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Human Enteric Infection with Canine Hookworms

John Croese, MB, BS; Alex Loukas, BSc (Hons); Joan Opdebeeck, PhD; Stephen Fairley, MB, BS; and Paul Prociv, PhD
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From the University of Queensland, Australia. Requests for Reprints: John Croese, MB, BS, 42 Ross River Road, Mundingburra, Townsville, Queensland, 4812 Australia. Acknowledgments: The authors thank Drs. Terrence Mulhearn and Neil Walker for referral of a patient and Associate Professor Rick Speare for assistance with identification and measurement of parasites (patients 4 and 8). Grant Support: By the National Health and Medical Research Council of Australia, the University of Queensland, and the Wenkart Foundation.

Copyright ©2004 by the American College of Physicians

Ann Intern Med. 1994;120(5):369-374. doi:10.7326/0003-4819-120-5-199403010-00003
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Objective: To describe a zoonotic ancylostomiasis (canine), acquired from domestic pets by patients living in developed, urban communities.

Design: An 8-year, retrospective case study.

Setting: A clinical gastroenterologic practice in Townsville and a university parasitology department in Brisbane, Australia.

Patients: Nine patients, each with enteric hookworm infection diagnosed by finding a single organism in situ; five were treated by us, and the rest were referred to us for parasite identification.

Measurements: Clinical and demographic data, complete blood examinations, total serum immunoglobulin E assay, and serologic testing with enzyme-linked immunosorbent assay and Western blot using excretory-secretory antigens of Ancylostoma caninum. Gut biopsy specimens were examined histologically, and hookworms were identified using morphologic criteria.

Results: The infections in three of the patients were diagnosed during the initial 6 years and six in the last 2 years. All owned a dog and described activity potentially exposing them to infection with canine hookworm larvae. Three patients had a laparotomy for acute abdominal pain, and six had colonoscopies (five with pain and one without symptoms). Six of the nine had blood eosinophilia (mean, 0.97 × 109/L), and five of eight had elevated immunoglobulin E levels (mean level, 756 µg/L); six of eight had eosinophilic inflammation of the gut. In six patients, the worm was identified as A. caninum, whereas in three, damage to the specimen did not allow specific identification; however, they were unlikely to be human parasite species. Although all parasites were in the adult stage, none were sexually mature. Positive serologic findings in seven of the eight patients tested confirmed presence of antibody to the parasite.

Conclusions: Human enteric infections with A. caninum are being diagnosed more frequently in northeastern Australia. Although infection may be subclinical, the chief symptom is abdominal pain, sometimes sudden and severe. The pathologic finding is focal or diffuse eosinophilic inflammation caused by a type 1 hypersensitivity response to secreted antigens. Infection by sexually immature worms is scant and nonpatent, indicating poor adaptation to the human host. Serologic testing assists in identification of occult infection. Advanced hygiene and sanitation afford little protection because the parasite reservoir is a large and growing pool of infected domestic pets.


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Figure 1.
Feeding hookworm in ileum (patient 4).

The worm, seen at colonoscopy, was feeding vigorously with blood present in and expelled from its gut. Localized hemorrhage into the mucosa appears at the point of attachment. The buccal capsule, necessary for morphologic identification, was damaged when extracted with biopsy forceps.

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Figure 2.
Scanning electronmicrograph (patient 6).A. caninum

Anterior extremity of formalin-fixed, 10-mm hookworm, clearly showing a pair of three ventral teeth in the buccal cavity; these plus spicule size clearly identify the specimen as (original magnification, × 700).

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Figure 3.
Immunoglobulin G and E Western blots comparing cases with controls.Tasmania

Molecular weight markers in the left lane. Numerals represent patient numbers. C = control (blood donor from ) serum. Reaction with a band at 68 kd signifies a positive reaction; other bands are ignored.

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