Mastitis in Animals (Staphylococcus and Streptococcus spp.)
Introduction
Mastitis is an inflammation of the mammary gland, usually caused by bacterial infection, and is one of the most economically important diseases in dairy animals worldwide. Among the numerous causative agents, Staphylococcus and Streptococcus species are the most significant. Mastitis leads to reduced milk production, altered milk quality, increased treatment costs, and culling losses. It is a major concern in dairy cattle, sheep, and goats.
Etiology
Major Causative Agents
- Staphylococcus aureus (contagious, often chronic)
- Streptococcus agalactiae (contagious mastitis)
- Streptococcus dysgalactiae (environmental and contagious)
- Streptococcus uberis (primarily environmental)
Characteristics
- Gram-positive bacteria
- Adapted to survive in mammary tissue and/or environment
- Produce toxins and enzymes contributing to tissue damage
Classification
- Contagious mastitis: spread during milking (e.g., S. aureus, S. agalactiae)
- Environmental mastitis: acquired from surroundings (e.g., S. uberis)
Epidemiology
Species Affected
- Dairy cattle (most significant)
- Sheep and goats
Transmission
- During milking via contaminated hands, equipment, or towels
- From infected quarters to healthy ones
- Environmental contamination (bedding, manure, water)
Risk Factors
- Poor milking hygiene
- Faulty milking machines
- Wet and dirty bedding
- Teat injuries
- High milk production
Pathogenesis
Entry of Pathogens
Bacteria enter the mammary gland through the teat canal, especially when the teat sphincter is relaxed after milking.
Colonization
- Staphylococcus aureus adheres to mammary epithelium and forms microabscesses
- Streptococcus spp. multiply in milk and ducts
Inflammatory Response
- Recruitment of leukocytes (somatic cells)
- Release of inflammatory mediators
- Damage to milk-producing tissue
Outcomes
- Acute inflammation (clinical mastitis)
- Chronic infection (subclinical mastitis)
- Fibrosis and loss of gland function
Clinical Forms
Clinical Mastitis
- Visible changes in milk (clots, flakes, watery appearance)
- Swelling, heat, pain in udder
- Reduced milk yield
- Systemic signs in severe cases (fever, depression)
Subclinical Mastitis
- No visible signs
- Increased somatic cell count (SCC)
- Reduced milk quality and yield
Chronic Mastitis
- Persistent infection
- Intermittent flare-ups
- Fibrosis and permanent damage
Summary for Practitioners
Subclinical mastitis is far more common than clinical cases and often goes unnoticed. Regular monitoring of somatic cell counts is essential for early detection and herd health management.
Postmortem Findings
Gross Lesions
- Swollen, firm mammary gland
- Abscess formation (especially with S. aureus)
- Fibrosis in chronic cases
Microscopic Lesions
- Inflammation of mammary tissue
- Leukocyte infiltration
- Destruction of alveoli
Diagnosis
Clinical Examination
- Inspection and palpation of udder
- Observation of milk
Screening Tests
- California Mastitis Test (CMT)
- Somatic cell count (SCC)
Laboratory Diagnosis
- Bacterial culture of milk samples
- PCR for pathogen identification
Differential Diagnosis
- Mastitis caused by coliform bacteria (e.g., E. coli)
- Mycoplasma mastitis
- Traumatic udder injury
Summary for Practitioners
Accurate identification of the causative organism is essential for effective treatment and control strategies. Routine milk testing is recommended in dairy herds.
Treatment
Antibiotic Therapy
- Intramammary antibiotics (common approach)
- Systemic antibiotics in severe cases
- Choice based on culture and sensitivity
Supportive Therapy
- Frequent milking to remove infected milk
- Anti-inflammatory drugs
- Fluid therapy in severe cases
Dry Cow Therapy
- Long-acting antibiotics administered at drying-off
- Effective in eliminating subclinical infections
Summary for Practitioners
Treatment success varies by pathogen. Staphylococcus aureus infections are often difficult to cure due to abscess formation and intracellular survival.
Control and Prevention
Milking Hygiene
- Pre- and post-milking teat disinfection
- Use of clean towels for each animal
Milking Machine Management
- Regular maintenance and sanitation
- Proper vacuum levels
Environmental Management
- Clean, dry bedding
- Proper manure management
Herd Health Programs
- Regular screening for subclinical mastitis
- Culling chronically infected animals
Vaccination
- Available in some regions (limited effectiveness)
Summary for Practitioners
A comprehensive mastitis control program combining hygiene, monitoring, and management practices is essential for reducing disease incidence and improving productivity.
Zoonotic Importance
Some mastitis pathogens may pose a risk to humans through contaminated milk. Proper milk handling and pasteurization are critical for food safety.
Economic Importance
Mastitis is one of the most costly diseases in dairy production due to decreased milk yield, discarded milk, treatment expenses, and culling of affected animals.
Summary
Mastitis is a multifactorial disease primarily caused by Staphylococcus and Streptococcus species. It significantly impacts animal health and dairy production. Effective control requires a combination of good hygiene, regular monitoring, and appropriate treatment strategies.
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