Human Enteric Infection with Canine Hookworms

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 x 10(9)/L), and five of eight had elevated immunoglobulin E levels (mean level, 756 micrograms/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.