Canine Distemper (NAVLE Notes)
Canine distemper is a viral disease caused by the canine distemper virus (CDV), which affects multiple organ systems and can lead to severe systemic and neurologic symptoms.
Classic Case
- Initial Signs (3-6 days post-infection):
- Fever
- Serous to mucopurulent oculonasal discharge
- Lethargy and anorexia
- Vomiting and diarrhea
- Neurologic Signs (may appear with initial symptoms or months later):
- Forebrain signs (more common in younger dogs): Behavior changes, seizures, pacing, head-pressing, visual deficits
- Cerebellar signs (more common in older dogs): Ataxia, hypermetria, intention tremors
- Brainstem signs (more common in older dogs): Nystagmus, head tilt, facial and tongue paralysis, swallowing difficulties
- Spinal cord signs (more common in older dogs): Hyper-reflexive paresis or paralysis
- Chronic Signs in Survivors:
- Paw pad and nasal planum hyperkeratosis
- Enamel hypoplasia
- Myoclonus (involuntary, rhythmic muscle movements)
- “Chewing gum fits” (rhythmic jaw movements)
Diagnosis
- Etiology: Canine distemper virus (CDV) in the paramyxovirus family
- Systemic Disease:
- CBC: Leukopenia, particularly lymphopenia, early in the disease
- Ophthalmic Exam: Keratoconjunctivitis sicca
- RT-PCR: Conjunctival, vaginal, buffy coat smears, urine, bone marrow; quantitative RT-PCR can distinguish infection from vaccination
- CNS Disease:
- Ophthalmic Exam: Hyperreflective retinal lesions
- CSF Cytology: Normal or with lymphocytic pleocytosis and elevated protein
- CSF PCR and antibody titer comparison in serum vs. CSF
Treatment
- Supportive Care:
- Fluids, antibiotics for secondary bacterial infections, anticonvulsants, antipyretics, analgesics
- Anti-inflammatory doses of prednisone (if pleocytic CSF is present)
Prevention
- Vaccination:
- Modified-live virus vaccine every 3-4 weeks from 6-16 weeks of age, then a booster at 1 year, and every 3 years thereafter
- Avoid modified-live vaccine in pregnant or lactating females
Key Points
- Prognosis: Generally poor if neurologic signs are progressive; guarded for systemic disease.
- CDV Stability: CDV is sensitive to many disinfectants and is unstable in the environment.
- “Old Dog Encephalitis”: Rare, forebrain signs may appear in dogs over 5 years without systemic signs and usually up-to-date on vaccinations.
NAVLE-Style Practice Questions on Canine Distemper
Question 1
A 6-month-old mixed-breed dog presents with lethargy, anorexia, and a mucopurulent nasal discharge. The dog was recently adopted from a shelter, and its vaccination history is unknown. Physical exam reveals a mild fever and oculonasal discharge. What is the most likely diagnosis?
- A) Kennel cough; initiate cough suppressants
- B) Canine distemper; perform RT-PCR for confirmation
- C) Canine influenza; initiate supportive care
- D) Allergic rhinitis; monitor for spontaneous improvement
Correct Answer: B
Explanation: The dog presents with signs consistent with canine distemper, including lethargy, fever, and mucopurulent nasal discharge, in an unvaccinated animal. RT-PCR testing can confirm the diagnosis by detecting viral RNA.
Question 2
An 8-year-old Labrador with a complete vaccination history presents with sudden seizures, head-pressing, and visual deficits. The owner reports that the dog has had no recent exposure to other animals. What is the most likely explanation?
- A) Primary epilepsy; initiate anticonvulsants
- B) Old dog encephalitis; associated with prior distemper exposure
- C) Canine influenza; submit for serology
- D) Chronic liver disease; perform liver function tests
Correct Answer: B
Explanation: Old dog encephalitis is a rare presentation of canine distemper virus that affects older, vaccinated dogs, presenting with forebrain signs such as seizures and behavior changes. Unlike primary epilepsy, it is linked to previous distemper exposure, even if systemic signs are absent.
Question 3
A young, unvaccinated Border Collie presents with high fever, vomiting, and severe diarrhea. Over the next week, the dog develops ataxia and intention tremors. What is the most likely diagnosis, and what diagnostic test should be prioritized?
- A) Canine parvovirus; conduct an ELISA
- B) Leptospirosis; perform serology
- C) Canine distemper; initiate RT-PCR on a conjunctival smear
- D) Canine adenovirus; conduct an antibody titer
Correct Answer: C
Explanation: This dog shows classic signs of systemic canine distemper (fever, GI symptoms) followed by neurologic signs. RT-PCR of a conjunctival smear is recommended to confirm distemper, as it directly detects viral RNA.
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