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Infectious Agents > Dermatophilus, Nocardia, Actinomyces > Flashcards

Dermatophilus, Nocardia, Actinomyces Flashcards

1
Q

Dermatophilus congolensis

A

Infection of the epidermis

- lesions characterized by exudative dermatitis with scab formation

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2
Q

D. congolensis host range

A

Most frequently affected: cattle, sheep, goats, horses

Rarely affected: pigs, dogs, cats

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3
Q

What is the term for cattle, goat, and sheep infection?

A

Cutaneous streptothrichosis

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4
Q

What is the term for sheep infection?

A

Lumpy wool

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5
Q

Alligator infection with Dermatophilus

A

Represents a new species
- scrapes are common on free edge of ventral scales, creating a good environment for dermatophilus infection (aka free edge scale rot)

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6
Q

D. congolensis morphology

A

Gram-positive, non acid fast, facultative anaerobic actinomycete
- 2 characteristic forms: filamentous hyphae and motile zoospores

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7
Q

Filamentous hyphae

A

Characterized by branching filaments (1-5 um) that fragment by both transverse and longitudinal septation into packets of coccoid cells

  • coccoid cells mature into flagellated ovoid zoospores
  • zoospores swim out of wet skin to create new lesions
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8
Q

What factors influence development and transmission of dermatophilus?

A
  • prolonged wetting by rain
  • high humidity
  • high temperature
  • various ectoparasites that reduce or permeate the natural barriers of the integument
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9
Q

Dermatophilus can exist in a _______ form

A

Quiescent; lives in epidermis until infection is exacerbated by climatic conditions

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10
Q

Epidemics of dermatophilus usually occur during the ______

A

Rainy season

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11
Q

How does high humidity contribute to dermatophilus infection?

A

Increases number of biting insects that act as mechanical vectors (ex: flies, ticks)

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12
Q

______, _______, or ______ an infected animal into a herd can spread infection

A

Shearing, dipping, or introducing

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13
Q

What attracts zoospores to the skin?

A

Respiratory efflux of low concentrations of carbon dioxide from the skin
- zoopores then germinate to produce hyphae, which penetrate into the living epidermis and spread in all directions

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14
Q

Chronic dermatophilus infection

A

Invaded epithelium cornifies and separates in the form of a scab
- in wet scabs, moisture enhances the proliferation and release of zoospores from hyphae

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15
Q

Dermatophilosis is most prevalent in _______

A

Young animals chronically exposed to moisture, and immunosuppressed hosts

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16
Q

What environmental factor speeds healing?

A

Onset of dry weather

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17
Q

What are the primary economic consequences?

A
  • damaged hides in cattle
  • wool loss in sheep
  • lameness and loss of performance in horses (when affected around the pastern)
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18
Q

3 stages of observed lesions in cattle

A
  • hairs matted together as paint-brush lesions
  • crust or scab formation as the initial lesions coalesce
  • accumulations of cutaneous keratinized material forming wart-like lesions that are 0.5-2 cm in diameter
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19
Q

Typical lesions consist of

A

Raised, matted tufts of hair

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20
Q

Chronic, lumpy wool infection characterizaiton

A

Pyramid-shaped masses of scab material bound to wool fibers

- crusts are primarily on dorsal surfaces

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21
Q

Lesions on horses with long winter coats

A

Similar to cattle, develop with matted hair and paint-brush lesions leading to crust or scab formation with yellow-green pus present under larger scabs

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22
Q

Histopathologic examination

A

Characteristic branching hyphae with multidimensional septations, coccoid cells, zoospores in the epidermis
- organisms are abundant in active lesions, but can be sparse in chronic lesions

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23
Q

Diagnosis

A

Depends on appearance of lesions and demonstration of D. congolensis in stained smears

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24
Q

What is the most practical diagnostic test?

A

Cytologic examination of fresh crusts and/or impression smears of the underside of freshly avulsed lesions

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25
Organisms under oil immersion appear as _____
2-6 parallel rows of gram-pos cocci that look like railroad tracks
26
Dermatopholius organisms are susceptible to ____
- erythromycin - spriamycin - penicillin G - ampicillin - chloramphenicol - streptomycin - amoxicillin - tetracyclines - novobiocin
27
Chronic injections can be cured with
Single IM injection of procaine penicillin and streptomycin
28
What is the downside of streptomycin?
It persists in the body for years | - would not send this cattle to slaughter
29
Treatment in horses
Lesions should be soaked and removed | - chlorhexidine and benzoyl peroxide are recommended
30
What are methods used to break the infective cycle of Dermatophilus?
- isolating clinically affected animals - culling affected animals - controlling ectoparasites
31
Nocardiae
Gram-positive, strictly aerobic, nonmotile, pleomorphic, and nonsporeforming - may take the form of rods, cocci, or diphtheroids - sometimes produce branching filaments and aerial hyphae - reduce nitrate, produce catalase, oxidize sugars
32
Some nocardiae are partially ______
Acid-fast
33
Where are norcardiae commonly found?
Soil, decaying vegetables, compost, other environmental sources
34
How do nocardia enter the body?
Through contamination of wounds or by inhalation
35
What contributes to the virulence of norcardiae?
Cell wall mycolic acids - trehalose 6,6'-dimycolate (allows for survival of phagocytosis) - membrane bound catalase and superoxide dismutase probably mediate resistance to killing by neutrophils
36
N. otitidiscaviarum secretes a toxin that
Kills all other bacteria and fungi in the area
37
Nocardiosis resistance is primarily ____
Cell mediated
38
What is the first clinical sign of N. asteroides?
Appearance of an indurated nodule or pustule, which ruptures and suppurates
39
Infection of bovine mammary gland causes ____
Mammary tissue to become enlarged and firm, with draining tracts - milk contains a viscid exudate, with discrete blood clots and microcolonies of N. asteroides - could disseminate from mammary gland to other organs to cause suppurative granulomatous lesions
40
Canine thoracic nocardiosis
Supperative pleuritis or peritonitis | - abscessation of heart, liver, kidneys, and brain
41
Nocardial abortion may occur in ______
Horses and pigs
42
N. brasiliensis
Isolated from suppurative wounds in various animal species
43
N. otitidiscaviarum
Occurrence in guinea pig ear infections | - more important as a cause of bovine mastitis and pneumonia
44
N. farcinica
Associated with bovine farcy
45
N. salmonicida and N. seriolae
Cause granulomatous lesions in salmonid fish
46
Crossiella (C equi)
Nocardioform actinomycetes from placentitis and abortion in horses in some areas of the USA
47
What are 3 forms of norcardia disease?
- draining fistulas/tracts - draining pyocavities - old, organized abcesses
48
Presumptive diagnosis of norcardia
Based on pathology and presence of gram-positive, acid fast, branching beaded filaments in smears of affected tissues
49
Colonies of norcardia adhere to
Surface of blood or chocolate agar, with the leading edge embedded in the agar
50
Are beta-lactam antibiotics effective for nocaridal infection?
No, due to antimicrobial resistance
51
Novobiocin combined with nitrofurazone
Infused into udder for 3-5 days for treatment of bovine nocardial mastitis
52
What are nonmastitic forms of nocardia treated with?
- sulfamethoxazole-trimethoprim (best drug) - sulfonamides - novobiocin - ampicillin - tetracyclines
53
Nocardia branches are _______, actinomyces are _____
Beaded; not
54
Actinomyces spp.
Are normal flora of oral and nasopharyngeal mucous membranes - gram-pos, non acid fast rods - filamentous or branching - brances are <1 um in diameter
55
A. bovis
The etiologic agent of lumpy jaw in cattle - isolated from nodular abscesses in lungs of cattle and from infrequent infections in sheep, pigs, dogs, and other mammals - causes chronic fistulous withers and chronic poll evil in horses
56
Lumpy jaw
Chronic, progressive, indurated, granulomatous, suppurative abscess that most frequently involves the mandible, maxillae, or other body tissues in the head
57
Disease occurs when A. bovis is introduced to ____
Underlying soft tissue, via penetrating wounds of the oral mucosa from wire or coarse hay or sticks
58
Involvement of adjacent bone frequently results in
Facial distortion, loose teeth, dyspnea from swelling into the nasal cavity
59
Diagnosis of actinomyces
Demonstration of gram-pos rods in yellowish "sulfur granules" form aspirated purulent material
60
Is treatment successful in chronic cases?
No due to poor penetration of antibacterial agents into the site of infection (esp bone)
61
In acute cases ______ may be effective
Penicillin
62
A. hordeovulneris
Causes localized abscesses and systemic infections such as pleuritis, peritonitis, visceral abscesses, and septic arthritis in dogs
63
What is a common predisposing factor for A. hordeovulneris?
Presence of tissue-migrating foxtail grass particles
64
A. israelii
Associated with chronic granulomatous infections in humans | - isolated rarely from pyogranulomatous lesions in pigs and cattle
65
A. naeslundii
Isolated from suppurative infections in several animal species - most common being aborted porcine fetuses
66
A. (corynebacterium) pyogenes
Reclassified as Aracanobacterium pyogenes - changed again to Trueparella based on genomic findings - wide range of complete hemolysis - suppurative mastitis, suppurative pneumonia, septicemia, vegetative endocarditis, endometriosis, septic arthritis, wound infections, seminal vesiculitis, summer mastitis
67
A. pyognes causes ___ in feedlot cattle
Liver abscesses
68
____ is the number 1 bacterium in the rumen and reticulum of ruminants and the intestines of pigs
A. pyogenes | - is not present in dogs, cats, humans
69
A. suis
Pyogranulomatous porcine mastitis - characterized by viscid, yellow pus surrounded by a wide zone of dense connective tissue - yellow sulfur granules scattered throughout the pus - chronic deep-seated abscesses may fistulate
70
Sows will develop
Pyogranulomatous infections in lungs, spleen, kidneys, other organs
71
A. viscosus
Chronic pneumonia, pyothorax, localized subcutaneous abscesses in dogs - thoracic lesions are pyogranulomas - cutaneous lesions are granulomatous abscesses, often with fistulous tracts

Infectious Agents (44 decks)

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