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Canine Leptospirosis: A Comprehensive Review

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1. ETIOLOGY

The Organism

"Leptospira species are spirochetes belonging to the order Spirochaetales and the family Leptospiraceae... Sixty-four Leptospira species with pathogenic (17 species), intermediate (21 species), and nonpathogenic (26 species) status have now been described." — Harrison's Principles of Internal Medicine, 21st Ed., p. 5334

Classification

There are >260 known pathogenic serovars arranged into 26 serogroups based on antigenic composition (lipopolysaccharide [LPS] of the outer membrane). (Harrison's, p. 5334)

Serovars of Major Importance in Dogs

Epidemiological note (Greene's Infectious Diseases of the Dog and Cat, 5th Ed.): Historically, L. canicola and L. icterohaemorrhagiae were the predominant serovars in dogs. Since widespread vaccination against these serovars, the "emerging" serovars — particularly Grippotyphosa, Pomona, Bratislava, and Autumnalis — have become increasingly prevalent in clinical canine disease.

Transmission and Epidemiology

• Rural environment or farm access
• Contact with wildlife (raccoons, skunks, opossums, rodents)
• Access to stagnant or slow-moving water
• Flooding/heavy rainfall events
• Intact male dogs
• Hunting or working dog breeds
• Immunosuppressed animals

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2. PATHOGENESIS

Phase 1 — Entry and Leptospiremia

Phase 2 — Organ Colonization and Injury

1. Direct cytotoxicity: Sphingomyelinase C (SphC) and hemolysins (LLO) lyse cell membranes → tubular necrosis, hepatocyte injury
2. Endothelial damage: Vasculitis → hemorrhage, increased vascular permeability → thrombocytopenia, DIC
3. Outer membrane proteins (OMPs): OMP LipL32 (highly expressed) activates TLR2/TLR4 → pro-inflammatory cytokine cascade (TNF-α, IL-1β, IL-6)
4. LPS: Structurally distinct from enterobacterial LPS; activates TLR2 predominantly → inflammatory injury

Renal Pathogenesis (Most Critical in Dogs)

Leptospiremia
     ↓
Renal cortical/tubular colonization
     ↓
Tubular epithelial cell damage (proximal convoluted tubules primarily)
     ↓
Tubular necrosis → Glycosuria, proteinuria, cylindruria
     ↓
Interstitial nephritis → Fibrosis (chronic cases)
     ↓
Acute kidney injury (oliguric or polyuric phase)

Hepatic Pathogenesis

Pulmonary Pathogenesis

Persistent Renal Carrier State

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3. CLINICAL SIGNS

Classification by Severity

Systemic Clinical Signs

Serovar-Associated Clinical Syndromes

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4. DIAGNOSIS

Diagnostic Algorithm

Suspect canine leptospirosis
          ↓
History + Clinical signs + Signalment
          ↓
Minimum Database: CBC, Serum Chemistry, UA, Urinalysis
          ↓
    ┌─────────────────────┐
    │  Specific Tests     │
    │  • MAT (paired sera)│
    │  • PCR (urine/blood)│
    │  • ELISA / SNAP     │
    └─────────────────────┘
          ↓
Confirm serovar / epidemiological data

Hematological and Biochemical Abnormalities

Urinalysis Findings

Specific Diagnostic Tests

A. Microscopic Agglutination Test (MAT) — Gold Standard

B. PCR (Polymerase Chain Reaction)

C. ELISA / Rapid Tests (SNAP Leptospirosis, Witness Lepto)

D. Culture

E. Dark-Field Microscopy

• Fresh urine or blood examined immediately
• Low sensitivity and specificity (artifacts mimic organisms)
• Not recommended as sole diagnostic test
• Useful only as a rapid, presumptive test

F. Histopathology / Immunohistochemistry

Differential Diagnoses

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5. TREATMENT

Hospitalization and Supportive Care

Antibiotic Therapy

"Severe leptospirosis should be treated with IV penicillin as soon as the diagnosis is considered. Leptospira are highly susceptible to a broad range of antibiotics, including the β-lactam antibiotics, cephalosporins, aminoglycosides, and macrolides, but are not susceptible to vancomycin, rifampicin, metronidazole, and chloramphenicol." — Harrison's Principles of Internal Medicine, 21st Ed., p. 5349

Antibiotic Treatment Protocol — Dogs

Drugs NOT Effective

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6. MANAGEMENT

Isolation and Zoonotic Precautions

Vaccination

Environmental Management

Monitoring During Recovery

Prognosis

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7. SUMMARY TABLE — Canine Leptospirosis at a Glance

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Key References

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Canine Parainfluenza Virus (CPIV): A Comprehensive Review

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1. ETIOLOGY

The Pathogen

Paramyxoviridae is classified under the order Mononegavirales, and parainfluenza viruses fall within this family. — Harrison's Principles of Internal Medicine, 21st Ed., p. 14802 (index reference); detailed classification in chapter 184

Taxonomic Classification

Greene's Infectious Diseases of the Dog and Cat, 5th Ed. (Greene CE, 2012): CPIV belongs to the genus Rubulavirus (CPI-5, formerly known as Simian Virus 5 or SV5) and is antigenically related to but distinct from human parainfluenza viruses (hPIV1–4). CPI-2 (canine parainfluenza type 2) is a separate Respirovirus closely related to human PIV-2.

Virion Structure

Physicochemical Properties

Strain Variation and Genotypes

Reservoir and Epidemiology

Transmission Routes

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2. PATHOGENESIS

Entry and Initial Infection

Virus aerosol/droplet inhalation
          ↓
Deposition on nasal epithelium / oropharynx
          ↓
HN glycoprotein binds sialic acid receptors on ciliated epithelial cells
          ↓
F protein mediates membrane fusion → viral entry into host cell
          ↓
Replication in cytoplasm (RNA-dependent RNA polymerase)
          ↓
Progeny virions bud from apical cell surface
          ↓
Lateral spread to adjacent epithelial cells

Tissue Tropism

Cellular and Molecular Mechanisms

Synergism in CIRDC (Kennel Cough Complex)

Progression of Infection

Immune Response

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3. CLINICAL SIGNS

Classification by Disease Severity

Detailed Clinical Signs

"Goose Honk" Cough — Pathognomonic Feature

Sykes' Canine and Feline Infectious Diseases, 2nd Ed. (Sykes JE, 2014): The pathognomonic sign of uncomplicated CIRDC/CPIV infection is the sudden onset of a harsh, paroxysmal, non-productive honking cough easily reproduced by gentle pressure on the trachea ("tracheal pinch test"). This reflects the tracheobronchitis that is the hallmark of CPIV infection.

Clinical Signs by Age Group

Tracheal Sensitivity Test (Diagnostic Maneuver)

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4. DIAGNOSIS

Diagnostic Approach Overview

History: kenneling, exposure, vaccination status, onset
          ↓
Physical examination: tracheal sensitivity, auscultation, fever
          ↓
Presumptive diagnosis: Uncomplicated CIRDC (clinical diagnosis)
          ↓
If complicated / non-responsive: Minimum database + specific testing
          ↓
CBC, Chemistry, Thoracic radiographs, PCR panel, Culture

Minimum Database Findings

Hematology (CBC)

Serum Chemistry

Urinalysis

• Usually normal in uncomplicated cases
• Proteinuria and casts in severe systemic disease

Specific Diagnostic Tests

A. Thoracic Radiography

Ettinger & Feldman, Textbook of Veterinary Internal Medicine, 8th Ed.: Thoracic radiographs are indicated in any dog with CIRDC showing systemic signs (fever >40°C, dyspnea, anorexia) to rule out bronchopneumonia. Cranioventral alveolar consolidation is the hallmark of secondary bacterial pneumonia.

B. Polymerase Chain Reaction (PCR)

C. Virus Isolation / Culture

D. Serology

E. Cytology and Bronchoalveolar Lavage (BAL)

F. Immunofluorescence (IFA) / Immunohistochemistry (IHC)

Differential Diagnoses

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5. TREATMENT

Treatment Decision Algorithm

Suspected CIRDC/CPIV
          ↓
     ┌────────────────────────────────────┐
     │ Uncomplicated?                     │
     │ • Alert, eating                    │
     │ • Temp < 39.5°C                    │
     │ • No radiographic pneumonia        │
     └────────────────────────────────────┘
           ↓                    ↓
     YES → Outpatient      NO → Hospitalize
     supportive care            + aggressive
                                treatment

Antiviral Therapy

Important: No specific licensed antiviral agents are available for CPIV. Treatment is primarily supportive for viral infection, with antibiotics reserved for secondary bacterial infections.

Supportive Care

Cough Suppressants (Antitussive Therapy)

Only used in non-productive (dry) cough — CONTRAINDICATED if productive cough or pneumonia present, as coughing is a defense mechanism.

Greene's Infectious Diseases of the Dog and Cat, 5th Ed.: Antitussive therapy is beneficial for the welfare of the dog and owner compliance but must be discontinued if pneumonia develops.

Antibiotic Therapy

Antibiotics are NOT indicated for uncomplicated viral tracheobronchitis. They are indicated when:

• Secondary bacterial infection confirmed or strongly suspected
• Mucopurulent discharge
• Pyrexia >39.5°C persisting >3–5 days
• Radiographic pneumonia
• Immunocompromised host or puppies

Sykes' Canine and Feline Infectious Diseases, 2nd Ed.: Doxycycline is the drug of choice for Bordetella bronchiseptica co-infections because it achieves high respiratory tract concentrations and is active against Mycoplasma spp. simultaneously. Fluoroquinolones are reserved for culture-confirmed resistant Bordetella in adults (avoid in growing puppies — cartilage toxicity).

Bronchodilator Therapy

Anti-inflammatory Therapy

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6. MANAGEMENT

Infection Control in Group Settings (Kennels/Shelters)

Vaccination Protocols

WSAVA and AAHA Vaccination Guidelines

Vaccination Schedule

WSAVA Vaccination Guidelines (2022): CPIV is classified as a non-core vaccine for low-risk pet dogs but is considered core in at-risk dogs (kenneled, boarded, shelter, showing, hunting). The intranasal route is strongly preferred for dogs entering high-risk environments due to its rapid onset and superior mucosal protection.

AAHA Canine Vaccination Guidelines (2022): For dogs with anticipated kennel exposure, intranasal CPIV/Bordetella vaccination should be administered at least 72 hours prior to entry, with annual boosters for dogs with ongoing exposure risk.

Monitoring and Recovery Management

Prognosis

Oxygen Therapy (Severe Cases)

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7. SUMMARY TABLE — Canine Parainfluenza Virus at a Glance

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Key References