an epidemiological study of listeriosis in dairy cattle

monocytogenes was also isolated from these samples with the exception of soil on
farms A and D and water on farm D.
Listeria spp. were isolated from bulk milk tank on 4 of the 5 farms and L.
monocytogenes was isolated from 3 farms (Farm A, B and D). L. monocytogenes was
persistently isolated from the bulk milk tank between October and March on farm D.
6. 3. 2. Serology
The results of ELISA assays for each farm are presented in the appendix 6.
There were only few animals that were seronegative at the beginning of the study. 0.9%
(1/109), 1% (1/96) and 1.6% (2/122) of animals were seronegative on farms A, B and D
respectively. There were no seronegative animals on farms C and E. The number of
animals that had increased or decreased level of antibodies to L. monocytogenes is
presented in the table 6. 17. A significant number of animals had increased antibodies
on the farm A after the first and second sampling and only few animals were found to
have increased or decreased antibodies on the other farms (Table 6.17).
Table 6. 17. Antibody changes during the period of the study
difference between
collections
first and second 32.9%
(27/82) i
second and third 30.8%
(24/78)i
first and third 42.8%
(33/77)i
Farm A Farm B Farm C Farm D Farm E
1.4%
(1/71)d
1.4%
(1/72)i
1.5%
(1/67)i
3.8%
(2/53)d
15.4%
(8/52)d
9.4%
(5/53)d
9.1%
(7/77)d
5.2%
(5/97)i
1.6
(1/64)d
1.1%
(1/87)i
1.5%
(1/65)d
2.2%
(2/93)d
i number of animals that had increased antibodies, d number of animals that had decreased antibodies
6. 3. 3. RAPD:
193