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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
Q

Organisms under oil immersion appear as _____

A

2-6 parallel rows of gram-pos cocci that look like railroad tracks

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26
Q

Dermatopholius organisms are susceptible to ____

A
  • erythromycin
  • spriamycin
  • penicillin G
  • ampicillin
  • chloramphenicol
  • streptomycin
  • amoxicillin
  • tetracyclines
  • novobiocin
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27
Q

Chronic injections can be cured with

A

Single IM injection of procaine penicillin and streptomycin

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28
Q

What is the downside of streptomycin?

A

It persists in the body for years

- would not send this cattle to slaughter

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29
Q

Treatment in horses

A

Lesions should be soaked and removed

- chlorhexidine and benzoyl peroxide are recommended

30
Q

What are methods used to break the infective cycle of Dermatophilus?

A
  • isolating clinically affected animals
  • culling affected animals
  • controlling ectoparasites
31
Q

Nocardiae

A

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
Q

Some nocardiae are partially ______

A

Acid-fast

33
Q

Where are norcardiae commonly found?

A

Soil, decaying vegetables, compost, other environmental sources

34
Q

How do nocardia enter the body?

A

Through contamination of wounds or by inhalation

35
Q

What contributes to the virulence of norcardiae?

A

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
Q

N. otitidiscaviarum secretes a toxin that

A

Kills all other bacteria and fungi in the area

37
Q

Nocardiosis resistance is primarily ____

A

Cell mediated

38
Q

What is the first clinical sign of N. asteroides?

A

Appearance of an indurated nodule or pustule, which ruptures and suppurates

39
Q

Infection of bovine mammary gland causes ____

A

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
Q

Canine thoracic nocardiosis

A

Supperative pleuritis or peritonitis

- abscessation of heart, liver, kidneys, and brain

41
Q

Nocardial abortion may occur in ______

A

Horses and pigs

42
Q

N. brasiliensis

A

Isolated from suppurative wounds in various animal species

43
Q

N. otitidiscaviarum

A

Occurrence in guinea pig ear infections

- more important as a cause of bovine mastitis and pneumonia

44
Q

N. farcinica

A

Associated with bovine farcy

45
Q

N. salmonicida and N. seriolae

A

Cause granulomatous lesions in salmonid fish

46
Q

Crossiella (C equi)

A

Nocardioform actinomycetes from placentitis and abortion in horses in some areas of the USA

47
Q

What are 3 forms of norcardia disease?

A
  • draining fistulas/tracts
  • draining pyocavities
  • old, organized abcesses
48
Q

Presumptive diagnosis of norcardia

A

Based on pathology and presence of gram-positive, acid fast, branching beaded filaments in smears of affected tissues

49
Q

Colonies of norcardia adhere to

A

Surface of blood or chocolate agar, with the leading edge embedded in the agar

50
Q

Are beta-lactam antibiotics effective for nocaridal infection?

A

No, due to antimicrobial resistance

51
Q

Novobiocin combined with nitrofurazone

A

Infused into udder for 3-5 days for treatment of bovine nocardial mastitis

52
Q

What are nonmastitic forms of nocardia treated with?

A
  • sulfamethoxazole-trimethoprim (best drug)
  • sulfonamides
  • novobiocin
  • ampicillin
  • tetracyclines
53
Q

Nocardia branches are _______, actinomyces are _____

A

Beaded; not

54
Q

Actinomyces spp.

A

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
Q

A. bovis

A

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
Q

Lumpy jaw

A

Chronic, progressive, indurated, granulomatous, suppurative abscess that most frequently involves the mandible, maxillae, or other body tissues in the head

57
Q

Disease occurs when A. bovis is introduced to ____

A

Underlying soft tissue, via penetrating wounds of the oral mucosa from wire or coarse hay or sticks

58
Q

Involvement of adjacent bone frequently results in

A

Facial distortion, loose teeth, dyspnea from swelling into the nasal cavity

59
Q

Diagnosis of actinomyces

A

Demonstration of gram-pos rods in yellowish “sulfur granules” form aspirated purulent material

60
Q

Is treatment successful in chronic cases?

A

No due to poor penetration of antibacterial agents into the site of infection (esp bone)

61
Q

In acute cases ______ may be effective

A

Penicillin

62
Q

A. hordeovulneris

A

Causes localized abscesses and systemic infections such as pleuritis, peritonitis, visceral abscesses, and septic arthritis in dogs

63
Q

What is a common predisposing factor for A. hordeovulneris?

A

Presence of tissue-migrating foxtail grass particles

64
Q

A. israelii

A

Associated with chronic granulomatous infections in humans

- isolated rarely from pyogranulomatous lesions in pigs and cattle

65
Q

A. naeslundii

A

Isolated from suppurative infections in several animal species
- most common being aborted porcine fetuses

66
Q

A. (corynebacterium) pyogenes

A

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
Q

A. pyognes causes ___ in feedlot cattle

A

Liver abscesses

68
Q

____ is the number 1 bacterium in the rumen and reticulum of ruminants and the intestines of pigs

A

A. pyogenes

- is not present in dogs, cats, humans

69
Q

A. suis

A

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
Q

Sows will develop

A

Pyogranulomatous infections in lungs, spleen, kidneys, other organs

71
Q

A. viscosus

A

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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