Mastitis pathogens Flashcards
What is mastitis?
Inflammation of the udder
The level of what is measured to show infection levels?
Somatic cell counts
- Increase in SCC reflects the raise in neutrophils which indicates the presence of infection
What are the two types of mastitis?
Clinical and sub-clinical
Describe subclinical mastitis
Infection present but no visible clinical signs
Changes in somatic cell counts, milk quality and milk yield
What are the different grades of clinical mastitis, describe them
Grade 1 - mild milk changes
Grade 2A - acute, changes in milk, udder hot, painful
Grade 2C - Chronic, changes in milk, udder hard and lumpy
Grade 3 - Changes in milk and udder, cow is sick
How do contagious pathogens spread and cause mastitis?
From other infected cows
- during milking via fomites (clusters, milker’s hands, communal teat cloths, teat brushes)
When is the key risk period for environmental pathogens to infect cows?
Just as cows are coming in to be milked when the canal opens (in response to the tangible signals the cow picks up …time of day, sound of the parlour, being rounded up), and after milking for around half an hour (the time taken for the sphincter to close after being milked)
Name the two main environmental pathogenic causes of mastitis
Streptococcus uberis
Coliforms e.g. Escherichia coli
Give 4 examples of contagious pathogens that cause mastitis
- Staphylococcus aureus
- Streptococcus dysgalactaie
- Streptococcus agalactiae
- Mycoplasma spp
Describe how you culture bacteria for identification
- Grow the bacteria
- Bacteria must be alive
- No antibiotics for at least 7 days prior to culture
- Must be shedding on the day of sampling (luck!).
How do you use a PCR to detect pathogens causing mastitis?
- Detects bacterial DNA
- Dead/alive
- Before/during/after antibiotics
What are some reasons a sample to identify bacteria might fail?
- Contamination
- Testing panel
- Not shedding
- Poor storage/handling
- Unknown pathogen
Name the most common contagious mastitis pathogen
Staphylococcus aureus
How would Staphylococcus aureus appear on blood agar?
White colonies with rings of haemolysis
What are the sources of infection of Staphylococcus aureus?
Cows and fomites
Fly spread
Spread among heifers pre-calving by teat sucking
Which features of Staphylococcus aureus make it difficult to treat?
- Intracellular
- Survives in biofilms
- Damages the duct system which leads to abscesses
- Antibiotics are poorly accessible
- Often responsible for recurrent/chronic infections
Describe the main features of clinical grade 3 mastitis
- Usually newly calved cow (periparurient immunosuppression)
- Peracute toxaemic sick cow (massive release of a toxin)
- Gangrene of udder tissue, udder cold, blue, then necrotic and finally sloughs
- Milk often dark red and bloody
Why is the shedding pattern of Staph.aureus important?
Every 5-6 days the levels of bacteria rise are are detectable, between these periods the animal will appear negative as the animal is not shedding
Give some control methods for Staph.aureus
- Prevent introduction of infection, check any new cows cell count and examine udder
- Reduce existing infection in the herd by treating cases and culling chronic cases
- Dry cow therapy
- Prevent spread within the herd, most importantly the milking parlor
How can spread within the milking parlour be controlled?
- Wear Gloves
- No common udder cloths/ wipes
- Early detection and treatment
- Post milking teat disinfection
- Milking order
How does Streptococcus agalactiae appear on blood agar?
Very small, pin prick colonies
Non-haemolytic
Describe some of the features of Streptococcus agalactiae and its spread
Gram +ve cocci
Contagious
Not associated with persistent infections
Controlled by good parlour hygiene
Small pin prick colonies form on which type of agar medium for Streptococcus dysgalactiae?
Edwards medium
What are the two species of Mycoplasma that cause mastitis?
Mycoplasma bovis
Mycoplasma californicum
Describe the features of an M.bovis infection
Infertility, metritis, otitis media, arthritis, keratoconjunctivitis, pneumonia
What is the treatment of cows with Mycoplasma infections?
Must be culled
Why can you not treat mycoplasma spp with antibiotics?
Lack a cell wall therefore non-responsive to beta-lactam antibiotics (penicillins and cephalosporins)
Describe the aetiology of mastitis caused by Mycoplasma spp
Lipoprotein on outer surface -> stimulates host immunity -> alveolar epithelium degenerates -> massive leucocyte outpouring -> abscesses, alveolar hypertrophy, fibroplasias around ducts -> destroyed quarter
How does Escherichia coli appear on blood agar?
Creamy white colonies
Describe the main features of the E.coli pathogen
Gram -ve rods
Source = bovine faeces
Which cows are most at risk of an E.coli infection?
Those that are housed
Describe the pathogenesis of mastitis caused by E.coli
- Contamination of teat end is followed by invasion of teat canal
- Proliferates rapidly producing LPS endotoxin damages vascular and secretory tissue
- Clinical outcome of the infection will depend on the quantity and speed of neutrophil influx
Describe grade 1 and 2A of E.coli mastitis clinical disease
Grade 1 = clots in milk, should self-cure
Grade 2 = Clots in milk, hard hot painful quarter
Describe grade 3 of clinical mastitis caused by E.coli
- Very sick cow, endotoxemia shock (usually post calving peri-parturient immunosuppression) udder variable can be cold or hot, hard or soft
- Milk varies from clots to blood
- Common
How can E.coli infections be controlled?
- Infection particularly common in dry period and early lactation
- Pre-milking teat preparation: remove the muck
- Dry cow therapy
- Vaccination
Describe the vaccination of cows against E.coli
“Startvac”
- Give to each cow every few months
- Will not eliminate disease
- Reduced severity of clinical disease if having problems with Grade 3 per-acute toxic mastitis
Which pathogen has both environmental and contagious strains?
Staphylococcus uberis
What is the source of Staphylococcus uberis ?
Bovine faeces
• Straw yard housing
• Straw bedded cubicles
• Muddy fields at end of summer / crowded shade
Describe the pathogenesis of Staphylococcus uberis
- Intracellular in mammary epithelial cells so avoid detection by the immune system
- Hyaluronic acid capsule : protective shell prevents attachment of antibodies or the neutrophils
- After phagocytosis some strains can resist killing by neutrophils
How can Staphylococcus uberis be controlled?
- Pre-milking teat preparation
- Milking order
- Cull chronic cases
- Dry Cow Therapy
Which cows are affected by summer mastitis?
• Typically affects DRY cows and HEIFERS OUTDOORS IN SUMMER in fields but is also seen occasionally in steers and bulls and can occur in housed cows in winter
What is the vector of summer mastitis?
Hydrotea irritans the sheep head fly
What are the clinical signs of summer mastitis?
Classically hot hard swollen very painful udder with a thick purulent secretion. The cow may also be lame and systemically ill
Describe the milking order to minimise transmission
- 1st parity heifers first
- Healthy cows next (SCC low)
- High SCC cows
- Cows with clinical mastitis
