In Powys, 473 farmers were eligible to take part; 72 (15%) did not have dogs, 112 (24%) could not be contacted, and 16 (3%) declined to cooperate. Therefore, a total of 273 farmers who were contacted and were eligible agreed to take part. Equivalent figures on response rates were unavailable for Gwent. A total of 1,178 dogs were on these farms (990 from Powys and 188 from Gwent), and fecal samples were obtained from 1,164 (588 dogs and 576 bitches). In 75 farms, sheep, cattle, or both had been slaughtered as part of FMD controls; FMD was recorded on 27 of these farms.

The Echinococcus coproantigen ELISA was positive in 94 (8%) of 1,164 of farm dogs. Of farms surveyed, 22% contained at least 1 dog with a positive coproantigen result. Prevalence of positive coproantigen tests in the previous hydatid-intervention area was 8.5% (79/928), compared with 6.4% (15/233) in the former nonintervention areas.

Univariate analysis of questionnaire data showed that male and female dog coproantigen-positive rates did not differ significantly. Younger dogs had a tendency for higher positive rates (≤5 years, p = 0.03). Prevalence of dog coproantigen positivity was significantly associated with farm onsite slaughter of sheep (home-slaughter), the occurrence of free-roaming dogs, and low frequency of dog anthelmintic treatment by owners (Table 1). Coproantigen-positive rates in dogs for FMD and non-FMD farms were similar. Farms that reported feeding food scraps or offal to dogs, or allowing them to scavenge freely, were also associated with a significantly higher risk of an Echinococcus coproantigen-positive result (Table 1).

Multilevel modeling was used to examine risk factors for dogs, farms, and districts, but the variation between farms was not significant. In a single-level multivariate logistic regression model that used backward stepwise variable selection, allowing a dog to roam free and administering anthelmintic treatment infrequently were significant risk factors for Echinococcus coproantigen positivity (Table 2). Using this logistic regression model, we calculated, for example, that a dog that had been reportedly prevented from roaming free and that had received anthelmintic treatment 4 times a year had a probability of a positive coproantigen result of 0.07 {1/[1+ exp –(-2.52)]}. In contrast, a dog that was allowed to roam and was given anthelmintic treatment only once per year had a probability of 0.4 {1/ [1+exp – (-2.52+1.15+1.07)]} for an Echinococcus-positive coproantigen result.

We conducted a study to investigate the concern that human cystic hydatid disease, or cystic echinococcosis, could reemerge in mid-Wales as a consequence of FMD control measures in which large numbers of sheep carcasses lying in fields were potentially accessible to dogs and foxes for several weeks. Although we found no statistical association with FMD-affected farms, we did confirm that canine echinococcosis had reemerged in dogs living in previously hydatid-free areas. The coproantigen-positive rate of 8% in the 2002 farm dog survey was significantly higher than the 3.4% prevalence recorded in the same localities in 1989 to 1993 (7). Risk factors for coproantigen-positive dogs were allowing farm dogs to roam free and infrequent anthelmintic treatment.

Why an association between canine echinococcosis coproantigen positivity and FMD-affected properties was not found is not clear. The lack of an association may be because the large piles of FMD-culled sheep carcasses were in designated government-regulated areas with relatively poor access for scavenging dogs. Moreover, dogs from non-FMD farms might have had the same access to culled carcasses as dogs from FMD farms. However, we were not able to identify whether dogs from non–FMD-affected farms had access to carcasses of slaughtered sheep on FMD farms. Dogs that scavenged may also have been already infected.

The absence of a statistical association with FMD and the findings of earlier surveys suggest that the high prevalence of canine echinococcosis is due to failure of the control strategy. The supervised dog-dosing hydatid-intervention program initiated in south Powys under the auspices of the U.K. Ministry of Agriculture, Fisheries and Food from 1983 to 1989 reduced transmission of E. granulosus to sentinel lambs. Moreover, the incidence of hospital-treated human cystic echinococcosis disease in the intervention area in Powys fell from 4/100,000 to 2.3/100,000 from 1984 to 1990. In May 1993, prevalence of Echinococcus in dogs, as measured by a highly genus-specific coproantigen test, was 0% in the intervention area (lower 95% CI 0%–3.4%). However, 10%–18% of older sheep (>3 years) at slaughter remained infected (7).

In 1989, the supervised dog-dosing program was replaced by a health education program aimed at schoolchildren and farmers in Powys to encourage dog owners to dose their dogs every 6 weeks. Following this, a sentinel lamb study in the former intervention area from 1995 to 1996 (13) found that 5% of sentinel lambs became infected (10% in the adjacent nonintervention areas), indicating that pastures were recontaminated. A coproantigen survey of farm dogs at the same time (1995–1996) showed that 6% of dogs in the former intervention area were positive as were 24% of those in nonintervention areas (13). Our study used the same Echinococcus-specific coproantigen ELISA (11,12) and indicated that E. granulosus tapeworm infection in dogs was widespread in both the former intervention and nonintervention areas. Because of the latency of human cystic echinococcosis, children and adults exposed to infected dogs since 1989 may not have clinical disease for several decades.

A study conducted to evaluate the effectiveness of the health educational program on control of transmission of E. granulosus in south Powys (after 1989) demonstrated that the educational campaign alone was unable or insufficient to prevent transmission of E. granulosus in that region. This study also suggested that lifting the “fast-track” attack phase of treating dogs every 6 weeks with praziquantel after only 5 years was premature (13).

Reemergence of human cystic echinococcosis as a public health problem has occurred in other countries when hydatid-control programs ceased. For example, in Cyprus, cystic echinococcosis reemerged after the breakdown of an islandwide hydatid-control program following partitioning of the island (14). In Bulgaria, human cystic echinococcosis rates increased after hydatid campaigns were ended or reduced (15). And in Kazakhstan, human cystic echinococcosis incidence rates increased 4-fold within 10 years after post-Soviet independence, with its dismantling of collectives and changes in organized livestock and farming practices (16).

In conclusion, reemergence of E. granulosus in dogs in the last 10 years in south Powys, Wales, appears to be due to the withdrawal of the supervised dog-dosing control scheme and a reversion to risky practices of farmers (e.g., allowing farm dogs to roam free and infrequent or no anthelmintic treatment). The FMD outbreak in 2001 did not appear to increase the risk for canine echinococcosis. Urgent efforts are needed to address farm dog owner–associated risk factors if hydatid disease is to be brought back under control in this area.