The Epidemiological Investigation of Trichinella Infection in Brown Rats (Rattus norvegicus) and Domestic Pigs in Croatia Suggests That Rats are not a Reservoir at the Farm Level

Whether the brown rat (Rattus norvegicus) is a reservoir of Trichinella spp. infection or merely an accidental host, which may be vector of Trichinella spp., continues to be debated. We estimated the prevalence of Trichinella sp. infection in brown rat populations and in domestic pigs in 2 villages in Croatia, where Trichinella sp. infection in pigs has been endemic in the past 10 yr. Trichinella spiralis larvae, identified by a multiplex polymerase chain reaction analyses, were the only species detected in both rats and pigs. In 2001 and 2002, 2,287 rats were collected on 60 farms with different levels of sanitation and with, or without, T. spiralis–infected pigs. The prevalence of infection in rats ranged from 0.2 to 10.7%. Infected rats were detected only on farms with T. spiralis–positive pigs and low sanitation or formerly with low sanitation (P = 0.007, Fisher's exact test), yet no infected rat was detected on farms with T. spiralis–negative pigs. The finding that no infected rat was found on farms with T. spiralis–negative pigs suggests that, in the investigated area, the brown rat is not a reservoir but only a victim of improper pig slaughtering.