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Overview of Gastrointestinal Parasites of Pigs

By Lora R. Ballweber, MS, DVM, College of Veterinary Medicine and Biomedical Sciences, Colorado State University

In pigs, GI helminths are almost always present; their main effects are loss of appetite, reduction in daily gain, poor feed utilization, and potentiation of other pathogens. Only rarely do they cause death. Adequate nutrition helps reduce the adverse effects of parasitism on feed efficiency and average daily gain.

Management and control of GI helminths depends entirely on the production system in place, with individual programs developed for the circumstances of the specific farm, including the knowledge of which parasites are present. Maintaining pigs on concrete or entirely on slatted floors, as on intensive farms, can successfully control those parasites that have intermediate hosts or that require pasture conditions for transmission. Steam cleaning is highly effective in killing eggs and larvae. The management approach for outdoor situations and nonconcrete floors is aimed at avoiding a buildup of eggs and larvae within the area. Good sanitation is critical because fecal-oral transmission, through the contamination of food, soil, or bedding, is the primary route by which pigs become infected. Direct sunlight or dry conditions shorten the survival of some eggs and larvae because moisture and warmth are needed for their development and survival, which probably accounts for decreased transmission during hot and cold months. Thermophilic composting of feces and/or bedding before use as fertilizer inactivates Ascaris suum and Trichuris suis eggs. Both can survive for a few hours at 50°C but only a few minutes at 55°C. Most disinfectants in use on farms, unfortunately, are not effective against parasite eggs, especially those of A suum and T suis. Moving "clean" animals to safe pastures will help reduce parasite buildup, but it must be remembered that eggs of A suum and T suis are capable of surviving 6–9 and 5–11 yr, respectively, in the environment, and reinfection will occur even with 2–3 yr of pasture rest. If it is not possible to rotate pastures, pigs may occupy uncleanable ground for many years. In these situations, parasites can build up quickly, and control may be impossible without the regular use of anthelmintics. Anthelmintic treatments can be incorporated into any broader program as needed but should not be the sole basis of a control program.

Various anthelmintics are available, although not all are available in every country. Benzimidazoles, including fenbendazole and flubendazole, are available for in-feed administration. Flubendazole is available for in-water and top dressing use, whereas fenbendazole has an oral formulation. Two avermectin compounds, ivermectin and doramectin, are available as injectables, whereas only ivermectin can be used in-feed. Both pyrantel tartrate and levamisole are available as in-feed formulations, but only levamisole can be used in water. Dichlorvos, an organophosphate compound, was the first broad-spectrum dewormer available for pigs and is still in use as an in-feed formulation. Piperazine salts are an older generation of anthelmintic. Despite its narrow spectrum of activity, it is still widely used, available as an in-feed or in-water formulation.

Although anthelmintic-resistant populations of Oesophagostomum sp were identified as early as 1987, resistance does not appear to be a widespread problem. In addition, there is no justification for routinely rotating classes of dewormers; rather, choice of product should be made on the expected efficacy against the parasites present (including ectoparasites).