Furthermore, no international scientific consensus exists concerning the definition and verification of JD-free zones or regions (Table 2–3).

Numerous JD prevalence studies have been completed in domesticated-animal populations of various countries (Kennedy and Benedictus, 2001). Differences in sampling design and diagnostic strategies make direct comparison of the studies difficult, but critical evaluation of published surveys suggests considerable variation in the prevalence of infected herds in different countries and within specific geographic areas. The prevalence of Map-infected animals and clinical JD also varies greatly within affected herds. Several estimates for JD herd prevalence exist (Tables 2–3 and 2–4).

The most extensive surveys for JD and Map across multiple states in the United States have been completed by the United States Department of Agriculture (USDA). Merkal and colleagues (1987) cultured ileocecal lymph node specimens from clinically normal cull cattle at slaughterhouses in 32 states during 1983–1984. They isolated Map from 119 of 7540 cattle; isolates from dairy cattle culls were more than 250 percent higher than were those from beef culls (2.9 percent and 0.8 percent, respectively). USDA’s National Animal Health Monitoring System (NAHMS) serologically tested a sample of dairy and beef cattle using ELISA to obtain estimates of the prevalence of JD in herds and in individual animals. In the U.S., 32,622 cows were tested from 1004 dairy operations. Herd prevalence for JD was estimated at 21.6 percent (NAHMS, 1997a). Testing of 10,371 beef cows from 380 herds in 1997 generated an estimate of 7.9 percent infected herds, although the results are not directly comparable to those from dairy cattle because of differences in the investigators’ definitions of a positive test in a herd (Dargatz et al., 2001). Nevertheless, the surveys confirm the beliefs that JD is widespread in the United States and that dairy herds are more likely to be infected than are beef herds.

Prevalence data for sheep in the United States will be available when the NAHMS Sheep 2001 report is released. No prevalence studies have been conducted on goats in the United States.