Diagnosis and control of anthelmintic-resistant Parascaris equorum

Abstract

Since 2002, macrocyclic lactone resistance has been reported in populations of Parascaris equorum from several countries. It is apparent that macrocyclic lactone resistance developed in response to exclusive and/or excessively frequent use of ivermectin or moxidectin in foals during the first year of life. The development of anthelmintic resistance was virtually inevitable, given certain biological features of Parascaris and unique pharmacologic characteristics of the macrocyclic lactones. Practitioners can utilize the Fecal Egg Count Reduction Test to detect anthelmintic resistance in Parascaris, and the same technique can be applied regularly to confirm the continued efficacy of those drugs currently in use. In the face of macrocyclic lactone resistance, piperazine or anthelmintics of the benzimidazole or pyrimidine classes can be used to control ascarid infections, but Parascaris populations that are concurrently resistant to macrocyclic lactones and pyrimidine drugs have been reported recently from Texas and Kentucky. Compared to traditional practices, future recommendations for ascarid control should feature: 1) use of only those anthelmintics known to be effective against indigenous populations, 2) initiation of anthelmintic treatment no earlier than 60 days of age, and 3) repetition of treatments at the longest intervals which prevent serious environmental contamination with Parascaris eggs. In the interest of decreasing selection pressure for anthelmintic resistance, horse owners and veterinarians must become more tolerant of the passage of modest numbers of ascarid eggs by some foals. Anthelmintic resistance is only one of several potential responses to genetic selection.Although still only theoretical, changes in the immunogenicity of ascarid isolates or reduction of their prepatent or egg reappearance periods could pose far greater challenges to effective control than resistance to a single class of anthelmintics.

Investigation of strongyle EPG values in horse mares relative to known age, number positive, and level of egg shedding in field studies on 26 farms in Central Kentucky (2010–2011)

“…However, while frequent use of antiparasitic compounds has been so effective on large strongyles, resistance of small strongyles and ascarids to several of the parasiticides has emerged (Kaplan 2002;Kaplan et al 2004;Reinemeyer 2009a). In the Lexington, Kentucky area and several other geographic locations worldwide where chemical control of parasites has been used routinely, small strongyles are resistant to fenbendazole, oxibendazole, and pyrantel pamoate (Kaplan et al 2004).…”

Monitoring the avermectin and pyrantel resistance status of nematode parasites of horses in the Czech Republic

“…The efficacy of pyrantel products is often described in the context of their use against ivermectin-resistant ascarid populations. Such studies were conducted in the USA and Europe and all of them confirmed a good effect of tetrahydropyrimidines on resistant ascarid populations (Slocombe et al 2007;von Samson-Himmelstjerna et al 2007;Reinemeyer 2009;Reinemeyer et al 2010).…”

“…Ascarid resistance against pyrantel has so far only been described in North America (Craig et al 2007;Lyons et al 2008). It has been hypothesized that pyrantel resistance on some farms may have been selected for as a result of daily administration of pyrantel tartrate as a prophylactic agent (Reinemeyer 2009). This is a so-called continuous antiparasitic program, which consists in daily administration of pyrantel tartrate to horses at a dosage of 2.6 mg/kg in a pelleted product incorporated into (Kaplan and Nielsen 2010).…”

“…The ascarid is most often found in the small intestine of foals and less commonly in weanlings and young horses. Slow growth, weight loss, cough and colic are all signs of potential massive gastrointestinal infection (Reinemeyer 2009;Nielsen et al 2014). Cyathostomins are found in the large intestines of horses; aggregation of the developmental stages in the mucosa of the large intestine can lead to clinically apparent disease which manifests itself as diarrhoea, hypoproteinaemia, subcutaneous oedema and metabolic acidosis (Lyons et al 2000).…”

El nematodo Caenorhabditis elegans como modelo para evaluar el potencial antihelmíntico de extractos de plantas

“…A comienzos de 1960 por primera vez se reportó resistencia antihelmíntica a la droga fenotiazina por parte del parásito gástrico hematófago Haemonchus contortus (28) y después en pequeños estróngilos típicos del caballo (29) . En 1961 se liberó el tiabendazol en el mercado, un fármaco anunciado como el primero en combinar una eficacia nematicida de amplio espectro y una baja toxicidad.…”