Once in the host gut, "Necator" tends to cause a prolonged infection, generally 1 to 5 years (many worms die within a year or two of infecting), though some adult worms have been recorded to live for 15 years or more. "Ancylostoma" adults are short-lived, surviving on average for only about 6 months. However, the infection can be prolonged because dormant larvae can be "recruited" sequentially from tissue "stores" (see Pathology, above) over many years, to replace expired adult worms. This can give rise to seasonal fluctuations in infection prevalence and intensity (apart from normal seasonal variations in transmission).