Fecal PCR panel flagged twice as many parasite-positive samples as antigen testing and flotation combined

A fecal quantitative polymerase chain reaction (qPCR) panel detected parasites in twice as many canine and feline fecal samples as antigen testing and centrifugal flotation combined, according to a study published in Parasites & Vectors.¹ The panel's advantage was not uniform across parasite types. Detection was comparable for roundworms. The hookworm antigen test detected more hookworm positives than the qPCR panel, although that difference was not statistically significant.¹

Researchers compared the KeyScreen GI Parasite PCR panel (Antech Diagnostics) with the Fecal Dx Antigen Profile with Giardia and zinc sulfate centrifugal flotation. Both comparison tests were run at IDEXX Laboratories.¹ The 1,013 samples (882 canine, 131 feline) came from 19 states and were collected in May and June 2025. They were drawn from residual flotation submissions at Antech reference laboratories in the Atlanta, Chicago, and Dallas areas.¹ Each sample was split in 2 and tested with all 3 methods in a blinded fashion.¹

The qPCR panel targets 20 parasites. It also screens for genetic markers associated with benzimidazole resistance in Ancylostoma caninum and for Giardia duodenalis assemblages with zoonotic potential.¹ The antigen panel targets 6 parasite groups: roundworms, hookworms, whipworms, flea tapeworm, Giardia, and Cystoisospora.¹

How the 3 methods compared

The qPCR panel detected at least 1 parasite in 27.2% of samples. Antigen testing detected parasites in 10.9% of samples. Flotation detected them in 6.5%.¹ Taken together, antigen testing and flotation identified parasites in 13.6% of samples.¹

Overall, 70.9% of samples were negative on all 3 methods.¹ Another 15.5% were positive only on the qPCR panel. Conversely, 1.9% were positive on antigen testing or flotation but negative on the qPCR panel.¹

The researchers also limited the comparison to the 6 parasite groups that both the antigen panel and the qPCR panel cover. Within those groups, the qPCR panel detected parasites in about 18% of samples, compared with 11.4% for antigen testing or flotation. The qPCR detection rate was roughly 1.6 times higher.¹

Results varied by parasite. The qPCR panel's detection rates were higher for G duodenalis, flea tapeworm (Dipylidium caninum), and Cystoisospora species.¹ Whipworm detection was also higher with qPCR, although not to a statistically significant degree.¹ Roundworm detection was comparable between the methods.¹

Hookworms went the other direction. The antigen test detected more hookworm positives than the qPCR panel, although that difference was not statistically significant.¹ According to the study team, the hookworm result can be explained by Ac-ASP-5 proteins. Adult hookworms secrete these proteins from the brush border membrane of the alimentary canal before they begin producing eggs. The pre-egg stage is not associated with the release of detectable nucleic acid.¹

The qPCR panel also detected protozoa that the antigen panel does not target, including Tritrichomonas blagburni, Cryptosporidium canis, and Cryptosporidium felis.¹

Eimeria species were the most common finding among the qPCR-only detections (44.6%).¹ The authors noted that Eimeria findings are typically regarded as indicators of coprophagy, through spurious parasitism. The researchers added that reporting Eimeria detections can still give veterinarians context for conversations with pet owners about behavior.¹

The qPCR panel also identified more co-infections. The panel detected 81 samples with 2 or more parasites, or 49 when Eimeria was excluded. Antigen testing detected 16 co-infections and flotation detected 6.¹

Resistance markers and zoonotic Giardia

Of the 32 samples positive for Ancylostoma on the qPCR panel, 6 carried genetic markers associated with benzimidazole resistance.¹ All 6 were also positive for hookworms on flotation or antigen testing. However, the study team noted that the potential resistance would have gone undetected with conventional tests alone.¹ According to the investigators, the markers prompt veterinarians to evaluate treatment efficacy or consider combination treatment alternatives. The paper points to guidance from the American Association of Veterinary Parasitologists on those decisions.¹

RELATED: AAHA guidelines spotlight 12 emerging parasites in dogs and cats

Among the 116 samples positive for G duodenalis on the qPCR panel, 10 carried assemblages with zoonotic potential: 7 of 108 dogs and 3 of 8 cats.¹ The Giardia antigen test detected 4 of those 10 samples.¹ The researchers noted that dogs mostly carry assemblages C or D and cats mostly carry assemblage F. Knowing the assemblage, the study team wrote, could inform a veterinarian's risk assessment. In patients without clinical signs, the risk assessment could lead to modifying treatment or not treating at all.¹

Dogs and cats younger than 1 year had the highest Giardia positivity rates in the study.¹

Limitations and context

The authors described the study as descriptive and said it was not designed to test whether any method was superior.¹ Higher qPCR positivity does not necessarily equal diagnostic accuracy, the investigators wrote, because there is no independent gold standard for comparison.¹ The study team also noted that the presence of parasite nucleic acid does not necessarily indicate active infection.¹

Because the analysis was retrospective, the researchers had no information on:¹

• Clinical presentation or history
• Home environment
• Travel or deworming history
• Whether each visit was for wellness or illness

Repeat submissions from the same animal also could not be ruled out.¹ Each method is also affected by low parasite burdens, intermittent shedding, and spurious passage.¹ The study was not designed to establish true parasite prevalence in the population tested.¹

The researchers cited the Companion Animal Parasite Council's recommendation to combine antigen testing and fecal qPCR with microscopic examination. According to the paper, the combined approach provides the widest breadth of detection.¹ Of the 28 samples positive on flotation but negative on antigen testing, 5 involved parasites the antigen panel targets. The authors said the 5-sample result supports running antigen testing alongside flotation.¹

The study was funded by Antech Diagnostics. Twelve of the 14 authors list an Antech affiliation. Coauthors also included researchers from Colorado State University and Universidad Nacional de Colombia.¹

References

1. Jimenez Castro PD, Leutenegger CM, Vasilatis D, et al. Comparison of gastrointestinal parasite detection methods in fecal samples from dogs and cats in the United States: qPCR, coproantigen immunoassays, and centrifugal flotation. Parasit Vectors. Published online November 7, 2026. doi:10.1186/s13071-026-07735-0