Molecular identification of Balantioides coli in asymptomatic pigs from Norwegian farms.

Balantioides coli is a ciliated intestinal parasite of pigs with known zoonotic potential. Although Norway maintains high biosecurity standards and restricts live animal imports, the prevalence of B. coli in Norwegian pig herds has not been formally evaluated. We investigated the occurrence of B. coli in faecal samples from 125 pigs across eight commercial farms and one research facility. Microscopic examination revealed trophozoites and cysts in 48 % of wet-mount preparations and 28 % of McMaster flotation samples. PCR targeting the 18S rRNA gene identified B. coli in 70.4 % of animals, with prevalence ranging from 33 % to 100 % across farms. All four age groups tested positive, with the highest detection rate in finisher pigs (93.5 %) and the lowest in suckling piglets (16.7 %). Sequencing confirmed the identity of the PCR products, and phylogenetic analysis clustered all samples within the previously described Type II group associated with domestic pigs. No clinical signs of infection were observed, consistent with the generally asymptomatic nature of B. coli in pigs. However, its high prevalence, even under strict biosecurity measures, indicates that the parasite is endemic in Norwegian pigs. The potential impact on animal welfare and productivity remains uncertain. This initial survey provides a baseline for continued surveillance and the standardisation of detection methods to better understand the impact of Balantioides coli on animal welfare and productivity in intensive pig production systems.