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.     

The application of PCR-ELISA to the detection of Trypanosoma brucei and T. vivax infections in livestock

Teneral tsetse flies infected with either Trypanosoma brucei or T. vivax were fed on healthy cattle. Blood samples collected daily from the cattle were examined by microscopy for the presence of trypanosomes, in thick smear, thin smear and in the buffy coat (BC). All the cattle fed upon by infected tsetse developed a fluctuating parasitaemia. DNA was extracted from the blood of these cattle and subjected to polymerase chain reaction (PCR) using oligonucleotide primers specific for T. brucei or T. vivax. The PCR products unique to either T. brucei or T. vivax were identified following amplification of DNA from the blood samples of infected cattle, whereas none was detectable in the DNA from the blood of the cattle exposed to non-infected teneral tsetse. In a concurrent set of experiments, one of the oligonucleotide primers in each pair was biotinylated for use in PCR-ELISA to examine all the blood samples with this assay. Both the PCR and the PCR-ELISA revealed trypanosome DNA in 85% of blood samples serially collected from the cattle experimentally infected with T. brucei. In contrast, the parasitological assays showed trypanosomes in only 21% of the samples. In the blood samples from cattle experimentally infected with T. vivax, PCR and PCR-ELISA revealed trypanosome DNA in 93 and 94%, respectively. Microscopy revealed parasites in only 63% of the BCs prepared from these cattle. Neither PCR nor PCR-ELISA detected any trypanosome DNA in blood samples collected from the animals in the trypanosome-free areas. However, both assays revealed the presence of trypanosome DNA in a number of blood samples from cattle in trypanosomosis-endemic areas.     

Bovine trypanosomiasis in southern Tanzania: Investigation into the incidence of infection and duration of chemoprophylaxis

Before implementing chemoprophylaxis to control bovine trypanosomiasis it is essential to have epidemiological data upon which to base control regimes. A study was conducted under natural tsetse challenge with two groups each of 12 calves grazing their first season. Group 1 received isometamidium treatments prophylactically at intervals during the rainy season and calves in group 2 were treated individually with diminazene as they become infected with trypanosomes. Infections were first detected in the unprotected calves and indicated that the onset of challenge was approximately four weeks after the rainy season began. Trypanosoma vivax accounted for 21 of the 30 infections detected in blood smears, and although one infection remained unspeciated, the remaining eight were T. congolense. It was concluded that a prophylactic regime beginning one month after the start of the rains with repeat treatments of isometamidium at 1 mg/kg at intervals of 10 weeks could be expected to give good control of trypanosomiasis at this location.     

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

Summary

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 1mg/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.     

The transmissibility of Trypanosoma congolense seems to be associated with its level of resistance to isometamidium chloride

In large parts of Africa the control of livestock trypanosomiasis relies on the use of trypanocidal drugs. Resistance against the available compounds is developing rapidly in the trypanosome population. The effect of the development of drug resistance on the fitness of the trypanosome is not well known. To determine the effect of the development of resistance to isometamidium chloride on the trypanosome's transmissibility, transmission experiments were conducted. Use was made of three isogenic clones of Trypanosoma congolense with different susceptibility to the drug. The infection rate in Glossina morsitans morsitans differed significantly between clones and was significantly higher in tsetse flies infected with the T. congolense clone with the highest level of drug resistance.     

Isometamidium chloride prophylaxis against Trypanosoma congolense challenge and the development of immune responses in Boran cattle

Twenty-four Boran cattle were injected with isometamidium chloride (1 mg/kg bodyweight) to investigate the duration of drug-induced prophylaxis against infection by metacyclic forms of Trypanosoma congolense and to determine if specific antibody responses to the organism were mounted by animals under chemoprophylactic cover. Complete protection against either single challenge by five tsetse flies infected with T congolense, or repeated challenge at monthly intervals by five tsetse flies, lasted for five months. Six months after treatment, two-thirds of the cattle were resistant to challenge, irrespective of whether subjected to single or multiple challenge with trypanosome-infected tsetse flies, or titrated doses of in vitro-cultured metacyclic forms of T congolense (5 X 10(2) to 5 X 10(5) organisms), inoculated intradermally. No animal which resisted infection developed detectable skin reactions at the site of deposition of metacyclic trypanosomes or produced trypanosome-specific antibodies. It was concluded that drug residues effectively limited trypanosome multiplication at the site of deposition in the skin, thus preventing subsequent parasitaemia or priming of the host's immune response.     

Drug-resistant Trypanosoma congolense in naturally infected donkeys in north Omo Zone, southern Ethiopia

A three-part study was conducted to determine the efficacy of isometamidium chloride in donkey populations naturally infected with trypanosomes in north Omo Zone, southern Ethiopia. In the first, 373 randomly selected donkeys from four villages were examined for trypanosome infections by the dark ground/phase contrast buffy coat technique (BCT) in November 1999. The trypanosome prevalence was 18.2% (95% confidence interval (CI): 14.4, 22.5) and Trypanosoma congolense was the most common species accounting for 66.2% of the overall infections. In the second part, 40 infected donkeys were selected and treated with a prophylactic dose of 1.0mg/kg of isometamidium chloride and thereafter monitored every 14 days for 90 days. Trypanosomes were detected in eight donkeys within 1 month and in 20 donkeys within 2 months of treatment. About 16% (5/32) of donkeys infected with T. congolense were detected parasitemic 1 month after treatment. In addition, the result also revealed that all relapse/breakthrough infections were due to T. congolense. In the third part of this study mice were infected with two T. congolense field isolates from donkeys that were found to be parasitemic within 1 or 2 months after isometamidium treatment. The mice were treated with ranges of doses of isometamidium chloride or diminazene aceturate and thereafter followed for relapse infection. Isometamidium chloride at doses 0.5-4 mg/kg body weight and diminazene aceturate at doses of 3.5-28 mg/kg body weight failed completely to cure T. congolense infections in any of the mice.     

Protective efficacy of isometamidium chloride and diminazene aceturate against natural Trypanosoma brucei, Trypanosoma congolense and Trypanosoma vivax infections in cattle under a suppressed tsetse population in Uganda

The protective efficacy of isometamidium chloride (ISMM) and diminazene aceturate (DIM) against Trypanosoma brucei, Trypanosoma congolense and Trypanosoma vivax infections in cattle under a suppressed tsetse population was assessed in southeast Uganda. A total of 66 and 57 trypanosome-infected cattle were treated with ISMM and DIM, respectively together with 177 trypanosome-free animals not treated were followed for 12 months, checked every 4 weeks. There was no statistical difference in the mean time to infection with any trypanosome species in animals treated with ISMM or DIM. However, the mean time to trypanosome infection was significantly longer for treated animals than controls. The mean time to infection with each of the three trypanosome species differed significantly, with the average time to T. vivax infection the lowest, followed by T. congolense and then T. brucei. The protective efficacy of DIM was as good as that of ISMM; implying curative treatments against trypanosomosis are sufficient for combination with tsetse control. Isometamidium chloride or DIM had the highest impact on T. brucei and T. congolense infections in cattle.     

Vectorial capacity of Glossina palpalis gambiensis (Bobo Dioulasso) for Trypanosoma brucei brucei EATRO 1125]

A total of 440 teneral Glossina palpalis gambiensis received one single bloodmeal on a guinea pig infected chronically with Trypanosoma brucei brucei EATRO 1125. Metacyclic infections were present in 11.29% of the flies, in 2.32% infections were limited to procyclical stages. No significant difference in vectorial capacity was observed between male and female flies, the level of metacyclic infections being 13.19% in the former and 9.55% in the latter. The parasitaemia level, the percentage of stumpy forms at the moment of the blood meal and the maintenance conditions of the flies seemed to influence the infection of the flies.     

Effect of the number of health meals before an infectious meal on the vectorial competence of Glossina morsitans morsitans infected by Trypanosoma congolense IL 1180]

The purpose of this work was to assess the influence of several healthy meals (0, 1 and 2) prior to the infectious one on the vectorial competence of Glossina morsitans morsitans (Mall). The teneral flies (< 32 h old) of this line were divided into three groups. The tsetse flies of group A received no meal. The ones of group B received one healthy meal on day 1, whereas those from group C were given two consecutive healthy meals on days 1 and 2. All the flies were experimentally infected with Trypanosoma congolense IL 1180 when the maximum age reached 32 h for flies with no meal, 56 h for those with one healthy meal and 80 h for those who received two healthy meals. When both sexes were considered, the meso-procyclic and metacyclic indexes as well as the vectorial competence (VC) of the flies receiving no meal were 0.99 +/- 0.01, 0.96 +/- 0.02 and 0.95 +/- 0.03. Considering the flies which were fed one healthy meal, the respective values were 0.42 +/- 0.13, 0.50 +/- 0.01 and 0.21 +/- 0.06, whereas the values for the flies receiving two healthy meals were 0.45 +/- 0.11, 0.29 +/- 0.19 and 0.13 +/- 0.05. The meso-procyclic and metacyclic indexes as well as the VC in both sexes were more important in the flies which received no meal than those fed with one or two healthy meals. The meso-procyclic and metacyclic indexes and VC did not show any significant differences between the flies fed one or two healthy meals, whereas the metacyclic index of male flies which received one healthy meal was significantly higher than those fed two healthy meals. These results indicate that the number of non-infected (healthy) meals prior to an infected meal reduces the interaction between G. m. morsitans infected and T. congolense.     

Role of insects in the transmission of bovine leukosis virus: potential for transmission by stable flies, horn flies, and tabanids

The ability of stable flies (Stomoxys calcitrans), horn flies (Haematobia irritans), and tabanids (Diptera: Tabanidae) to transmit bovine leukosis virus (BLV) was investigated. Stable flies and horn flies were fed on blood collected from an infected cow, and the flies' mouthparts were immediately removed, placed in RPMI-1640 medium, ground, and inoculated into sheep and calves. Infection of sheep occurred with mouthparts from as few as 25 stable flies or 25 horn flies. However, sheep were not infected when removal of stable fly mouthparts was delayed greater than or equal to 1 hour after blood feeding. Infection of calves occurred after inoculation of mouthparts removed immediately after feeding from as few as 50 stable flies or 100 horn flies. Infected blood, applied by capillary action to the mouthparts (labella) of 15 deer flies (Chrysops sp) and a single horse fly (Tabanus atratus) caused infection in each of 2 sheep. Infection did not occur in 2 calves inoculated daily for 5 days with mouthparts from 50 horn flies collected after feeding on a BLV-infected steer. Four calves receiving bites from 75 stable flies interrupted from feeding on a BLV-positive cow also were not infected. Seronegative cattle held for 1 to 4 months in a screened enclosure with positive cattle in the presence of biting flies were not infected with BLV. The feeding behavior of each insect is discussed to assess their potential as vectors of BLV.     

Isometamidium-dextran complex: therapeutic activity against Trypanosoma vivax infection in Zebu cattle

Isometamidium-dextran complex was prepared by adding a 4% solution of dextran sulphate to an equal volume of a 4% solution of isometamidium chloride. The resulting 2% suspension was administered subcutaneously at 0.5, 1, and 2 mg/kg to three groups of Zebu bulls infected with Trypanosoma vivax Y58. The fourth group received isometamidium at 0.5 mg/kg intramuscularly. The parasite was cleared from all groups within 5 days, and recrudescence occurred to either preparation only at 0.5 mg/kg during the 90 day observation period. A firm movable subcutaneous nodule formed at the site of injection of the complex. The skin over the nodule appeared thickened due to oedema. Histologically, the nodule was characterized by diffuse connective tissue proliferation, with round cells and giant cell infiltration. There were focal areas of necrosis in the underlying granuloma associated with yellowish-brown staining drug deposits at the centre. The average growth rate of the treated groups was better than the non-treated group but inferior to the non-infected group. It was concluded that the complex at 1 or 2 mg/kg s.c. could be expected to protect cattle against trypanosomiasis and still yield good carcass and hide grading.     

Occurrence of multiple drug resistance in Trypanosoma brucei rhodesiense isolated from sleeping sickness patients

The occurrence of cross-resistance among melarsoprol-resistant Trypanosoma brucei rhodesiense isolates was investigated in this study. The isolates, T. b. rhodesiense KETRI 237, 2538, 1992, 2709, 2694 and 3530, had been obtained from sleeping sickness patients in Kenya and Uganda between 1960 and 1985. Five groups consisting of six mice each were inoculated intraperitoneally with 10(5) parasites of each isolate, and 24 h later treated with either melarsoprol, homidium chloride, diminazene aceturate or isometamidium chloride. The control group comprised infected but untreated mice. The mice were monitored for cure for a period of 60 days post-treatment. The mean prepatent period in the control mice was 5 days while the mean survival period was 22 days. Five of the stabilates, KETRI 237, 2538, 2709, 2694, and 3530, were confirmed to be melarsoprol resistant. Cross-resistance was observed, with the majority of the isolates being resistant to homidium chloride (5/6) and diminazene aceturate (5/6), but all were sensitive to isometamidium chloride (6/6). However T. b. rhodesiense KETRI 1992, which was previously considered as melarsoprol resistant, was sensitive to all the drugs tested. In conclusion, our study has revealed the existence of cross-resistance among the melarsoprol resistant isolates which could only be cured by isometamidium.     

Biting flies and Trypanosoma vivax infection in three highland districts bordering lake Tana, Ethiopia

An epidemiological study was conducted to determine the prevalence of trypanosomosis in cattle, small ruminants and Equidae, and to identify biting flies; potential mechanical vectors of trypanosomes in the three districts of Bahir Dar Zuria, Dembia and Fogera, bordering lake Tana, Ethiopia. About 1509 cattle, 798 small ruminants and 749 Equidae were bled for the prevalence study using the buffy-coat method and the measurement of the hematocrit value. Sixty-six NGU and 20 monoconical traps were deployed for the fly survey. The results indicated the presence of trypanosomes in 6.1% (92/1509) of the cattle with a maximum during the late rainy season (9.6%) than the early dry season (3.6%) at Fogera district. Prevalence at the district level varied from 4% to 9.6%. Only one sheep (1/122) and one goat (1/676) were found positive for T. vivax-like trypanosomes and none of the Equidae was positive. All the trypanosomes encountered in cattle belong to the single species of T. vivax. The PCV was negatively associated with detection of T. vivax (21.6% in infected versus 25.4% in non-infected cattle). A total of 55,398 biting flies were caught of which 49,353 (89.08%) belong to Stomoxys, 4715 (8.51%) to horse flies and 1330 (2.4%) to Chrysops species. There was no tsetse fly. Species identification has indicated the presence of Atylotus agrestis, Chrysops streptobalia, Stomoxys calcitrans, S. nigra, S. pulla, S. pallida, S. sitiens, S. taeniata, S. uruma, Haematopota lasiops and Hippobosca variegata. The overall apparent density was 214.7flies/trap/day. Seasonal comparison showed higher fly catches in the late rainy season than the early dry season. This study indicated that T. vivax infections culminate in cattle at the same time as mechanical vectors such as Stomoxys sp. and Atylotus agrestis. Therefore, attention towards T. vivax infection in cattle is essential to control the impact of the disease on productivity. A further study on biting flies is recommended.     

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.     

Interference between drug-resistant and drug-sensitive stocks of Trypanosoma congolense in goats

A study was undertaken in goats to investigate the ability of two unrelated stocks of Trypanosoma congolense, one of which is highly sensitive to isometamidium chloride and one which is drug-resistant, to become established in the presence of an existing infection with the other stock. The goats, which were initially infected with the sensitive strain and were then challenged with the resistant strain, were cured by treatment at 0.1 mg kg-1 isometamidium, indicating that the resistant stock did not establish an infection. Goats initially infected with the resistant stock, which were then challenged with the sensitive stock, experienced temporary remission of infection followed by relapse after treatment at 0.1 mg kg-1 isometamidium. In contrast, the goat infected only with the resistant stock remained parasitaemic following treatment at 0.1 mg kg-1. This suggests that superinfection with the sensitive stock resulted in the establishment of infection, which suppressed the resistant stock to below the limit of detection of the method used. These observations suggest that isometamidium-resistant stocks may be less viable than sensitive strains, and could explain the relative scarcity of isometamidium resistant in the field.     

Effect of chemotherapy on elevated ejaculation time and deteriorated semen characteristics consequent to bovine trypanosomiasis

The effect of the trypanocidal drug Novidium on elevated ejaculation time and deteriorated semen characteristics was studied in Zebu cattle infected with T. vivax and T. congolense. Two groups, comprising six bulls per group, were infected with Trypanosoma vivax or Trypanosoma congolense while three bulls served as controls. Chemotherapy was carried out 12 weeks post-infection on three bulls from each group, leaving three bulls untreated while three bulls served as uninfected controls. Blood samples from treated bulls were all negative for trypanosomes 3 days post-chemotherapy. The animals also had normal body temperature. As the study progressed, clinical signs associated with trypanosomiasis, such as anaemia and cachexia, disappeared gradually in treated bulls. There was some improvement in semen characteristics of some of the bulls at 10 weeks post-chemotherapy with Novidium. However, all bulls infected with T. vivax or T. congolense irrespective of Novidium chemotherapy still had poor semen characteristics manifested by all or some of the following: decreased volume of semen, oligospermia, azoospermia and elevated incidence of spermatozoa morphological abnormalities. They were thus unsuitable for breeding.     

Role of horse flies in transmission of wquine infectious anemia from carrier ponies

Equine infectious anemia virus was transmitted from an acutely ill and an inapparently infected pony to uninfected ponies by the interrupted feeding of horse flies (tabanids). Transmission from acutely ill ponies was not accomplished following: (1) the interrupted feeding of a single horse fly, (2) bites of horse flies that had fed on an acutely affected pony 24 hours earlier, (3) bites of horse flies that had oviposited after feeding on an acutely affected pony, or (4) the inoculation of larval material derived from horse flies that had fed to repletion. It was concluded that horse fly transmission of equine infectious anemia virus is mechanical only and that infected horses that are free of clinical signs can be a source of virus for insect transmission.     

Susceptibility of buffaloes, cattle and goats to infection with different stocks of Trypanosoma vivax transmitted by Glossina morsitans centralis

A comparison was made of the susceptibility of buffaloes, cattle and goats to infection with Trypanosoma vivax transmitted either by Glossina morsitans centralis or by syringe inoculation. Three different isolates of T vivax (two from East Africa, one from West Africa) were used to compare skin reactions, parasitaemia, anaemia and the development of trypanosome-specific antibodies in buffaloes, cattle and goats. African buffaloes reared in captivity in an area free from trypanosomiasis proved to be highly resistant to infection with the three stocks of T vivax tested, irrespective of whether infection was by tsetse transmitted metacyclic forms or by intradermal or intravenous inoculation of bloodstream forms of the parasite. The bites of 19 tsetse infected with a West African T vivax stock did not cause local skin reactions, detectable bloodstream infections or antibody responses in two buffaloes. Following the bites of 120 tsetse flies infected with the same stock, two different buffaloes showed no local skin reactions, but had detectable bloodstream infections without showing signs of anaemia. Cattle and goats infected in a similar way showed severe local inflammatory skin reactions, high levels of parasitaemia and severe anaemia. The two East African stocks of T vivax caused no local skin reactions and only a transient parasitaemia in buffaloes following tsetse-transmitted infection or intradermal inoculation of bloodstream forms. On the other hand, cattle and goats infected with the East African stocks showed high parasitaemias but local skin reactions only occurred in the goats.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of T. vivax infection in west African dwarf goats on energy and nitrogen metabolism.

To investigate how T. vivax affects metabolism in dwarf goats, nine wethers (infection group) given alfalfa pellets ad libitum were infected intravenously and food intake was recorded up to 49 days after infection in the infection group and in the control group (n = 9). Controls received the same diet, ad libitum before infection and in restricted amounts after infection in order to obtain similar intakes in the two groups. Digestible organic matter intake (DOMI) and nitrogen balance (NB) were determined during four balance trials. All animals were bled regularly to measure parasitaemia, packed cell volume (PCV) and a number of serum metabolites. All infected animals showed symptoms typical for T. vivax infection as judged by parasitaemia, PCV and rectal temperature. Infection had a non-uniform negative effect on food intake. Compared with controls at equal DOMI, NB was lower in infected animals, the difference being significant 4 weeks after infection. This was caused by a gradual increase in NB at equal DOMI of the control group. The NB of the ad libitum fed infected animals 2 and 4 weeks after infection was comparable to values normally found in healthy ad libitum fed dwarf goats with an equal DOMI. NEFA values in serum were significantly elevated after infection. Except for two infected animals with an extremely low food intake towards the end of the experiment, no rise in serum ketone bodies was evident. After infection, serum protein increased, differences with controls being significant 4 and 7 weeks after infection.(ABSTRACT TRUNCATED AT 250 WORDS)