[Biology of gastrointestinal nematodes of ruminants]. / Biologia dei nematodi gastrointestinali dei ruminanti.

The development and survival of free-living stages of gastro-intestinal nematodes of small ruminants are influenced by several abiotic and biotic factors. Within the abiotic factors, most important are the environmental temperature and humidity. They regulate the development of larvae from eggs dispersed on the pasture by the animals faeces. Each parasite species that infect ruminants requires a different time to development, depending on temperature and humidity. Among trichostrongylids, Ostertagia, Teladorsagia and Nematodirus show a strong adaptation to low temperatures. Nematodirus larvae are able to survive to winter inside the egg shell. Temperature and humidity influence the distribution and survival of larvae on pasture. The larval third stage can migrate from faeces to pasture vegetation and they accumulate at the basis of vegetation where stay during the day or in the soil to avoid the desiccation. The forage species affects the migration of larvae on herbage too. Many biological factors contribute to disperse the larvae on the pasture. Dung burying beetles, coprophagous beetles and earthworms can greatly reduce the larvae of some trichostrongylids on pasture. They contribute to the spread of the faecal material on the pasture and allow the larval death as a consequence of drying.

Effect of cool storage of faecal samples containing Haemonchus contortus eggs on the results of an in vitro egg development assay to test anthelmintic resistance.

An in vitro egg development assay was used to test the resistance of eggs from a benzimidazole susceptible and a resistant strain of Haemonchus contortus to four benzimidazoles. Storage of eggs contained in faecal samples at 4 degrees C for four, 24 or 72 hours did not appear to impair the results from the in vitro egg development assay or alter the LD50. Storage for one week, however, proved to be lethal for the eggs. The average LD50 values for thiabendazole, albendazole, mebendazole and cambendazole were 0.06, 0.07, 0.96 and 2.47 ppm for the susceptible strain. For the resistant strain the values averaged 0.26, 0.24, 1.07 and 5.11 ppm.

The ageing process in infective larvae of the roundworms Haemonchus contortus and Nippostrongylus brasiliensis: carbohydrate content.

Trehalose, glycogen and traces of glucose were the only anthrone sensitive carbohydrates identifiable. The variation of 13-22% of the dry weight in different populations of Haemonchus contortus L3 is shown to be due to their capacity to synthesize glycogen during ageing. This contrasts with the larvae of Nippostrongylus brasiliensis in which a low level of carbohydrate remains constant with time. It is suggested that H. contortus can convert lipid to carbohydrate as is the case for several other nematodes. H. contortus L3 show some evidence of physiological adaptation.