Longitudinal Study on Mycobacterium avium subspecies paratuberculosis Infection in Goats

A longitudinal epidemiological study was conducted from May 2022 to May 2023 in three Italian goat flocks that tested positive for Mycobacterium avium subspecies paratuberculosis (MAP) infection in a previous cross-sectional study carried out in Macerata Province (Marche Region). The aims were to assess: -the dynamics of immune response in blood, milk and bulk tank milk (BTM); the dynamic of faecal excretion by qPCR; -the incidence trends of MAP infection; -the effects of a one year 'test and cull' and biosecurity measures application on strongly shedders goats as control program of caprine Paratuberculosis; -the efficacy of the whole IDVet system for MAP analysis in faeces and the use of TPC-MAP as decisional threshold for estimation of culling priority. Goat population was stratified by age (young: ≤6 months; adult:6-24 months; elderly: ≥24 months), and sex to be screened at T0, after 6 (T6) and 12 (T12) months. Blood (n=200), milk (n=114), and bulk tank milk (BTM: n=9) samples were collected for indirect diagnosis (ELISA-IDScreen®Paratuberculosis, ID.vet, France), while faecal samples (n=402) were submitted to qPCR IS900 investigation (IDGene®-Easy-Preparation, and IDGene™-Paratuberculosis-Duplex, ID.vet, France). Blood-seroprevalence decreased from 8.29% (T0) to 0.99% (T6) to 0% (T12). At T0, T6 and T12, milk-seroprevalences of 22.22%, 4.26% and 4.48% were observed. From T0 to T12, MAP incidence rates decresead to 0% and to 3.77% testing blood and milk, respectively. The BTM confirmed the blood seronegativity observed in all flocks at T6, while at T12 the individual milk seropositivity of 12% (3/25) in one flock was revealed by BTM seropositivity (S/P% 17.128), although all goats resulted not strong/active MAP shedders at T12. The study highlights a milk "fluctuating" antibody trend in blood seronegative and non-shedder goats. The use of PCR with TPC as a threshold, proved to be a useful tool to prioritize culling among seropositive animals.