Although the etiology of
paratuberculosis has been known for decades, several questions
concerning the pathogenesis and epidemiology of the disease are
still open.
While many features of
infection caused by M. paratuberculosis are similar across
ruminant species, the clinical presentation, and the availability,
performance, and interpretation of diagnostic tests differs between
cattle and other ruminants such as sheep, goat.
In the present study we
analysed 1820 adult sarda breed sheep from 4 flock. We performed a
first ELISA test of screening on serum. A second ELISA of
verification was performed on serum and milk of the positive
individual .
We collected feaces from
positive sheep and carried out PCR on the specific insertion
sequence IS900.
From our results the
seroprevalence among flocks were from 0,7% to 11%. The 54% of the
seropositive animals were also positive in milk ELISA. Individual
showing an higher value of S/P are more likely to be positive in
both tests. So we confirm that the ELISA S/P value is an useful
tool in the diagnosis and control of paratuberculosis, particularly
in subclinical cases.
PCR analysis has
confirmed as positive only the 11% of the samples, difficulties are
experienced in recovering DNA from small number of organisms in
clinical specimens, especially in complex samples such as faeces.
The low sensitivity could be attributed to the presence of a
intermittent shedding of the MAP in faeces or PCR inhibition by
faecal constituents.
Mycobacteria are
commonly found in soil and water. Since this widespread
distribution the present study was performed also to determinate if
genetically identifiable individuals may have different tendency to
develop paratuberculosis when exposed to the same infectious
agent.
Two genes that seem to
have a major influence on the outcome of infection with
Mycobacteria in many species, including mice and humans are the
NRAMP1 gene and the CARD15/NOD2 gene.
Genetic analysis was
carried out on 31 sheep (18 infected and 13 healthy) We searched
for polymorphisms linked to susceptibility or genetic
predisposition to paratuberculosis in sheep. We sequenced exon 1
and exon 2 of NRAMP1 and we didn't find any SNPs.
Concerning CARD 15 we
sequenced exon 1 (270bp), exon 2 (500 bp) , exon 3 (235 bp), exon 4
(2000 bp), exon 11(120 bp) and intron 1-2 (1008 bp) intron 5-6 (300
bp) and the promoter region (541 bp). The exons 1, 2 and 11 were
monomorphic as well as the intron 1-2.
The exon 4 and the
intron 5-6 were polymorphic. The sequences of exon 4 and exon 2 are
published in the database Gene Bank (Number of accession
EF141018).
We found 4 haplotypes
with different frequency estimates. We analysed the data with
χ2 test , and fisher's exact test.
Up till now wee found no
significant associations between variation in CARD15 and disease
status. Further step of the study is to investigate on a large
cohort of infected animal and controls.
