Differences in sensitivity of KenyanTrypanosoma vivax populations to the prophylactic and therapeutic actions of isometamidium chloride in Boran cattle

Summary Isometamidium chloride was administered as a single prophylactic dose of 0·5 mg kg⁻¹ body weight to each of 10 Boran (Bos indicus) steers. At monthly intervals following drug administration, groups of five cattle each were challenged with one of two differentTrypanosoma vivax populations transmitted by infectedGlossina morsitans centralis; one with a stock (IL 2982) from Galana, Kenya and the other with a stock (IL 2986) from Likoni, Kenya. Prophylaxis was afforded for less than one month against the GalanaT. vivax and for one month against the LikoniT. vivax. In a therapeutic study a further 10 Boran steers were similarly infected with either of theT. vivax populations; five steers per population. Eleven days after infection all animals were treated with 0·5 mg kg⁻¹ isometamidium chloride and all were cured. These findings demonstrate that, as defined in the field, the two KenyanT. vivax populations express a high level of resistance to the prophylactic action of isometamidium yet a low level of resistance to the therapeutic action of the drug. The results also indicate that differences in drug resistance between different isolates play a major role in determining the apparent period of prophylaxis afforded by isometamidium chloride.

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Resumen Se administró cloruro de isometamidio en dosis profilácticas sencillas de 0·5 mg kg⁻¹ de peso corporal a cada uno de 10 novillos Borán (Bos indicus). Con intervalos de un mes después de la administración de la droga, grupos de cinco animales cada uno recibieron una descarga con una de dos cepas diferentes deT. vivax, transmitidas porGlossina morsitans centralis infectadas; un grupo con la cepa (IL 2982) de Galana Kenya y el otro con la cepa (IL 2986) de Likoni, Kenya. La acción profiláctica duró menos de un mes contra la cepa Galana y por un mes contra la cepa Likoni. En un estudio terapéutico, otros 10 novillos Borán fueron infectados con una de las dos cepas (cinco animales por grupo). Once días después de la infección, todos los animales se trataron con 0·5 mg kg⁻¹ de cloruro de isometamidio, curandose todos. Estos hallazgos demuestran que como en el campo, las dos cepas deT. vivax tienen un alto nivel de resistencia a la acción profiláctica del isometamidio y una baja resistencia a la acción terapéutica de la droga. Los resultados también demuestran que la diferencia en la resistencia a la droga de las dos cepas, juega un papel importante y determinante en el efecto profiláctico inducido por el cloruro de isometamidio.

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Résumé Du chlorure d'isométamidium a été administré à la dose individuelle unique de 0,5 mg par kg de poids vif à 10 bouvillons Boran (Bos indicus) à titre prophylactique. A un mois d'intervalle, après l'administration du produit, deux groupes de 5 animaux ont été soumis à l'une des deux populations différentes deTrypanosoma vivax transmises parGlossina morsitans centralis; l'une avec la souche IL 2982 provenant du Galana (Kenya) et l'autre avec la souche IL 2986 de Likoni (Kenya). La protection a été inférieure à un mois contreT. vivax Galana et égale à un mois pourT. vivax Likoni. Lors d'une étude thérapeutique, un autre lot de 10 bouvillons Boran a été infecté dans les mêmes conditions avec l'une et l'autre des populations deT. vivax, à raison de cinq animaux pour chancune d'elles. Onze jours après l'infection, tous ont re?u une dose unique individuelle de 0,5 mg par kg de chlorure d'isométamidium et tous ont été guéris. Ces résultats démontrent que, telles qu'elles sont présentes sur le terrain, les deux souches kenyannes deT. vivax présentent un haut degré de résistance à l'action prophylactique de l'isométamidium, en dépit d'un niveau peu élevé de l'action thérapeutique du même produit. Les résultats montrent également que la variation de la résistance au produit entre différents isolats joue un r?le majeur dans la détermination de la période apparente de protection assurée par l'isométamidium.

     

Therapeutic and prophylactic activity of isometamidium chloride in Boran cattle against Trypanosoma vivax transmitted by Glossina morsitans centralis

Ten Boran steers were infected with Trypanosoma vivax, transmitted by Glossina morsitans centralis; five steers with a T vivax clone from Nigeria and five with a T vivax clone from Kenya. Eleven days after infection all 10 animals were treated with 0.5 mg kg-1 isometamidium chloride. Four steers infected with the Nigerian T vivax and all five infected with the Kenyan T vivax were completely cured. When different steers received a single prophylactic dose of 0.5 mg kg-1 isometamidium chloride and subjected to monthly tsetse-transmitted challenge with the same T vivax clones, complete protection was afforded for at least two months against challenge with the Nigerian T vivax, but for less than one month against the Kenyan T vivax. The findings indicate that the level of sensitivity of a T vivax population to the prophylactic activity of isometamidium chloride cannot be concluded from sensitivity studies based on the therapeutic action of the drug.     

Notes on the routine intravenous use of isometamidium in the control of bovine trypanosomiasis on the Kenya coast

Summary Various chemotherapeutic regimes were used to control trypanosomiasis in 3,000 Boran cattle on an estate on the Kenya coast. Recently the therapeutic use of isometamidium by the intravenous route was adopted to treat individual trypanosome-infected cattle. This was in order to overcome tissue reactions encountered after intramuscular injection and also to control a thin cow syndrome attributed to chronic trypanosomiasis. Toxic side effects were eliminated by careful attention to the intravenous technique which was safely used in calves, pregnant cattle and bulls. Weekly blood sampling and treatments of infected individuals resulted in a reduction of cases from 2,187 to 208 out of 46,495 and 46,329 samples examined in 1985 and 1986 respectively. The standard of management was very high and although this routine successfully controlled bovine trypanosomiasis on this estate its application elsewhere is likely to be limited.

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Notas Sobre El Uso Intravenoso Rutinario De Isometamidio En El Control De Tripanosomiasis Bovina En La Costa De Kenia

Resumen Se usaron varios regímenes quimioterapéuticos, para controlar tripanosomiasis, en 3,000 bovinos Boran en un estado de Kenia localizado en las costa. El uso terapéutico de isometamidio vía intravenoso, se adoptó recientemente para tratar individualmente animales con tripanosomiasis. Esta práctica se instituyó para evitar las reacciones tisulares resultantes de la inyección intramuscular y para controlar también el síndrome de la vaca flaca atribuido a la tripanosomiasis crónica. Los efectos tóxicos colaterales fueron eliminados, mediante las atención cuidadosa a la técnica de la inyección intravenosa usada en terneras, hembras preñadas y toros. El muestreo semanal de sangre y el tratamiento de los animales infectados, resultó en la reducción de casos de 2,187 a 208, a partir de 46,495 y 46,329 muestras examinadas en 1985 y 1986 respectivamente. El estandar de manejo fue alto y aunque esta rutina controló exitosamente la tripanosomiasis bovina en ese estado, la aplicación de la misma en otros lugares podría ser limitada.

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Note Sur l'Utilisation Intraveineuse En Routine De l'Isometamidium Pour Le Controle De La Trypanosomose Bovine Sur La Cote Kenyane

Résumé Plusieurs regimes chimiothérapeutiques ont été mis en oeuvre pour contrôler la trypanosomose chez 3.000 bovins Boran d'une propriété de la côte du Kenya. On a adopté récemment l'utilisation de l'isométamidium par voie intraveineuse pour traiter individuellement des bovins infectés de trypanosomes. Cette pratique a été institutionalisée dans le but de surmonter les réactions tissulaires rencontrées à la suite des injections intramusculaires et aussi de contrôler le syndrôme vache maigre attribué à une trypanosomose chronique. Les effets toxiques secondaires ont été éliminés par une attention particulière à la technique intraveineuse; on a pu innoculer sans accident des veaux, des vaches pleines et des taureaux. Des prises de sang et des traitements hebdomadaires des animaux infectés ont amené une réduction des cas de 2.187 à 208 sur 46.495 et 46.329 échantillons examinés respectivmeent en 1985 et 1986. Le standard de l'élevage était excellent; bien que cette pratique de routine ait permis avec succès un contrôle de la trypanosomose bovine dans cette propriété, il est probable que son application ailleurs soit limitée.

     

Action of isometamidium chloride on the insect vector form of Trypanosoma vivax

The effect of isometamidium chloride upon developing and mature Trypanosoma vivax occurring in Glossina palpalis palpalis flies was evaluated. Newly emerged G p palpalis flies were infected with T vivax by allowing them to feed on parasitaemic animals. Two experiments were conducted and in each the flies were divided into two groups. One group of infected flies was fed in vitro through a membrane on defibrinated cow blood containing isometamidium chloride at 0.1 mg ml-1, after which they were dissected and examined for trypanosomes, and the other group was fed in the same way on unmedicated blood. The results showed that out of a total number of 129 flies which fed on medicated blood, none was infected, while 55 out of 127 flies which fed on unmedicated blood were infected. The results indicate that isometamidium chloride eliminated the insect vector form of T vivax. These findings are of potential significance in the control of trypanosomiasis in the field, particularly in the operation of the sterile insect technique.     

Field detection of resistance to isometamidium chloride and diminazene aceturate in Trypanosoma vivax from the region of the Boucle du Mouhoun in Burkina Faso

A longitudinal study assessed the chemoresistance to isometamidium chloride (ISM) and diminazene aceturate (DA) in the region of the Boucle du Mouhoun in Burkina Faso. A preliminary cross-sectional survey allowed the identification of the 10 villages with the highest parasitological prevalences (from 2.1% to 16.1%). In each of these 10 villages, two herds of approximately 50 bovines were selected, one being treated with ISM (1mg/kg b.w.) and the other remaining untreated as control group. All animals (treated and untreated herds) becoming infected were treated with DA (3.5mg/kg b.w.). In total, 978 head of cattle were followed up. Fortnightly controls of the parasitaemia and PCV were carried out during 8 weeks. The main trypanosome species was Trypanosoma vivax (83.6%) followed by Trypanosoma congolense (16.4%). In two villages, less than 25% of the control untreated cattle became positive indicating no need to use prophylactic treatment. These two villages were not further studied. Resistance to ISM was observed in 5 of the remaining 8 villages (Débé, Bendougou, Kangotenga, Mou and Laro) where the relative risk (control/treated hazard ratios) of becoming infected was lower than 2 i.e. between 0.89 (95% CI: 0.43-2.74) and 1.75 (95% CI: 0.57-5.37). In contrast, this study did not show evidence of resistance to DA in the surveyed villages with only 8.6% (n=93) of the cattle relapsing after treatment. Our results suggest that because of the low prevalence of multiple resistances in the area a meticulous use of the sanative pair system would constitute the best option to delay as much as possible the spread of chemoresistance till complete eradication of the disease by vector control operations.     

Evaluation of isometamidium levels in the serum of sheep and goats after prophylactic treatment against trypanosomosis

Isometamidium chloride has been used for the control of trypanosomosis in animals for over 36 years, but recently there have been reports of prophylaxis failure under natural conditions. In this study, use of the drug for prophylactic purpose against trypanosomosis in small ruminants was investigated. Forty-two sheep and 44 goats were divided into four treatment groups. Groups 1 and 2 were treated with isometamidium chloride (Samorin, Rhone Merieux, Lyon, France) at 3-month intervals while groups 3 and 4 were used as controls. All the animals were exposed to natural tsetse challenge and monitored for serum isometamidium levels and anti-trypanosome antibodies. Seven days after drug administration, isometamidium levels were significantly higher in goats 13.7+/-0.07 ng/ml than in sheep 6.2+/-0.06 ng/ml. However, the elimination half-life in the sheep was 14.2+/-0.92 days and was significantly higher (P> 0.05) than that of the goats 12+/-0.5 days. This study established that isometamidium metabolism differs between sheep and goats and this difference may have important implications in high tsetse challenge areas.     

Studies on the influence of non-steroidal anti-inflammatory drugs upon trypanosomiasis in goats and sheep

The non-steroidal anti-inflammatory drug (NSAID) flurbiprofen caused a rise in parasitaemia in goats infected with Trypanosoma vivax, Trypanosoma congolense and Trypanosoma brucei. All trypanosome-infected goats treated with flurbiprofen showed many dividing trypanosomes. This also included the short-stumpy forms of T. brucei. In T. vivax-infected goats flurbiprofen treatment resulted in 100% mortality in the acute and chronic stages of the infection. The increase in parasitaemia of T. brucei infected goats, treated with flurbiprofen, was not associated with an increase in mortality. The increase in parasitaemia of T. congolense-infected goats, treated with flurbiprofen, tended to be associated with a somewhat higher mortality but this was statistically not significant. The significant rise in parasitaemia could be reproduced in T. brucei-infected sheep without, however, killing the animals. Two other NSAIDs were also studied. Suprofen caused a rise in parasitaemia and 100% mortality when given to goats in the acute stage of T. vivax infection. Results with flunixin meglumine, when tested in T. brucei infected goats, were not conclusive.     

The response of pigs experimentally infected with Trypanosoma brucei to isometamidium chloride therapy and the relation to nutrition.

Growing pigs were placed on feeds with high (Group A), medium (B) and low (C) dietary energy and were infected with a virulent stock of T. brucei. Eight weeks later, the infected pigs were treated with isometamidium chloride at 1 mg/kg live weight and all pigs were subsequently placed on a high energy diet to investigate their response to therapy. Clearance of T. brucei from blood was completed 72h after treatment. There was no evidence of relapsed infection up to eight weeks after treatment. Red blood cell parameters returned to normal four to six weeks after treatment with responses being fastest in Group A, B and C had gained about two-thirds of the live weight gains of their non-infected pair-fed controls. It appears that the retarded weight gain as a result of the infection persisted after therapy since drug-treated pigs did not gain as much weight as their non-infected controls.     

Pathophysiology of ovine trypanosomiasis: ferrokinetics and erythrocyte survival studies.

The haematological changes, erythrokinetics and ferrokinetics of sheep were investigated after infection with Trypanosoma congolense. Following the detection of parasites in blood, the infected sheep developed macrocytic hypochromic anaemia. Studies with 51Cr-red cells, 125I-albumin and 59Fe as ferric citrate 11 weeks after infection revealed that infected sheep had significantly lower mean circulating red cell volumes but higher plasma and blood volumes than control sheep. The infected sheep also had enhanced erythropoietic activity as judged by significantly higher plasma iron turnover rates, faster disappearance of radio-labelled iron and higher iron incorporation rates than control sheep. The rate of disappearance of 51Cr-labelled red cells was greater in infected than in control sheep. It was concluded that the anaemia observed at this stage of infection was due to an increased rate of removal of red cells from the circulation coupled with haemodilution, with no evidence of dyshaemopoiesis.     

Development of an enzyme-linked immunosorbent assay for the detection and measurement of the trypanocidal drug isometamidium chloride in cattle

An enzyme-linked immunosorbent assay (ELISA) was developed to measure accurately levels of the trypanocidal drug isometamidium in the serum of treated cattle. The assay requires only 5 microliters of test serum, is sensitive to a level of 0.5 pg ml-1 and is highly specific. Cross reactivity does not occur with the two other widely used trypanocidal drugs diminazene aceturate and homidium bromide. Serum drug levels are detectable for up to six months in cattle after a single dose of 1 mg kg-1 intramuscularly, the maximum period under field conditions for which effective prophylaxis can be maintained against tsetse challenge. Application of the assay will aid the rationalisation of treatment campaigns and assist in assessing the occurrence of drug-resistant trypanosome populations.     

Prevalence of domestic animal trypanosomiasis in the Fontem sleeping sickness focus, Cameroon

Three hundred-fourteen domestic animals: 114 goats, 93 sheep, 67 dogs and 30 pigs in the Fontem sleeping sickness focus (Cameroon) were screened for infection with trypanosomes using parasitological and serological tests. Nannomonas was the only sub-genus detected in the animals with a prevalence of 28.3%. The card agglutination test (Testryp CATT) for trypanosomiasis showed a positivity rate of 38.2%, indicating that it allowed a better estimation of animal trypanosomiasis. The absence of trypanosomes of the sub-genus Trypanozoon seems to indicate that human African trypanosomiasis is not a zoonosis in this sleeping sickness focus.     

Response of Trypanosoma vivax and Trypanosoma congolense in zebu cattle in North Cameroon to prophylactic treatment with two formulations of isometamidium

We tested the efficacy of two formulations of isometamidium in a tsetse-infested farm in North Cameroon from 20 August 2000 to 5 January 2001. A total of 90 adult cattle were used in three groups of 30 each corresponding to two treated and one untreated control. Drug efficacies were evaluated in terms of reduction of parasite incidence in the host's blood, maintenance of packed-cell volume (PCV) and weight gains. Both drugs reduced the incidence of parasites even though re-infections 2 weeks after treatment were common. PCV values were similar in both treated groups but higher than in the untreated control. Body weight changes followed a similar trend with the control losing weight from a mean of 427+/-119kg at the beginning to 398+/-93kg in 4 months. Weights increased from 375+/-76 and 396+/-110 to 396+/-69 and 418+/-112kg in the Veridium and Trypamidium groups, respectively. Efficacy was similar between the two formulations of isometamidium in the prophylaxis of bovine trypanosomosis. However, the presence of parasites in some animals barely 2 weeks after treatment suggested that either infections were not cleared or residual drug effects were not sufficient to prevent re-infections.     

Effect of dietary chloride content on the elimination of bromide by dogs

The effect of dietary chloride content (0·2, 0·4 and 1·3 per cent chloride on a dry matter basis) on the disposition of a single oral dose of bromide (14 mg kg⁻¹ was evaluated in normal beagles. Increasing the dietary chloride content from 0·2 to 1·3 per cent resulted in a significant decrease in the mean apparent elimination half-life from 69 ± 22 days to 24 ± 7 days. The mean area under the concentration curve ( ) for dogs fed 1·3 per cent chloride was significantly smaller than the for dogs fed 0·2 per cent chloride. Dietary chloride had no effect on the maximum serum concentrations (C_max) or on the time (T_max) to reach the maximum concentrations. The steady-state serum bromide concentrations predicted from the single dose data for daily doses of 14 mg kg⁻¹ of bromide were significantly lower in dogs fed 1·3 per cent chloride (310 ± 150 mg litre⁻¹) than in dogs fed 0·2 per cent chloride (1950 ± 1140 mg litre⁻¹). The predicted mean daily doses of bromide necessary to maintain serum levels within the therapeutic range for dogs fed 1·3 per cent chloride (43 ± 13 mg kg⁻¹) were almost twice as high as the dose estimated for dogs fed 0·4 per cent chloride (22 ± 3 mg kg⁻¹) and nearly three times as high as the dose estimated for dogs fed 0·2 per cent chloride (15 ± 4 mg kg^−l). These differences were statistically significant (P=0·002).