Drug sensitivity of trypanosome populations from cattle in a peri-urban dairy production system in Uganda.

Cattle from 50 farms in Mukono County, Uganda, were monitored for trypanosomes every second month over an 18-month period (1995-1996) by mini-anion exchange chromatography and haematocrit centrifugation techniques. Eighteen trypanosome isolates collected from cattle during this period were characterised in cattle, goats and mice for their sensitivity to homidium, isometamidium and diminazene; 10 of the isolates were selected randomly, 8 were from animals that had the highest serum isometamidium concentrations at the time the isolates were collected. All the isolates contained only Trypanosoma brucei and/or T. vivax. In nai;ve Boran (Bos indicus) cattle the isolates exhibited low pathogenicity and were sensitive to diminazene aceturate at 3.5 mg/kg body weight (bw) and isometamidium chloride at 0.5 mg/kg bw. In goats, 5 of 8 isolates were highly pathogenic, producing clinical signs indicative of central nervous system involvement within 60 days of infection; all such isolates contained T. brucei. However, all 8 populations were sensitive in goats to diminazene aceturate at 3.5 mg/kg bw. In contrast, 4 populations were refractory to treatment with isometamidium chloride at 0.5 mg/kg bw in at least 1 out of 3 goats each. Furthermore, 5 populations were refractory to treatment with homidium chloride at 1.0 mg/kg bw in a minimum of 2 out of 3 goats each. In mice, the 50% curative dose values for 11 Mukono isolates that contained T. brucei ranged from 0.30 to 1.89 mg/kg bw for diminazene aceturate, from 0.02 to 0.17 mg/kg bw for isometamidium chloride and from 0.90 to 4.57 mg/kg bw for homidium chloride. Thus, by comparison to reference drug-sensitive populations, all the stabilates were highly sensitive to diminazene and isometamidium, while some expressed low levels of resistance to homidium.

Use of a PCR assay for the specific and sensitive detection of Trypanosoma Spp. in naturally infected dairy cattle in peri-urban Kampala, Uganda.

The objective of this study was to compare the sensitivity and specificity of the polymerase chain reaction (PCR) with the hematocrit centrifugation technique (HCT) and the mini-anion-exchange centrifugation technique (m-AECT) for diagnosis of trypanosome infections in livestock. In a cross-sectional study, 486 cattle from 50 randomly selected farms in Mukono County, Uganda were investigated in June 1994. The direct parasitological techniques were performed in the field, resulting in 45 (9.3%) animals positive by HCT and 78 (16%) positive by m-AECT. The total prevalence (combined evidence of HCT and m-AECT) was 18.9%, with 78.2% Trypanosoma brucei only, 10.9% T. vivax and 10.9% mixed (T. bruceil T. vivax) infections. Trypanosomes of the subgenus Nannomonas were not detected. DNA was prepared by lysis from 181 randomly selected blood samples and amplified by PCR using species-specific oligonucleotide primers. Overall, the PCR gave positive results in 63 (34.8%) blood samples, with 76.2% positive only for T. brucei, 20.6% positive only for T. vivax and 3.2% positive for mixed (T. bruceil T. vivax) infections. The preliminary results from this study demonstrate that the detection rate of PCR is about two times higher than that of the direct parasitological techniques, suggesting a higher sensitivity. The higher proportion of T. vivax infections detected by PCR as compared to HCT/m-AECT is likely to be due to false parasitological classifications which might occur under field conditions.