A screening sampling plan to detect Mycobacterium avium subspecies paratuberculosis-positive dairy herds

Abstract

Mycobacterium avium ssp. paratuberculosis (MAP) is the etiological agent of paratuberculosis, a chronic contagious bacterial disease primarily affecting dairy cattle. Paratuberculosis represents a dual problem for the milk production chain: in addition to economic losses to affected herds, MAP may have zoonotic potential. Infected herds must be identified in order to implement programs designed to reduce the incidence of disease within and between herds and to prevent MAP from entering the food chain. The objective of this study was to evaluate the sensitivity and specificity of a screening sampling plan (SSP) to detect MAP-positive dairy herds by repetitive analysis of bulk tank milk (BTM) samples by ELISA and in-line milk filter (ILMF) samples by PCR. Samples from BTM and ILMF were collected twice from 569 dairy herds in southern Italy. Additionally, 12,016 individual milk samples were collected: 9,509 from 102 SSP-positive herds (SSP MAP-positive) and 2,507 from 21 randomly selected SSP-negative herds (SSP MAP-negative). There was a total of 126 SSP MAP-positive herds (i.e., 21.3% SSP MAP-positive herds; 95% confidence interval=18.0-24.9); the within-herd apparent prevalence (AP) ranged between 0.00 and 22.73% (mean 6.07%). A significant difference in within-herd AP was shown between SSP MAP-positive herds and SSP MAP-negative herds. A highly significant association was shown between the median AP herd status (>5%) and positivity to at least one ILMF or BTM sample. The SSP detected a minimum of 56.25% of low AP herds (AP ≤ 2.0%) up to a maximum of 100% of herds with a within-herd AP ≥ 8.0%. Overall, the SSP detected 85.57% of herds in which at least one individual milk sample was positive by ELISA. The proposed SSP was an inexpensive and useful tool to detect MAP-positive herds with a higher risk of infection diffusion and milk contamination. Although the SSP cannot be used for MAP-free certification of herds, it could be useful to prioritize appropriate control measures aimed at reducing the prevalence of infection in dairy herds and milk contamination.

Short communication: Investigation into Mycobacterium avium ssp. paratuberculosis in pasteurized milk in Italy

“…A previous investigation on MAP performed in the same dairy plants detected an apparent mean prevalence of 6.7% by ELISA in the animals of the farms delivering milk to the plants (Serraino et al, 2014a). This result is similar to the prevalence reported in other studies (Nielsen and Toft, 2009;Carter, 2012).…”

“…Because the public health significance of low numbers of MAP is not known and there are public concerns about human exposure to MAP, we performed a large investigation in 569 Italian farms delivering milk to 3 industrial dairy plants (Marchetti et al, 2013;Serraino et al, 2014a,b). The apparent prevalence in the investigated dairy herds was 6.07% (range 0.00 to 22.73%; Serraino et al, 2014a). We used the findings to perform a quantitative risk assessment of MAP survival in pasteurized milk, estimating an overall percentage of 0.55 to 0.98 of pasteurized milk bottles having a MAP contamination >0 cfu/L and 0.04 to 0.11% of liters having a contamination >100 cfu/L (Serraino et al, 2014b).…”

Serological survey of paratuberculosis in dairy cattle in Garfagnana district (Tuscany)

“…Concerning the level of contamination of bovine bulk tank milk, it has been proven that it can contain a median load of 32.4 Map cells mL -1 and maximum load of 1424 Map cells mL -1 (Ricchi et al, 2016). With reference to this, in Italy, as suggested by previous studies, not only bovine raw milk, but also pasteurized milk is a significant source of Map exposure for consumers (Giacometti et al, 2012;Serraino et al, 2014a;Serraino et al, 2014b). Unfortunately, while the disease has been highlighted in the Tuscan caprine and ovine population (Galiero et al, 2015;Galiero et al, 2016), no official data have been published on the occurrence of paratuberculosis in cattle in Tuscany.…”

Mean effective sensitivity for Mycobacterium avium subsp. paratuberculosis infection in cattle herds

“…When evaluating control programs for MAP in groups of cattle, it is also necessary to consider the test specificity [ 11 ]. The test specificity of ELISA, faecal culture and PCR are not entirely accurate for two primary reasons: a) false-positive reactions occur in immunological tests due to cross-reacting antibodies [ 12 ]; b) MAP may be excreted by non-infected animals in high-prevalence herds due to passive (pass-through) shedding of the bacteria [ 13 , 14 ], or because infected but non-infectious cattle are detected by agent-detecting tests.…”