Toxoplasma gondii in naturally infected goats : monitoring of specific IgG levels in serum and milk during lactation and parasitic DNA detection in milk

The zoonotic protozoa Toxoplasma gondii is one of the major abortive pathogens in small ruminants. Nevertheless, data on T. gondii infection in goats during lactation and on the presence of T. gondii in goat milk are lacking. A longitudinal study was planned in a T. gondii naturally infected dairy goat farm with the aim of (i) evaluating the variation of anti-T. gondii antibodies in blood and milk during the lactation; (ii) identifying the optimal phase during lactation for T. gondii monitoring; (iii) detecting the presence of T. gondii DNA in the milk. From March to July 2017, 30 goats in a farm were fortnightly visited seven times and sampled for blood and, when in lactation, for milk. Individual data regarding age, reproductive disorders, and the day of lactation were recorded. For the detection of anti-T. gondii antibodies in blood and milk a commercial ELISA kit was used. Milk samples (n = 63) of selected nine seropositive animals were also molecularly analysed to amplify a sequence within the ITS1 region of T. gondii. The seroprevalence of T. gondii infection was 63.3% (19/30); a high agreement was obtained between serum and milk results (Spearman's coefficient = 0.793 and Kendall's tau = 0.624), particularly between the 15th and the 60th day of lactation. In the statistical analysis, performed with generalized linear mixed models (GLMMs), the variable "phase of lactation" was strongly associated to ELISA values obtained in both serum and milk (p-value = 0.0001, F = 5.197, and p-value = 0.016, F = 2.755, respectively). Finally, molecular analyses revealed the presence of parasitic DNA in 20.6% (13/63) of milk samples, with a discontinuous parasite excretion; statistical analyses did not reveal any association among the parasite excretion and the considered variables. Milk could be considered as a valid alternative to blood for monitoring T. gondii infection in goat herds. Moreover, the detection of T. gondii DNA in milk enhanced the possibility for raw goat's milk consumption to be considered as a risk to public health.