Abstract
The infective third-stage larvae of the hookworms Necator americanus and Ancylostoma duodenale infect their human hosts by active skin invasion, but A. duodenale is in addition capable of oral infection. The behaviour of the larvae when crawling on surfaces has already been described. Here we analyse in various in vitro systems the other behavioural invasion phases: activation, penetration, and orientation within the host. The larvae normally remained in a motionless, energy-saving, resting posture. An activation to sinusoidal locomotion was stimulated in both species by similar cues such as touch, vibration, water currents, heat, light, and chemicals. Human breath in addition stimulated searching and waving (“nictating”) behaviour, which facilitates a change-over to the host. Activating cues in air streams were warmth and moisture; CO2 activated only in combination with warmth and/or moisture. Penetration behaviour in both species was stimulated by warmth and skin extracts. The stimulating components of skin extracts were fatty acids, but their stimulating characteristics differed from those inducing schistosome cercarial skin penetration. After penetration into agar substrates, both species showed thermo-orientation, but only A. duodenale followed gradients of serum. The directing serum cues were not amino acids and glucose (the supposed cues for schistosome blood vessel localization), but Ringer’s solution attracted the larvae. The host-finding and host-invasion behaviour of both hookworm species is well adapted to the invasion of the human skin, and there seems to be no particular adaptation of A. duodenale behaviour to the oral infection mode. Hookworm host-finding behaviour is not as complex as that of schistosome cercariae but seems well adapted to the ecological conditions in the transmission sites.
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Acknowledgements
This work was carried out at the Research Center of the Hasanuddin University, Makassar, Indonesia and at the Institute for Zoology, Erlangen, Germany. We thank our Indonesian counterparts Drs. A. Mangali, I. Patellongi, A.M. Afdal, E.Y. Singka and the members of their teams for their valuable help with the field surveys and the sample collections, and Christina Loy and Bety Sapada for their expert technical work. We also wish to thank Professor Gerhard Schad for his encouragement and advice during this research project. This research was supported by the Deutsche Forschungsgemeinschaft, the Bundesministerium für wirtschaftliche Zusammenarbeit und Entwicklung, and DAAD. The experiments performed in this work comply with the current laws of Germany and Indonesia.
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Haas, W., Haberl, B., Syafruddin et al. Behavioural strategies used by the hookworms Necator americanus and Ancylostoma duodenale to find, recognize and invade the human host. Parasitol Res 95, 30–39 (2005). https://doi.org/10.1007/s00436-004-1257-7
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DOI: https://doi.org/10.1007/s00436-004-1257-7