Infectious disease Flashcards
How should swabs for bacterial culture be handled if their is a delay expected?
> 3 hours - transport medium
4 hours - refridgerarion
How long can most aerobes survive in a) tissue and b) fluid
a) 48 hours (refrigeration)
b) 1-2 hours at 20oC, 24 hours at 4oC or 72 hours at 4oC with transport medium
Which viral infection can be associated with inclusions in circulating lymphocytes, neutrophils and erythrocytes in dogs?
CDV
What infections are spread by Ixodes ticks?
Borrelia, Anaplasma, Ehrlich, Babesia, Bartonella, tick-borne encephalitis
Describe the life cycle of borrelia
Transstadial, not transovarial transmission in ticks
Ticks have 2y life cycle
Eggs hatch outdoors, larvae attach to birds/mice/small mammals and become infected
Overwinter, become nymphs, infect birds/mice/small mammals/dogs/deer/people next spring
Nymphs feed, moult and emerge the following autumn and transmit to third host - often larger mammals
How does Bb develop following a tick bite?
Migrates interstitially, hides with collagen and fibroblasts
Does not circulate in blood or body fluids
How do Bb and tick-borne relapsing fever infections vary?
Bb generally does not circulate in the blood or body fluids
What % of dogs seropositive for Bb have signs of lameness?
<5% - although suggested that 40% are false +ves, true number may be nearer <3%
What % of dogs seropositive for Bb have Lyme nephritis?
<2%
What are the 5 Lyme antigens?
OspA - vaccines, also host
OspC - increased 2-3 weeks after exposure, declined after 3-5 months, some vaccines
OspF - rises 6-8 weeks after exposure, persists
p39 - 88% naturally exposed
SLP
What are the members of the mycobacterium tuberculosis complex? What are their main reservoir hosts? Which affect dogs/cats?
M. bovis (C, D) - cattle
M. microti (C) - field voles
M. tuberculosis (C, D) - humans
What is the main risk factor for M. microti infection?
Hunting rodents
What are the routes of infection for tuberculous mycobacteriosis?
Skin, GI, respiratory tracts
What are the most common manifestations of TB in cats?
SC masses with draining tracts and regional lymphadenopathy, with non-specific systemic signs
What are the most common manifestations of TB in dogs?
Non-specific - lethargy, anorexia, weight loss, cough, dyspnoea, v/d, pyrexia
How is TB infection confirmed?
Demonstrating acid-fast bacteria on histo
Culture
How is TB treated in cats?
Surgical debridement
2 months rifampicin, FQ + clarithromycin/azithromycin, followed by 4-6 months of rifampicin and FQ or macrolide
What are the saprophytic mycobacterial species in dogs and cats? How are they classified?
Rapid growing - M. fortuitum, M. smegmatis (C)
Slow growing - M. avid (D/C)
How do slow and rapid growing saprophytic mycobacteriosis present?
Slow - local/systemic gramulomatous disease - weight loss, vomiting, diarrhoea, dyspnoea. Peripheral lymphadenopathy and pyrexia
Rapid - diffuse infections, panniculitis of ventral abdomen
How is saprophytic mycobacteriosis diagnosed?
Acid-fast staining, PCR
How does treatment of saprophytic mycobacteriosis differ from that of tuberculous disease?
Greater resistance to treatment
How do leproid syndromes present? Are they reported in cats or dogs?
Discrete cutaneous lesions.
Both
How is feline leprosy transmitted?
Rodent bites
When is feline leprosy more common?
Colder months
Where is canine leprosy reported? When is it more common?
Zimbabwe, Australia, Brazil, Warmer months
How is canine leprosy transmitted?
Insect bites
How are younger and older cats affected by leprosy?
Young - rapidly progressive, ulcerated
Old - diffuse, non-ulcerated slowly progressing lesions
How is leproid infection diagnosed?
Acid fast - impression smears
PCR
How are leproid syndromes treated?
May not be needed, spontaneous regression - dogs > cats
Surgical resection and dual AB therapy
Where is actinomyces most commonly found?
Mucous membrane commensal
GI and urinary tract
What are the common presentations of actinomyces infection?
SC or soft tissue abscess, pleuritic, pneumonia
How do actinomyces appear on cytology?
Non-acid fast filamentous organisms
Where are nocardia spp commonly found?
Soil
How does nocardia infection present?
Cutaneous lesions, pneumonia, pyothorax
Disseminated disease in young/immunocompromised
What empirical AB can be chosen in actinomyces infection?
Penicillin
What empirical AB can be chosen in nocardia infection?
Sulphonamide ABs
How is brucellosis shed?
Urine, vaginal discharges, aborted tissues, milk, saliva, nasal secretions
What happens following brucella crossing a mucous membrane?
Phagocytosed by macrophages and moved to LN
Following infection with brucella, when is bacteraemia seen and how long does it persist?
7-30 days
Up to 6 months
What are the clinical signs of Brucella infection?
Abortion, infertility, acute epididymitis, lethargy, weight loss, back pain, lymphadenopathy, poor vision
When can brucella serological testing be performed?
4 weeks after infection
How can the specificity of a brucella RSAT be improved?
By the addition of 2-mercaptoethanol
Which diseases are associated with clostridial organisms?
Tetanus and botulism
How do the susceptibility of dogs and cats to tetanus differ?
Cats 10x more resistant to infection than dogs
What exotoxins are associated with tetanus? What do they do?
Tetanolysin - damages otherwise viable tissue
Tetanospasmin - causes clinical syndrome of tetanus
What is the structure and function of tetanospasmin?
Heavy chain - affinity for ganglioside surface receptors on motor end plates. Responsible for internalisation, cytosolic translocation and retrograde axonal transport of light chain.
Light chain - presents neurotransmitter release by cleaving and inactivating synobrevin - essential or docking of NT vesicles with presynaptic membrane. Can also cross-link synaptic vesicles to cytoskeleton
What cells are affected by tetanospasmin?
Motor, then sensory and autonomic nerves
Can spread to brainstem via spinal cord
Predominantly affects inhibitory neurons
What are the consequences of autonomic inhibition by the tetanus toxin?
Sympathetic overactivity and excess plasma catecholamine levels
What is the explanation for the long duration of clinical tetanus?
Neuronal blinding of toxin is irreversible, recovery requires growth of new nerve terminals
When do clinical signs of tetanus become apparent?
Normally within 5-12 days of infection, can take up to 3 weeks
What is the mortality rate of tetanus?
8-50%
What autonomic signs are seen with tetanus?
Bradycardia, t tachycardia, hypertension, vasoconstriction, hyperthermia. Dysuria, urinary retention, constipation
What is the tetanus severity classification system?
I - facial signs
II - generalised rigidity/dysphagia
III - I + II + recumbency/seizures
IV - I + II + III + abnormal HR/RR/blood pressure
What biochemical abnormality is present in >50% of dogs with tetanus?
Elevated CK
How can tetanus be definitely diagnosed?
Measurement of serum antibodies against tetanospasmin
PCR for detecting toxin gene in wounds described but not available
What are the aims of treating tetanus?
1 - toxin neutralisation
2 - destruction of organism
3 - minimise effects of toxin
What is the preferred route of equine tetanus antitoxin? What is the risk?
IV
Anaphylaxis
How should a wound in a tetanus patient be managed?
Radical debridement and 3% hydrogen peroxide
Which AB has been shown to be superior for management of clinical tetanus?
Metronidazole
Which botulinum toxin has been associated with disease in dogs and cats?
C
Where is botulism toxin found?
Rancid food, dead birds
Rarely following colonisation of tissue and coprophagia
What is the pathogenesis of botulism?
Toxin released from spores, binds to protein complexes - forms progenitor toxins
Absorbed from SI => lymphatics => blood stream
Heavy chain binds with presynaptic peripheral nerve terminal
Modifies SNARE proteins needed for exocytosis of ACh
What are the clinical signs of botulism?
Afebrile flaccid paralysis
+/- cholinergic signs - altered HR, pupil changes (mydriasis and reduced PLR), KCS, urinary retention, constipation
What is the vector for Bartonella?
Blood sucking arthropods
Mostly cat fleas, also detected in Pulex fleas, Ixodes and Rhipicephalus
What are the targets of Bartonella infection?
Erythrocytes, endothelial cells, bone marrow progenitor cells
What affects the severity of clinical signs with Bartonella infection?
In primary host may be persistent bacteraemia without clinical signs
When non-adapted host infected, clinical signs more severe
What is the life cycle of Bartonella?
Replicate in midgut of arthropod and excreted in faeces
Inoculated through bite or scratching of area
Infect microglial cells, macrophages and CD34+ progenitor cells
What is responsible for Bartonellas invasion?
Adhesins - mediate bacterial adherence
Type IV secretion systems - transport DNA into cell
What is responsible for Bartonellas virulence?
Bartonella-effector proteins
What structure characterised the invasion of Bartonella?
Invasive - well organised bacterial aggregate engulfed and internalised by the targeted cell
How is Bartonella acquired by its vector?
Bacterial released from blood-seeding niche, bind to and invade erythrocytes without causing haemolysis
Released into circulation at 5 day intervals
What cells are suppressed to cause the immunosuppression seen with Bartonella?
CD8+ lymphocytes
How is Bartonella infection distributed in the body?
All tissues can be involved
What are the common clinical manifestations of Bartonella infection in dogs?
Pyrexia
Lymphadenopathy
Endocarditis
Myocarditis
Arthritis
Disseminated granulomatous disease (skin, LeNs, liver, spleen)
Neuro signs
Pleural, pericardial, peritoneal effusions
What proportion of canine endocarditis are caused by Bartonella?
19-28%
Which Bartonella species is commonly associated with endocarditis?
B. vinsonii subs. berkhoffi
In Bartonella endocarditis in dogs, which valve is most often affected?
Aortic
What lab abnormalities are associated with Bartonella infection?
Normally none
Non-specific
Hypoglubulinaemia
What clinical pathological finding has been associated with a 4x higher risk of being diagnosed with Bartonella?
Hypoglobulinaemia
What samples are best tested for Bartonella culture and PCR?
Tissue and non-blood fluids
What limits serology in Bartonella infection?
Over half of dogs have bacteraemia without ABs
How should Bartonella be treated in dogs?
Exact protocol not known
Combination of AB with high plasma and intracellular concentrations
What is a potential side effect of treating Bartonella in dogs? How can it be avoided. How should it be managed?
Jarisch-Herxheimer reaction - lethargy, fever, vomiting
By starting ABs 5-7 days apart in clinically stable dogs
Avoid interrupting treatment, anti-inflammatory steroids
Which species of Bartonella is most common in cats?
B. henslae
What are the clinical signs of Bartonella infection in cats?
Uveitis
Aortic valve endocarditis
Myocarditis
Lymphadenopathy
Pyrexia
Mild neuro signs
Usually subclinical
How is Bartonella diagnosed in cats?
Culture definitive but not sensitive
Serology - limited value, can be useful for assessing exposure but false negatives possible
PCR - no more sensitive than normal blood culture
Combined PCR and culture preferable
What is the recommended treatment for bartonella in cats?
Doxycycline and pradofloxacin
What is the main reservoir host of leptospirosis?
Rodents
How do leptospires differ from other gram-negative bacteria?
Do not cause fulminant septic disease shortly after onset of infection - low endotoxic potential of leptospiral lipopolysaccharide
How do leptospires evade the host immune response?
Binding inhibitors of complement activation on their surface
After the host response, where can leptospires persist?
Eye and renal tubules
Which organs are commonly involved in lepto infection?
Kidneys (tubules and glomeruli)
Liver
Lung
What are the hallmarks of leptospiral pulmonary haemorrhage syndrome?
Intra-alveolar haemorrhage in the absence of a marked inflammatory cell infiltrate or vasculitis
In a study of a cohort of dogs with lepto, what were the most common clinical syndromes (in order)?
Renal
Lung
Hepatic
What are the typical radiographic lung findings with lepto?
Pulmonary change in the caudodorsal fields, ranging from mild interstitial to severe reticulonodular
+/- mild mediastinal or pleural effusion
What diagnostics are available for lepto?
Culture - challenging, can take 6 months
Darkfield microscopy - low sens/spec
Serology
PCR
How long to vaccinal antibodies to lepto persist?
Normally up to 15 weeks, can persist up to 12 months
How should LPHS be treated?
Limited evidence exists in humans to suggest benefit of immunosuppression
What infections are spread by rhipicephalus sanguineus? Where are they found?
E. canis
A. platys?
R. rickttsii
Worldwide
What infections are spread by amblyomma americanum? Where are they found?
E chaffeensis
E ewingii
USA
What infections are spread by Ixodes scapularis? Where are they found?
A. phagocytophilum
USA
What infections are spread by Ixodes pacificus? Where are they found?
A. phagocytophilum
USA
What infections are spread by Ixodes persulcatus? Where are they found?
A. phagocytophilum
Eastern Europe and Asia
What infections are spread by Ixodes ricinus? Where are they found?
A. phagocytophilum
Europe
What infections are spread by Dermacentor variabilis? Where are they found?
R ricketsii
USA
What infections are spread by Dermacentor andersoni? Where are they found?
R ricketsii
USA - Rocky Mountain states
What disease is caused by E Canis?
CME
Where is E Canis distributed?
Worldwide
What are the clinical signs of CME
Acute - non specific, LN enlargement, splenomegaly
Ocular,nasal discharge, peripheral oedema
Petechiae/ecchymoses
Neuro
Chronic - mild to life threatening
Non specific + weight loss, lymphadenopathy, splenomegaly, anterior uveitis
Bleeding
What are the most common clin path findings in CME?
Panctopenia - BM hypoplasia
Elevated globulins (mono or polyclonal)
PLN
How is CME diagnosed?
Morulae within monocytes
Serology - ELISA/IFA
PCR - blood, LN, splenic FNA, BM
What is the sensitivity of BM PCR for diagnosis of chronic CME?
25%
What tick carries E Canis?
Rhipicephalus sanguineus
How should CME be treated?
Doxy x 28 days
Where is E. ewingii found? What is the main cause of transmission?
USA, Brazil, Cameroon
Amblyomma americanum
What are the clinical signs of E. ewingii?
Lethargy, anorexia, v/d, neuro signs, pyrexia, polyarthritis
What are the common Clinical path findings with E ewingii
Anaemia, mild leucopenia or leukocytosis, thrombocytopenia, hyperglobulinaemia, ALP elevation
Where is E chaffeensis seen? What spreads it?
USA
Amblyomma americanum
What are the clinical signs of E chaffeensis?
Fever, anaemia, leukopenia, thrombocytopenia, lymphadenopathy, epistaxis
What causes canine granulocytic ehrlichiosis? What spreads it?
A. phagocytophillum
I. scapularis/pacifinus/ricinus
What are the clinical signs of CGE?
Subclinical in many
Nonspecific - pyrexia, lethargy, lameness, stiffness, LN++, splenomegaly
Polyarthritis
Thrombocytopenia in >80%
How is CGE diagnosed?
Morula in neutrophils
ELISA serology (rising titre) - cross reactivity with platys
PCR (whole blood)
What causes thrombocytic anaplasmosis? What is the vector? Where is it seen?
A. platys
R. sanguineus
USA, South America, Australia, Asia, Europe
What are the clinical signs of A. platys infection?
Most subclinical
Transient thrombocytopenia
What causes salmon poisoning disease?
Neorickettsia helminthoeca
What is the life cycle of Neorickettsia helminthoeca?
Flukes => snails => fish => dogs
What happens following infection with N helminthoeca?
Disseminates to LNs, spleen, liver, lungs, brain
What are the clinical signs of SPD?
Weight loss, LN+++, v/d, thrombocytopenia in 90%
What clinical pathology findings are common in SPD?
Thrombocytopenia, v Na, K, alb
^ LEs
How is SPD diagnosed?
Trematode eggs in faeces
Neorickettsiae on LN aspirate examination
PCR on lymphoid tissue
How is SPD treated?
doxycycline + praziquantel
What causes RMSF? What spreads it and where is it found?
R. ricketsii
Dermacentor in USA
R. sanguineus in Arizona
What are the clinical signs of RMSF?
Fever, lethargy, anorexia, lymphadenopathy
Oedema and erythema
Stiffness
Ocular signs
Bleeding
Neuro signs
What are the clin path changes seen with RMSF?
Leukocytosis, anaemia, thrombocytopenia
How is RMSF diagnosed?
Serology - IFA/ELISA
What is the most common species of mycoplasma in a) cats and b) dogs?
a) Candidatus M. haemominutum
b) M. haemocanis
What is the most pathogenic feline mycoplasma?
M. haemofelis
What are the haematological fingers with acute/chronic mycoplasma haemofelis infection>
A - regenerative anaemia - microcytic and hypochromic
C - no significant anaemia
What is the sensitivity of cytology for diagnosing mycoplasma infection?
0-37%
How is clostridium perfringens typed? How many phenotypes are there based on this method?
Toxins - alpha, beta, epsilon, iota
Phenotypes - A, B, C, D, E
What is a known virulence factor for clostridium perfringens>
CPE
What is the suspected pathogenesis of clostridium perfringens-associated illness?
Massive sporulation of commensal strains, triggered by diet change, ABs, coinfection => CPE released
How does CPE cause clinical signs?
Interacts with epithelial tight junction proteins, forming protein complex. Then interacts with host proteins, forming larger complex. Provides CPE access to occludin.
How is clostridium perfringens diagnosed?
Is culture helpful?
CPE detection in faecal samples in combination with PCR detection of cpe gene
NO - isolated from 80% healthy dogs
How should clostridium perfringens be treated?
Uncomplicated diarrhoea - no treatment needed
Systemic illness - ampicillin, MNZ, tylosin
What toxins are associated with clostridium difficile?
TcdA - enterotoxin
TcdB - cytotoxin
What clinical disease is associated with CDI?
Association between TcdA toxin and AHDS in dogs
What diagnostic tests are available for CDI?
CTA - detects TcdA - gold standard but £££
Recommended approach is positive culture and/or antigen test AND ELISA detection of TcdA/TcdB
How is CDI treated?
MNZ treatment of choice
When is campylobacter jejuni shedding most commonly detected?
Dogs <6m
Summer and autumn
What toxin is associated with campylobacter?
Cytolethal distending toxin
Proteins CdtA, CdtB, CdtC