Exam 3 Flashcards
General Features of Mycobacterium
o aerobic, “Gram-positive rods” o Facultative intracellular specific to macrophages o non-spore forming, non-motile o mycolic acids & lipids in cells wall o must be acid-fast stained o grow very slowly o Complex egg-based media is required for growth o Chronic/progressive dz
Major Pathogenic Mycobacteria
M. bovis:
• Primarily infects cattle
• Can affect others
M. tuberculosis
• Primarily Human, but dogs, rodents, swine can get infected
M. avium (paratuberculosis )
• Cattle, sheep and goats
Non-tuberculous Mycobacterium (NTMs)
• Several species
Bovine Tuberculosis (M bovis) source of infection & survival in environment
- Infected animals are source of infection.
- Bacteria are in exhaled respiratory droplets, sputum, milk, feces, urine, vaginal discharge.
- Survives in environment for 4 - 28 days
- May survive longer in presence of organic material.
Bovine Tuberculosis (M bovis) Entry, Multiplication, Spread, Damage
- Bacteria inhaled or ingested ->
- taken up by macrophages.
- multiply intracellularly and travel inside of macrophages to regional lymph nodes ->
- May enter lymphatics and blood and disseminate widely ->
- Two possible outcomes:
- Latency
- tuberculosis & systemic granulomas (Pathognomonic Lesion)
Bovine Tuberculosis (M bovis) Clinical Signs, Diagnosis, Treatment
Clinical Signs
• Respiratory signs:
moist cough, dyspnea, weight loss
• Rarely mastitis
• Enlarged bronchial, mediastinal and mesenteric nodes
Diagnosis
• Caudal fold test (cross-reactivity common)
• tubercles on necropsy
• culture (time consuming)
• PCR (definitive & fast but difficult if no clinical signs)
Treatment & Control
• No treatment = slaughter
• Test new animals
• No Vx
Bovine Paratuburculosis or Johne’s (M. avium) Encounter, Entry, Multiplication, Spread
Encounter
• Environment contaminated w/ fecal material from infected animals
Entry, Multiplication, Spread
• Feces Ingested shortly after birth ->
• Invades macrophages in Peyer’s patches ->
• Multiply & kill macrophages ->
• Spread to adjacent cells ->
• Inflammatory response ->
• Thickened intestine & loss of absorption
Bovine Paratuburculosis or Johne’s (M. avium) Clinical Signs, Diagnosis, Treatment
Clinical Signs
• Perinatal period
• reduced milk production, diarrhea, weight loss, normal appetite.
• shedders are often not clinically ill
Diagnosis • Direct microscopy • DNA based PCR test • Johnin test • Culture of organisms from manure or ileal node (good, takes long time, need multiple samples)
Treatment/Control
• No treatment = slaughter
• Do not accept new animals
Non-Tuberculous Mycobacterium (NTM) Clinical Signs & Diagnosis
Clinical Signs
• Granulomatous inflammation in dogs & cats
• Localized or systemic
• Skin infections, pneumonia, or GI infection
Diagnosis of NTMs
Histology
• Acid fast stain
• Pyogranulomatous inflammation
PCR
• On tissue sections or culture
Culture & Sensitivity
• Use for treatment w/ antibiotics
Basics of Mycoplasma
o Facultative anaerobes o Smallest self-replicating bacteria o obligate parasites o no cell walls o need giemsa stain o resistant to penicillin, cephalosporin o Extremely fragile o “fried egg” colonies o “fastidious bacteria” (must use special media w/ penicillin to ward off gram (+) & thallium acetate to ward off gram (+) )
Encounter/Entry Mycoplasma
Encounter
o introduced by clinically healthy carrier animals
o Prefer upper respiratory, intestinal, genital tract, joints, conjunctiva and mammary glands
Entry
• direct droplet of oral, ocular, or genital secretions
• contaminated equipment or blood transfusion)
• Some transmitted via tick bite (mechanical)
4 Virulence Factors of Mycoplasma
Adhesins
• used for binding of bacteria to
the host cells
Capsules
• For biofilm = impede host defense & persist in environment
Hydrogen peroxide
• Affects ciliary movement in trachea and induces hemolysis
Biofilm
• resistance for dessication, heat and complement mediated lysis
Chronic Respiratory Disease caused by M gallisepticum Basics, Encounter, & Entry
o Affects chickens, turkeys, game birds
o Localized mycoplasma infection
o exogenous
Encounter/Entry
• Infection via respiratory route or thru infected eggs
• Stress = asymptomatic carriers become sick & shed in respiratory aerosols
Chronic Respiratory Disease caused by M gallisepticum Multiplication/spread, damage, symptoms
Multiplication / Spread
• attaches ciliated epithelium of trachea & multiplies
Damage
• Damages cilia
• Sinusitis, tracheitis, airsacculitis
Symptoms
• coughing, sneezing, nasal discharge, dyspnea, reduced growth, decreased egg production
• high morbidity, low mortality
Chronic Respiratory Disease caused by M gallisepticum Diagnosis, Treatment, Control
Diagnosis • Culture • FA • PCR from exudate & tissue • ELISA on serum
Treatment
• Tylosin, tiamulin, chlortetracycline, lincomycin
Control
• Depopulation & disinfection
Basics of Invasive Mycoplasma Infections; two outcomes
o penetrate epithelial barriers and enter the blood stream
infection / acute septicemia
o fever and sudden death
Brief period of inapparant mycoplasmemia
o localization in serosal cavities and joints ->
o chronic inflammation
Feline hemotrophic mycoplasmosis Basics & mycoplasmas involved
- cause of hemolytic anemia in cats
- can be endogenous or exogenous
Mycoplasmas involved
• M hemofilis (clinical symptoms)
• M hemominutum
• M turicensis
Feline hemotrophic mycoplasmosis Predisposing Factors & Encounter for Exogenous infection
Predisposing factors:
o Surgical stress, FIV/FelV, abscess, corticosteroids
Encounter for Exogenous • Arthropod vectors? • Biting and fighting • queens to new borne • blood transfusion
Feline hemotrophic mycoplasmosis 4 Phases
Pre-parasitemic phase
o Lasts 1-3wk post infection
o Bacteria not detectable
o Mild reduction HCT
Acute Phase
o ~30 days
o cyclic high number of bacteria in blood
o Parasitized RBCs sequestered in spleen w/ release of non-parasitized RBCs
o rapid decrease in HCT followed by rapid increase
o W/o treatment, 1/3 die of anemia
Recovery Phase
o time from last bacteremia until HCT has stabilized
o sufficient immune response or treated w/ antibiotics & recover
o regenerative bone marrow response
Chronic/Carrier Phase
o recovery from acute infections = clinically normal & chronically infected
o Low numbers of organisms may/may not be detectable
Feline hemotrophic mycoplasmosis Damage & Clinical Signs
Damage • Regenerative anemia w/ polychromasia & reticulosytosis • Precipitous drop in HCT Clinical Signs Acute o Fever, o marked mental depression, o tachypnea, o weakness, o anorexia, o pale mucous membranes, o dehydration
Chronic
o Mild anemia
Feline hemotrophic mycoplasmosis Diagnosis, Treatment
Diagnosis • No culture • Reduced HCT, reticulocytosis, icteric plasma • Blood smear may show mycoplasma on RBC • PCR highly sensitive
Treatment
• Tetracycline / doxycycline (gold standard)
• Enrofloxacin (alternative)
• Antibiotic does not clear parasite
Defense Mechanisms of Mammary Glands
Physical Barrier • Sphincter muscle tightens teat canal • Keratin plug • Keratinized squamous epithelium (prevents adherence) • Flushing milk
Innate & Adaptive Immune Response
• Macrophages (normal 66-88%)
• Neutrophils (normal should not have many)
• Abs neutralize bacteria/toxins
• B & T cells enhance immune response & kill infected cells
Soluble mediators
• Lactoferrin: iron binding protein prevents bacterial iron usage
• Lysozyme: cleaves peptidoglycans in gram (+) cell wall
Risk Factors for Mastitis
Host
• Age, stage of lactation, teat lesions, genetics
Environment
• Poor milking hygiene, milking technique, contaminated env
Microbial
• Contagious Vs environmental agent, virulence factors, habitat
Entry of Pathogens in Mastitis
o Systemic infection with localization in mammary gland
o Lymphatic spread
o Direct penetration
Breakdown of teat sphincter barrier (most COMMON)
• Teat sphincter open 2hrs post milking
• Bacteria ascend during this period
Pathogenesis of Mastitis
o If not eliminated by immune response -> multiply in mammary ->
Produce virulence factors • Adhesins: help adhere to mammary epithelial cells • Capsule: Anti-phagocytic • Exotoxins: produced by Gram (+) & (–) • Endotoxin: Released by Gram (-)
Induce leukocytes and epithelial cells to release chemo-attractants, including cytokines ->
Infiltration of polymorphonuclear neutrophils (PMNs) to the site of infection
• engulf/destroy bacteria
• destroy few epithelial cells = reduced milk production & release of enzymes
PMNs destroyed by macrophages ->
Dead epithelial cells & leukocytes secreted into milk = high milk somatic cell counts (SCCs) ->
Bacteria may spread into deeper mammary ductal system (eg., Staphylococcus aureus) or may float in milk secretion (eg., E. coli).
• Systemic signs from system infection OR endotoxin
Damage in Mastitis
o No persistent damage w/ proper treatment
Persistent infection • Damage to mammary gland alveoli • Breach of blood-milk barrier • Extensive damage can result in leakage of blood in milk • swelling w/in mammary epithelium
Chronic Dz due to uncleared infection
• Abscessation and gangrenous reaction
• Atrophy of mammary alveoli
• Fibrosis of mammary tissue leading to further damage
Clinical Signs & Diagnosis of Mastitis
Clinical Signs
o Clinical
• Inflammation (SHARP)
• Abnormal milk (flecks, clots, off color)
o Subclinical
• No visible signs
• (+) SSC, CMT, & sterile milk culture
Diagnosis
o Direct Tests
• Multiple samples of Sterilely collected milk & gram’s stain or bacterial culture
• Biopsy (uncommon)
o Indirect Tests
• Somatic cell count (milk tank)
• California mastitis test (MST) – increased DNA = gel
• Electrical conductivity of milk to look for Na & Cl
Contagious Pathogens in Mastitis
o Obligate parasites o Obligate pathogens o Subclinical mastitis more common o Mycoplasma bovis o Staph aureus o Strep agalactiae
Clinical significance of mycotic infections & fungal structure
Clinical Significance
o mimic other types of diseases
o frequently associated with local debilitation or immune deficiency
Fungal Structure
o Eukaryotes (antibiotics don’t work)
o cells have ergosterol and zymosterol
(target for antifungal)
o cell walls high in polysaccharide (used for diagnosis w/ histochemical stain)
o anti-phagocytic capsule
Growth/Repro of Fungus
Molds
• Multicellular
• Hyphal elongation & division
• Mycelium: tangled hyphae (cottony) seen on agar for diagnosis
Yeasts
• Unicellular
• Reproduce by budding & form moist colonies
Dimorphic • Yeast in tissue • Mold in environment • Transition mediated by temp change • Exception: Candida albicans forms pseudo hyphae in tissue but yeast in culture
Important Fungi not Dimorphic
• Aspergillus fumigatus = mold in environment and tissue
• Cryptococcus neoformans is always yeast.
Types of Fungal Dz’s
cutaneous mycoses (ringworm)
subcutaneous mycoses (sporotrichosis, Rhinosporidium)
systemic mycoses
• opportunists (Candida albicans)
• primary pathogens (Blastomyces dermatitidis, Histoplasma capsulatum)
Encounter for Fungal Dz
o Most free living in environment o Some specific in animals • H. capsulatum : bat or chicken feces • Cryptococcus neoformans: pigeon feces • Microsporum canis: obligate paraiste • Candida albicans: skin & mucous membranes o inhalation or traumatic implantation from an exogenous source o usually not contagious o some have carriers
What Allows Entry of Fungal Dz
o Innate resistance from skin barrier (low pH, fatty acids, normal flora)
o Infection usually self-limiting
o Weakly virulent
Requires diminished host resistance • Loss of cutaneous barrier • Loss of normal flora • Local Immunosuppression • Decreased systemic resistance (malnuitrition or immunosuppression)
Multiplication/Spread & Damage for Fungal Dz
Multiplication/Spread o Most are aerobes o Don’t multiply well in body temp o Growth limited due to need for Fe++ o First line of defense is phagocytosis o 2nd line defense = T lymphocytes
Damage
o No toxins
o destruction of tissue by fungal multiplication & host inflammatory response
o granuloma formation is hallmark
Diagnosis of Fungal Dz; why pursue? presumptive & difinitive
Why pursue etiologic diagnosis?
• differentiate from other diseases characterized by loss of functional tissue by cellular infiltration
• differentiate between opportunistic and pathogenic fungi
• selection of appropriate drugs
presumptive diagnosis
• identification of hyphae or yeast on smear & cytology or histo & biopsy
• serology or skin tests
definitive diagnosis
• Saboraud’s Dextrose Agar (with antibiotics)
• Blood Agar
• up to 3-4 weeks for diagnosis
Antifungal Therapy basics; therapeutic index, dosing strategy
o Some may not need treatment
o opportunistic infections resolve when underlying problem corrected
o anti-fungal drugs toxic to host
o limited anti-fungal drugs
o fungi can develop resistance but sensitivity testing not done
therapeutic index:
• ratio between antimicrobial efficacy and toxic effects to host animal
dosing strategy • target organ • lowest effective dose • schedule • combination therapy
Polyene Anti-fungal Drug; compounds, mechanism, uses, notes
Compounds
• amphotericin B, nystatin
Mechanism
• Disturbs cell membrane (higher affinity for ergosterol than cholesterol)
Uses
• systemically (IV) for systemic infections
• topically for superficial infections (candidiasis)
Notes • Not water soluble • must be given IV for systemic infections • poorly penetrate CSF • nephrotoxic
Allylamines Anti-fungal Drug; compounds, mechanism, uses,
Compounds
• Terbinafine
Mechanism
• inhibits ergosterol biosynthesis
Uses
• Broad spectrum
• oral or topical for superficial & sub-cutaneous infections
• less toxic than amphotericin B
Azoles Anti-fungal Drug; compounds, mechanism, uses,
Compounds
• clotrimazole, miconazole, itraconazole, fluconazole, ketoconazole
Mechanism
• inhibits ergosterol biosynthesis
Uses • Broad spectrum • PO, IV for systemic infections • topically for superficial infections (ringworm), • less toxic than amphotericin B
Pyrimidine Anti-fungal Drug; compounds, mechanism, uses, notes
Compounds
• 5-fluorocytosine (5FC)
Mechanisms
• inhibits DNA and RNA synthesis
Uses
• PO for systemic infections
Notes
• Narrow spectrum
• resistance develops rapidly (use combo w/ other)
• enters CSF in high concentration
Grisines Anti-fungal Drug; compounds, mechanism, uses, notes
Compounds
• griseofulvin
Mechanisms
• inhibits microtubule assembly
Uses
• PO for superficial infection
Notes
• Not effective topically
• Teratogenic especially in cats
Cutaneous Mycoses; common name. 3 main sources
o Ringworm
Geophilic:
• dermatophytes that live (grow & replicate) in soil.
• prefer warm and humid climate
• poorly transmitted in animals
Zoophilic:
• dermatophytes that are obligate parasites
• spread rapidly among animals
• zoonotic
Anthropophilic:
• dermatophytes that are obligate animal parasites but predominately found on humans
• Ex: Athlete’s foot
Ringworm Host-parasite relationships in domestic animals
Microsporum canis
o natural host is the cat (is zoophilic)
o 15% human ringworm = zoonotic
o children very susceptible
Microsporum gypseum o reservoir is soil (is geophilic) o 1-10% cat infections o 25% dog infections o most common ringworm in horses in southern U.S. o poorly zoonotic
Virulence Factors Mycoplasma Bovis (Mastetitis)
Adhesins:
• adhere to epithelium, hematogenous spread, proliferation in lact ducts
Phospholipase:
• Breaks connective tissue = purulent interstitial inflammation & abscess
Virulence Factors Staph Aureus (Mastetitis)
Hemolysins:
• lyse erythrocytes -> paralysis & necrosis of blood vessels -> gangrene
Toxic Shock Syndrome Protein
• Cytokine release & systemic shock
Capsule
• Antiphagocytic
Adhesins
• help in adherence
• Protein A aids evasion from immune response
Virulence Factors Staph agalactiae (Mastetitis)
Hemolysins:
• lyse erythrocytes
E. coli role in Mastatitis
- Most common environmental mastitis pathogen
- usually cause clinical mastitis of short duration
- rarely have systemic signs.
- does NOT adhere to the mammary epithelium
- Does NOT commonly spread into the mammary parenchyma.
- Spontaneous resolution common
release of ENDOTOXIN
• edema and necrosis of mammary tissue
• endotoxemia
• Bacteremia may in up to ~50% of cases
Why do Microbiological Diagnosis of Mastitis?
o Required for clinical and subclinical mastitis
o differentiation between contagious vs environmental
o Important determinant of treatment and control practices
Strategy for Microbiological Diagnosis of Mastitis
o gram stain -> o (-) rods -> MacConkey o lactose (-) = salmonella, proteus, pseudomonas o lactose (+) -> idole o indole (+) = E coli o indole (-) = klebsiella
o gram stain ->
o (+) cocci -> catalase test
o catalase (-) = strep
o catalase (+) = staph
o CAMP test for strep species
o coagulase test for staph species
3 Treatments for Mastitis
Intra-mammary
• Infusion of antibiotics into udder
• Streptococcus - Penicillin
• Staphylococcus - Penicillin, cephalosporin classes
• Antimicrobials may fail to reach location of infection due to abscessation or fibrosis
• Antimicrobial resistance due to β-lactamase production or altered penicillin binding
proteins
Systemic therapy • Needed if systemic signs • Staphylococcus – exotoxins • E. coli - endotoxin • Antibiotics IV or IM • Supportive therapy • Remove toxins by Frequent milking
Dry Cow Therapy
• stop milking
• contagious mastitis
• Larger dose, longer acting product
Prevention of Mastitis
o hygiene to prevent cow-cow transmission at milking
o Teat dipping pre- and post- milking (Iodines, Chlorhexidine)
o Identification of chronic/subclinical cases
o Antibiotic therapy
o Detection and segregation of infected animals
o Culling chronically infected cows
o Quarantine/testing of new herd additions
o Adequate nutrition
Vaccines
• No Vx for S. agalactiae
• Mycoplasma bovis: Vx efficacy questionable.
• Lysigin, a S. aureus bacterin Vx helpful in prevention of chronic infection but not in prevention of new infections
Important Pathogens of Mastitis in Sheep & Goats
o Staphylococcus aureus o Coagulase-negative Staphylococcus sp. o Streptococcus agalactiae o Pasturella multocida o Mannheimia haemolytica
Entry & Multiplication/Spread of Cutaneous Mycoses
Entry
• normal skin has fungicidal fatty acids
• requires debilitated skin barrier
• exacerbated by high humidity and low sunlight
• primarily outbreaks in young animals in close contact
Multiplication & Spread
• Arthroconidia enter abraded skin
->
• arthrospores germinate to hyphae in the stratum corneum
(adjacent to hair follicles) ->
• limited to epidermis by temperature range (25-32C) and dependence on keratin
Damage, Diagnosis, Treatment of Cutaneous Mycoses
Damage
• inflammation due to contact dermatitis
• chronic inflammation results in loss of hair and hyperkeratosis
• most infections self-limiting due to cell-mediated immune response
Diagnosis
• puritic or non-pruritic, non-healing focal lesions
• vary from red, moist lesions (acute) to dry, flaky lesions (chronic)
• detection with UV light (M. canis)
• KOH digestion and examination
• skin biopsy and histo
• in house cultivation
to diagnose ringworm
• lab cultivation to determine species
Treatment
• Self-limiting in large animals (increase sun)
• Clipping & topical iodide or miconazole
• Oral ketoconazole, terbinafine(choice) or grisans (toxic)
Pythiosis Basics
- Pythium insidiosum
- Subcutaneous mycoses
- Not considered true fungi
- Affects horses in Gulf Coast states
- Also affects dogs and rarely cats, cattle and humans
- Wet environments essential for reproduction of fungi
- Enters via skin wounds (common) or by ingestion
- Chronic, non-healing, severe granulation tissue lesions
- rapid tissue destruction due to allergic response to presence of fungal hyphal element
Pythiosis Diagnosis
Isolation
o definitive diagnosis
o grow on agar or blood agar
Serology ELISA
o common in labs
Microscopy
o typical, wide, sparsely septate,
branching filamentous hyphal elements
Histology
o Tissue section stained with PAS
PCR
o DNA extracted from tissue samples; rapid & specific
Pyhtiosis Treatment
Surgical removal
Systemic antifungals
o Amphotericin B and azoles
Therapeutic vaccine
o Effective in acute lesions
Sporotrichosis Basics, Encounter, Entry
- Sporothrix schenckii
- subcutaneous abscesses in horses and dogs occasionally cats
Encounter • dimorphic • free-living hyphae in soil • worldwide distribution • more common in hunting dogs and male cats
Entry
• requires implantation of conidia or mycelia in wounds
• most common in head, neck, paws
Sporotrichosis Multiplication/Spread/Damage & Diagnosis
Multiplication/ Spread/Damage
• yeast form grows in subcutaneous tissue
• spreads via lymphatics
= lymphangitis
• resolves via T-lymphocyte mediated macrophage activation
Diagnosis:
• clinically suspect with recurrent, non-healing nodules
• may underlie chronic Staphylococcus infection
• deep pyoderma that is non-responsive to antibiotics
• cytology or biopsy by histopathology
• indirect fluorescence on tissue detects Ag in tissues
Sporotrichosis Treatment & Zoonotic Potential
Treatment
• surgical excision
• supersaturated KI
for 30 days PO (Monitor signs of toxicity - esp. cats)
• ketoconazole or itraconazole
Zoonotic
• Cats to people
Cryptococcosis; fungus, encounter, entry, Multiplication/spread
• Cryptococcus neoformans = most common systemic mycotic infection in cats
Encounter
• Free living in soil where there is pigeon feces
Entry • Inhaled as spore • Most infections inapparent • Penetrates respiratory epithelium o Upper – cats o Lower – dogs & cats
Multiplication & Spread
• Proliferates as yeast
• Polysaccharide capsule = avoid phagocytosis
• Systemic spread
Cryptococcosis; damage, clinical disease in cats Vs dogs
• replicates and replace host tissue
immunosuppressed patients
o no/minimal response
immunocompetent patients
o granulomatous response
o nasal mass
o meningoencephalitis
clinical disease in cats: o >50% have rhinitis, sinusitis, or nasal mass o ~40% have pulmonary lesions o ~40% have cutaneous lesions o ~25 have ocular lesions o ~25% have CNS lesions
clinical disease in dogs: o 75% have CNS lesions o 65% have ocular lesions o 42% have disseminated visceral lesions o 20% have cutaneous lesions
Cryptococcosis; Diagnosis & Treatment
Diagnosis • Cytology of skin lesions, nasal discharge, tracheal wash, CSF = high leukocyte count & encapsulated organisms • histopathology • cultivation (48hrs-6wks) • detection of Ag
Treatment
o Itraconazole or Fluconazole
o Amphotericin B
(Does not cross bbb well)
o 5-fluorocytosine (use w/Amphotericin B)
• Ag test to evaluate therapeutic efficacy
Aspergillosis; fungus, animals affected, encounter, entry
- Aspergillus fumigatus
- respiratory disease in closely housed young birds
- sporadic occurrence in all animals
- guttural pouch mycosis in horses
Encounter
• soil contaminant
• found on skin and feathers of normal animals
• multiplies in moist environment
Entry
• Inhaled as conidia
• Must be immunosuppressed or high organism count
Aspergillosis; multiplication/spread, damage, diagnosis, treatment
Multiplication/Spread
• conidia vegetate and form hyphae in the nasal cavity, lungs, and air sacs
• in pregnant ruminants, may spread systemically to the placenta and fetus
Damage
• Granulomatous response
Diagnosis
• branching septate hyphae on cytology or histo
• cultivate on Saboraud’s Dextrose Agar
Treatment
• control predisposing causes
• ketoconazole or amphotericin B
Candidiasis; fungus, animals affected, encounter, entry
- Candida albicans
- stressed captive birds
- sporadically in all species of animals
Encounter
• Normal flora on skin, oral cavity, genital tract
Entry • poor nutrition • prolonged antibiotic therapy • overcrowding • immunosuppression
Candidiasis; multiplication/spread, damage, diagnosis, treatment
Multiplication/Spread
• Yeast germinate into hyphae above 37 degrees C
Damage
• Shallow ulcers on mucosal surfaces & GI
Diagnostics
• appearance of white-pseudomembrane on epithelial surfaces
• cultivation on Saboraud’s Dextrose Agar (1-2 days at room temperature)
• Gram stain to identify budding yeast
• grow on Blood Agar
Treatment
• control predisposing causes
• topically = Nystatin
• systemically = Amphotericin B, 5-
fluorocytosine
Fungal Otitis; basics, encounter, spread, damage, diagnosis, treatment
- Malassezia pachydermatis
- otitis externa in dogs w/ chronic bacterial otitis
- likes warm moist environment
encounter
• normal flora of canine skin in small numbers
multiplication/spread
• secondary problem to bacterial otitis externa
damage
• no specific damage, contributes to the chronicity of the problem
diagnosis:
• direct cytology w/ identification of budding yeast
treatment
• clean ears
• resolve bacterial otitis
Mycotic Abortion in Cattle; most common fungi & diagnosis
• 5-25% of abortions in cattle
most common fungi
• Aspergillus fumigatus
• other Aspergillus
• Mucor spp.
diagnosis:
• fungal hyphae in the placenta and fetal stomach contents
Mycotic Mastitis in Cattle; basics & most common fungi
- positive correlation with use of intramammary antibiotics
- due to direct inoculation from needle
most common fungi
• Candida sp.
• Cryptococcus neoformans
Mycotic Rumenitis; predisposition & most common fungi
predisposition:
• antibiotic use in calves
• lactic acidosis in older cattle
most common fungi
• Candida albicans
• Mucor spp.
• Rhizopus spp.
Fungi tht Cause Systemic Infections
- Blastomyces dermatitidis (blastomycosis)
- Coccidioides immitis (coccidioidomycosis)
- Histoplasma capsulatum (histoplasmosis)
Basics of Systemic Fungal Infections
- strong geographic distribution
- entry by inhalation
- most infections subclinical
- slow onset with granulomatous response
- once established, are life-threatening
- no vaccines
- are not true zoonoses
- therapy is long-term
Coccidiomycosis, basics, encounter, entry
- Coccidioides immitis
- severe pneumonia and systemic disease in dogs
Encounter
• enzootic in soil in desert southwest and central valley of California
• fecal contamination by burrowing rodents may enhance growth
• sporulation following rainfall
Entry
• inhalation by dogs and humans
• outbreaks during dust storms
• requires few (<10 in dogs) arthrospores
• arthrospores lodge in bronchioles and then alveoli
Coccidiomycosis, Spread, Dz in dogs, Damage
Multiplication/ Spread
• arthrospores -> large spherules
Dz in dogs • 58% seroconvert without signs • mild upper respiratory signs • severe pneumonia • disseminate to bone, CNS, skin, abdominal viscera also joints, heart, pericardium, testicles, eyes • course of months to years • high case fatality
Damage
• pyogranulomatous response
• chronic and progressive
Coccidiomycosis, Diagnosis, Treatment, Human Dz
Diagnosis
• radiographic evidence of granulomatous pneumonia or osteomyelitis
• serology – (+) 2 wks after exposure, (-) after 4-5 weeks, may become (+) again
• titer: <16 early or focal disease, >16 disseminated disease (does not consistently rise 4x)
• ID of Coccidioides immitis spherules on TTW & cytology = confirmatory
• culture: 72 hrs & risk to humans
Treatment
• surgical curettage
• itraconazole and fluconazole are drugs of choice
Human Dz
• rare zoonosis mot cases from the environment
Blastomycosis; basics, geo distribution, encounter, entry, spread
• Blastomyces dermatitidis
• dimorphic
• mycelia in environment
• yeast in tissue
• severe morbidity and high case fatality in dogs
geographic distribution:
• most frequently in central & eastern US
encounter:
• appears to be located in old buildings and soil.
entry:
• organism is inhaled and invades via the lungs
multiplication/spread:
• spread to skin, subQ tissue, CNS, bone
• disseminates to viscera
Blastomycosis; Damage, Diagnosis, Treatment
damage:
• inapparent
primary infection in lung
• epithelioid granulomas to chronic suppuration, necrosis, and fibrosis
• epithelial hyperplasia
• Large budding yeast cells with broad bases in microabscesses.
diagnosis:
• geographic predisposition
• pulmonary radiography
• organism in lesion (cytology or histopathology)
• cultivation on Saboraud’s Dextrose Agar (days)
• serology
Treatment
• ketoconazole is drug of choice
Histoplasmosis; basics, geo distribution, encounter, entry, syndromes
- Histoplasma capsulatum
- dimorphic
- mycelia in the environment
- budding yeast in tissue
- affects dogs, rarely cats and horses
geographic distribution:
• Ohio and Mississippi River valleys
• Other countries
encounter:
• free-living in soil enriched with bird or bat excreta
entry:
• inhaled & enters lower respiratory tract
Syndromes: • inapparent infection (90%) • mild upper respiratory disease • severe bronchopneumonia • disseminated disease (CNS, skin, bone, viscera)
Histoplasmosis; Spread & Damage
Multiplication/Spread • phagocytosis by alveolar macrophages • multiply within macrophages • macrophage activation -> organism eliminated -> small granuloma formation -> calcification OR • disseminates via infected macrophages
Damage
• Acute: many yeast found in macrophages
• Over time: epithelioid granulomas that contain plasma cells, lymphocytes, macrophages, neutrophils and giant cells
• resolved disease: calcification may be prominent.
Histoplasmosis; Diagnosis & Treatment
diagnosis:
• geographic predisposition
• pulmonary radiography
• organism in lesion (cytology or histopathology)
• cultivation on Saboraud’s Dextrose Agar (days)
• serology
treatment
• ketoconazole is the drug of choice
Basics of Anaerobic Infections & Pathogens involved
o O2 is toxic
o Can be in sites exposed to ambient air
o Endogenous opportunistic infections
Gram (+)cocci
• Peptococcus,
• Peptostreptococcus
Gram (+) rods • Clostridium spp., • Actinomyces spp., • Bifidobacterium, • Eubacterium, • Lactobacillus, • Proprionibacterium
Gram (-) rods
• Bacteroides
• Fusobacterium
Anaerobic Infections; encounter, entry/multiplication
Encounter
• Normal flora of mucous membranes & skin
• Can be found in soil
Entry/Multiplication
• Breakdown of host defense barriers
• Damage to blood supply or necrosis = low O2
• facultative help obligates by reducing O2, producing necrosis & beta-lactamases
• obligates help falcultative by destroying tissue & impairing host defenses
Anaerobic Infections; Damage, Clinical Signs, Diagnosis
Damage
• tissue destruction
collageases
• digest stroma, allow extension of infection
lecithinases
• dissolve cell membranes
leukocidins
• impair host defenses
Clinical Characteristics • foul, putrid odor • gas in lesion • black discoloration • "sterile" culture
Diagnosis
• Preserve anaerobic environment
• Direct gram stain of initial sample
• Requires special equipment to culture
Anaerobic Infections; Treatment & Resistance
Treatment • Surgery for drainage & debridement • Prolonged antibiotic therapy necessary • Antibiotics to use • penicillin (Gram (+) anaerobes) • metronidazole (only works on anaerobes) • clindamycin (resistant strains of B. fragilis; no horses!) • Chloramphenicol (not in food animals)
Resistance
• plasmid-mediated resistance can occur
• sensitivity testing can be done
Contagious Ovine Foot Rot bacteria involved
Fusobacterium necrophorum • anaerobe • gram (-) • normal flora • present in feces • survives on pasture ~10 months • requires damaged tissue to multiply on skin
Dichelobacter nodosus • gram (-) • Obligate parasite • Obligate pathogen • survives less than 14 days on pasture • infected animals act as reservoir
Entry, Virulence Factors, & helper of F. necrophorum in Contagious Ovine Foot Rot
Entry
• Any damage to skin & hoof allows multiplication
dermotoxin
• lyses cells
leukotoxin
• kills phagocytic cells
exotoxin and endotoxin
• inflammation
Helper • Trueperella pyogenes • Gram (+) facultative anaerobe • secretes growth-enhancing molecule • scavenges free oxygen • growth facilitated by necrophorum leukocidal activity
Entry & Virulence Factors of D. nodosus in Contagious Ovine Foot Rot
• invades inflamed interdigital area
Pili
• binds hoof epithelium
exotoxin
• protease dissolves hoof matrix
factor
• enhances infectivity and invasiveness of F.
necrophorum
Treatment of Contagious Ovine Foot Rot
• Hoof trimming
Topical
• 5% oxytetracycline, 20% cetrimide or 5% formaldehyde
Foot bath
• 5% copper sulfate, 10% zinc sulfate or 5% formaldehyde)
Immunity Control for Ovine Foot Rot
• no immunity to F. necrophorum
Antipilus Ab blocks D. nodosus binding to hoof epithelium
• requires high titer
• recovered sheep immune for limited period
vaccine available for D. nodosus
• not much cross-protection
• used w/ other management practices
Basics & Classifications of Wounds
- All wounds have potential to become infected
- Endogenous or exogenous infections
- Usually opportunistic anaerobes or aerobes
- Anaerobes usually always involved
Causal types
o Traumatic wounds
o Bite wounds
o Surgical wounds
Clinical Types
o Clean wound
o Clean-contaminated wound
o Contaminated wound
Predisposing Factors for Wound Infection
- extent of tissue damage
- presence of clotted blood
- devitalized tissue
- duration of wound exposure -“golden period”
- presence of foreign bodies
- type, number, dose and resistance of bacteria
- factors influencing host defense
Diagnosis & Treatment of Infected Wounds
Diagnosis • Surgical biopsy • Syringe aspirate • Swab may be contaminated • Gram stain (presumptive) • Culture (definitive)
Treatment • Clean • Lavage w/ sterile saline • Suture depending on wound • Systemic or topical antibiotics depending on deepness
4 Protective Barriers for Skin
Physical
• Hair, stratum corneum, temp
Chemical
• Fatty acids, inorganic salt, transferrin
Normal Flora
• Influenced by:
• Hydration, health, environment
• Resident & transient
Lymphocyte/Ag interaction
Resident Vs Transient Flora on Skin
Resident Flora o Live & replicate on skin o Obligate parasites o Permanent o Normally harmless
Transient flora o from environment or mucous membranes o do NOT multiply on skin o are transient, CAN be removed o may be pathologic = secondary invaders
Primary Vs Secondary Skin Infections
Primary Infections
• bacteria initiate and cause most of the pathology
• occurs in “healthy” skin
• single bacterial species is dominant
• characteristic disease pattern
• antibacterial therapy alone is effective
Secondary infections
• most common
• secondary to other, primary, skin disease
• diseased, non-healthy skin
• multiple species of bacteria
• disease pattern comprised of several diseases
• must treat of underlying cause
Surface Pyoderma
- epidermis only
- sequelae to self-trauma and allergic skin disease
- EX: hot spots, early skin fold dermatitis
Superficial Pyoderma
o skin down to and including intact hair follicles (folliculitis)
o pustules
o usually secondary to other disease
o recurrence is common and long term management may be difficult
o Ex: puppy pyoderma
Deep Pyoderma
o tissues deeper than hair follicles - dermis and subcu o ALWAYS secondary to other conditions o not common o VERY difficult to treat o EX: bacterial cellulitis
Conditions that lead to secondary skin infections
o Skin infected w/ parasites, virus, fungi
o systemic disease
o physical or chemical trauma
o immunosuppression
Diagnosis of Bacterial Infections
Bacterial culture
o distinguish infection from colonization
o Gram or wright’s stain
o Histo & biopsy of intact pustules
Staph Infection; basics & encounter for S. aureus, pseudintermedius, hyicus, epidermidis
o Facultative anaerobe o Gram (+) cocci o Aureus, pseudintermedius, hyicus, epidermidis
Encounter
o Long lived in environment
S. aureus
• transient flora
S. pseudintermedius
• transient flora
• disease in dogs
S. hyicus
• transient flora
• exudative epidermitis in pigs
S. epidermidis
• resident flora,
• rarely a skin pathogen
• can cause deeper opportunistic infections
Staph Infection; Entry, Immunity, Diagnosis, Treatment
Entry
o Little resistance to staph colonization
o High resistance to deeper infection or dz
o Colonizes by binding to fibronectin on damaged epidermis
Immunity
o Opsonization by Abs
o phagocytosis by neutrophils and macrophages
Diagnosis o smears – Gram’s stain and cytology o culture and sensitivity o surgical biopsy and histopathology o commonly see mixed bacterial infections
Treatment
o must correct underlying/predisposing causes
o antibiotics
o need sensitivity test
Staph Infection; virulence factors
o not all strains produce all virulence factors
o host factors play a major role
o balance btwn staph growth and opsonization/phagocytosis
Capsule
• resist phagocytosis
proteases
• enzymes aid spread by digesting tissue & damaging skin
exotoxins
• leukocidin kills leukocytes
• alpha hemolysin causes vasoconstriction & dermonecrosis
• coagulase forms clot & protects from phagocytosis
Dermatophilus congolensis; basics & encounter
o Gram (+)
o Facultative anaerobe
o obligate parasite
o divides longitudinally, then transversely
o forms parallel rows of coccoid cells (railroad tracks)
Encounter
• On skin of carrier animals
• Does not survive in soil but can persist in scabs for up to 42Mo
• Motile bacteria spores (zoospores)
• Direct contact btwn animals
• Indirect contact via mechanical vectors
Dermatophilus congolensis; Entry & Damage
Entry
• Motile bacteria spores invade debilitate epidermis ->
• migrate to epidermal surface beneath stratum corneum due to increased [CO2]
->
• bind to epidermal cells ->
• colonize at epidermal-dermal junction
->
• form elongated bacteria (hyphae) ->
• hyphae divide into motile cocci (zoospores)
Damage
• exudative epidermitis
• activates alternative complement pathway ->
• neutrophils
->
• acute inflammation and dermal cell necrosis ->
• new layer of epidermis forms below damaged upper layer
->
• separation and scab formation ->
• organisms remain primarily in scab
Dermatophilus congolensis; diagnosis, treatment, prevention
Diagnosis
• clinical signs
• most commonly seen in cattle, sheep, horses
• rarely seen in dogs, cats, humans
• painful, but NOT pruritic
• impression smear of fresh lesion
• Wright-Giemsa or Gram’s
stain
• visualize cocci and “hyphal” structures
• bacterial cultivation (rarely necessary)
Treatment
• Eliminate predisposing conditions
• Remove crusts and treat w/ iodine or dyriung agent
• Penicillin
Prevention
• Vx w/ D. congolensis in tropical countries
