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Publications 3

Abstract Gastrointestinal nematode infections, including Haemonchus contortus, are one of the main causes of economic losses to ovine farmers worldwide. In order to contribute to the control of nematode infections and avoid parasite spreading we generated divergent resistant and susceptible sheep breeds and evaluated the adaptive immunity of these animals developed upon experimental infection against H. contortus. The selection of resistant or susceptible animals from the Corriedale Breed has been based on Expected Progeny Differences for faecal egg counts per gram. Furthermore, animals from the resistant Corriedale line were inseminated with imported semen from Australian Rylington Merino rams. Thus, the objective of this work was to analyze the adaptive immune response in both susceptible and resistant obtained lambs. Our results indicate that there is a potent parasite-specific local and systemic immune response in resistant animals and that although susceptible lambs can produce high levels of IgA antibodies during the infection, their antibody response is delayed which, together with an impaired specific-Th2 response, does not contribute to initial parasite elimination. Our results shed light into the immune mechanisms that mediate resistance to H. contortus and could constitute important assets to sheep farmers, not only as a means to detect resistance, but also to enhance the efficiency of selection in stud flocks.

Bovine coronavirus (BCoV) is a recognized cause of severe neonatal calf diarrhea, with a negative impact on animal welfare, leading to economic losses to the livestock industry. Cattle production is one of the most important economic sectors in Uruguay. The aim of this study was to determine the frequency of BCoV infections and their genetic diversity in Uruguayan calves and to describe the evolutionary history of the virus in South America. The overall detection rate of BCoV in Uruguay was 7.8% (64/824): 7.7% (60/782) in dairy cattle and 9.5% (4/42) in beef cattle. The detection rate of BCoV in samples from deceased and live calves was 10.0% (6/60) and 7.6% (58/763), respectively. Interestingly, there was a lower frequency of BCoV detection in calves born to vaccinated dams (3.3%, 8/240) than in calves born to unvaccinated dams (12.2%, 32/263) (OR: 4.02, 95%CI: 1.81–8.90; p = 0.00026). The frequency of BCoV detection was higher in colder months (11.8%, 44/373) than in warmer months (1.5%, 3/206) (OR: 9.05, 95%CI: 2.77–29.53, p = 0.000013). Uruguayan strains grouped together in two different lineages: one with Argentinean strains and the other with Brazilian strains. Both BCoV lineages were estimated to have entered Uruguay in 2013: one of them from Brazil (95%HPD interval: 2011–2014) and the other from Argentina (95%HPD interval: 2010–2014). The lineages differed by four amino acid changes, and both were divergent from the Mebus reference strain. Surveillance should be maintained to detect possible emerging strains that can clearly diverge at the antigenic level from vaccine strains.

Several oral ivermectin (IVM) formulations for use in sheep are available in the pharmaceutical veterinary market in different countries. All of them are indicated at the same dose rate to treat the gastrointestinal nematodes. However, there is a lack of information on the relative systemic exposure (plasma bioavailability) and clinical efficacy among oral formulations routinely used in sheep. The main goal of the work reported here was to perform a pharmaco-parasitological assessment of three different IVM oral formulations in lambs infected with multiple resistant gastrointestinal nematodes. The comparative drug systemic exposure (IVM plasma concentrations) and nematodicidal efficacies (clinical efficacy) in lambs were determined for a reference (RF) and two different test (T1, T2) IVM oral formulations. One hundred and fifty six (n= 156) healthy Corriedale lambs, naturally infected with multiple resistant gastrointestinal nematodes were allocated into four experimental groups (n=39). Animals in each group received treatment (200 μg/kg) with either the RF, one of the test IVM formulations or were kept as untreated control. Blood samples were collected over 15 days post-treatment (n=8). The IVM plasma concentrations were measured by high performance liquid chromatography with fluorescence detection. The faecal nematode egg count reduction test (FECRT) (n=39) and evaluation of the clinical efficacy were performed at day 14 post-treatment (n=6), where a predominance of IVM highly resistant nematodes was observed.