World Veterinarian Quiz 36

Canine Distemper

• CD is a highly contagious, systemic, viral disease of dogs, characterized by a diphasic fever, leukopenia, GI and respiratory catarrh, and frequently pneumonic and neurologic complications.
• first recorded case described in 1905 by French veterinarian Henri Carre

Synonym:

• Carre's Disease ( Due to scientist name)
• Hard-pad disease (Skin/Foot pad → Viral replication in stratum spinosum → Dysfunction in cell replication and differentiation → Orthokeratotic hyperkeratosis).
• Old dog encephalitis : (Direct or indirect effect of virus leads to oligodendrocyte necrosis and loss of myelin sheath (demyelination)

 Etiology:

•      Canine distemper virus – Pantropic – SS RNA

•      Genus:  Morbillivirus

•      Family: Paramyxoviridae

•      Virulence factors

•      Hemagglutinin (H):

•      Attachment to host cells

•      Fusion (F) protein:

•      Cell membrane penetration

•      Syncytia formation

Host:

•      Primarily a disease of Dog / Canine

•      Wide range of terrestrial carnivores

•      Canidae (dog, fox, wolf)

•      Ferrets, mink, raccoons

•      Red Panda

•      Bear

 

Transmission:

•      Direct contact 

•      Secretion from nasal and oral cavity

•      Aerosol

•      Contaminated food, water, fomites

Pathogenesis:

•      Virus reach to nasopharyngeal mucosa→ binds to host CD150 on activated T cells, B cells and dendritic cells of tonsils and regional lymph nodes →  Virus replication in first 24 hours → Cell-associated viremia by 2 days post infection (PI) → Spread to all lymphoid tissues and blood lymphocytes by 2-5 days PI → Virus replication in cells → Lymphocytolysis → Leukopenia → Immunosuppression .

•      Further development depends on immune status of the host, the age of the host, and the strain of virus

❶ Adequate humoral / cellular immunity

❷ Delayed / intermediate humoral / cellular immunity:

❸Failure to develop neutralizing antibody by 8-9 days PI

 

❶ Adequate humoral / cellular immunity

•      Neutralize virus by 14 days PI – No clinical disease

❷ Delayed / intermediate humoral / cellular immunity:

•      Viral infection / persistence in mucosal epithelium and brain → may develop neurologic disease

❸Failure to develop neutralizing antibody by 8-9 days PI

•      Virus disseminates to respiratory, GI, urogenital, and central nervous systems; integumentary, exocrine and endocrine systems also affected → virus shedding in secretion and excretion  → secondary infections common

•      CNS → Viral enter in CNS through infected lymphocytes / cell free virus state → Virus replication in endothelium cells → Infect Astrocytes, Microglial cells and Choroid plexus epithelium/Ependymal cells → Spread in CSF → Infect Neurons (Polio encephalomyelitis) and Oligodendrocyte (Leukoencephalomylitis)  

•      Virus replication in neurons leads to neuronal necrosis

•      Direct or indirect effect of virus leads to oligodendrocyte necrosis and loss of myelin sheath (demyelination)

•      Development of CNS signs

•      Respiratory → Viral replication in Pneumocyte, Bronchiolar epithelium and alveolar macrophages → Death of these cells → Inflammation and immunosuppression → Secondary bacterial infection → Development of bronchopneumonia

•      Skin/Foot pad → Viral replication in stratum spinosum → Disfunction in cell replication and differentiation → Orthokeratotic hyperkeratosis (Hard pad disease) → Secondary bacterial infection → Impetigo

•      Virus replicate in many other tissue  - e.g. In ameloblasts → defective enamel production → multifocal enamel hypoplasia

Clinical Signs

•      Disease most common in 12-16 week-old puppies

•      Early:

•      Transient fever after 3–6 days PI - unnoticed

•      After few days again fever (Diphasic Fever), conjunctivitis cough, vomiting, diarrhea, depression, anorexia, serous to mucopurulent oculonasal discharge

•      Signs of Pneumonia

•      Diarrhea – Dehydration / Emaciation

•      Pustules on ventral abdomen/Inner thigh

•      Hyperkeratosis of Digital pads (Hard Pad)

•      Keratitis / Retinitis – Blindness

•      Later (1-4 weeks): Neurologic

•      Epilepsy

•      Chewing movements

•      In coordination

•      Muscular twitching  (myoclonus) in face, head, neck or shoulder muscles

•      May see minimal or no signs of epithelial infection and only neurologic signs in some dogs.

Macroscopic Pathology:

•      Integument

•      Hyperkeratosis of footpads and nose

•      Secondary pyoderma (pustular dermatitis, especially ventral abdomen)

•      Lungs

•      Patchy red-tan, rubbery subpleural and marginal lesions (bronchointerstitial pneumonia)

•      May be edematous and consolidated (secondary bronchopneumonia)

•      Eyes/conjunctiva: Conjunctivitis, keratitis

•      Lymphoid tissues: Tonsillar enlargement, thymic atrophy

•      Teeth: Enamel hypoplasia

Teeth: Enamel hypoplasia

Teeth: Enamel hypoplasia

                                                        Interstitial bronchopneumonia with edema 

  

Hyperkeratosis of Digital pads (Hard Pad)

  Microscopic Pathology:

•      Eosinophilic intracytoplasmic (IC) and/or intranuclear (IN) inclusion bodies (IB) with syncytia

•      Most numerous 10-14 days PI

•      Most obvious in brain (often intranuclear) and epithelium (usually intracytoplasmic), especially in urinary bladder

•      Integument:

•      Orthokeratotic and/or parakeratotic hyperkeratosis of footpad, nose with inclusion bodies (IB)

•      Lungs:

•      inclusion bodies (IB) with syncytia in bronchial/bronchiolar epithelium

•      Alveoli: Filled with edema, fibrin, mononuclear cells, necrotic epithelium

•       Septa expanded by mononuclear cells; Syncytial cells (Viral protein that mediates fusion of an infected cell with neighboring cells leading to the formation of multi-nucleate enlarged cells called syncytia.)

•       Central nervous system:

•       White matter: Demyelination

•       Gray matter  - IB in neurons, neuronal necrosis, MNC infiltrate surrounding necrotic neurons , perivascular  cuffing

•       Lymphoid tissues:

•       Early lymphoid depletion and lymphocytic necrosis

•       Teeth

•       Cystic degeneration of ameloblastic epithelium

•       Other epithelia

•       Degeneration and IB

 

Viral inclusion bodies, canine distemper, brain, dog. Note the intranuclear eosinophilic inclusion bodies in glial cells. 

chronic inflammation, as seen with some viral infections, consists of an exudate of lymphocytes with occasional macrophages and plasma cells.central nervous system, these cells can have a perivascular pattern of distribution.In certain animal species (exotic wildlife species, horses) and specific disease categories (para­sitic, protozoal, viral), perivascular chronic inflammatory exudates may also contain variable numbers of eosinophils.

 

 

Old-dog encephalitis

•      Occur in mature adult dogs

•      Rare variant

•      Possibly caused by infection with replication-defective virus

•      Chronic progressive neurologic disease

•      Nervous signs as like CD

•      Pathology  - CNS  - similar to CD

Diagnosis

•      Clinical signs

•      Histopathology

•       Laboratory tests

•      Virus isolation

•      Virus neutralization tests   

•      Enzyme-linked immunosorbent assay (ELISA)

•      Polymerase chain reaction

•      Serological tests

Canine Distemper Virus Antigen Lateral Flow Assay kit

Test principle:  This kit uses the principle of Colloidal Gold Immunochromatography assay. The sample will move together with the colloidal gold marker along the chromatography membrane. If Canine Distemper Virus (CDV) antigen exist in the samples, it will combine with the colloidal gold marker to make the detection line appear a purple color. Otherwise, it will not show the color reaction.

Sample preparation

1. Nasal fluid, saliva and conjunctival secretion：Swab the nasal fluid, saliva or conjunctival secretion with stroke-physiological saline solution cotton swabs. Immediately, insert the cotton swab into the Sample Diluent, stir the swab until the sample is dissolved into the sample diluent fully. Discard the cotton swab after wiping it against the wall of the tube. Make sample solution stand for later use.

2. Serum, urine：Add 4~5 drops (about 100 μL) of serum or urine samples to the Sample Diluent, mix fully, make the sample solution stand for later use.

3. Bring all reagents to room temperature for 30 min before use.

Note: In the initial stage of canine distemper virus infection, it is better to take blood as the sample. Because there are no symptoms such as conjunctivitis, dry cough, diarrhoea and so on. If suspected symptoms of canine distemper virus infection have appeared, it is more convenient to take the conjunctival epithelial cells or urine as the sample.

Assay procedure

1. Take out the detection card and put it on a clean table.

2. Take the sample supernatant with the pipette, add 2~3 drops (about 60 μL) of sample to the sample well vertically and slowly (Avoid foaming).

3. Incubate for 5 to 10 minutes and then judge the results immediately.

Judgment of result

1. Negative: Only the control line region (C) shows a purple line in the observation well.

 2. Positive: Both the test line region (T) and the control line region (C) show a purple line in the observation well.

3. Invalid: No purple line shows in the observation well of the control line region (C).

Interpretation of the results

1. The negative result reveals that there is no CDV antigen in the sample. If there is a corresponding acute symptom, then CDV infection cannot be excluded.

2. The positive result reveals that there is CDV antigen in the sample. It might be infected with CDV, and the result should be combined with other methods to analyse.

3. As the CDV vaccine is generally with low virulence, the virus will increase in the body for a period of time which shows a positive result in the process of immunizing. The phenomenon will disappear in 3~10d after immunization. Animals treated with monoclonal antibodies may exhibit false-positive for a long time because the animals produce second antibodies to the anti-monoclonal antibodies in the body.

Treatment

·         We all know that viral disease has no treatment so treatment involves managing the various symptoms and secondary infections. Even with treatment, distemper can be fatal.

·        Treatment depends on the symptoms shown and may include

·         Fluids to combat dehydration,

·         Medication to reduce vomiting,

·         Antibiotics and other medications to treat pneumonia, antibiotics for secondary infections,

·         Anticonvulsants to treat seizures.

·         Neurological symptoms may get progressively worse and not respond to treatment, and even with recovery, some neurological effects may persist.

How to Prevent Distemper

·         Vaccination is effective at preventing distemper. Puppies are typically vaccinated starting at six weeks of age and regular intervals until they are 14 to 16 weeks old (as with other vaccines, the presence of antibodies received from the mother can interfere with vaccines so a puppy is not considered fully protected until the final vaccine in the series has been given).

·         Vaccination should be repeated a year later, then at regular intervals. Your vet will discuss an appropriate vaccination schedule for your dog based on your dog's history and risk factors.

·         Until puppies have received all the vaccination in the series (at 14 to 16 weeks) it is prudent to be careful about exposing them to unknown dogs such as at dog parks to avoid exposure to the virus as much as possible.

REFERANCES :

Pathologic Basis of Veterinary Disease Expert Consult

6th edition

By: James Zachary, M. McGavin

Canine Distemper Virus Antigen Lateral Flow Assay kit Catalog No: E-AD-C025 50T2018-2019 Elabscience Biotechnology Inc.