Factors associated with the fertility of the helminth parasite Ascaris lumbricoides: an exploratory study in a rural Venezuelan community

The helminth parasite Ascaris lumbricoides remains a major global health burden, yet factors influencing its fertility and infection intensity are not fully understood. This cross-sectional study explored associations between host characteristics, worm biometrics, and parasite reproductive output in a rural Venezuelan community. Complete fecal evacuations were collected from 128 participants (57% of consenting population) across 45 houses. Following descriptive analyses of worm-related variables (count, length, weight, sex, male-to-female ratio, maturity), egg-related variables (eggs per gr of feces [EPG], fertile and infertile EPG, infertile-to-fertile ratio), and host characteristics (gender, age, household), both univariate methods and multivariable regression analyses were performed to assess associations. Worm biometrics showed non-significant associations with infection type (unisexual vs. bisexual), although male worms in unisexual infections tended to be heavier. A non-significant crowding effect was observed, with higher worm counts often linked to lower average worm length and weight. Worm length and weight were strongly correlated with egg production, though this relationship weakened in bisexual infections, likely due to reduced female fecundity. Male worm presence appeared to be the main determinant of egg fertility, with higher male-to-female ratios showing borderline significant association with lower ratios of unfertilized to fertilized eggs. Host age and household clustering were associated with worm count, whereas host gender was not. These findings support key biological principles of A. lumbricoides, including density-dependent crowding effects and male worm presence in egg fertility. The study also highlights the complexity of worm-specific and host-related factors influencing infection intensity and fecundity, providing insights for future research and more targeted deworming strategies.