Molecular diagnosis of an immature Ascaris lumbricoides infection with negative parasitological examinations.

Ascariasis is one of the most prevalent parasitic infections worldwide, particularly in developing countries, and is caused by Ascaris lumbricoides. Diagnosis can be challenging during the early stages of infection, especially when adult helminths have not yet become established in the intestine and routine parasitological examinations yield negative results. A 40-year-old female patient was referred to a hospital in South Tehran, Iran, with various clinical manifestations, including gastrointestinal symptoms, abdominal cramps, respiratory distress, cough, wheezing, localized skin itching, and blood-tinged sputum. Routine laboratory investigations were within normal limits. On November 28, 2024, following the expulsion of an immature helminth, the specimen was sent to the Helminthology Laboratory, School of Public Health, Tehran University of Medical Sciences, for detailed parasitological examination. Three stool samples were examined using direct smear, formalin-ethyl acetate concentration, zinc sulfate flotation, and agar plate culture techniques. No helminth eggs were detected in any of the samples, and all parasitological examinations yielded negative results. Molecular characterization of the immature helminth was performed using conventional polymerase chain reaction (PCR) targeting the Cox1 gene, which yielded the expected 520-bp amplicon and confirmed the diagnosis of A. lumbricoides. This case underscores the importance of a comprehensive laboratory workup for the diagnosis of ascariasis in patients with heterogeneous clinical presentations, particularly during the early stages of infection. The combined use of molecular and parasitological methods can facilitate the early detection of cases in which adult helminths have not yet developed and routine stool examinations are negative.