Ancylostoma Duodenale

If you have unexplained iron deficiency anemia, persistent eosinophilia (high counts of a specific type of white blood cell), or vague gut symptoms after time in a tropical or subtropical region, a parasite quietly feeding in your small intestine is one of the explanations a routine blood panel will not catch. Ancylostoma duodenale (A. duodenale) is a hookworm that latches onto the intestinal wall and draws blood every day, sometimes for years before anyone connects the symptoms to a parasite.

Testing your stool for this organism answers a specific question: is a worm the reason your iron stores keep dropping? It is one of the few infections that can mimic a slow gastrointestinal bleed without an obvious source on standard endoscopy.

What This Test Actually Detects

The test looks for evidence of A. duodenale in a stool sample. Older methods identify hookworm eggs under the microscope. Newer molecular methods (multi-parallel quantitative PCR, a technique that copies and counts parasite DNA) can distinguish A. duodenale from its close cousin Necator americanus and detect much lighter infections. In one study of an Argentinian community, qPCR found A. duodenale in 19.1% of samples and N. americanus in 36.4%, and identified combined hookworm infections in 37.4% of people compared to 21.2% by microscopy. The hookworm qPCR had a sensitivity of 95.5% and a negative predictive value of 98.4%.

Telling the species apart matters. A. duodenale draws roughly 2 to 10 times more blood per worm than N. americanus and is consistently linked to worse hemoglobin and ferritin (iron storage) levels at the same egg burden.

Iron Deficiency and Anemia

The defining injury from A. duodenale is chronic blood loss at the spot where each worm anchors to the small bowel. Multiply that by tens or hundreds of worms over months and years, and your iron reserves drain faster than your diet can refill them.

In Malawian preschool children, multiplex real-time PCR found hookworm in 34.1% of samples, while microscopy found it in only 5.6%. Higher A. duodenale DNA loads were tied to a stepwise rise in the odds of severe anemia and bone marrow iron deficiency. In Tanzanian schoolchildren, communities with a higher proportion of A. duodenale (rather than N. americanus) had significantly more anemia and iron deficiency at comparable egg counts.

What this means for you: if you have iron deficiency anemia that is not explained by diet, menstruation, or a clear gastrointestinal source, and you have lived in or traveled to an endemic region, this test can find a treatable cause that other workups miss. A single case report described a patient with hemoglobin of 5.5 g/dL and an eosinophil count of 2240 per microliter, with the worms only located after capsule endoscopy when standard tests came back negative.

Growth, Development, and Pregnancy

In children, chronic A. duodenale infection is linked to malnutrition, slowed growth, and impaired cognitive development. Longitudinal data from Ecuador using molecular detection found that polyparasitism (multiple intestinal parasites at once) had the strongest negative effects on height-for-age, weight-for-age, and hemoglobin trajectories during early childhood.

In infants, hookworm is rare but documented, with one case report describing transmission via breastfeeding and possibly across the placenta, presenting with vomiting, weight loss, anemia, and eosinophilia. Persistent unexplained eosinophilia in an infant from an endemic area is a reason to test.

Where Hookworm Is Found

A. duodenale is endemic across many tropical and subtropical regions. National mapping in Ethiopia required mass drug administration plans for 18 million school-aged children to meet the 75% coverage target set by the World Health Organization. Studies have documented hookworm in Uganda, Latin America and the Caribbean, parts of Australia (especially in Indigenous communities of the Kimberley region of north west Australia and the Northern Territory), and among migrant workers in Malaysia, where 388 workers were screened and hookworm was molecularly identified in food-related industries.

Transmission usually happens when larvae in soil contaminated by human feces penetrate the skin, often through bare feet. A. duodenale can also infect through ingestion and may undergo a period of arrested development before maturing, which is one reason symptoms can appear long after exposure.

Reference Ranges and What a Result Means

This test reports presence or absence of A. duodenale, and with PCR-based methods, an estimate of intensity (often expressed as DNA load or cycle threshold value). There is no "normal level" of hookworm to aim for: any detection is abnormal and warrants treatment.

Reported categorical thresholds vary by method and lab. Use the framework below as orientation rather than universal cutpoints.

Compare results within the same lab over time for the most meaningful trend, since assays and reporting units differ.

Tracking Your Trend

A single negative stool test does not entirely rule out hookworm, especially with microscopy at low worm burdens. Egg shedding fluctuates, and a worm that has not yet matured will not pass eggs at all. If your suspicion is high (unexplained iron deficiency, eosinophilia, relevant exposure history), repeat testing or a PCR-based method gives you a more reliable answer.

After treatment, retest stool around 3 to 6 weeks later to confirm clearance, then track hemoglobin and ferritin every few months until your iron stores recover. If you continue to live in or travel to endemic regions, periodic stool testing is reasonable, since reinfection from contaminated soil is common.

When Results Can Be Misleading

• Microscopy misses light infections: in Malawian children, microscopy detected hookworm in only 5.6% of samples while PCR detected it in 34.1%. A negative microscopy result with strong clinical suspicion should prompt PCR or repeat testing.
• Species cannot be distinguished by microscopy alone: A. duodenale and N. americanus eggs look essentially identical, so microscopy cannot tell you which species you have. PCR is required to identify the species.
• Recent stool sample timing: worms that have not yet reached egg-laying maturity will produce a falsely negative test. If exposure was recent (within weeks), retesting later may be necessary.
• Sample handling: stool samples need to be collected and transported per the lab's protocol. Improper preservation can degrade DNA and reduce sensitivity.

What to Do If Your Result Is Positive

A positive A. duodenale result calls for a coordinated next step rather than just retesting. Order or review a complete blood count, ferritin, and iron studies to gauge how much damage has been done. Albendazole was highly effective in an Australian Aboriginal community study, while pyrantel at 10 mg/kg failed in the same setting, suggesting it should not be relied on as first-line. A successful infant case used mebendazole.

If your iron stores are depleted, treating the worm without repleting iron leaves you anemic for months longer than necessary. Discuss oral or intravenous iron with a clinician based on the depth of your deficiency. If the test is negative but anemia persists, consider capsule endoscopy or specialist evaluation for other small-bowel sources of bleeding, since hookworms have been found this way after standard endoscopy missed them.