Observations on flea attachment at low hair densities on man

Summary

In tests of the ability of Xenopsylla cheopis and Ctenocephalides felis to lodge on a human host, it was found that the ability to lodge was directly related to the net quantity of hair, as expressed in cm of hair per cm² of skin surface. Below 20 cm of hair per cm², lodgement becomes exceedingly difficult. Correlation between the ability to settle upon a host with hair density (number of hairs/cm²) and average hair length (L) was shown to be much less reliable than with hair quantity as expressed in cm per cm². The number of actual bites received was directly proportional to the ability to lodge on man, except in an area of high apocrine secretion. Here, there was a marked decrease in the proportion of bites of C. felis relative to the ability to lodge after the subject had not bathed for 24 hours or more. If tests were run immediately after bathing, this difference disappeared. This suggests the possibility that apocrine secretion may serve at least a minor role as a natural ‘insect repellent’ to certain exogenous ectoparasites. Thus, human skin, through hair loss and through its distinctive apocrine secretion in certain areas where hair remains, may serve as a barrier to the transmission of zoonotic diseases carried by these fleas not specifically adapted to man.