Musculoskeletal Pathogens

Question 1

What are the antimicrobial defense mechanisms of the musculoskeletal system?

Answer 1

• Predominantly circulatory immune system
• bone resistant to infection: constant remodeling

Question 2

How are MS infections initiated?

Answer 2

• Direct inoculation by trauma or iatrogenic events
• extension of infection from contiguous foci
• hematogenous spread/septicemia

Question 3

Which bone sites are predisposed to infection?

Answer 3

• Sites of traumatic injury
• areas of active growth with high vascularity
• sites w/ special vascular features - discontinuous epithelium of capillaries in vertebral end plates & metaphyses

Question 4

What are the primary bacterial agents in arthritis, discospondylitis, and myositis?

Answer 4

Question 5

What are the primary bacterial agents that cause osteomyelitis?

Answer 5

• Actinomyces
• Brucella canis (dogs)
• Staph pseudintermedius

Question 6

What is the primary bacterial agent that causes necrotizing fasciitis?

Answer 6

B-hemolytic Strep

Question 7

What is the bacterial agent responsible for polymyositis?

Answer 7

Lepto

Question 8

What two fungal agents cause MS infections in dogs?

Answer 8

• Aspergillus (diskospondylitis, myositis, osteomyelitis)
• Blastomyces dermatitis (osteomyelitis)
• Cocciodiodes immitis (osteomyelitis)

Question 9

What viral agent causes arthritis in cats?

Answer 9

Feline syncytium-forming virus

Question 10

What are the contributing factors for bacterial bone infections?

Answer 10

• Open fracture repair
• joint penetration
• systemic sepsis

Treatment and outcome vary based on source of infection, microbe, and duration of infection

Question 11

Describe the features of bacterial bone infections

Answer 11

• Usually a single pathogen involved
• Staph species most common - usually Staph pseudintermedius
• Also Strep spp. Or Gram neg aerobes
• Some anaerobes: Bacteroides, Fusobacterium, Actinomyces, Clostridium spp., Peptococcus spp. And Peptostreptococcus

Question 12

Describe the common features of anaerobic osteomyelitis

Answer 12

• Follows fractures, trauma, or bite wounds
• Have sequestra
• Putrid exudate or gas in soft tissues
• ”sterile” cultures despite signs of infection
• multiple microbes in Gram-stained specimens
• Lack of response to abx

Question 13

What are some special problems with treating bacterial bone infections?

Answer 13

• Orthopedic infections expensive and challenging to treat
• parenteral abx therapy followed by long term oral abx admin
• may need surgical intervention
• prognosis is often poor