73. Canine distemper.

Question 1

History, Occurence?

Answer 1

Canine distemper

History, occurrence:

• known since the 18th century, world-wide occurrence, frequent
• Causative agent:
• Paramyxoviridae, Paramyxovirinae, Morbilli virus, Canine Distemper virus, CDV
• Resistance in the environment is weak: heat, UV, detergents
• Generalised disease
• Paramyxoviruses are continuously searching for new hosts! & able to kill them
• WIDE HOST RANGE - Relatively euryxen: Canidae ʹ dogs, Phocidae ʹ seals, Mustelidae ʹ ferrets etc,
• Prycyonidae ʹ racoon, Ailuridae ʹ red panda, Ursidae ʹ bears, Viverridae ʹ civet cat, Herpestidae ʹ
• mongoose, Felidae ʹ (large) cats, Suidae ʹ swine (subclinical), Cercopithecidae ʹ macaque (Macca fuscata)
• Killed several whales & dolphins, encephalitis in lions, dogs etc (lethal)
• In cats & humans unapparent, self-limiting infection
• 1 serotype with virulence variants - Snyder Hill: polyoencephalomyelitis, A/75/17, R252: demyelination
• Uniform virus, 7 genotypes BUT 1 serotype ʹ so can vaccinate!
• Difference in virulence, enveloped
• weak resistance

Question 2

Epizootiotiology?

Answer 2

Epizootiology

• Shedding begins day 7 PI
• Virus in resp excretesʹair-borne infections:
• Droplets infection -> very contagious ;main source of transmission)
• Virus presence in other tissues & secrets; shed via urine
• Transplacental transmission is possible
• Shedding even for 2-3 months, but usually shorter
• Direct contact, feed, drinking water, contaminated tools are potential transmitters
• Subclinical infections in 25-75% of dogs ʹ reservoirs
• Seasonal: In spring & summer more frequent, in autumn & winter more severe cases
• Clinical manifestation mainly in 3-6 month old pups ʹ clearance of maternal Abs
• Good vaccine and immunity, so dont see signs in dogs <3 months due to maternal antibodies
• Intro into naïve population initiates outbreak
• Brachycephalic breeds are more resistant than dolichocephalic ones
• Some dogs will survive without clinical symptoms (majority of the dogs)
• Lethality is high, number of animals that die when clinical symptoms are present is relatively high

Question 3

Pathogenesis?

Answer 3

Pathogenesis

• Air- Borne infection -> Primary replication in tonsils, lns, mucosal macrophages ;24hr -> throat bronchi
• lymphoid tissues (days 2- 4)
• further lymphoid tissues (spleen, stomach & small intestine lamina propria, mesenteric LNs, liver Kupffer cells, day 4-6)
• 1st febrile period, leukopenia (day 3-viraemia (in cells & in serum, day 8-9):
• intensity depends on the immune response
• Colonisation in epithelial cells ʹ shedding through excretes
• Good immune response:
• on day 14 complete recovery, high IgG level,
• clears and inactivates virus, heals, get immune
• mature Atb to puppy
• Intermediate immune response:
• virus clearance from most tissues, but persistence in the skin (pads), uvea, CNS->after recovery long
• term immunity ʹ but virus will still stay
• Weak immune response:
• generalised virus multiplication (skin, glands, airways, enteric tract, urinary mucosa) ʹ severe signs,
• virus persistence until death
• Bacterial complications influence, but has no major role
• Abs against envelope glycoproteins (HN) are protecting from CNS infection
• Major role of cellular immunity in the protection
• Infection of the CNS ʹ most severe problems
• Frequent but not always manifest
• Through perivascular spaces (meninx, plexus choriodeus, ependymal cells)
• Spread in the brain by blood & liquor
• Acute encephalitis: direct CPE, demyelinisation, mild inflammation
• kills animal
• Subacute, chronic encephalitis: virus multiplication decr, severe inflam.
• old dog encephalitis rare persisting CNS infections in immunocompetent dogs
• virus remains, destroys neurons and chronic inflammation appears, permanent convulsions in life (if more virulent)
• “inclusion body polioencephalitis” after vaccination T cell mediated inflam.

Question 4

Clinical signs?

Answer 4

Clinical signs

• (mainly in 3-4 month old dogs)
• Incubation 3 ʹ 7 days, viremia
• fever, mucous membrane clinical signs
• Initial fever, leukopenia, anorexia
• Eyes: conjunctivitis ʹ mucoid then purulent, uveitis, neuritis, retinitis, blind
• Lungs: dry cough, then wet and nasal discharge
• GI: vomit and diarrhoea
• Skin: pustule hyperkeratosis/para on nose, sole, papule belly
• CNS 2nd phase: 1 ʹ 3 weeks after general signs: dullness, spasm, ataxia, convulsions, lame, hyperesthesia
• Transplacental: mom , pup: abort, stillbirth, weak ʹ cardiac myopathy, enamel hypoplasia
• CNS: 4-6 weeks, immunodeficiency
• Young dogs: metaphysis osteosclerosis (in long bones), hypertrophic osteodystrophy (may be after vaccination too)

Question 5

Pathology, Histopathology?

Answer 5

Pathology, histopathology

• Pharyngitis, tonsillitis, bronchitis, interstitial pneumonia ʹ lungs, mucous membrane epithelia
• GI: gastro-enteritis
• CNS: lymphocytic encephalitis (NOT purulent), demyelinisation & cytoplasmic inclusion bodies

Question 6

Diagnosis?

Answer 6

Diagnosis

• Epi ʹ cl signs ʹ pm
• Lab tests (leukocytopenia - lymphopenia, thrombocytopenia)
• Detect agent: Virus isolation, IF, ELISA, PCR
• Detect Atbs: ELISA, VN, HAI (paired sera ʹ 2 weeks)
• Additional tests
• X-ray (interstitial pneumonia)
• CNS analysis (increased protein content & cell count)
• Immunofluorescence (conjunctival epithelia)
• Immunohistochemistry (spleen, tonsils, urinary bladder, brain)

Question 7

Differential diagnosis?

Answer 7

Differential diagnosis

• Respiratory signs: Kennel cough, influenza, laryngotracheitis
• Vomiting, diarrhoea: CadV, CPV-2, CECoV, Infectious canine hepatitis, Parvo
• Skin, eye lesions: bacterial dermatitis, CHV
• CNS: Rabies, aujeszky

Question 8

Therapy?

Answer 8

Therapy

• Supportive: in generalised phase (good Immune response & antigenicity of virus)
• Hyperimmune serum in early phase
• Inform the owner about the possibility of CNS disease
• AB therapy against bacterial (e.g. B. bronchiesptica) complications
• Vomiting, diarrhoea ʹ IV electrolyte therapy
• CNS signs
• Against convulsions: Phenobarbital, 2 mg/kg, 12h
• Anti-inflammatory: Dexamethasone IV 1-2 mg/kg daily
• Status epilepticus: Diazepam 5-10 mg rectal or slow IV

Question 9

Prevention?

Answer 9

Prevention

• Maternal Ab halftime 8, 4 days; protection until 1-4 weeks, clearance in 12-14weeks
• Vaccinations usually in 6-16 weeks, repetition in 3-4 weeks
• Convalescence or repeated vaccination provides long immunity
• Inactivated vaccines usually less efficient (canarypox vector)
• Weaker protection
• Attenuated vaccine: residual virulence ʹ combo: better effect, licensed for DOG
• Dangerous in others!
• Vaccinate: 3 month 2x, (inhib by mat atbs), 1 yr old 1 x, 2 year yearly, then every 2-3 year
• Repeat vaccine Æ Several year protection!
• 1:20 VN titre or above is protective
• Public health important: Scelerosis multiplex? Pagets disease
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