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

Abstract

Despite their high pathogenicity, limited knowledge is available on intra-host migration pathways and microhabitat distribution of lungworms of the family Pseudaliidae. 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. Lung perfusion appears to be the driving factor behind the parasite’s large-scale distribution as evidenced by the clear correlation between the two factors both on a longitudinal scale and also when comparing parasite burden between the left and right lungs. This relationship, when coupled with the nesting pattern of colonization exhibited by this parasite indicates that, like many other metastrongyloids, H. delphini larvae arrive at the lung via the circulatory system. On a smaller scale, 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 maximise the diffusion of larvae to the environment and minimize the distance that these larvae have to 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. This project was supported by projects AICO2021/022, Generalitat Valenciana, and VARACOMVAL, Biodiversity Foundation, MITECO.