Antje Hoppenheit

Best-bet integrated strategies for containing drug-resistant trypanosomes in cattle

BackgroundAfrican animal trypanosomosis is a major constraint to the rearing of productive livestock in the sub-humid Sudan-Sahel zone of West Africa where cotton is grown. Trypanosomosis is mainly controlled using trypanocidal drugs, but the effective use of drugs is threatened by the development of widespread resistance. This study tested integrated best-bet strategies for containment and/ or reversal of trypanocide resistance in villages in south-east Mali where resistance has been reported.MethodsFour sentinel villages each from an intervention area (along the road from Mali to Burkina Faso) and a control area (along the road from Mali to Côte d’Ivoire) were selected for the study. Tsetse control was based on deltamethrin-treated stationary attractive devices and targeted cattle spraying between March 2008 and November 2009. Trypanosome-positive cattle were selectively treated with 3.5 mg/kg diminazene aceturate. Strategic helminth control using 10 mg/kg albendazole was also undertaken. During the intervention, tsetse densities along drainage lines, trypanosome infections and faecal egg counts in risk cattle (3 to 12 months of age) were monitored.ResultsCatch reductions of 66.5 % in Glossina palpalis gambiensis and 90 % in G. tachinoides were observed in the intervention area. Trypanosome prevalence was significantly (p < 0.05) lower in the intervention area (2.3 %; 1.3-3.6 %) compared to the control area (17.3 %; 14.8-20.1 %). Albendazole treatment resulted in a faecal egg count reduction of 55.6 % and reduced trypanosome infection risk (2.9 times lower than in the placebo group) although not significantly (p > 0.05). Further studies are required before confirming the existence of albendazole resistant strongyles in the study area.ConclusionIntegration of best-bet strategies in areas of multiple drug-resistance is expected to reduce trypanosome infection risk thus contributing to containment of trypanocidal drug resistance. Integrated best-bet strategies could therefore be considered a viable trypanosomosis control option especially in areas where multiple drug-resistance has been reported.

Drug quality analysis through high performance liquid chromatography of isometamidium chloride hydrochloride and diminazene diaceturate purchased from official and unofficial sources in Northern Togo

Trypanocidal drugs remain the most accessible and thus commonly used means of controlling tsetse transmitted animal African trypanosomosis. In Togo, trypanocides are sold on official as well as unofficial markets, but the quality of these trypanocides is undocumented so a drug quality assessment study was conducted from May 2013 to June 2014. Trypanocides supplied by European, Indian and Chinese pharmaceutical companies and sold on official and unofficial markets in Togo were purchased. In total fifty-two trypanocides were obtained, 24 of these samples from official markets and 28 from unofficial markets made up of a total of 36 diminazene diaceturate and 16 isometamidium chloride hydrochloride samples. The samples were analysed in the reference laboratory of the OIE (World Organisation for Animal Health), Laboratory for the Control of Veterinary Medicines (LACOMEV) in Dakar which uses galenic testing and high performance liquid chromatography (HPLC) testing as standard reference analysis methods. The results revealed a high proportion of trypanocides of sub-standard quality on the Togolese market: 40% were non-compliant to these quality reference standards. All of the HPLC non-compliant samples contained lower amounts of active ingredient compared to the concentration specified on the packaging. Non-compliance was higher in samples from the unofficial (53.57%) than from the official markets (25%; p=0.04).The main drug manufacturers, mostly of French origin in the study area, supply quality drugs through the official legal distribution circuit. Products of other origins mostly found on illegal markets present a significantly lower quality.

Host preference of tsetse: an important tool to appraise the Nagana risk of cattle in the cotton zone of Mali

ZusammenfassungDie durch Tsetsefliegen übertragene Trypanosomose der Rinder, Nagana, stellt für Zugochsen in den Baumwollanbaugebieten Malis eine ständige Bedrohung dar und führt durch krankheitsbedingte Leistungsabnahme und hohe Sterblichkeit zu gravierenden finanziellen Verlusten bei betroffenen Kleinbauern. Ein regelmäßiger Trypanozideinsatz stellt derzeit die häufigste Bekämpfungsmethode dar, wobei als Folge dieser mono-kausalen Bekämpfung bei Rindern multiple Resistenzen gegen die nur in begrenzter Zahl verfügbaren Trypanozide im gesamten Baumwollgürtel Westafrikas zu verzeichnen sind. Wirksamkeit und Nachhaltigkeit dieser Strategie werden so zunehmend in Frage gestellt. Daher wird ein neuer Ansatz zum Grundverständnis der ökologischen Basis des Nagana-Infektionsrisikos und zu seiner effektiven Bekämpfung angestrebt, wobei der Bestimmung der Wirtstierpräferenzen von Tsetsefliegen eine bedeutende Rolle zukommt. Aus diesem Grunde wurden von November 2008 bis April 2009 in zwei südostmalischen Dörfern insgesamt 474 Tsetsefliegen gefangen, phänotypisch bestimmt, auf Trypanosomeninfektionen untersucht und ihre Blutmahlzeiten auf FTA-Filterpaper® aufgetragen. Einhundertzwanzig ausgewählte Proben wurden zur Blutmahlzeitbestimmung extrahiert und mit universellen mitochondrialen Cytochrom b-Primern amplifiziert, wobei sich 74 Proben als Wirtstier-DNS-haltig erwiesen. Nach anschließender Amplifikation mit Rinder-spezifischen Cytochrom b-Primern zeigten 52 von ihnen entsprechende Banden in der Gelelektrophorese. Die restlichen 22 Proben wurden sequenziert und zur Wirtstieridentifizierung mit den verfügbaren Sequenzdaten aus Genbank® durch BLASTN® verglichen. Neben dem Rind wurden in 19 Fällen Menschen als Wirte der untersuchten Tsetsefliegen sowie in zwei Fällen Krokodile identifiziert. Eine Probe konnte nicht zugeordnet werden.SummaryNagana, a vector-borne epizootic caused by trypanosomes, severely constrains the use of draught animals in the cotton zone of south-eastern Mali. The disease causes considerable economic losses for the local farmers due to high mortality and morbidity ensuing productivity losses. Nagana is routinely controlled by the use of trypanocides and an overreliance on their use throughout past decades resulted in multiple drug resistance of trypanosomes in most parts of West Africas cotton belt. Designing alternative, effective vector control strategies requires an identification of the preferred hosts of tsetse flies through blood meal analysis as a prerequisite for estimating infection risk. A survey was, therefore, conducted between November 2008 and April 2009, catching 474 Glossina species which were dissected. Blood meals were smeared on filter paper (Whatman®-FTA-Cards) for laboratory analysis. DNA extractions and amplification using universal vertebrate cytochrome b primers of 120 assorted samples detected 74 DNA-containing specimens. The subsequent use of cattle-specific primers yielded 52 visible amplicons in the gel electrophoresis. Sequencing and BLASTN® analysis of the remaining samples revealed 19 blood meals matching with existing sequences of the human genome in Genbank®. Two samples originated from crocodiles whereas one was unidentifiable.

Multiple host feeding in Glossina palpalis gambiensis and Glossina tachinoides in southeast Mali

Changes in agricultural practices and the resulting extinction of wildlife have led to the reduction or disappearance of savannah tsetse species. Riparian tsetse such as Glossina palpalis gambiensis Vanderplank 1949 and Glossina tachinoides Westwood 1850 (Diptera: Glossinidae) continue to persist in peridomestic sites, transmitting trypanosomiasis. At present, little is known about interspecies differences in feeding behaviour in these two species in southeast Mali, or of the phenomenon of multiple bloodmeals. To study these topics, 279 samples of G. p. gambiensis and G. tachinoides containing host DNA, caught in the Sikasso region between November 2008 and April 2009, were analysed by applying host species‐specific primers and sequencing. Human accounted for > 66% of G. p. gambiensis bloodmeals, whereas G. tachinoides contained in equal parts DNA of human, cattle or both, showing a significantly higher proportion of multiple host use. Further, the trypanosome infection rate was found to be three‐fold higher in G. tachinoides. Logistic regression analysis revealed double‐feeding and infection to be independent of one another, but showed infection to be correlated with engorgement in G. p. gambiensis and female sex in G. tachinoides. Enhanced host‐seeking activities paired with the high trypanosome infection rate found in G. tachinoides would indicate that this species has a higher vectorial capacity than G. p. gambiensis.

Cattle breeding, trypanosomosis prevalence and drug resistance in Northern Togo

African Animal Trypanosomosis (AAT) is a major disease of cattle in Togo and its control is essentially based on chemotherapy. However, because of excessive use of trypanocides during the past decades, chemo-resistance in the parasites has developed. In order to assess the current situation of AAT and resistance to trypanocidal drugs in Northern Togo, a study was conducted on cattle from December 2012 to August 2013 in the regions of Kara and Savanes. An initial cross-sectional survey was carried out in 40 villages using the Haematocrit Centrifugation Technique (HCT). Out of these, 5 villages with a trypanosome prevalence of >10% were selected for a block treatment study (BT) with diminazene diaceturate (DA: 3.5mg/kg for a 14-day follow-up) and isometamidium chloride (ISM: 0.5mg/kg for a 28-day follow-up). Positive blood samples collected during the parasitological surveys and an equivalent number of negatives were further analyzed by PCR-RFLP for trypanosome species confirmation and molecular diagnosis of resistance to DA in Trypanosoma congolense. The results from 1883 bovine blood samples confirmed a high overall trypanosome prevalence of 10.8% in Northern Togo. PCR-RFLP revealed that T. congolense is the dominant pathogenic trypanosome species (50.5%) followed by T. vivax (27.3%), and T. brucei (16.2%). The BT showed varying levels of treatment failures ranging from 0 to 30% and from 0 to 50% for DA and for ISM respectively, suggesting the existence of resistant trypanosome populations in the study area. Our results show that AAT still represents a major obstacle to the development of cattle husbandry in Northern Togo. In areas of high AAT risk, a community-based integrated strategy combining vector control, rational use of trypanocidal drugs and improving the general condition of the animals is recommended to decision makers.

Aberrant use and poor quality of trypanocides: a risk for drug resistance in south western Ethiopia

BackgroundTrypanocidal drugs have been used to control African animal trypanosomosis for several decades. In Ethiopia, these drugs are available from both authorized (legal) and unauthorized (illegal) sources but documentation on utilization practices and quality of circulating products is scanty. This study looked at the practices of trypanocidal drug utilization by farmers and the integrity of active ingredient in trypanocides sold in Gurage zone, south western Ethiopia. The surveys were based on a structured questionnaire and drug quality determination of commonly used brands originating from European and Asian companies and sold at both authorized and unauthorized markets. One hundred farmers were interviewed and 50 drug samples were collected in 2013 (Diminazene aceturate = 33 and Isometamidium chloride = 17; 25 from authorized and 25 from unauthorized sources). Samples were tested at the OIE-certified Veterinary Drug Control Laboratory (LACOMEV) in Dakar, Senegal, by using galenic standards and high performance liquid chromatography.ResultsTrypanosomosis was found to be a major threat according to all interviewed livestock keepers in the study area. Diminazene aceturate and isometamidium chloride were preferred by 79% and 21% of the respondents respectively, and 85% of them indicated that an animal receives more than six treatments per year. About 60% of these treatments were reported to be administered by untrained farmers. Trypanocidal drug sources included both unauthorized outlets (56%) and authorized government and private sources (44%). A wide availability and usage of substandard quality drugs was revealed. Twenty eight percent of trypanocidal drugs tested failed to comply with quality requirements. There was no significant difference in the frequency of non-compliance between diminazene-based and isometamidium chloride products (P = 0.87) irrespective of the marketing channel (official and unofficial). However, higher rates of non-compliant trypanocides were detected for drugs originating from Asia than from Europe (P = 0.029).ConclusionThe findings revealed the presence of risk factors for the development of drug resistance, i.e. wide distribution of poor quality drugs as well as substandard administration practices. Therefore, it is strongly recommended to enforce regulatory measures for quality control of veterinary drugs, to expand and strengthen veterinary services and to undertake trypanocidal drug efficacy studies of wider coverage.