasite-positive by MI. Sixty-three camels (34%) tested positive on Ag-ELISA. Of the 24 camels which could not be detected by BCE, Ag-ELISA detected 18 (75%). Ab-ELISA detected 90 (49%) positive camels. Of all the parasite-positive camels (61), Ag-ELISA detected 93% and Ab-ELISA 95%. Based on the results of 55 camels, there was a significant statistical difference (P < 0.0001) in Ag-ELISA optical density (OD) values (of either serum or plasma antigen analysis) between parasite-positive and parasite-negative camels. No significant difference was observed in Ab-ELISA OD values between parasite-positive and parasite-negative camels. Diagnosis of T. evansi infection in camels by the use of Ag-ELISA alone or in combination with BCE could therefore be a more preferred approach in assessing patient infection than the use of Ab-ELISA.

Trypanosomal antigen and antibody levels in field camels following treatment with two trypanocidal drugs

The efficacy of treatment in 61 naturally trypanosome-infected camels was evaluated by antigen and antibody detection. Following treatment of 14 infected field camels with an arsenical drug (RM110) no trypanosomal antigens could be detected in the animals which were treated with 0.6 mg/kg body weight and 1.2 mg/kg body weight, 90 days thereafter. In two out of three camels treated with 0.4 mg/kg body weight no trypanosomal antigens could be detected by day 90 post-treatment. However, there was evidence of trypanosomal antigens in camels treated with 0.2 mg/kg body weight and untreated positive controls. Antibody levels were still high in all the 14 camels, 90 days post-treatment. In another group of 55 field camels, of which 47 camels were parasite-positive and eight parasite-negative, trypanosomal antigens could not be detected in 42 camels, 28 and 48 days post-treatment with Quinapyramine Prosalt. However, antigen levels were still high in five parasite-positive camels, 48 days post-treatment. In all the parasite-positive camels, antibody levels were still high 48 days after treatment. In the eight parasite-negative camels, antigens were detected in four camels before treatment. By day 48 post-treatment, all the four camels were antigen-negative. However, four of the eight parasite-negative camels were still antibody-positive by day 48 post-treatment. These observations indicated that antigen-detection could be used to evaluate the success of therapeutic trials where trypanosome detection tests may fail to pick low patent infections.

An enzyme-linked immunosorbent assay (ELISA) for the detection of trypanosomal antigens in goat serum using a monoclonal antibody

An IgM murine monoclonal antibody (MAb) TEA 1/23.3.4.6 raised against circulating trypanosome antigens was used in a sandwich ELISA to assay trypanosomal antigens in a trypanosome lysate preparation and in sera from goats infected with Trypanosoma brucei evansi. As little as 1.25 ug/ml of trypanosomal antigen could be detected by this assay. Following infection, trypanosomal antigens were first detected in goat serum 24 hours after the intravenous (i/v) or 6 days after the intramuscular (i/m) inoculation of trypanosome parasites. Antigen levels remained detectable during the course of infection. After treatment with diminazene aceturate, antigens dropped to undetectable levels between day 12 to 41, suggesting that this assay offers a promising approach to the diagnosis of African Trypanosomiasis.

Evaluation of Procyclic Agglutination Trypanosomiasis Test (PATT) for the immunodiagnosis of Trypanosoma brucei rhodesiense sleeping sickness in Kenya

Documented sera from 156 patients admitted to Alupe Sleeping Sickness Hospital in Western Kenya were tested to determine the potential usefulness of Procclic Agglutination Trypanosomiasis Test (PATT) for the diagnosis of Trypanosoma brucei rhodesiense African sleeping sickness. A total of 490 serum samples were tested, including 42 controls. Anti-trypanosome antibodies were detected in 99% of the sera taken prior to trypanocidal drug therapy. Antibody levels remained high during course of treatment. In cured cases antibodies declined to negative or low levels 4 months to one year after treatment. High antibody levels persisted in patients who relapsed. Although the results showed a high sensitivity and specificity, confirming the potential usefulness of the test for serodiagnosis of African sleeping sickness, PATT, in its present form is unsuitable for routine diagnosis. This is due to difficulties inherent in the use of live trypanosomes as detector antigen.

Application of luminol-dependent chemiluminescence to assay opsonizing antibodies to procyclic forms of Trypanosoma congolense in the sera of dogs experimentally infected with heterologous stocks

Luminol-dependent chemiluminescence (LCL) responses of dog granulocytes were used to assay opsonizing antibodies to procyclic culture forms of T. congolense. A high degree of sensitivity was demonstrated and LCL levels were high, when the phagocytic cells were incubated with the sera of infected dogs even at dilutions as high as 1:400 as compared to pre-infection or negative sera. The levels of opsonizing antibodies were elevated in all the dogs throughout the time of observation. The technique was sensitive, could be automated and, therefore, allows a rapid evaluation of large numbers of serum samples for Trypanosoma specific antibodies.