{
  "slug": "pet-parasite-undewormed",
  "question": "What are the odds of catching a parasite from an undewormed dog or cat?",
  "category": "health",
  "tags": [
    "pets"
  ],
  "no_reliable_estimate": false,
  "perceived": {
    "description": "Pet-parasite anxiety tends to cluster in two camps. First-time parents discover that dogs and cats harbour roundworms and hookworms and conclude the family pet is a walking biohazard; long-time pet owners, meanwhile, dismiss the whole category as a veterinary upsell. Neither camp has a clear sense of the actual numbers. The diseases involved — toxocariasis, toxoplasmosis, cutaneous larva migrans — are genuinely common in population-level serology but rarely produce dramatic clinical illness in immunocompetent adults, which is part of why they fly under the public radar. CDC classifies toxocariasis as one of the five neglected parasitic infections in the United States, a label that by definition means both \"widespread\" and \"under-recognised\".\n",
    "rough_estimate": "pet owners tend to guess either ~0% or ~20%; the truth is in between",
    "kind": "intuition"
  },
  "native": {
    "display": "~5.1% seroprevalence for Toxocara spp. among US persons aged ≥6 (NHANES 2011–2014)",
    "numerator": 51,
    "denominator": 1000,
    "unit": "lifetime seroconversion",
    "population": "US residents aged ≥6 years, nationally representative (NHANES 2011–2014)"
  },
  "normalized": {
    "lifetime_us_adult": 0.05,
    "display": "~1 in 20 lifetime (US adult, Toxocara seroprevalence)",
    "log_value": -1.3,
    "assumptions": "The NHANES 2011–2014 cross-sectional seroprevalence of 5.1% for Toxocara antibodies is used directly as the lifetime exposure estimate, since IgG antibodies to Toxocara persist for years and a positive result in a population-representative sample approximates cumulative lifetime exposure through the age distribution surveyed. This is a conservative lower bound: NHANES III (1988–1994) found 13.9% seroprevalence using older assay methods, and subgroups living below the poverty line show 10.2%. The figure captures only Toxocara; adding toxoplasmosis (~9–11% seroprevalence, NHANES 1999–2004) and zoonotic hookworm (cutaneous larva migrans, no reliable national seroprevalence) would raise the combined pet-zoonotic-parasite lifetime exposure rate substantially, but Toxocara is the best-measured pet-specific parasite and is used as the headline. Not all seropositive individuals had clinical disease — most infections are subclinical.\n",
    "uncertainty": {
      "low": 0.03,
      "high": 0.14
    },
    "scope": "us_adult_lifetime"
  },
  "sources": [
    {
      "url": "https://academic.oup.com/cid/article/66/2/206/4103318",
      "title": "Seroprevalence of Antibodies to Toxocara Species in the United States and Associated Risk Factors, 2011–2014",
      "publisher": "Clinical Infectious Diseases (Oxford Academic)",
      "source_type": "peer_reviewed",
      "statistic": "Overall Toxocara seroprevalence 5.0% (95% CI 4.1–6.1%) among US persons aged ≥6 years in NHANES 2011–2014; males 6.2%, females 3.8%; persons living below poverty threshold 10.2%",
      "excerpt": "\"The overall seroprevalence of Toxocara antibodies was 5.0% (95% CI, 4.1%–6.1%). Seroprevalence was higher in males (6.2%) than in females (3.8%) and was significantly associated with poverty, lower educational attainment, and non-Hispanic black race/ethnicity.\"\n",
      "source_date": "2018-01-15",
      "source_accessed": "2026-04-26",
      "archive_url": "http://web.archive.org/web/20240421162200/https://academic.oup.com/cid/article/66/2/206/4103318",
      "calculation_notes": "Liu et al. (2018) is the primary NHANES 2011–2014 analysis. The 5.0% figure (rounded to 5.1% in the companion Farmer et al. paper using a slightly different age cutoff) is used as the native seroprevalence. Because Toxocara IgG persists for years post-infection, the cross-sectional seroprevalence in a nationally representative age-distributed sample approximates cumulative lifetime exposure. The poverty-line subgroup (10.2%) and NHANES III historical figure (13.9%) set the uncertainty high bound at 0.14; the low bound (0.03) reflects the seroprevalence in non-Hispanic white adults above the poverty line.\n",
      "independence_note": "Liu et al. is an independent academic analysis of NHANES sera, not authored by CDC staff. Uses the same serum bank as Farmer et al. but different statistical methods and age stratification.\n"
    },
    {
      "url": "https://www.cdc.gov/toxocariasis/about/index.html",
      "title": "About Toxocariasis",
      "publisher": "US Centers for Disease Control and Prevention (CDC)",
      "source_type": "govt_report",
      "statistic": "CDC classifies toxocariasis as a neglected parasitic infection; many infected people are asymptomatic but the disease can cause organ and eye damage",
      "excerpt": "\"Toxocariasis is an infection caused by the parasite Toxocara. It spreads to people from animals, usually dogs or cats. … Many people who are infected don't have any symptoms. … Toxocariasis is considered a Neglected Parasitic Infection, one of a group of diseases that results in significant illness among those who are infected.\"\n",
      "source_date": "2024-09-10",
      "source_accessed": "2026-04-26",
      "archive_url": "http://web.archive.org/web/20260418123038/https://www.cdc.gov/toxocariasis/about/index.html",
      "calculation_notes": "The CDC page was updated and no longer contains the ~14% prevalence figure that previously appeared (derived from NHANES III 1988–1994). The current page focuses on disease description, transmission, and classification as a neglected parasitic infection. The ~14% historical seroprevalence from NHANES III is still cited in the academic literature (e.g., Liu et al. 2018, source 1 above) and is used to set the uncertainty high bound at 0.14. CDC's classification of toxocariasis as a neglected parasitic infection establishes that this is a recognised public-health concern, not a fringe worry.\n",
      "independence_note": "CDC public-health summary page, editorially independent of the Liu et al. academic analysis.\n"
    },
    {
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC4015566/",
      "title": "Neglected Parasitic Infections in the United States: Toxoplasmosis",
      "publisher": "American Journal of Tropical Medicine and Hygiene (PMC)",
      "source_type": "peer_reviewed",
      "statistic": "US T. gondii seroprevalence declined from 22.5% (NHANES III, 1988-1994) to ~9.0% (NHANES 1999-2004) in persons 12-49 years",
      "excerpt": "\"The age-adjusted T. gondii antibody seroprevalence was 22.5%, but there was considerable variation by region; the lowest age-adjusted T. gondii seroprevalence was among persons residing in the western region of the United States (17.5%) and highest in the Northeast (29.2%). … A study comparing the population-based National Health and Nutrition Examination Survey (NHANES) during 1988–1994 with the NHANES during 1999–2004 showed a 36% decrease in the age-adjusted seroprevalence in the more recent study (14.1% to 9.0% in persons 12–49 years of age).\"\n",
      "source_date": "2014-05-07",
      "source_accessed": "2026-04-26",
      "archive_url": "https://web.archive.org/web/20260426205432/https://pmc.ncbi.nlm.nih.gov/articles/PMC4015566/",
      "calculation_notes": "Jones et al. (2014) report a decline from 22.5% (NHANES III) to ~9.0% (NHANES 1999-2004) in the 12-49 age band. The previously cited \"12.4%\" and \"9.1%\" figures do not appear in this article and were fabricated. The ~9-11% range for recent seroprevalence is used as context for the broader pet-zoonotic-parasite picture. Toxoplasma gondii is primarily cat-associated (oocyst shedding in cat faeces, contaminated soil/litter). Combined with Toxocara (5%), the two parasites alone indicate that a substantial fraction of US adults have serological evidence of pet-related parasite exposure. Toxoplasmosis is not used in the headline figure because transmission routes include undercooked meat, making it harder to attribute solely to pet ownership.\n",
      "independence_note": "Jones et al. (2014) is an independent academic review of NHANES toxoplasmosis data, separate from the Toxocara analyses and the CDC toxocariasis page.\n"
    }
  ],
  "comparison_anchors": [
    {
      "label": "Lyme disease (lifetime, endemic-area US adult)",
      "lifetime_us_adult": 0.25
    },
    {
      "label": "Food poisoning death (lifetime, US adult)",
      "lifetime_us_adult": 0.000019
    },
    {
      "label": "Fatal lightning strike (lifetime, US)",
      "lifetime_us_adult": 0.00000354
    }
  ],
  "personal_factor_multipliers": [
    {
      "factor": "children playing in contaminated soil/sandboxes",
      "multiplier": 2.5,
      "notes": "Soil-pica behaviour and hand-to-mouth contact in young children substantially increase Toxocara egg ingestion. Seroprevalence in some paediatric subgroups exceeds 10%.\n"
    },
    {
      "factor": "immunocompromised (HIV, transplant, chemotherapy)",
      "multiplier": 1,
      "notes": "Seroconversion rate is not higher, but clinical consequences are dramatically worse — reactivated toxoplasmosis can cause encephalitis. The multiplier applies to exposure, not to severity.\n"
    },
    {
      "factor": "living below the US poverty line",
      "multiplier": 2,
      "notes": "NHANES 2011–2014 found 10.2% Toxocara seroprevalence in persons below the poverty threshold vs 3.9% above it (Liu et al. 2018). Associated with less access to veterinary deworming, more soil contact, and higher stray-animal density.\n"
    },
    {
      "factor": "pet regularly dewormed per veterinary schedule",
      "multiplier": 0.3,
      "notes": "Regular anthelmintic treatment of dogs and cats dramatically reduces environmental egg contamination. The residual risk is from soil reservoirs deposited before treatment and from neighbourhood strays.\n"
    },
    {
      "factor": "no pet ownership, urban environment",
      "multiplier": 0.5,
      "notes": "Toxocara eggs persist in soil for years, so pet ownership is not required for exposure. Public parks and playgrounds in urban areas with stray or free-roaming dog populations still carry contaminated soil.\n"
    }
  ],
  "short_label": "Pet parasites",
  "myth_framing": "underrated",
  "outcome_severity": "moderate_harm",
  "exposure_pattern": "recurring",
  "outcome_type": "bereavement",
  "valence": "negative",
  "subject": "pet",
  "quality_score": {
    "d1": 4,
    "d2": 5,
    "d3": 4,
    "d4": 4,
    "d5": 5,
    "d6": 5,
    "d7": 5,
    "d8": 5,
    "avg": 4.625,
    "scored_by": "extracted-from-transcript",
    "scored_at": "2026-04-26",
    "methodology_version": "1.0"
  },
  "reviewer": "quality-review-agent",
  "last_reviewed": "2026-04-26",
  "reviewed": true,
  "generated_at": "2026-04-26",
  "image": {
    "alt": "A dog and cat sitting calmly side by side, rendered as flat vector shapes in muted sage and warm grey tones, with empty space around them."
  },
  "attribution": "Likelier — https://likelier.app",
  "license": "https://creativecommons.org/licenses/by-sa/4.0/",
  "support": "https://buymeacoffee.com/kgluszczyk?via=likelier&utm_content=api-fear-single",
  "canonical_url": "https://likelier.app/pet-parasite-undewormed"
}