Fine-scale distribution of the lungworm Halocercus delphini in the lungs of the striped dolphin, Stenella coeruleoalba: implications about migration pathways and functional significance

Despite their high pathogenicity, limited knowledge is available on intrahost migration pathways and microhabitat distribution of pseudaliid lungworms. In this study, the distribution of Halocercus delphini in the lungs of the striped dolphin, Stenella coeruleoalba, was analyzed on three scales: between the right and left lungs, within the lungs, and between worm clusters. Evidence of a relationship between the distribution of H. delphini and the perfusion of the lungs of S. coeruleoalba is provided by the consistent correlation of these two factors, both on a longitudinal scale and by the difference in parasite burden between the left and right lung. This relationship, when coupled with the nested pattern of colonization, suggests that this species, like many other metastrongyloids, migrates to the lungs via the circulatory system. Additionally, the concentration of lungworms around the major airways could be a further reflection of the well-perfused nature of these passageways. Equally, this distribution could be a strategy to minimize the distance that larvae must travel to exit the lungs via the trachea, as do most other metastrongyloids. On a more localized scale, the tendency of H. delphini to form distinct heterosexual clusters even at low infection intensities indicates active mate-seeking behavior for reproduction.