an epidemiological study of listeriosis in dairy cattle

all cases* 403 384 371 (96.6%) 9 (2.3%) 8 (2.1%)
silage eye 339 331 328 (99%) 3 (1%) 0
s. eye and n. signs 29 29 26 (89.7%) 1 (3.4%) 2 (6.9%)
nervous signs 20 19 13 (68.4%) 4 (21.1%) 2 (10.5)
abortion 10 4 4 (100%) 0 0
mastitis 4 0 0 0 4 (100%)
s. eye and s. death 1 1 0 1 0
n number of the cases * excluding those whose clinical signs were not reported
2. 3. 8. Validation of the questionnaire:
The frequency of individual signs selected by farmers is given in the Table 2. 7.
Abortion (57.8%), nervous sign (56.8%), silage eye (49.4%) and diarrhoea (24.1%) were
reported most frequently. Of 894 respondents, 41% (366/894) did not answer this question,
6% (54/894) answered “don`t know” and 53% (474/894) identified one or more clinical
signs of listeriosis. When the diagnosis made by veterinarian or V.I.C. was taken as the
gold standard, the sensitivity of farmers reporting individual symptoms was 67.2% for
silage eye, 49.2% for nervous signs and 21.9% for abortion The sensitivity was high when
more than one clinical signs was reported. It was 96.1% (123/128) for farmers reporting a
combination of nervous signs, silage eye or abortion and 87.5% (112/128) for farmers
reporting nervous signs or silage eye. (Table 2.7).
Table 2. 7. The frequency of clinical signs chosen by farmers and sensitivity of farmers
reporting correct clinical signs.
Frequency of clinical
Clinical signs
signs n α sensitivity of farmers
=474 (%) reporting n β =128 (%)
58