Efficacy of commonly used anthelmintics: First report of multiple drug resistance in gastrointestinal nematodes of sheep in Trinidad

Case report: Assessment of a quarantine treatment for sheep on the Caribbean Island of St. Kitts

Quarantine treatments can be used to prevent bringing resistant parasites onto a farm. However, in the face of growing anthelmintic resistance and variations in farm practices, assessing efficacy of such treatments before full implementation is needed. In this case report, a combination treatment of ivermectin (injectable formulation) and fenbendazole (both approximately double doses) administered orally within minutes of each other was assessed in 19 sheep. The mean pretreatment Strongylid eggs per gram of feces, determined using a McMaster, was 2639. The mean post treatment count (at 14 days) was 2663 with 12 animals having a decrease in egg counts. There was an average increase of 0.9% using pre and post treatment egg count means. This combination treatment was not effective as a quarantine treatment.

A field study on the occurrence of gastrointestinal nematodes in sheep over the wet and dry seasons in two West Indian Islands

Gastrointestinal nematode (GIN) infestations are a major constraint to sheep production in the West Indies (WI). Intensive and semi-intensive management systems are most commonly employed. These islands display tropical weather patterns with wet and dry seasons. Semi-intensive farming combined with increased rainfall during the wet season has been reported to be most favourable for development and survival of GIN. This study was conducted to determine whether there was a relationship between GIN burdens in sheep with seasonality and management practices of farmers in Trinidad and Tobago (T&T). Farms were visited on a monthly basis from January to December 2017. A maximum of ten sheep, three to nine months of age, were selected from each farm. A total of 3,053 faecal samples were collected and analysed using the Modified McMaster technique. Environmental data on daily precipitation and temperature were collected from the Trinidad and Tobago Meteorological Office during the period of sampling. A mixed effects negative binomial regression model was constructed to analyse the relationship between gastrointestinal nematode faecal egg counts (GINFEC) with season, management system and use of dewormers as fixed effects and farm as a random effect. Average diurnal temperatures of T&T fluctuated between 23.2°C to 32.6°C and 23.9°C to 32.3°C in the dry and wet seasons, respectively. Average daily precipitation ranged between 1.6-1.8 mm and 6.1-8.5 mm during the dry and wet seasons, respectively. A decreased risk of 0.34 (95% CI 0.25-0.47, p < .0001) for GINFEC was observed in dewormed animals versus not dewormed. Semi-intensive management systems experienced an increased risk of GINFEC by 1.39 (95% CI 1.05-1.84, p = .021) compared with intensive and the risk of GINFEC was reduced by 0.40 (95% CI 0.33-0.49, p < .0001) in the wet season versus the dry. A higher prevalence of GIN was observed during the drier months of the year. Climatic conditions observed in T&T remained favourable for GIN survival, development and distribution year-round. Proper management is therefore required for reducing the occurrence of GIN in sheep of T&T throughout the year. This is the first reported study in the WI on the influence of seasonality and management on GIN infestations in sheep during the dry and wet seasons. Further investigation is needed to elucidate why GIN burdens appear to be higher in the dry season than the wet season. This study can be used as a baseline for public education in T&T as well as other developing countries.

Gastrointestinal parasites in small ruminants from Grenada, West Indies: A coprological survey and a review of necropsy cases

Gastrointestinal parasites are important in small ruminant farming because they can impact negatively on the productivity of animals. The objectives of the present study were to estimate the prevalence of gastrointestinal parasites and to assess mortality attributable to gastrointestinal parasite infection in sheep and goats. We collected fecal samples from 114 sheep and 292 goats from 34 farms for coprological examination. In addition, we evaluated necropsy records for sheep and goats that were submitted from 2002 to 2016 to the pathology diagnostic laboratory in the School of Veterinary Medicine at St. George's University, Grenada. Out of 406 small ruminant (292 goat and 114 sheep) fecal samples examined, 385 were positive for gastrointestinal parasites, giving an overall prevalence of 95% (95% confidence interval (CI) 92% to 97%). All the 34 farms visited were found to have positive animals to at least one type of gastrointestinal parasite; 100% herd prevalence (95% CI: 88% to 100%). Among the 292 goat fecal samples examined, 285 were positive for gastrointestinal parasites (98%; 95% CI: 95% to 99%) whereas the proportion of positive fecal samples in sheep was 88% (95% CI: 80% to 93%). There was a significant difference in prevalence of gastrointestinal parasites between sheep and goats (p = .0002). The proportion of infection with coccidia in goats and sheep was 76% and 75%, respectively. For helminthes, the proportions were as follows: Moniezia spp., 14% in goats and 4% in sheep; Strongyloides spp., 36% in goats and 21% in sheep; strongyle type eggs 89% in goats and 66% in sheep. Mixed infections in both sheep and goats were more common (92%) than single ones (8%). Out of 220 necropsy records evaluated, 29% of mortality was due to Haemonchus contortus infection. Moniezia spp and Oesophagostomum spp. were also commonly found.

Field evaluation of the efficacy of common anthelmintics used in the control of gastrointestinal nematodes of sheep in Dabat district, Northwest Ethiopia

Background

Gastrointestinal nematode (GIN) infections are the main impediments that restrict the welfare and productivity of small ruminant in the world. Effective management of GINs in grazing sheep relies heavily on the use of highly efficacious anthelmintic drugs. However, anthelmintic resistance is becoming a significant concern in the world, and this phenomenon severely threatens the potential utilisation of this control strategy. Therefore, this study was conducted 1) to evaluate the efficacy of commonly used anthelmintic on GINs in naturally infected sheep and 2) to assess the farmers’ perception on anthelmintics utilisation practices in Dabat district, Northwest Ethiopia.

Methods

One hundred twenty nematode infected sheep were used in this study. Sheep were selected based on the egg count (≥150 eggs per gram of faeces). The animals were allocated randomly into four groups (30 animals per group). Group-I, II and III were treated with Albendazole, Tetramisole, and Ivermectin, respectively. The 4th group was left untreated (as control). Faecal samples were collected on day 0 (before treatment), on day 3, 7, 10 and 14 (post-treatment). The modified McMaster technique was used for quantifying the eggs. Faecal egg count reduction test (FECRT) was applied to determine the efficacy of anthelmintic at day 14 (post-treatment). In addition, a questionnaire survey was conducted on 100 randomly selected sheep owners.

Results

All anthelmintics tested revealed significant (P < 0.05) reduction in nematode egg excretion in the sheep post-treatment. Faecal egg count reduction (FECR) levels for Albendazole, Tetramisole, and Ivermectin were 97.2, 98.9 and 97.7%, respectively. Post-treatment egg counts and percentage reduction of egg counts were not significantly different (P > 0.05) among the treatment groups. The nematode genera identified before treatment were Haemonchus, Trichostrongylus, Cooperia, Trichuris, Teladorsagia, Bunostomum, and Strongyloides. Haemonchus and Trichostrongylus were detected after treatment with Albendazole and Ivermectin. The questionnaire survey revealed that Albendazole was the most commonly (90%) used anthelmintic to treat nematodes in sheep, followed by Tetramisole (36%) and Tetraclozan (Tetramisole-Oxyclozanide combination) (20%). Respondents expressed that anthelmintic selection was made based on veterinarian prescription (84%), colour (27%), efficacy (4%), price affordability (1%) and availability (1%).

Conclusion

This study demonstrated that the tested anthelmintics had an acceptable level of efficacy against GINs of sheep.

Improving liveweight gain of lambs infected by multidrug-resistant nematodes using a FECRT-based schedule of treatments

The aim of this study was to compare the liveweight gain of lambs, infected by multidrug-resistant nematodes, treated by conventional schemes of helminth control or using a schedule based on fecal egg count reduction test (FECRT). The flock was selected after a FECRT (experiment 1) which revealed a parasite population resistant to benzimidazoles, imidazothiazoles, macrocyclic lactones (ivermectin), salicylanilides, nitrophenols, and organophosphates. Despite the parasite resistance to ivermectin (an avermectin), the moxidectin (a milbemycin) was effective against the gastrointestinal nematodes (PR > 90%). In experiment 2, 48 suckling lambs were distributed in four randomized blocks (G1, G2, G3, and G4) by previous body weighings. G1 was kept as untreated control; G2 was treated following a FECRT-based schedule with drugs chosen based on fecal analysis (first drench with moxidectin, second drench with a combination of moxidectin and levamisole, and third drench with praziquantel, an anti-cestode drug); G3 and G4 received three drenches with ivermectin or disophenol, respectively. Body weighings and fecal analysis of these lambs were performed every 2 weeks over a 98-day period. An effective control of gastrointestinal nematodes was obtained with two nematicidal drenches following the FECRT-based schedule of treatments. On the other hand, eggs per gram of feces (EPG) counts were no different among untreated control, G3, and G4. Lambs treated using the FECRT-based schedule had the greatest liveweight gain among the groups tested. Additionally, liveweight gain was no different among the groups G3, G4, and G1. The FECRT-based schedule of anthelmintic treatments was beneficial regarding productivity and sustainability of helminth control in lambs infected by multidrug-resistant nematodes.