Caprine Paratuberculosis: Cross-Sectional Study in Italy and Evaluation of an Indirect ELISA Test’s Performance in Milk

A cross-sectional epidemiological study was carried out on goats reared in Macerata Province (Marche Region, Italy) in order to: -assess the apparent and true Mycobacterium avium subsp. paratuberculosis (MAP) seroprevalence at flock- and animal-level; -evaluate the performance and the applicability of PARAS (ID.vet, France) on goat milk and bulk tank milk (BTM), as screening tool for flock health status; -evaluate the efficacy of the whole IDVet system for MAP analysis in faeces. In May 2022, a simple randomized sampling at farm-level, and a screening at animal-level (n=217) were conducted in 5 flocks (CI99%), representative of goat flock population reared in Macerata Province (Italy), stratifying the animalsaccording to age (young: ≤6 months; adult:6-24 months; elderly: ≥24 months) and sex. Indirect ELISAs and qPCR IS900 were performed on blood, milk and bulk tank milk (BTM) sera,and faecal samples.MAP prevalence at farm-level was 80% (4/5) while the goat apparent- and true-blood seroprevalences at animal-level were 8.29% (18/217) and 14.02%, respectively. No significant differences were observed for seroprevalence and antibody level in relation to age (elderly:9.8%, S/P%=19.73±37.04; adult:8%, S/P%=13.71±23.91; lambs:2.5%, S/P%=11.73±32.15; p=0.9). Male goats (16.67%, 3/18) resulted seropositive but not shedders. Milk seropositivity of 22.22%(26/117) was observed andELISA test on BTM confirmed the 80% of infected flocks. In females, significant higher seroprevalence was recorded in milk vs. blood (22.22%-7.54%, p=0.0001),both in adult (25%-6%, p=0.0192) and elder goats (21.50.02%, p=0.0206). The strong and weak/passive-intermittent faecal shedders were 2.80% and 6.54%, respectively. All strongly shedders were elder female and seropositive, both in blood and milk. Considering the bovine (30%) and sheep (>21.38%) cuts off, the ELISA ID Screen® Paratuberculosis Indirect Screening test (ID.vet, France) on goat milk showed the following performance: Sensitivity=92.3%, Specificity=86.5%, Positive and Negative predictive values of 46.2% and 98.9%, respectively;Accuracy=87.2% and a moderate agreement (Cohen kappa=0.55).