The effects of closantel treatment on the ultrastructure of Haemonchus contortus

Anthelmintic resistance in commercial sheep farms in Costa Rica

Forty-eight commercial sheep farms were sampled between the years 2017 and 2019 to evaluate the percentage of reduction of the three families of broad-spectrum anthelmintic drugs available in Costa Rica - benzimidazoles (albendazole), macrocyclic lactones (ivermectin) and imidazothiazoles (levamisole) - in grazing animals by using the fecal egg count reduction test. Animals were selected based on their egg per gram counts after their fecal samples were processed by a modified McMaster technique. The remaining fecal samples were taken to the laboratory for fecal culture and larval identification. The prevalence of farms with albendazole resistance was 100%, ivermectin 96% and levamisole 17%. Seven (n = 47) farms resulted with triple resistance, 39 with double and 1 farm was resistant to 1 AH tested. Haemonchus spp. was the most commonly isolated parasite in pre- and post-treatment larval culture. This is the first report of Oesophagostomum spp. and Teladorsagia sp. resistant to albendazole, Oesophagostomum spp., Teladorsagia sp., Chabertia sp. and Cooperia sp. resistant to ivermectin, and the presence of strains of Haemonchus spp. and Trichostrongylus sp. resistant to the 3 anthelmintics tested. The results of this study demonstrate that anthelmintic resistance is widespread, particularly in Haemonchus spp., and that the major drugs available in the country have lost much of their effectiveness against sheep nematodes.

Chemical constituents of Calotropis procera latex and ultrastructural effects on Haemonchus contortus

Abstract This study aimed to evaluate the anthelmintic and ultrastructural effects of Calotropis procera latex on Haemonchus contortus. C. procera latex was twice centrifuged at 10,000×g and dialyzed to obtain a fraction rich in proteins, named LP (latex protein), and at 3,000 rpm to obtain a fraction rich in secondary metabolites, named LNP (latex non-protein). Specimens of H. contortus exposed to LNP, LP and PBS in the Adult Worm Motility Test (AWMT) were submitted to scanning (SEM) and transmission (TEM) electron microscopy to verify changes in their ultrastructure. Phytochemical tests in the LNP indicated the presence of phenols, steroids, alkaloids and cardenolides. High-Performance Liquid Chromatography (HPLC) characterized the presence of the compounds gallic acid and quercetin in the LNP. The protein content in the LP was 43.1 ± 1.1 mg/mL and 7.7 ± 0.3 mg/mL in LNP. In AWMT, LNP and LP inhibited the motility of 100% of the nematodes, with LNP being more effective than LP and ivermectin more effective than both (p <0.05). Cuticle changes were observed by SEM and TEM in nematodes treated with LP and LNP. Calotropis procera latex has anthelmintic effects against H. contortus, causing damage to its cuticle and other alterations in its ultrastructure.

Ultrastructural study of adult Haemonchus contortus exposed to polyphenol-rich materials under in vivo conditions in goats

This study assessed the ultrastructural changes caused in adult Haemonchus contortus obtained from goats fed fodder based on polyphenol-rich plants Lysiloma latisiliquum or Onobrychis viciifolia or from goats drenched with quebracho extract, Schinopsis spp. The H. contortus were obtained from artificially infected goats used as models to investigate the anthelmintic effect of feeding or drenching with the polyphenol-rich materials. Nematode populations were exposed to polyphenol-rich plant materials by feeding host goats for 8 consecutive days (D28 to D35 post-infection) with (a) L. latisiliquum fodder at 800 g fresh basis/day, (b) O. viciifolia fodder offered ad libitum, and (c) drenched with a solution containing quebracho extract (90 g/day). Meanwhile, control H. contortus were obtained from goats fed polyphenol-free diets. The H. contortus specimens were recovered from the goats on D36 post-infection, and transmission electron microscopy (TEM) was used to identify ultrastructural changes. In vivo exposure to different polyphenol-rich plant materials caused vacuolization of the nematodes’ intestinal, muscular and hypodermal cells. These alterations represent the first evidence of cell damage caused in H. contortus when hosts were fed or drenched with polyphenol-rich materials. Ultrastructural changes affecting several types of cells could explain modifications in worm motility and nutrition, eventually affecting H. contortus reproductive success. This study contributes to our understanding of the mechanisms of action of polyphenol-rich plants against H. contortus when given as nutraceuticals to goats.

Use of P-glycoprotein gene probes to investigate anthelmintic resistance in Haemonchus contortus and comparison with Onchocerca volvulus

A P-glycoprotein gene probe from the sheep parasitic nematode Haemonchus contortus was developed and used to analyse restriction fragment length polymorphisms between susceptible isolates and isolates resistant to either benzimidazole; levamisole and benzimidazole; or benzimidazole, ivermectin and closantel. No polymorphism could be correlated with any of the different resistances. A P-glycoprotein gene probe was also isolated from the human nematode parasite Onchocerca volvulus and an Onchocerca-specific PCR was developed.

In vitro culture of Oestrus ovis (Linné 1761) first instar larvae: its application to antiparasitic drug screening

A culture medium in which 1st instar larvae of Oestrus ovis can survive for up to 2 months has been developed with Dulbecco's Modified Eagle's Medium (DMEM) pH 7.7, penicillin 100 U/ml, streptomycin 100 micrograms ml-1, gentamicin 10 micrograms ml-1 and foetal calf serum (50%) added. Larvae were incubated in flat plastic tissue culture bottles (3 ml of medium) in a 5% CO2 atmosphere at 37 degrees C in darkness. Subsequently an antiparasitic in vitro screening test was developed with moxidectin and closantel. These drugs were not as effective in vitro as in vivo. This might be due to the fact that they cause damage to parasites and host immune responses, then contribute to their death.