Resolving Taxonomic Ambiguities in <i>Ascaris</i> Species: Insights From a Scanning Electron Microscopy Study of <i>Ascaris lumbricoides</i>

Ascariasis, caused by the parasitic roundworm Ascaris lumbricoides, is a major public health issue, especially in developing nations such as Pakistan. It impacts millions, causing significant morbidity through starvation, stunted growth in children, and a variety of gastrointestinal issues. The taxonomy of the Ascaris genus, notably the distinction between A. lumbricoides and Ascaris suum, has led to ongoing debate among parasitologists. Consequently, the current study intends to provide morphological characterization of A. lumbricoides from Pakistan, using scanning electron microscopy to uncover precise anatomical traits that may aid in resolving the taxonomic controversy surrounding the Ascaris genus. A cross-sectional survey of 1641 individuals was undertaken. Participants filled out structured questionnaires and provided informed consent. After anthelmintic treatment, expelled worms were collected in sterile jars, washed, and preserved in a glycerin-alcohol solution for morphometric examination. Histological examination of transverse section of female worm reproductive system was performed. Scanning electron microscopy was used to investigate the head, cuticle, and caudal regions of the worms. Statistical analyses were performed using t-tests and ANOVA, with significance determined as p ≤ 0.05. When the worms were collected, they ranged in hue from light to pale pink to reddish, then grayish-white to creamy white. Female were distinguished on their large size, straight posterior end with no copulatory bursa and vulvar waist, while male worms were dorsally curved at posterior end. Of the 90 worms measured, 33 were males and 57 were females. The adult female Ascaris worms were significantly (p ≤ 0.0001) larger in body length and width as compared to adult male worms. Furthermore, adult females from different districts had significant differences in body length (p = 0.003) and width (p = 0.00004), although male body length did not differ substantially among districts (p = 0.243). Scanning electron microscopy of A. lumbricoides revealed a head with two subventral lips and a dorsal lip, as well as dentigerous ridges and a triradiate mouth. The cuticle had thick, transversely striated patterns, with clear contrasts between the ventral and dorsal surfaces. The male's caudal area contained mammiliform precloacal papillae and a rectangular anal orifice, but the female had a knob-like structure with uneven striation pattern. The transverse section of female reproductive system consists of two large uteri containing developing eggs, coiled ovaries, and oviducts. Overall, the study revealed valuable insights on this nematode's complicated morphology. By adding new data to the current body of knowledge, this study seeks to improve our understanding of ascariasis and its implications for public health in affected regions.