Week 8 - Infectious Flashcards
Why do we perform diagnostic tests? (4)
- to rule out dz - dz presence or absence
- gauge severity
- monitor response to therapy - how well are you treating dz
- inform prognosis
What is sensitivity?
proportion of [dz positive] that actually [test positive]
TP/(TP+FN)
100 dogs have an infection and 90 test positive. What is the sensitivity?
90/100 = 90%
What is specificity?
proportion of [dz negative] that actually [test negative]
TN/(TN+FP)
100 dogs are NOT infected, 95 of those test negative. What is the specificity?
95/100 = 95%
What’s the pros to a highly (100%) sensitive test?
A highly sensitive test catches every animal with the disease, with some false positives. But if the test is negative, we can feel comfortable it is a TRUE negative.
If you test positive, it COULD be a false positive. (so they could actually be disease free)
You don’t get false negatives.
What’s the pros to a highly (100%) specific test?
A highly specific test catches every animal without the disease, with some false negatives. But if the test is positive, we can feel comfortable it is a TRUE positive.
If you test negative, it COULD be a false negative. (so they could actually have the disease)
You don’t get false positives.
What is a Positive Predictive Value?
Proportion of the test positives that actually have the disease
TP/all positives
all positives = true and false positives
What is a Negative Predictive Value?
Proportion of the test negatives that don’t actually have disease
TN/all negatives
all negatives = true and false negatives
What are the two major categories of diagnostic tests for infectious diseases?
- Organism Detection
- Antibody Detection
What are some examples of Organism Detection tests? Remember you can assess for:
whole organisms
antigen
nucleic acid (DNA or RNA)
Cytology and Histopathology
-can be insensitive
Culture and Identification
-culture allows for antimicrobial susceptibility testing
-false negatives with low speciment size or after abx
-some unculturable
-loss of viability with storage
-False positives from contamination by commensals
-expensive
Antigen Assays (ELISA)
-detect organic proteins
-False negatives with low antigen levels
-False positives from cross-reaction
-Variable sensitivity and specificity
Nucleic Acid Assays - PCR
What are some examples of Antibody Detection tests?
ELISA
Western Blot
Lateral flow assays
Indirect IFA
Agglutination tests
Gel immunodiffusion
Pros and cons to organism detection?
PROS
-Positive implies presence of organism
-Can localize the disease process
-Sensitive in the immunocompromised
-Quantification of organism numbers may be possible
CONS
-False positives possible
-Positive test doesn’t always imply disease
-No sense of chronology
-Low sensitivity for some infections
What are some examples of antigen detection assays?
FeLV SNAP test
Parvovirus fecal antigen SNAP test
Heartworm test (4DX)
When do we consider PCR for Organ Detection?
When it is difficult or dangerous to culture
Prior to robust antibody production (acute disease)
In animals that won’t mount a strong antibody response – immunocompromised
For Organism Detection via PCR – what are some PCR cons?
False negatives if insufficient sample type/size
False negative if there is strain variation
Inhibition of enzymes from some bodily fluids
False negative from degradation of nucleic acid – especially RNA
False positives from contamination
Can detect inactivated organisms if nucleic acid still present
What does antibody detection mean?
There is/was evidence of infection.
There are two types of antibody titers for antibody detection. What are they?
- Paired acute and convalescent antibody titers required to document infection for acute diseases
- Leptospirosis, anaplasmosis - Single antibody titers can be accurate for some chronic, persistent infections
- Lyme disease, FIV
What are the cons to antibody detection?
Antibodies must be present to be detected!
- Negative early for acute diseases
- Before a good Ab response - Negative with localized disease
- When you don’t get a good systemic response - Negative in immunocompromised patients
-When they can’t mount a good Ab response - False positives are common
- Previous exposure or infection
- Cross-reactivity
- After vaccination (except DIVA assays)
DIVA = Discrimination of infected and vaccinated animals
What are some examples of antibody detection assays?
FIV test
Tick born disease on 4DX
Leptospirosis MAT
What is hyperthermia?
-Normal set point retained
-Body overheats due to undesirable heat retention or over-production of heat
What are examples of hyperthermia?
-Heat stroke, excitement, seizures, tetanus, adverse drug reactions, strenuous exercise
-Not responsive to anti-pyretics, can be severe and rapidly fatal
What is fever?
- Exogenous pyrogens (eg. LPS) stimulate release of
endogenous pyrogens by macrophages - Il-1, Il-6 and TNF-α
- Alter hypothalamic set point
- Humoral mechanism
What is “Drug Fever”?
-NOT fever
-technically hyperthermia
-Increased body temperature due to drug-induced alterations in muscle activity OR sensitivity of hypothalamic neurons to changes in body temperature
-
What types of “Drug Fever” are there?
- Malignant hyperthermia
-Autosomal dominant mutation of the ryanodine (RYR1) receptor in dogs - Serotonin syndrome in humans
- Opioids in cats
-Excitement, excessive sedation, staring, hyperthermia
What factors modify fever?
- Extremes of age
- Renal failure
-Uremic toxins are endogenous cryogens or
antipyretics, or alter basal metabolic rate
-Fever = > 101F - Immunosuppression
- Anti-inflammatory drugs
There are 3 types of fevers, what are they?
- Persistent = above normal throughout day, does not
vary more than 2 degrees F - Remittent = above normal throughout day, varies more than 2 degrees F e.g. endocarditis
- Intermittent or relapsing e.g. Borrelia, cyclic neutropenia
What is a fever of unknown origin? FUO
-Prolonged fever of > 3 weeks duration associated with vague, nonspecific signs of illness
-Temperature > 1.5oF above normal on several occasions
-Diagnosis uncertain after 1 week of hospitalization involving repeated physical examination and routine laboratory tests
- Three outpatient visits OR
- Three days in the hospital without elucidation of a cause OR
- One week of “intelligent and invasive” ambulatory (outpatient) investigation
Fever implies ____________
INFLAMMATION
not infection
Why do we vaccinate?
- To improve the specific immune response in an animal
-provides protection against an infectious disease (or toxin exposure)
-lowers the risk of developing signs of illness when naturally exposed or reduces the clinical signs associated with infection if contracted - Less morbidity (animal and client suffering)
- Less mortality
4.Lower cost of pet care (illness $$$ > vaccine $)
FVRCP vaccines includes what?
FVR: feline herpes virus (feline viral rhinotracheitis)
C: calicivirus
P: Panleukopenia
Which are the core vaccines for cats?
FVRCP
FelV - sometimes
Rabies
Which are the core vaccines for dogs?
Rabies
Canine Distemper (D)
Canine adenovirus 2 (A)
Canine parvovirus (P)
Leptospira +/-
What are vaccine protocols?
▪6-8 weeks, then every 3-4 weeks until at least 16 weeks for FVRCP or DAP
-trying to aim for time where maternal antibodies aren’t enough to protect animal anymore
▪Booster within 1 year then every 1 or 3 years except for
-Leptospira and Borrelia (bacterins)
-Bordetella
-FHV1 and FCV in high-risk situations
What is Canine Distemper?
▪Enveloped RNA virus
▪Family Paramyxoviridae, Genus Morbillivirus
▪Readily inactivated in the environment
▪Disease in dogs, raccoons, ferrets, exotic felids
▪Strain virulence and neurotropism varies
How is Canine Distemper virus shed?
▪Shed in respiratory secretions, feces and urine (all body secretions) for up to 3 months after infection
▪Spread by direct contact, aerosol, or respiratory droplet exposure
▪Raccoons may be a source
▪Many infections subclinical
▪Infections often occur when maternal antibody wanes
What are the CS for Canine Distemper Virus?
Early signs:
▪Lethargy, inappetence, fever
▪Conjunctivitis, cough, serous ocular and nasal discharge
Progression to:
▪Obtundation, anorexia, vomiting, diarrhea
▪Mucopurulent ocular and nasal discharge
▪Moist cough, tachypnea
▪Neurologic signs
▪Nasal and footpad hyperkeratosis (‘hard pad’)
▪Optic neuritis and chorioretinitis (‘gold medallion lesions’)
▪ENAMEL HYPOPLASIA
Neuro signs:
▪May be delayed up to 12 weeks
▪Development unpredictable
▪Hyperesthesia
▪Ataxia, circling, head tilt, tremors
▪Paralysis
▪MYOCLONUS
▪Partial or generalized seizures
Describe the pathogenesis of Canine Distemper virus?
There are 2 stages
Stage 1: Lymphoid Tissue
-Virus inhaled, contacts upper resp tract epithelium
-Replication in local macrophages -> lymphatic spread
-Tonsils and bronchial nodes
-Systemic lymphoid tissue - GIT, spleen, MLN, Kupffer
cells
-results in FEVER LYMPHOPENIA
Stage 2: Epithelial and Nervous Tissue
-Once in the lymphoid tissue, it will spread to the blood
-It will go into epithelial tissue and CNS via hematogenous spread:
1. Good humoral and Cell Mediated response > virus eliminated
2. Intermediate response > Persistent infection (CNS, cutaneous, ocular signs)
3. Poor response > Fulminant epithelial infection (severe GI signs, pneumonia, +/- CNS signs)
▪Immunosuppression is a key feature (lymphocytolysis)
▪Race between virus and host
▪Opportunistic infections can occur
How do you DIAGNOSE Canine Distemper Virus?
- CBC
▪Lymphopenia
▪Distemper virus inclusions - Conjunctival scrapings for inclusions
▪Fluorescent antibody
▪False positives and false negatives (more false
neg)
3.RT-PCR
▪Respiratory secretions, CSF, feces, urine
▪False positive possible within 1-3 weeks of vaccination
- Thoracic radiographs
▪Bronchopneumonia - NECROPSY AND HISTOPATHOLOGY are considered to be the gold standard
How do you TREAT Canine Distemper Virus?
Supportive care
▪Isolation
▪IV fluids
▪Parenteral antimicrobial drugs
▪Oxygen supplementation
Neurologic signs usually permanent
▪May or may not be compatible with life
▪Warn owners if not yet present
How do you PREVENT Canine Distemper Virus?
-vaccines! (Modified Live Vaccines)
-vax before shelter entry
-In shelter outbreaks, consider serological testing
▪Separate and vaccinate seronegative animals
▪Foster incoming seronegative animals until they seroconvert
▪Any positive titer is protective
If you’re seronegative that mean you do/don’t have antibodies.
If you’re SERONEGATIVE you DON’T have antibodies.
you are NOT protected
What is Infectious Canine Hepatitis? (ICH)
▪Caused by canine adenovirus-1 (CAV-1)
-related to CAV-2 (respiratory disease)
▪Systemic viral infection of dogs - usually young puppies
▪Targets endothelial cells and hepatocytes (liver issues)
How is Infectious Canine Hepatitis transmitted?
▪Oronasal exposure: animal-to-animal contact
or exposure to contaminated fomites
▪CAV-1 is shed in feces, urine, and saliva
▪Shedding of CAV-1 in the urine can last for
6-9 months.
What are the CS of Infectious Canine Hepatitis?
-mostly subclinical
Peracute form
▪Circulatory collapse
▪Death in 24-48 hours
Acute form
▪Puppies aged 6-10 weeks
▪Fever, anorexia, lethargy, tonsillitis
▪Cough, tachypnea
▪Hepatomegaly, abdominal pain, edema, ascites
▪Vomiting, diarrhea
▪Hemorrhages
▪CNS signs (hepatic encephalopathy, direct damage)
▪Fever common in early phase
▪Corneal edema (‘blue eye’) and anterior
uveitis
-Hallmark lesion
-Type III (immune complex) hypersensitivity
-May be the only sign
-Can be painful
How do you DIAGNOSE Infectious Canine Hepatitis?
Bloodwork
▪CBC: lymphopenia, neutropenia
▪Chemistry: Increased liver enzymes, hypoglycemia
UA: Bilirubinuria, proteinuria
Organism detection
▪PCR (e.g., on blood, respiratory secretions, urine)
▪Histopathology at necropsy
▪Intranuclear inclusions in Kupffer cells, hepatocytes,
glomeruli, blood vessels (meninges, renal tubular
vascular endothelium)
What is parvo?
-Panleukopenia in cats
▪Severe enteritis and leukopenia in dogs and cats
▪Highly contagious, often fatal if untreated
▪Parvovirus is is one of the world’s most common canine infectious diseases
-Panleuk does not infect dogs
What kind of virus is Parvovirus?
▪Tiny, non-enveloped viruses
▪Require rapidly dividing cells to replicate
▪Shed for max. 4 weeks after infection (rarely > 2 weeks)
▪Resist disinfection and survive > 1 year on fomites
What is the signalment of Parvovirus in dogs?
▪Puppies and kittens 6 weeks to 6 months
▪Declining maternal antibody
▪Rapidly dividing cells
▪Concurrent viral, bacterial and parasitic infections
▪Rottweilers, Dobermans, Americans Pit Bull Terriers, GSDs, Chihuahuas?
▪Prevalence highest in summer (3 times more likely in July, August, and September)– flies?
What is the transmission of parvovirus?
▪Transmission by contact with feces, vomit, fomites
What is the pathogenesis of Parvovirus?
-Oronasal exposure
-Oropharyngeal lymphoid tissue
-GI epithelium, lymphoid tissue, marrow (also lungs, spleen, liver, kidney, heart)
Causes:
Intestinal crypt cell destruction >
-Neutrophil sequestration
-Impaired cell turnover
-Villous blunting
-Malabsorption
-Increased permeability
+/- Intussusception
Results in Bacterial translocation > SEPSIS, ENDOTOXEMIA, DIC
What can happen if Parvovirus infects in utero <2weeks of age?
▪Dam subclinical
▪Myocarditis and CHF (congestive heart failure) in puppies (rare due to maternal
antibody)
▪Cerebellar hypoplasia in kittens (and rarely dogs)
-Also optic nerve atrophy, retinopathies
▪Reproductive failure or fading puppies/kittens
Feline parvo/panleuk is associated with what congenital abnormality?
Cerebellar Hypoplasia
▪Infection in utero or at <~ 9 days
▪Ataxia, intention tremors, incoordination, broad-based stance
▪Clinical signs appear at 2-3 weeks
▪Mental status normal, acceptable pets
▪Other signs less common
-Seizures
-Behavioral changes
-Retinal degeneration, folding
-Optic nerve hypoplasia
What are the CS for parvovirus?
▪Incubation period
-3-14 days CPV-2
-2-10 days FPV
▪Lethargy, fever, then inappetence, vomiting and diarrhea
-Usually bile-stained vomit in cats
-Yellow-gray, blood-streaked, or dark red malodorous
diarrhea
-Abdominal pain, dehydration
▪Leukopenia
▪Peracture form: Death in 1-2 days
-Secondary to gram-negative bacterial sepsis, DIC
How do you DIAGNOSE parvo?
▪History, clinical signs
▪CBC
-Leukopenia (not always present, not specific)
▪Chemistry
-Electrolyte abnormalities
-Hypoglycemia
-Prerenal azotemia
▪Fecal antigen ELISA
-Approx. 50% sensitive
-Detects FPV
-May get false positive post recent (10 days) vaccine -
modified live virus
▪Fecal PCR
-Positive after vaccination
▪Serology
-Tests for protective antibody titers, not for infection
▪Histopathology
-Intestinal crypt necrosis
-Intra-nuclear inclusion bodies
-Immunohistochemistry
How do you TREAT Parvo?
▪Isolation
▪Aggressive IV fluid therapy
▪Broad-spectrum IV antimicrobials
-Cefazolin
-Enrofloxacin/ampicillin
▪Intravenous dextrose
▪Plasma for hypoalbuminemia
▪Antiemetics
▪Immune plasma?
-Need large doses parenterally (6.6 – 11 mL/kg)?
-Best after infection but before clinical signs
▪NPO or early enteral feeding via NE tube
▪Central parenteral nutrition
▪Gradual reintroduction of water then food
▪Treat parasites
▪Outpatient protocol – SC fluids, maropitant and cefovecin
-Not optimal
How do you PREVENT parvo?
▪Vaccination
-Attenuated live vaccines
-Avoid use in pregnancy, kittens and puppies < 4 weeks
-Immunosuppressed animals
▪Pregnant queens in shelters?
▪Vaccinate to 16-18 weeks
▪Titers correlate with protection
-ANY antibody titer = protection in dogs > 20 weeks
-Lack of antibody titer does not necessarily mean lack of protection
▪Hygiene and appropriate disinfection
What is canine enteric coronavirus?
▪Enveloped RNA virus, fecal-oral transmission
▪Infects villus tips
▪Susceptible to desiccation and disinfection
▪Many strains
▪Widespread subclinical infection
▪Disease in pups < 6 weeks, often with co-pathogens
-Short incubation period
-Shedding for 2 weeks
-Usually mild, self-limiting diarrhea
How do you diagnose canine enteric coronavirus?
▪RT-PCR (‘fecal PCR panels’)
How do you prevent canine enteric coronavirus?
-hygiene
-vaccines - unproven benefit
What is Leptospirosis?
▪Wild and domestic animal reservoir hosts
-Shed in urine
-Different serovars/genotypes adapted to different reservoir hosts
▪Widespread subclinical exposure
▪Young, lepto-unvaccinated adult dogs
▪Rare in cats
▪Survives in stagnant or slow-moving, warmer water
▪Temperatures 0 to 25 degrees C (32-68 degrees F)
▪Increased rainfall/flooding is a risk factor but not
required
▪Disease seen in small-breed dogs from urban areas
How is Lepto transmitted?
▪Direct contact with contaminated urine, bite wounds or ingestion of infected tissues
▪Indirect contact with urine- contaminated food, water, soil, bedding
What is the PATHOGENESIS of Lepto?
▪Organisms penetrate intact mucous membranes or abraded skin
-Bacteremia with spread to liver and kidney as well as other tissues (pancreas, lung, meninges, genital tract, eye etc)
▪Extent of disease depends on strain virulence and host susceptibility
▪Acute kidney injury, +/- hepatic insufficiency, +/- hemorrhagic disease (liver dz, NOT liver failure)
What are the CS of Lepto?
▪Fever, inappetence, vomiting, dehydration
▪Reluctance to move
▪PUPD or anuria/oliguria
▪Abdominal pain
▪Mild peripheral lymphadenomegaly
▪Icterus
▪+/- uveitis
▪+/- tachypnea due to pulmonary
hemorrhage
What are some Lepto lab findings?
CBC
▪leukocytosis
▪anemia
▪thrombocytopenia (50-60%)
Chemistry
▪azotemia
▪+/- elevated liver enzymes (ALP>ALT)
▪ normal cholesterol
▪normo- or hypokalemia
▪hypoalbuminemia
▪ high CK
▪UA: casts, glucosuria, organisms not seen
▪Significant proteinuria not a feature (interstitial
nephritis)
▪Differential diagnosis: other causes of AKI
thoracic Rads
▪Normal
▪Mild interstitial to patchy or diffuse alveolar pattern
US
▪Hyperechoic renal cortices
▪+/- perirenal fluid
▪Renomegaly
How do you DIAGNOSE Lepto?
- History, clinical signs, laboratory findings
- Antibody-detection tests
▪Microscopic agglutination test, paired titers (interval 2-4 weeks)
▪Initial titers often negative
▪Positive titers from subclinical exposure and vaccination (up to 1:6400)
▪Fourfold rise in titer required over >2 weeks
▪Positive titers to multiple serovars due to cross-reactivity
▪Highest titer is NOT predictably the infecting serovar - SNAP Lepto
- WITNESS Lepto (Zoetis) - IgM based
- Darkfield microscopy of urine: insensitive
- Culture: special media, 4-6 weeks, not done
- PCR
- Kidney biopsy
How do you TREAT Lepto?
▪Ampicillin or penicillin for vomiting dogs
▪Doxycycline for 2 weeks after vomiting stops (d/c penicillin)
▪Aggressive IV fluid therapy
▪Diuretics
▪Antiemetics
▪Hemodialysis – the sooner the better if rehydrated and oliguric (low urine output)
Lepto prognosis
Good - 85% survival rate with aggressive therapy
CKD could be sequela
How do you PREVENT Lepto?
▪Treat co-exposed household dogs
▪Restriction of access to wildlife/rodents
▪Vaccination
-Shift to ‘core’
-annual vaccine
▪No need to place in isolation
What are vector borne diseases?
-Diseases (infections) transmitted by blood-feeding
arthropods (mosquitoes, ticks, fleas)
-can be viral, bacterial, protozoal, parasitic
What are some tick vectors in the US?
- IXODES
Ixodes pacficus
Ixodes scapularis (deer tick - black legged tick) - RHIPICEPHALUS
Rhipicephalus sanguineus (brown dog tick) - DERMACENTOR
Dermacentor Andersoni (rocky mountain wood tick)
Dermacentor variabillis (american dog tick) - AMBLYOMMA
Amblyomma aermicanum (lone star tick)
Ambylomma maculatum (gulf coast tick)
What is rickettsiae/rickettsial organisms? (big group of bacteria)
-Arthropod-transmitted
-Gram-negative pleomorphic BACTERIA - coccobacilli
-Obligately intracellular, may form morulae
-seen with bacteria: Ehrlichia spp., Anaplasma spp., Rickettsia spp., Neorickettsia spp.
The bacteria rickettsiae responds to which abx?
Doxycylcine!
The dz of Erlichia and Anaplasma affect monocytes, granulocytes and platelets. Which bacterias affect which cells?
Monocytes:
-Ehrlichia canis
Granulocytes (neutrophils and eosinophils)
-Ehrlichia ewingii, Anaplasma phagocytophilum
Platelets
-Anaplasma platys
What dz can the bacteria Ehrlichia canis cause?
Canine Monocytic Ehrlichiosis
attacks monocytes
mainly in SE/SW states, warmer climates
rare in cats
Canine Monocytic Ehrlichiosis – caused by bacteria Ehlrichia Canis – is transmitted by which vector?
Rhipicephalus sanguineus - dog brown tick