ScienceNot yet confirmed elsewhere1 publisher2 min readPublished
Giardia strains that infect people turned up in about 1.2% of 157,616 tested North American cats
Margaret Wingerd and colleagues report in PLOS One that 6.3% of 157,616 North American pet cats tested positive for Giardia duodenalis. Of the positives, 18.5% carried assemblages A or B, the genetic groups that can infect people.
The Scientist · Science desk
6.3% of tested cats were positive for Giardia duodenalis. 18.5% of positive cats carried assemblages A or B. Kittens had the highest detection rate at 10.7%. In the U.S. Midwest, 7.8% of cats tested positive.
| Figure | Value | Note | Claim |
|---|---|---|---|
| Cats testing positive for Giardia duodenalis | 6.3% | 5 | |
| Positives with A or B | 18.5% | 1 | |
| Kittens, detection rate | 10.7% | 8 | |
| U.S. Midwest, positive | 7.8% | 11 |
What happened
- The records cover 49 U.S. states and five Canadian provinces, from March 2022 to August 2023.
- Most of the other positive cats carried cat-associated strains, chiefly assemblage F, which generally do not pose a risk to humans.
- Kittens had the highest detection rate at 10.7%, against 1.3% in senior cats.
- Detection was lowest in summer at 4.6% and higher in winter at 8.1% and fall at 7.7%.
- Giardia was most common in the Midwest at 7.8%, but among positive cats the human-transmissible share peaked in the Northeast (21.6%) and the West (20.0%).
Why it matters
- decision Households with young children, older adults or immunocompromised members face a screening call, and the authors advise routine fecal screening of their cats.
- constraint A positive Giardia result does not tell an owner which group the cat is in. The A and B screen was a second step run on positive samples.
- capability The sample gives a North American baseline for cat Giardia where earlier studies covered individual shelters or a few states.
Scaled to the full sample, 6.3% works out to about 9,930 positive cats [20]. Of those, 18.5% is about 1,840 cats [18], or roughly 1.2% of every cat tested [19]. All three figures are computed from rounded percentages, so they are approximate.
Among positive kittens, roughly one in five carried assemblage A or B [9], close to the 18.5% across all ages [1]. On that reading, kittens stand out because more of them test positive [8].
The design buys scale. This was a retrospective analysis of existing test records from a DNA-based PCR panel, and the researchers did not test the samples themselves [7]. Earlier work relied on small samples or on individual shelters and a few states [13], and its cat infection rates ran from 0.2% to 44.4% [14]. The new 6.3% sits inside that range [5]. The source does not say how the cats came to be tested, so 6.3% describes cats that had a stool test. It cannot be read as the share of all pet cats in North America.
The thing this doesn't tell you is how often a cat's A or B infection reaches a person. The panel detects Giardia DNA [7], and the team then assigned genetic groups to the positive samples [17]. No household was followed.
Assemblages A and B are the groups the source calls most important for public health, because they infect humans along with a wide range of other mammals [3]. We think that supports a bounded reading: a minority of infected cats carry them, and the study stops at carriage. Most infected pets and people show no signs of illness [16], so a healthy-looking cat could be in either group.
What to watch
- A study that types Giardia in cats and in the people living with them would answer the transmission question this one cannot.
- Prospective testing of randomly chosen cats, to see whether the 6.3% positive rate holds outside cats that already had a stool test.
- Whether veterinary guidance adopts the authors' advice on routine screening for households with young children, older adults or immunocompromised members.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence70
- Adoption
- Insufficient
- Hype gap+10
- Incentives
- Insufficient
- Confidence66
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
Among the infected cats, 18.5% carried assemblages A or B, genetic groups that can infect both humans and animals.
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing Wingerd et al., PLOS One2 sources— create a free account to open themView cited source - [2]
The remaining majority of infected cats carried strains associated primarily with cats, particularly assemblage F, which generally do not pose a risk to humans.
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing Wingerd et al., PLOS One2 sources— create a free account to open themView cited source - [3]
Assemblages A and B infect humans along with a wide range of other mammals, making them the most important for public health.
ReportedSupportedSource: phys.org (Sanjukta Mondal)2 sources— create a free account to open themView cited source - [4]
The study analyzed stool test data from 157,616 pet cats across 49 U.S. states and five Canadian provinces between March 2022 and August 2023.
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing Wingerd et al., PLOS OneView cited source - [5]
6.3% of the cats tested positive for Giardia duodenalis.
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing Wingerd et al., PLOS OneView cited source - [6]
The findings were published in PLOS One by Margaret Wingerd et al. (2026), 'Giardia duodenalis in domestic cats from the US and Canada: Prevalence and zoonotic potential'.
- [7]
The researchers conducted a retrospective analysis of existing test records and did not test the samples themselves; the data came from the KeyScreen GI Parasite PCR panel, a highly sensitive DNA-based test that detects Giardia duodenalis DNA.
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing Wingerd et al., PLOS OneView cited source - [8]
Kittens had the highest detection rate at 10.7%, compared with 1.3% in senior cats.
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing Wingerd et al., PLOS OneView cited source - [9]
Among the kittens that tested positive, roughly one in five carried A/B types.
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing Wingerd et al., PLOS OneView cited source - [10]
Rates were lowest in summer (4.6%) and higher in winter (8.1%) and fall (7.7%).
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing Wingerd et al., PLOS OneView cited source - [11]
Giardia was most common in the U.S. Midwest, where 7.8% of cats tested positive.
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing Wingerd et al., PLOS OneView cited source - [12]
Among cats that tested positive, human-transmissible strains were most common in the Northeast (21.6%) and the West (20.0%).
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing Wingerd et al., PLOS OneView cited source - [13]
Earlier research on Giardia in cats relied on small sample sizes or focused on very specific locations, such as individual shelters or a few select states, making it difficult to determine how widespread the parasite was across North America.
- [14]
Reported Giardia infection rates in cats range from 0.2% to 44.4%.
- [15]
The researchers note that people with pet cats, especially households with young children, older adults or immunocompromised people, should get routine fecal screening for their cats, particularly for parasite strains that affect both animal and human health; knowing which Giardia type a cat carries could help veterinarians have more informed conversations about treatment.
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing the study authors' recommendationView cited source - [16]
Most infected pets and people show no signs of illness; when Giardia becomes pathogenic it can cause diarrhea, digestive issues or weight loss.
- [17]
Among the samples that tested positive, the team screened for assemblages A and B.
ReportedSupportedSource: phys.org (Sanjukta Mondal), summarizing Wingerd et al., PLOS OneView cited source - [18]
About 1,840 positive cats carried assemblage A or B.
- [19]
Roughly 1.2% of all cats tested carried assemblage A or B.
- [20]
About 9,930 of the tested cats were Giardia-positive.
Sources
1 independent publisher whose own reporting we read for this story.
- phys.orgSome house cats carry a gut parasite that can infect humans, study finds
1 article · October 12, 2026
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