Overview of Gastrointestinal Parasites of Pigs

Also see Coccidiosis of Pigs.

Gastrointestinal helminths are almost always present in pigs. Their main effects are loss of appetite, decrease in daily gain, and poor feed efficiency. They rarely cause death. Dynamics of parasitism, including variety and number of species and parasite intensity, can vary with geographic location, climate, and management practices. Adequate nutrition and husbandry can help decrease 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 and the specific parasites present. The purpose is to decrease parasitic challenge to avoid clinical signs and production losses.

Maintaining pigs on slatted floors, as on indoor-intensive farm systems, can help successfully control those parasites that have intermediate hosts or that require specific pasture conditions for transmission. These systems typically have parasites with direct life cycles and include only a few helminth species (1).

The management approach for outdoor conditions and porous floors is aimed at avoiding a buildup of eggs and larvae within the area. Solid floors and bedding material used for animals in group housing conditions can create environments conducive to egg survival (2). Good sanitation is critical, because fecal-oral transmission via the contamination of food, soil, or bedding or through ingestion of intermediate hosts is the primary route by which pigs become infected.

Pigs managed outdoors typically have a higher diversity of parasitic species because of increased opportunities for exposure to intermediate hosts, environments that allow survival of eggs and larvae in feces, and potential exposure to wild boars or feral hogs, which are commonly infected with numerous GI parasites (1).

Direct sunlight or dry conditions shorten the survival time of some eggs and larvae that require moisture and warmth for development and survival. This probably accounts for decreased transmission during hot and cold months in some areas.

Thermophilic composting of feces or bedding before use as fertilizer inactivates Ascaris suum and Trichuris suis eggs, which can survive for a few hours at 50°C (122°F) but only a few minutes at 55°C (131°F) (2). For herds managed outdoors, practices used for ruminants, including pasture rotation or moving to clean pastures, combined with the use of anthelmintics can be beneficial (2).

Disinfectants in use on farms are often ineffective against parasite eggs, especially those of A suum and T suis. Moving noninfected animals to safe pastures helps decrease parasite buildup; however, eggs of A suum and T suis are capable of surviving 6–9 and 5–11 years, respectively, in the environment, and reinfection will occur even with 2–3 years of pasture rest (2).

If it is not possible to rotate pastures, pigs might have to continuously occupy infested ground that cannot be cleaned. In these situations, parasites can build up quickly, and control can be impossible without the regular use of anthelmintics. Anthelmintic treatments can be incorporated into any broader program as needed; however, they should not be the sole basis of a control program.

Various anthelmintics are available; however, 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, and fenbendazole has an oral formulation. Two avermectin compounds, ivermectin and doramectin, are available as injectables; however, only ivermectin can be used in feed. Pyrantel tartrate is available as an in-feed formulation. 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 a narrow spectrum of activity, they are still widely used and available as an in-feed or in-water formulation.

Anthelmintic-resistant populations of Oesophagostomum spp were identified as early as 1987 (2); however, anthelmintic resistance does not appear to be a widespread problem. It might develop over time if anthelmintics are used excessively. Treatments and timing can vary by management system and are typically strategic, treating the sow and specific groups or treating all animals at different times of the year (2). Regardless, the choice of product should be made on the expected efficacy against the parasites present (including other internal parasites, such as trematodes, coccidia, lungworm or kidney worm, and ectoparasites).