Falco et al reported the scutal index (SI) as a measure of tick feeding on a host. The duration of tick feeding has implications for transmission of Borrelia burgdorferi and other pathogens.
Tick species: Ixodes scapularis
A nymphal or female tick requires > 48 hours of feeding to efficiently transmit Borrelia burgdorferi.
During feeding the body length increases while the width of the scutum remains constant.
Measurements:
(1) body length from base of the basis capitulum to the tip of the abdomen in microns
(2) width of the scutum at its widest point in microns
scutal index =
= (body length) / (scutal width)
For nymphs:
LN(SI) =
= (0.008896 * (hours attached)) + 0.660
Re-arranged:
hours attached =
= (LN(SI) - 0.66) / 0.008896
For females:
LN(SI) =
= (0.007769 * (hours attached)) + 0.775
Re-arranged:
hours attached =
= (LN(SI) - 0.775) / 0.007769
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