7. Contagious Mastitis
Staphylococcus aureus (4)
- Can survive inside white blood cells (intracellular).
- Intermittently shed from the mammary gland, so milk must be cultured repeatedly to be sure a cow is truly negative.
- There is a 75% chance of detection with one culture from an infected cow.
- There is a 95% chance of detection with three cultures collected on consecutive days from an infected cow.
- In chronic cases, fibrosis and micro-abscess formation in the udder decrease the probability of adequate drug distribution to the site of infection.
- Colonizes the epithelial surface of teat ducts.
- The udder is the reservoir of infection.
- Toxin elaboration results in inflammation.
- Organisms are shed in the milk in high numbers.
- Antibiotic therapy for lactating cows is highly successful provided the bacteria are not resistant to the antibiotic used.