TRANSMISSION OF VARIOUS TYPES OF MASTITIS ORGANISMS
In attempting to control different types of infections, it is important to consider the source and means of transmission of the disease. Organisms that cause mastitis live in different environments (manure, bedding, skin, etc.). General cleanli-ness of cows and their housing, as well as good management procedures—especially at milking—are effective ways of controlling the spread of mastitis.
Streptococcus Agalactiae
Streptococcus agalactiae is the most common cause of subclinical infections but rarely causes severe illness (acute mastitis). This organism lives in the cow’s udder and survives only a short time outside the mammary gland. It spreads primarily during milking via the milking machine, contaminated operators’ hands, and materials (cloths) used to wash the udder (Figure 2). This organism may also infect the udder of a young calf if it is sucked by asecond calf that has been fed contaminated milk. The infection can remain indefinitely in the heifer’s mammary gland.
Streptococcus agalactiae can be eradicated from a herd by appropriate treatment combined with good milking practices. However, it may easily spread again in a herd after the purchase of an infected animal.
Staphylococcus Aureus
Staphylococcus aureus lives inside or outside the udder on the teat skin and causes many cases of both clinical and subclinical mastitis. It usually spreads the same way as streptococcus agalactiae (Figure 2). The infection tends to induce scarring, which results in pockets of infection walled off in the udder that are very difficult to reach with antibiotics. Such pockets may break open and spread to other partsof the gland later.
Streptococcus Uberis and Streptococcus Dysgalactiae
These organisms are found in bedding (especially organic bedding: straw, sawdust, etc.), standing water and soils. They can also be found on the cow’s skin(teat and belly) and in the reproductive organs. These two organisms are usually transferred from the environment to the teat between milking, but some transfer can also take place during milking. These organisms cannot be eliminated from a herd because they are part of the normal environment. The rate of infection from these bacteria tends to increase when conditions favor their growth—for example, during the wet and humid months of the year. Streptococcus uberis and streptococcus dysgalactiae are also responsible for most of the mastitis that occurs at either the beginning or the end of the dry period. In addition to these two species of bacteria, there are many other environmental streptococci (Strep. bovis, Strep fecalis) that can cause mastitis.
Coliform Bacteria
Coliform bacteria are normal inhabitants of soil and the intestines of cows. They accumulate and multiply in manure and bedding. Coliforms can cause mastitis only if contaminated particles from the environment come in contact with the udder. As opposed to previously described bacteria, the coliform do not attach to the ducts and alveoli in the udder, rather they multiply rapidly in the milk and produce toxins that are absorbed into the blood stream. As a result, coliform infections lead to acute clinical mastitis. The body temperature of the cow may rise above 40oC and the infected quarter will become swollen and sensitive to touch. The cow’sdefense mechanisms may eliminate the bacteria in the udder, but the toxins remain and the cow may die. Cows free of other mastitis-causing bacteria (streptococcus agalactiae and staphylococcus aureus) appear to be more susceptible to coliform bacteria.
