Pathology of bovine mastitis

Question 1

Mastitis

Answer 1

Inflammation of the mammary gland and is virtually always due to invasion of the gland by microbes

Question 2

What are the four sequential phases in mastitis?

Answer 2

Invasion (via teat canal)

Infection - bacteria multiply in milk sinus and ducts but do not cause clinical signs

Penetration of glandular tissue - produces an inflammatory response

Healing - by complete resolution (mild cases); by fibrosis (more severe cases). Acinar atrophies for the rest of that lactation, if fibrosis and damage extensive gland function may never recover.

Question 3

What can be found as part of the normal flora of the mammary gland?

Answer 3

Corynebacterium bovis and coagulase negative staphylococci.

Question 4

Most common causative agents of bovine mastitis

Answer 4

Streptococci, Staphylococci, Coliforms

Question 5

Most common Streptococcus species causing mastitis

Answer 5

Strep. uberis
Strep. dysgalactiae
Strep. agalactiae

Question 6

Other sporadic Streptoccal invaders in bovine mastitis

Answer 6

Strep. equi
Strep. zooepidemicus
Strep. pyogenes
Strep. pneumoniae

Question 7

Streptococcus agalactiae

Answer 7

Obligate udder organisms

Short survival time in environment

Infections usually permanent and organisms persist despite flow of milk and inflammation.

Question 8

Disease progression in mastitis caused by Streptococcus agalactiae

Answer 8

After becoming established there are brief periods when the bacterial population increases. This is accompanied by patchy penetration of the organisms through the epithelium into the interstitial tissue.

A series of repeated invasions and inflammatory responses with regression leads eventually to fibrosis and involution of the gland.

When bacteria penetrate to the interstitium there is oedema and neutrophil influx. Bacteria are phagocytosed and the disease regresses until the epithelium is breached the next time.

Question 9

Histology of mastitis caused by Streptococcus agalactiae

Answer 9

Epithelium is vacuolated and ragged and macrophages and fibroblasts accumulate.

Lymphocytic foci may develop in the interstitium.

Debris accumulates in the acini and there is stagnation of secretion. Sometimes this produces calcispherite formation.

Question 10

Clinical signs of mastitis caused by Streptococcus agalactiae

Answer 10

Clinically, the udder feels hard and often painful due to retained secretion.

Lobules of acini involute and there may be extensive fibrosis.

Sometimes polypoid ingrowths of granulation tissue occur in the ducts, partially obstructing their lumen.

Question 11

Staphylococcal mastitis

Answer 11

Generally, a younger age group is affected.

Pathogenic Staphylococci can be grouped as catalase positive or negative.
Pathogenic Staphylococci in the udder are usually catalase positive and haemolytic.

Clinically, staphylococcal mastitis can be acute and fulminating or chronic. As with Streptococci, Staphylococci produce various toxins to cause tissue damage, and may penetrate individual cells.

Question 12

Acute form of Staphylococcal mastitis

Answer 12

Occurs soon after parturition and may be associated with gangrene of the affected quarter and high mortality.

Only a little brownish fluid can be expressed from the teat.

Gangrene affects first the teat and adjacent areas.

The mammary tissue becomes blue/black and soft.

It feels cold (result of thrombosis) and is insensitive.

In a few days it exudes serum and begins to slough.

Peracute staphylococcal mastitis can be fatal (result of toxaemia).

Question 13

Disease process of Staphylococcal mastitis

Answer 13

Progresses in a similar way to Streptococcal mastitis.

Organisms invade through the epithelium and infect the interstitium.

Invade deeper and are more persistent than Streps.

Set up foci of infection with a granulomlatous response and a necrotic centre - these become walled off by fibrosis and so are not exposed to antibiotics.

Question 14

Which invade deeper in mastitis- Staphs or Streps

Answer 14

Staphs

Question 15

Milder form of Staphylococcal mastitis

Answer 15

Progessive fibrosis and acinar atrophy.

Question 16

Causative agents of coliform mastitis

Answer 16

Broad spectrum of Gram-negative bacteria:
- E. coli
- Enterobacter
- Klebsiella
- Citrobacter
- Serratia
- Proteus

Question 17

What is coliform mammary infection correlated with?

Answer 17

The weight of environmental exposure

Question 18

Disease progression of coliform mastitis

Answer 18

Usually clinically acute with a systemic reaction and often septicaemia - particularly with E. coli

Question 19

What type of herds are coliform mastitis cases more common?

Answer 19

Herds where other forms of mastitis have been eliminated.

Question 20

Damage caused by coliform mastitis

Answer 20

Damage and infection is due to endotoxins and their effects on the vasculature of the mammary gland.

Infection is often limited to one quarter and inflammation may be serous with much oedema or haemorrhage.

Damage and infection is due to endotoxins and their effects on the vasculature of the mammary gland. Infection is often limited to one quarter and inflammation may be serous with much oedema or haemorrhage.

Question 21

Histology of coliform mastitis

Answer 21

Microscopically, inflammation is centred on the ducts with the epithelium replaced by fibrinocellular exudate.

Acini are filled with serous fluid but few cells. Septae are oedematous since lymphatics contain plugs of fibrin. There may be haemorrhage into the stroma and acini. If inflammation persists for more than 2 days then extensive necrosis occurs.

Question 22

Causative agent of summer mastitis

Answer 22

Trueperella (Arcanobacterium) pyogenes

Question 23

Signalment of summer mastitis

Answer 23

It usually affects non lactating and immature glands of animals at pasture (dry cows and heifers).

Often a mixture of organisms is isolated along with T. pyogenes.

Not limited to the summer months.

Question 24

Clinical disease of summer mastitis

Answer 24

Infection via the teat canal is probably due to contamination by flies.

The condition can be fatal.

Question 25

Pathology of summer mastitis

Answer 25

A necrotizing suppurative galactophoritic infection of the teat canal with minimal acinar involvement – this produces large volumes of foul-smelling pus.

Abscesses occur where secretion is stagnant in the ducts. These may fistulate.

Granulation tissue may form followed by extensive fibrosis.

The teat cistern may be narrowed and the teat canal stenosed.

If not fatal, the ongoing pathology may lead to fibrosis and loss of whole quarter.

Question 26

Clinical signs of mycoplasmal mastitis

Answer 26

Sudden onset of agalactiae

The mammary gland (udder/quarter) is swollen, firm and painless.

The infection/disease spreads rapidly in the herd and animals in full lactation may be affected simultaneously in all four quarters.

Milk looks normal on first being drawn but rapidly forms a floccular deposit and clear supernatant on standing.

Question 27

Pathology of summer mastitis

Answer 27

Distinguishing features are abundant exudation of granulocytes in the early stages and hyperplasia of alveolar and ductal epithelium in later stages.

There may be lymphoid nodule formation in the interstitium and progressive septal fibrosis and acinar atrophy.

Hyperplasia and metaplasia also occur in the duct system.

Question 28

What are the different forms of tuberculous mastitis?

Answer 28

Disseminated miliary tuberculosis

Chronic organ tuberculosis

Caseous tuberculous mastitis

Question 29

How is tuberculous mastitis spread?

Answer 29

Blood borne and then spreads along ducts.

Question 30

Disseminated miliary tuberculosis

Answer 30

This is characterised by nodules up to 1cm diameter that tend to occur in groups.

They can be calcified or caseous.

There is a typical tubercle (granuloma) structure with heavy surrounding fibrosis.

Question 31

Chronic organ tuberculosis

Answer 31

This is the most common form.

Lesions begin as foci of granulation tissue within the lobule and expand to involve whole lobule.

Histologically, this process begins in the intralobular septa and diffuse tuberculous granulation tissue overcomes and obliterates the acinar tissue.

Typical tubercles do not form.

The surface of ducts may caseate and infection and lesions then spread within the duct system.

Question 32

Caseous tuberculous mastitis

Answer 32

There is great enlargement of the affected gland(s).

Large caseous areas with hyperaemic margins develop.

Histologically there are large areas of caseous necrosis with a margin of tuberculous granulation tissue similar to that seen in chronic organ tuberculosis.

Mammary tuberculosis develops insidiously without signs of acute inflammation except in a few cases of the diffuse caseous type.

There is a progressive increase in size of the affected gland and firmness.

Milk appears normal for a long time but contains bTB (M. bovis) organisms.

Question 33

Brucellus abortus and mastitis

Answer 33

Infected animals may have no clinical signs of mastitis and no mascroscopic changes in the milk.

Live organisms are present in the milk periodically - a zoonotic potential.

Question 34

Mastitis caused by cryptococcus, mycobacterium sp, and candida

Answer 34

Associated with infusion of udder with aqueous or oily penicillin

Question 35

Mastitis caused by cryptococcus

Answer 35

The gland is firm, greyish with haemorrhagic foci and often a rather shiny cut surface.

Histologically there is much liquefactive necrosis of acinar epithelium.

Many organisms are present and a massive macrophage response develops with large foamy cells.

Granulomas and fibrosis develop.

Question 36

Mastitis caused by Mycobacterium sp.

Answer 36

They are saprophytic acid fast organisms – produce a granulomatous response often surrounding an oil droplet that may contain large numbers of organisms.

Question 37

Most common causative agents of mastitis in sheep and goats

Answer 37

Staphylococcus aureus and Mannheimia haemolytica.

Question 38

Staphylococcal mastitis in sheep

Answer 38

Occurs soon after parturition.

Mortality may be up to 25% of flock

Question 39

Pasteurella (Mannheimia) mastitis in sheep

Answer 39

Occurs near the end of lactation

Early systemic effects may be seen but then subside.

Mammary gland develops bluish discolouration and widespread necrosis.

Question 40

Mastitis caused by Maedi-visna

Answer 40

Can affect both glands

Presenting signs are poor milk yield, poor growth of lambs, and progressive atrophy and induration of glands.

Virus is present in macrophages in mammary interstitium and produces local inflammatory response.

Degeneration and loss of epithelium occurs.

Question 41

Mastitis in the cat and dog

Answer 41

Uncommon

Usually occurs in early lactation or in pseudopregnancy

Staphylococci and Streptococci are most commonly present

Associated with abscess formation

May be superimposed on mammary hyperplasia or neoplasia

Question 42

Mastitis in the sow

Answer 42

Usually due to coliforms

Usually occurs shortly after parturition

Similar to coliform mastitis in cows

Affects more than one gland

Often systemic effects and cinical synovitis

May be part of mastitis - metritis - agalactia syndrome (12-48hrs after parturition)

Affected sows show lethargy, fever, swelling of mammary glands and agalactia.