great lakes dairy sheep symposium - the Department of Animal ...

1.2. IMI is the main factor influencing SCC
The inflammation caused by an infection is responsible for the increase of SCC, particularly
the PMNL cells. The increase of the SCC depends on several factors like the virulence of the
pathogen, the host, i.e. the sheep…
1.2.1. Clinical IMI
In case of clinical IMI, SCC are in general very high, usually over several million cells/ml.
But in this situation, SCC have no practical interest for the diagnosis since it can be based on a
clinical examination of the gland or the milk. Due to the gravity of the IMI, the first objective
would be the survival of the ewe. The prevalence of such clinical IMI is about 5%.
Staphylococus aureus is the major etiologic agent in more than 50 % of the samples in case of
clinical IMI. In an epiomiological survey carried out in France on 302 clinical mastitis cases in
72 flocks, the prevalence of Staphylococus aureus was 62 % (Fig. 1). On the other hand, with a
prevalence in the range of 14 % in dairy sheep, Coagulase-negative staphylococcus species
(CNS) cannot be considered as minor pathogens.
Figure 1. Aetiology of dairy sheep clincal IMI (Bergonier et al. 2006)
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Taking into account these results (low % of clinical IMI + high prevalence of S. aureus +
gravity of the infection + antibiotic treatment), the hygienic guidelines (in France) recommend
isolation of the ewe, stop milking this ewe with the rest of the flock, and if possible, cull the
animal.
In some rare cases, clinical IMI outbreaks are reported, and the prevalence may reach 50 %
of the flock. These outbreaks are due to S. aureus (or other S. uberis, agalactiae, suis…) or to
opportunistic pathogens such as Aspergillus fumigatus and Pseudomonas aerigunisa.
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S. aureus
CNS
Mannheimia spp.
Streptococcaceae
Enterobacteria
Other
Contaminated