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Leptospirosis is an important infectious disease of dogs. In the Midwest, Leptospirosis is usually
diagnosed in the late summer to fall time period especially if there is a sustained period of above
normal precipitation 1–3 months earlier. It is important to remember that all breeds and life
styles (city vs. rural) dogs are at risk of contracting Leptospirosis, but adult male dogs that spend
a considerable amount of time outdoors are at greatest risk

The Microscopic Agglutination Test (MAT) is the standard serological test used in the United States for diagnosis of Leptospirosis. The following six serovars are used in the assay: L. bratislava, L. canicola, L. grippotyphosa, L. hardjo-bovis, L. icterohaemorrhagiae and L. pomona. Generally, the serovar with the highest titer is the infecting serovar but cross-reactions do occur albeit at a lower level. Titers should be interpreted in the context of clinical findings, laboratory data and Leptospirosis vaccination history

Coagulase-negative Staphylococci (CNS) are normally found at the level of the teat, nasal mucosa, as well as on the hands of milking personnel. The CNS group is made up of over 50 bacteria and are most frequently isolated from infected glands. This group includes S. chromogenes, S. hyicus, S. simulans, and S. epidermidis. S. xylosus, S. saprophyticus, S. sciuri, and S. cohni are Novobiocin-resistant Staphylococci and found as free-living in the environment. These bacteria are considered environmental causes of mastitis. Due to their high prevalence, CNS infections are usually subclinical, but can result in a 2-3 times increase in SCC within the infected quarter. The amount of increase in SCC is reflective of the Staphylococcus species causing the infection.

E. coli and other coliform species, such as Klebsiella, Enterobacter, and Serratia, are gram negative bacteria found in the environment. These gram negative bacteria release endotoxin when they are engulfed by a white blood cell which can cause fever, decreased appetite, weight loss, a decrease in milk production and exacerbate the inflammatory response. Coliform mastitis will lead to inflammation of the mammary glands and damage of the mammary epithelial cells. An increase in vascular permeability in the mammary gland can also result in watery or serous milk.

Klebsiella species are Gram-negative coliform bacteria that can cause mastitis, leading to significant economic losses on dairy farms. K. oxytoca and K. pneumoniae are the species that are responsible for causing clinical mastitis.

Contagious Pathogens-Infection with contagious pathogens occurs from the milk of other infected animals. These infections can be prevented with proper milking hygiene including post-milking teat disinfection, milking infected animals last and effective management of clinical cases.
Gram-positive
Streptococcus agalactiae
Streptococcus uberis
Gram-positive, Coagulase-positive
Staphylococus aureus
Mycoplasma sp.
Prototheca sp.
Environmental Pathogens-Infection with environmental pathogens occurs from bacteria entering the teat end from dirt, manure, bedding, milking machines that have been contaminated with these pathogens. These infections can be prevented with proper hygiene, milk machine maintenance and pre-milking teat disinfection.

Due to the treatment and prevention programs set in place for Streptococcus agalactiae and Staphylococcus aureus, there has been an increase in Mycoplasma-induced mastitis occurrence. Mycoplasmas are very small microorganisms that lack a bacterial cell wall and can be cultured from various locations on both the bodies of sick and healthy cattle. Several species can cause mastitis, including M. bovis (the most common species cultured from the udder; commensal organism of the respiratory tract), M. alkalescens (commonly cultured from the respiratory tract as well), M. bovigenitalium (commonly cultured from the reproductive tract), and M. canadense (commonly cultured from the joints). M. bovis is an important cause of respiratory disease in calves and feedlot cattle. M. bovis has also been involved in joint infections, as well as in abortions and ear infections in calves.