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Diagnostic notes

March and April, 1997

Pig parasite diagnosis

Robert M. Corwin, DVM, PhD

College of Veterinary Medicine, University of Missouri, Columbia, Missouri 65211; email vmcorwin@vetmed.missouri.edu

Diagnostic notes are not refereed.

Parasites in swine have an impact on performance, with effects ranging from impaired growth and wasteful feed consumption to clinical disease, debilitation, and perhaps even death. It is particularly important to diagnose subclinical parasitism, which can have serious economic consequences and which should be treated with ongoing preventive measures.

Internal parasitism is caused by nematode roundworms and coccidia in the gastrointestinal tract, lungworms in the respiratory tract, and by ectoparasites. The most commonly encountered gastrointestinal parasites are the large roundworm Ascaris suum, the threadworm Strongyloides ransomi, the whipworm Trichuris suis, the nodular worm Oesophagostomum dentatum, and the coccidia, especially lsospora suis and Cryptosporidium parvum in neonates and Eimeria spp at weaning.

Diagnosis of internal parasites is best accomplished by fecal examination using a flotation technique and/or by necropsy. Although there are several flotation techniques, the net result is the microscopic appearance of nematode eggs and of coccidian oocysts. Fortunately, identification is relatively easy because pig parasite eggs and oocysts have such distinctive appearances. However, you should also consider size, so that you don’t incorrectly identify artifacts–e.g., pine pollen–as eggs. Use an ocular micrometer for measurements in microns ((micro)m).

You should also take the age of the pig into account when identifying parasites. Some parasites occur most often or in greatest numbers in young pigs, e.g., Strongyloides, Ascaris, and Isospora, whereas Oesophagostomum is often found in adult pigs because they have little immune response to it. The type of management and husbandry, e.g., pasture versus confinement, may determine the species of parasite present as well. Ascarids are ubiquitous and are found in confinement-reared pigs as well as in pigs reared on dirt. Others, such as nodular worms, lung worms, and, in southern climates, kidney worm (Stephanurus dentatum), are associated with dirt lots and pastures.

Prepatent period–the time it takes for the parasite to develop to reproductive age and produce eggs or oocysts –is another important identification factor. These periods are fairly specific and have a bearing on how early eggs could be expected to be found in pigs by fecal examination. The infection is then dependent on the initial time of exposure and the persistence or life span of the parasite.

Postmortem examination should reveal adult worms in their principal sites of infection, e.g., ascarids in the small intestine. Lesions associated with larval infection, such as nodules of Oesophagostomum in the colon may not have larvae present or apparent. Lungworms also have rather specific sites at least in young worm populations, viz., the bronchioles of the diaphragmatic lobes of the lungs.

All of these parasites are directly transmissible from the environment with ingestion of eggs or larvae. Strongyloides may also be passed in the colostrum or penetrate skin, and transmission of the lung worm and the kidney worm may involve earthworms.

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Ascaris suum –"large roundworm"

Strongyloides ransomi–"intestinal threadworm"

Trichuris suis–"whipworm"

Oesophagostomum dentatum–"nodular worm"

Metastrongylus spp–"lung worm"

Stephanurus dentatus–"kidney worm"

Isospora suis –"neonatal coccidiosis"

Cryptosporidium parvum –"cryptosporidiosis"

Eimeria spp–"coccidiosis" of older pigs

An excellent reference for identification of nematode eggs and of coccidian oocysts is: Sloss, Kemp, and Zajac. Veterinary Clinical Parasitology, 6th edition. Iowa State University Press:Ames Iowa.