Diagnostic tests used in swine:
- Fecal flotation: Fecal flotation gives a broad overview of nematode and protozoan parasites Results are assigned semi-quantitative results (Rare, few, moderate, high, very high).
- McMaster Count: This method is typically used to quantify nematodes in herbivores; it is not routinely used for parasites of pigs. Occasionally practitioners will request a McMaster count as a measure of coccidia (Cystoisospora) oocysts. While we occasionally perform the test for this purpose, submitting DVMs should be aware that it has relatively low levels of precision due to variability in oocyst shedding, the nature of the assay, and the vast number of organisms present in feces.
- Fecal/Baermann sedimentation: Sedimentation methods detect larvae and trematode Thus, they are rarely used in swine parasitology assessment.
Considerations for interpretation of results:
At a population level, it is expected that pigs will have some level of parasitism. In particular, in younger pigs, coccidia (Cystoisospora) is commonly detected. Therefore, diagnostic reports of parasitism should be critically interpreted before implementing herd-level recommendations. It is critical to rule out other differential diagnoses for the clinical sign of concern. In general, fecal flotation results of “rare” or “few” parasites are not considered to be clinically significant. Animals that have concurrent disease processes (bacterial, viral, nutritional, etc) are likely to have increased numbers of parasites as a result of a compromised immune system.
At a population level, under normal conditions, parasites are over dispersed. That means that a few individual animals have many parasites while most animals in the herd have a moderate to low level of parasites. In general, the fecal exam from a single animal or few animals from a large population are unlikely to represent the status of the entire group. It is recommended to run at least 10 samples from animals in the same age class when evaluating a herd. The prepatent period should also be considered in context with the age and clinical history as clinical signs from parasitism by some nematodes may precede detection of ova in a fecal float.
Interpretation of specific parasitology test findings:
Nematodes: In confinement pigs, nematodes are less commonly a problem. Occasionally confinement pigs are infected with Ascaris (large roundworm) and Trichuris (Whipworm). Ascaris is associated with decreased feed efficiency and can infect humans. Trichuris can cause diarrhea and rectal prolapse. Both of these parasites still occasionally occur in confinement pigs.
Pigs also become infected with other nematodes such as Strongyloides, stomach worms, lung worms, kidney worms, and strongyles. These parasites are rare in confinement but still occur in outdoor pigs. These nematodes are less commonly a cause of disease in ruminants in Iowa. Fecal flotation results of “high” or “very high” levels of these parasites may indicate clinical significance. Producers with outdoor pigs should consult with diagnostic staff about proper test submission if considering these parasites as disease agents. In initial assessment of outdoor pigs, basic fecal flotation to assess a broad range of parasites is recommended.
Protozoa: Enteric coccidia are commonly detected in younger pigs. Cystoisospora is typically found, however, pigs more rarely become infected with Eimeria. Eimeria tends to be asymptomatic unless found in high levels. McMaster counts are commonly requested for enumerating coccidia burden. Submitters should be aware that the precision of this test for enumerating coccidia has is relatively low and changes in oocyst count may not reflect success or failure of interventions. Practitioners should use a combination of diagnostic testing and resolution of clinical signs as a metric for success of interventions.