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

Objective: Gastrointestinal nematode (GIN) infestations of sheep are considered a major constraint to sheep production in the West Indies. Sheep are semiintensively managed under tropical conditions which are favorable for the development and survival of GIN. This study was conducted to determine if there was a relationship between GIN burdens in sheep with seasonality and management practices of farmers in Trinidad and Tobago (TT). Design and Methodology: Eighteen (18) farms were visited in Trinidad and 23 in Tobago on a monthly basis between January and December 2017. A maximum of ten sheep between three to nine months of age were selected using non-random sampling at each farm. Results: A total of 3053 fecal samples were collected and analyzed using the Modified McMaster Technique. A mixed effects Poisson regression model was constructed to analyze the relationship between eggs per gram (EPG) with season, management and deworming. The standard error was adjusted for clustering according to farm. EPG decreased according to wet season vs. dry season (coef. = - 0.6, 95% CI = -1.17 - -0.03, p = 0.039). Semiintensive management system experienced higher EPG than intensive system (coef. = 1.43; 95% CI = 0.72, - 2.14; p < 0.001). EPG did not vary significantly according to whether the farmer dewormed or not over the period (p = 0.54). Conclusion: Proper management is required for reducing the occurrence of GIN in sheep of TT throughout the year. Further investigation is needed to elucidate why EPG appear to be higher in the dry season than the wet season.

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

In Trinidad, small ruminant farms are semi-intensively managed under tropical conditions which support the development and survival of the infective stages of the helminths. Local farmers use anthelmintics to control gastrointestinal nematodes frequently. Frequent use of anthelmintics has the potential to select for populations of nematodes resistance to those chemicals. Hence, an attempt was made to study the efficacy of commonly used drugs on gastrointestinal nematodes of sheep. Three farms situated in different counties in Trinidad were selected. Sheep aged 6-15 months and not treated with anthelmintics for a minimum of six months previous and with faecal egg count (FEC)>150 eggs per gram were selected for study. They were allocated into 5 groups, each consisting 10 animals. The Group TA animals were treated once with albendazole (5mg/kg. b.wt.), group TF with fenbendazole (5mg/kg.b.wt.), group TI animals with ivermectin (200 µg/kg b.wt.), group TL with levamisol (7.5mg/kg b.wt.). The group NTC animals were not given any drug and served as control. The number of nematode eggs per gram of faeces from each animal was determined before treatment and at 14 days after treatment. The anthelmintic susceptibility to different drugs was detected by FECRT (in vivo) with EPG recorded at 14 day post-treatment. The data analysis using FECRT revealed that efficacy of albendazole (46-62%), fenbendazole (44-61%) and levamisol (53-81%) were reduced compared to ivermectin (95-97%). An attempt has also been made to find a suitable method for calculation of FECR (%).

Parasitological and clinical responses of lambs experimentally infected with Haemonchus contortus (L3) with and without ivermectin treatment

Haemonchus contortus is one of the most important parasites that infects sheep and exerts its pathogenic effects by sucking blood, causing disturbances of organ-functions and thus inducing alterations in various normal physiological parameters. Changes in live body weight, faecal egg count, kinetics of circulating eosinophils and PCV value were studied at weekly interval for a period of 84 days in 18 lambs of local breed after infection with a single dose of 5000 H. contortus (L(3)). In the two groups of lambs infected with nematodes both non-treated and treated with ivermectin (HcNT and HcIT), similar egg excretion patterns was observed starting from third week after infection, with a regular increase in FEC. Examination of whole abomasum of each animal revealed no developmental stage of nematode from treated and control lambs on day 84. The total mean number of H. contortus worms recovered at necropsy from abomasa of untreated infected lambs (group HcNT) was 2576.2 (+/-221.0). The significant loss of body weight, development of heavy worm burden and severe anaemia as indicated by reduced PCV in untreated infected lambs indicated high susceptibility of the lambs to H. contortus. On the other hand, complete absence of the parasite, improved PCV value and body weight after treatment of infected animals (HcIT) proved 100% efficacy of ivermectin against H. contortus.