Listeria Monocytogenes Excretion and Humoral Immunity in Goats in a Herd with Outbreaks of Listeriosis and in a Healthy Herd

In a herd of 65 goats with outbreaks of listeriosis (Herd A) blood, faeces and milk were collected just after the outbreaks, about 1 month later and at delivery about 4 months thereafter. Faeces and milk were examined bacteriologically and blood and milk serologically for Listeria monocytogenes (Lm), and the results were compared with those of 2 similar samplings in a healthy herd (Herd B). In Herd A Lm was isolated from faeces in 5 of 14 septicaemic does and in 6 of 48 other animals on the first sampling, and in 4 and 1 animals respectively, on the subsequent 2 samplings. In milk Lm was demonstrated just after the outbreaks only, viz. in 3 of 12 septicaemic does and in 16 of the other 32 examined. Four does excreted Lm in both faeces and milk on this date. In Herd B Lm was demonstrated only at delivery, i.e. from 10 of 43 animals. Most of the isolates belonged to serotype 1. Reciprocal geometrical mean titres (GMT) of antibodies in sera from the septicaemic group decreased from 236 to 140 and 136 respectively on the subsequent samplings, whereas GMT of the encephalitic animals and of the remainder of Herd A increased from about 20 to about 100 at delivery. GMT of Herd B increased toward delivery from 23 to 39, with largest increase for the does. GMT in whey were ≤ 18 for all groups.