[20, 21] explored the possibility of silent transmission of WPV in populations with high IPV coverage, emphasizing that "IPV-based protection alone might not provide sufficient population immunity to prevent poliovirus transmission after an importation"  and acknowledging the need to "consider the role of previously-vaccinated or infected individuals (i.e., partially infectible
individuals) who remain immune to paralytic disease, but not to reinfection, and their potential participation in silent transmission of the virus" .
If a foetus is infectible
, then the term b(N)N, which represents the number of newborn individuals, should be included in the equation of susceptible individuals.
Finally, if parasites provide a rare advantage, then recently common host clones should be more infectible than rare clones, which we tested in a laboratory infection experiment at the end of the field study.
In addition, experimental exposures to parasites showed that recently common clones were more infectible than rare clones, indicating that rare genotypes have an advantage under parasite attack [ILLUSTRATION FOR FIGURE 5 OMITTED].
Indeed, in both soybean and Macroptilium, root hairs older than 5 hours after initiation from the root meristem are no longer infectible. This is in contrast with root hairs of clover, which not only developed tip infections in the emergent root hair zone but also formed lateral or basal infections (initiated at a branch near the base of a hair) in the mature, fully elongated root hair zone (Callaham & Torrey, 1981).
Instead, Frankia, present in a septate hyphal form in the substrate, makes direct contact with an infectible, deformed root hair (Callaham et al., 1979; Berry & Torrey, 1983; Berry et al., 1986; Mansour & Torrey, 1991) to initiate the infection process.