-Although the molecular bases of resistance to anthelmintic families have been intensively studied, the contributing factors for the development of anthelmintic resistance are less well known. Clear recommendations must be given to farmers in order to delay the onset of anthelmintic resistance. Until now, the main advice has concerned the reduction of treatment frequency in order to slow down the spread of resistance. Anthelmintic resistance development depends mostly on an efficient selection pressure. This means that a high treatment frequency is neither necessary nor sufficient to select for resistance. The contribution of resistant worms, which have survived an anthelmintic treatment, to the subsequent generation is the key factor that controls resistance spread. This point is illustrated by five surveys conducted on sheep and goat farms from France and Morocco. In the 52 farms studied, less than three anthelmintic treatments were given each year. Three characteristics of breeding management can be identified in the build up of anthelmintic resistance: (1) the introduction of resistant worms through the purchase of sheep/goats or the use of common pastures, grazed by several herds/flocks, (2) under-dosing of hosts and the repeated use of one class of drugs, (3) the size of the population in refugia (infective larvae on pastures) at the time of the treatment. The role played by these breeding management factors in selecting for resistance is discussed. The most efficient way to limit the increase of anthelmintic resistance remains the reduction of the selection pressure by drugs, and optimal timing to maximise their efficacy. Bien que les bases moléculaires de la résistance aux différentes familles d'anthelminthiques aient été très étudiées, les facteurs permettant le développement de la résistance anthelminthique sont moins bien connus. Des recommandations claires sont nécessaires aux éleveurs si l'on souhaite retarder l'apparition de la résistance aux anthelminthiques. La principale recommandation a consisté à réduire la fréquence des traitements de façon à ralentir le développement de la résis-tance. Le développement de la résistance anthelminthique dépend essentiellement d'une pression de sélection efficace. Cela signifie qu'une forte fréquence de traitements n'est ni nécessaire ni suffisante pour sélectionner la résistance. La contribution des vers résistants, qui ont survécu au traitement anthelminthique, à la génération suivante est le facteur clé qui contrôle le développement de la résis-tance. Ce point est illustré par cinq enquêtes réalisées dans des élevages ovins et caprins de France et du Maroc. Dans les 52 élevages étudiés, moins de trois traitements anthelminthiques par an étaient réalisés. Trois conditions d'élevage ont pu être mises en évidence comme étant impliquées dans le dé-veloppement de la résistance anthelminthique :
Summary :We report the preliminary results of an epidemiological survey carried out in the locality of Ouled Hcein, province of Taounate (North Morocco) around one visceral leishmaniasis infant case. The strain isolated from the child was characterized by three methods as Leishmania infantum and its isoenzyme pattern was indistinguishable from zymodeme MON-1. The human survey in the locality of origin of the index case did not show any additional case and the serology was negative for the whole people sampled. The canine survey showed that the highest seroprevalence of the canine disease was found in the locality of Ouled Hcein (27.1 %) when compared to 4 surrounding localities. The entomological survey showed that amongst the demonstrated L. infantum vectors around the Mediterranean Basin, Phlebotomus longicuspis was the predominant species. Furthermore, the survey led to the indentification of one female of P. ariasi naturally infected with L. infantum, so this species should be at least one of the vectors of this parasite in this area. Thus, this study confirms that the transmision cycle of L. infantum in North Morocco is similar to the cycle found in the remaining Mediterranean area.
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