Infected fetuses can abort, or they can be born and not display their infection until they are adults. How in-utero infections affect diagnostic tests on those animals that survive to adulthood is not known. Water and feed. Water or forages that are contaminated with manure from infected animals are additional potential sources of infection. These sources are not well quantified and their risk must be assessed by estimating the degree of contamination, prevalence of infected animals, and age susceptibility of exposed animals.
CD is most prevalent in the northern, more industrialized regions of Europe and North America.
Its incidence has trended upward over the last four decades. It is generally agreed that CD is the consequence of the intestinal immune system over-responding to some stimulus. There is no cure however and individuals with CD alternate periods of remission with flare-up for life. Associations do not offer much guidance about the causal relationship between two factors. CD is a complex disease and extensive research will ultimately be needed to resolve the question of its cause.