Efficacy of RM110, a novel trypanocide, in the treatment of Trypanosoma evansi infections in camels

An annotated checklist of the horse flies (Diptera: Tabanidae) of the Sinai Peninsula Egypt with remarks on ecology and zoogeography

During a 20-year survey we routinely collected Tabanidae in the Sinai resulting in a checklist of 22 species. We recorded 2 species for the Levant (Tabanus mordax Austen, 1911 and Tabanus gratus Loew, 1858), 4 species for Egypt (Nemorius irritans (Ricardo, 1901), Chrysops flavipes Meigen, 1804, Haematopota coronata Austen, 1908 and Haematopota pallens Loew, 1871), 5 species for the Sinai (Atylotus farinosus (Szilády, 1915), Tabanus arenivagusAusten, 1920, Tabanus autumnalis Linnaeus, 1761, Haematopota minusculaAusten, 1920 and Dasyrhamphis nigritus Fabricius, 1794) for the first time and confirmed one doubtful record for the Sinai (Tabanus albifacies Loew, 1856). Furthermore we collected 10 more species that were previously known or could be presumed from the Sinai. The status of 4 species (Atylotus pallescens (Walker, 1871), Tabanus unifasciatus Loew, 1858, Tabanus politus (Walker, 1871) and Tabanus terminalis Walker, 1871) doubtfully recorded from the Sinai is discussed. For most of the 22 species, apart from zoogeographical notes, host and ecological observations are also given.

Establishment of a panel of reference Trypanosoma evansi and Trypanosoma equiperdum strains for drug screening

The animal pathogenic protozoan, Trypanosoma evansi, leads to a wasting disease in equines, cattle and camels, commonly known as Surra. It is extensively distributed geographically with a wide range of mammalian hosts and causes great economical loss. Trypanosoma equiperdum causes a venereal disease called Dourine in horses and donkeys. Chemotherapy appears to be the most effective form of control for T. evansi, whereas infections caused by T. equiperdum are considered incurable. Due to emerging drug resistance, efficient control of T. evansi is severely threatened, emphasising the urgent need to find new alternative drugs. A drug profile for a panel of T. evansi and T. equiperdum strains has been established for the four standard drugs currently used in treatment. The (3)H-hypoxanthine incorporation assay was used to obtain 50% inhibitory concentration (IC(50)) values for each standard drug against the various strains. The results indicate the presence (and in some cases, the emergence) of drug resistance in several strains. This panel of characterised strains with known drug sensitivities and resistances will be of great value for the screening of new active compounds, in comparison with the four standard drugs currently available.

Camel trypanosomosis in Morocco. 2. A pilot disease control trial

A first epidemiological study on camel trypanosomosis was conducted in 1997 and 1998 in five Moroccan Saharan provinces. It revealed two major foci at Merzouga (Tafilalet province) and Zagora (Ouarzazate province) where tour camel seroprevalences were 35.4 and 43.3%, respectively, for each region. The first area was chosen in the present study as a pilot region for a control program based on epidemiological data with the aim of evaluating the efficiency of the trial in terms of seroconversion, incidence and health condition. After finding the endemic focus at Merzouga, four other field studies were organised in this area, at 4-month intervals, in order, firstly, to control the camel reservoir by treating all the camels found in the region during the visit using melarsomine (Cymelarsan, Rhône-Mérieux, the only trypanocide registered in Morocco), and, secondly, to collect blood samples for studying temporal changes in seroprevalence as well as in anaemia rate. All the 291 tour camels of the area, that were present in at least one of the field visits were examined and included in the trial. Among them, 162 were treated once, 84 twice and 41 three times. A total of 676 serum samples were collected from these camels. At the end of the trial--1 year later--seroprevalence had dropped from 58% (May 1998) to 19% and the mean Ab-ELISA value had decreased from 0.52 (before treatment) to 0.12 (which is below the threshold level), after the third campaign. The haematocrit of the animals was also slightly improved, indicating that trypanosomosis was a major cause, but it was not the only incriminated factor. A seasonal effect was observed. The overall seroprevalence was reduced between spring 1999 and summer 1999, without treatment, whereas a negative effect was recorded on packed cell volume, more camels being found anaemic in summer than in spring. The application of these strategic treatments was associated with a large reduction in the seroprevalence of trypanosomosis, but there was no complete eradication because of the continual exchange of animals from other foci such that of Zagora. The overall seroconversion after 1 year reached 55% and no post-treatment complication was recorded, whereas the incidence due to new infections approached 4.3%. Moreover, several factors like the unusual way of life of the dromedaries, including stress, excessive work, overcrowding and continual contact with other animals coming from other infected regions contribute to the persistence of the disease.

Chemotherapy and delivery systems: haemoparasites

Chemotherapy of haemoparasitic diseases in domestic animals is dependent on a limited number of compounds, many of which are chemically closely related. In this review, a summary is given of each of the drugs currently available for treatment and prophylaxis of trypanosomosis and the tick-borne diseases theileriosis, babesiosis, anaplasmosis and cowdriosis. In contrast to the situation with the drugs used for tick-borne diseases, drug resistance appears to be becoming an increasing problem associated with the compounds used for trypanosomosis. The literature that has been reviewed, therefore, is that which relates to the methods used to identify and quantify drug resistance in trypanosome populations, reports of resistance to trypanocides, and cross-resistance between trypanosome populations, reports of resistance to trypanocides, and cross-resistance between trypanocides. The possible reason(s) for the apparent lack of development of resistance to the compounds used for treatment of tick-borne diseases is also discussed. Local toxicity at the site of injection is a problem that is particularly associated with many of the trypanocides when used on a long-term basis in individual animals. Various alternative preparations of the currently used trypanocides therefore have been evaluated in an attempt to reduce this toxicity, and are summarised. Finally, future developments in haemoparasitic chemotherapy are considered and, for trypanosomosis, highlight the importance of integrating chemotherapeutic and chemoprophylactic programmes with control of the vector when drug resistance becomes a significant constraint.

Drug sensitivity of Chinese Trypanosoma evansi and Trypanosoma equiperdum isolates

The drug sensitivities of eleven Trypanosoma evansi isolates from China were examined using two different in vitro assays, a 3H-hypoxanthine incorporation assay and a long incubation low inoculation test (LILIT). Better discrimination of the drug susceptibility of the strains was observed with the LILIT. The drug responses of all the isolates to the arsenical melarsoprol were very similar. In contrast, for suramin, minimal inhibitory concentrations (MIC) varied within a 27-fold range and for diminazene within a 55-fold range. Comparison of MIC values with expected drug levels in the host as well as in vivo experiments with selected isolates and drugs indicated that all the isolates examined would be sensitive to melarsoprol, diminazene and suramin under in vivo conditions. For isometamidium, the difference in MIC values between the most and the least sensitive isolate was 724-fold. Neither of two isolates tested in mice--the most resistant and the second most sensitive--was cured with the highest acceptable dose of 10 mg kg-1 isometamidium chloride. Comparison of our results with blood levels of drug to be expected in cattle support the assumption that the Chinese T. evansi isolates have more or less innate resistance to isometamidium under in vivo conditions. One Trypanosoma equiperdum isolate was tested in the 3H-hypoxanthine incorporation assay. The results indicated that this isolate was highly sensitive to melarsoprol, isometamidium and suramin; with regard to diminazene, T. equiperdum was not as sensitive as the most sensitive T. evansi strains.

The rapid development of drug-resistance by Trypanosoma evansi in immunosuppressed mice

The effect of immunosuppression on the development of drug resistance by trypanosomes was investigated in mice infected with Trypanosoma evansi. As a result of frequent passage in immunosuppressed mice given subcurative drug treatments clones of T. evansi rapidly developed high levels of resistance to mel Cy, diminazene aceturate and isometamidium chloride. Similar protocols in normal immunocompetent mice infected with the same parent clones did not lead to the development of drug-resistance. The resistant populations developed in immunosuppressed mice maintained their high levels of resistance when tested in normal mice. The mel Cy resistant clone was tested for cross-resistance to other trypanocides and was found to be also highly resistant to diminazene and pentamidine. The results indicate that impairment of the host immune system may lead to the rapid development of drug-resistance by T. evansi under experimental conditions in mice and may possibly play a role in the development of drug resistance by trypanosomes in the field.