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2c_CAT AND DOG VIRAL DISEASES

By Victoria Graham,2014-06-21 11:15
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2c_CAT AND DOG VIRAL DISEASES

    COMMON VIRAL DISEASES OF DOGS AND CATS

    ? Important points covered include the prevention and control of infectious diseases

    with regard to vaccination and isolation which is especially important in a shelter

    environment.

    ? There are numerous infectious diseases in dogs and cats; however, I will only

    have time to cover common ones seen on a daily basis by veterinary surgeons for

    which vaccines are available.

A. CANINE VIRAL DISEASES

? Distemper

    ? Parvo

    ? Parainfluenza (Kennel cough)

    1. DISTEMPER

a) Aetiology:

    ? Distemper is caused by a paramyxo virus spread by contact with faeces, nasal

    discharge and other body excretions and secretions.

    ? Incubation period is around 8-14 days after viral contact.

    ? The virus can continue to be shed from the body for up to 60-90 days after

    infection; however, dogs with CNS signs are not usually shedding the virus.

    ? The virus survives for around 20 minutes in exudates and is susceptible to

    most hospital disinfectants.

    ? The disease is commonly seen in unvaccinated puppies from pet shops,

    hawkers or dog farms.

    b) Clinical signs:

    ? The virus attacks the mucosa (epithelium) lining the respiratory tract and

    bowel causing a wide variety of clinical signs such as sneezing, nasal

    discharge, coughing, difficulty breathing (dyspnoea), eye (ocular) discharge,

    conjunctivitis, vomiting and diarrhoea.

    ? The initial signs may be any of the above but are most commonly fever

    (pyrexia), depression, tonsillar enlargement, coughing and nasal discharge.

    ? Later clinical signs can include thickening of the footpads or nose

    (hyperkeratosis).

    ? Nervous signs can develop due to viral encephalitis resulting in fitting, ataxia

    and chorea (myoclonus e.g. “chewing gum” seizures). The nervous signs can

    take anything from 1 week to several years to develop and are usually seen in

    dogs with poor immune status (low antibody levels).

    ? Young dogs which are infected while their permanent teeth are developing

    can suffer with poor enamel (hypoplasia) and discolouration of the teeth.

? It is important to note dogs can show all OR only one of the above clinical

    signs; there is a great variety of presentations to Distemper depending on age,

    immune status, environment and virus strain.

    c) Diagnosis:

? From the history and clinical signs.

    ? Haematology can be normal or have a persistent leucopenia and mild

    thrombocytopenia.

    ? Immunoassay test kits are now commercially available for detecting the

    distemper virus antigen e.g. “Anigen Rapid” CDV Ag Test. This test uses

    canine secretions of either fresh eye mucous (from conjunctiva), nasal

    discharge, saliva, urine, serum or plasma. Test results are available within 5-

    10 minutes. These tests should not be relied on for a definitive diagnosis

    rather they should be interpreted in the light of clinical signs and history as

    well.

    ? It is very important to distinguish Distemper from Kennel Cough (Infectious

    Tracheobronchitis caused by Parainfluenza virus and Bordatella

    bronchiseptica) as kennel cough carries a considerably better prognosis for

    recovery compared to distemper.

    d) Treatment Involves treating the clinical signs and supporting the animal whilst

    its own immune system fights the virus.

? Antibiotics can be used to treat secondary bacterial infections such as:

    a) Amoxycillin/Clavulanate (“Clavulox”) at 8.75mg/kg once daily by

    injection or 12.5-25mg/kg twice daily by mouth.

    b) Trimethoprim/ Sulphonamide (“Baprim” or “Chemoprim”) at 15mg/kg

    once to twice daily by injection or 15mg/kg twice daily by mouth.

    c) Fluoroquinolones such as Enrofloxacin (“Baytril”) at 5mg/kg by injection

    or by mouth once daily. Enrofloxacin should be used with caution in

    puppies less than one year as it can result in cartilage abnormalities (also

    in kittens less than 8 weeks). In life and death circumstances these side

    effects become less important; however.

    ? Respiratory Medications include:

    a) Mucolytics e.g. Bromohexine at 2.5mg/kg by mouth twice daily

    which is a bronchial secretolytic which helps reduce nasal and

    chest congestion.

    b) Bronchodilators e.g. Theophylline (“Nuelin”) at 20mg/kg by

    mouth 2-3 times daily which help open the larger airways and

    increases the clearance of mucus from the lungs.

    c) Antitussives e.g. Butorphanol (“Torbugesic” or “Torbutrol”) at

    0.05-0.1mg/kg by injection or 0.5-1mg/kg by mouth every 6-12

    hours will suppress coughing. This is useful for non productive,

    dry coughs.

    d) Nebulisation or oxygenation in a special chamber with either

    menthol type preparations or antibiotics such as Gentamicin or

    Enrofloxacin infused into the air or oxygen.

? Gastro-intestinal medications include:

    a) Anti vomiting drugs e.g. Metoclopramide (“Mecloma”) at 0.5-1mg/kg given

    by injection or mouth every 6-8 hours, and can also be placed into the drip bag

    and given as a continuous intravenous infusion at 1-2mg/kg over 24 hours.

    Intractable vomiting (not responding to Mecloma) can be treated with

    Ondansetron (“Zofran”) at 0.5mg/kg intravenously as a loading dose followed

    by 0.5mg/kg/hr infusion for 6 hours or 0.5-1mg/kg by mouth every 12-24

    hours.

    b) Anti diarrhoeal drugs e.g. “Buscopan” or “Lomotil” act as antispasmodic

    drugs providing relief from bowel spasm. Kaolin/ pectate available in liquid

    form coats and protects the intestinal lining given at approximately 1ml/kg

    (maximum dose is around 15ml) three times daily before feeding.

    c) Anti gastric ulceration drugs e.g. Cimetidine (“Tagamet”) at 5-10mg/kg by

    injection or mouth three times daily are often used when the vomitus contains

    blood indicated by a typical coffee granule appearance. When used orally

    together with metoclopropamide the dosing of these drugs should be staggered.

    Ranitidine (“Zantac”) is becoming more popular and is 4-10 times more

    potent than cimetidine at 2mg/kg by injection or mouth every 8-12 hours.

    d) Subcutaneous fluids can be used for mild cases of dehydration.

    e) Intravenous drips are used if there is more severe dehydration and/or

    persistent vomiting.

    ? Usual administration rate is 2-4ml/kg/hr for maintenance but this rate

    should be increased in the case of severe vomiting and dehydration.

    ? Infusion pumps enable the rate to be monitored accurately (to avoid

    over perfusion) and if the dog bends its leg the pump action will still

    deliver fluids to the patient.

    ? The choice of drip depends on various factors; most commonly

    Lactated Ringers solution is used supplemented with potassium

    chloride (20-40mEq/l) if there is chronic vomiting. If hypoglycaemia

    is suspected 2.5-5% Dextrose can be added to the drip.

    f) Intravenous and intraperitoneal plasma from vaccinated dogs can been used as

    a source of antibodies to boost the immune system. The dose rate is very

    variable but is usually around 5-10ml/kg. This can be very expensive and not

    all clients can afford particularly with large dogs.

? Anticonvulsant drugs such as “Valium” (diazepam) at 2-15mg by mouth three

    times daily or Phenobarbitone at 2-8mg/kg twice daily by mouth. These drugs

    are used in an attempt to control Distemper induced twitching and seizures but

    they are rarely effective. Euthanasia on humane grounds is recommended in

    these cases.

e) Prevention and Control:

It is definitely a better idea to prevent rather than attempting to cure the problem once

    the disease is present:

    ? VACCINATION (vaccine protocols will be discussed later).

    ? Ideally a puppy should be isolated until its vaccination course is complete to

    ensure an appropriate immune response has occurred. This is not always possible

    in a shelter environment but at least one vaccination should have been given and

    the puppy should be at least 8 weeks of age before being placed with others. At

    the SPCA dogs less than 8 weeks are placed with foster parents.

    ? Proper hygiene and isolation of any diseased puppies or dogs to reduce the spread

    of the disease is also important.

    ? Isolation facilities ideally should have separate drainage and air ventilation.

    Feeding bowls, utensils etc should all remain within the isolation area as they can

    contribute to disease spread.

    ? One good point is as the virus is very labile it can be easily destroyed with

    hospital disinfectants such e.g. 3M Neutral Quat.

    ? In a shelter environment euthanasia of severely affected animals is essential so

    time and resources can be spent on vaccination and treating less severely affected

    dogs.

    2. PARVO VIRUS

a) Aetiology:

    ? Parvo virus is spread through faeces and is very resistant in the environment

    where it can live for up to one year.

    ? The incubation period from ingestion of the virus to developing clinical signs

    is around 4-14 days and the virus is normally excreted for about 2 weeks post

    infection.

    ? Certain breeds of dog appear more susceptible than others to the virus such as

    Dobermans, Labrador Retrievers and Rottweilers.

     b) Clinical signs:

? Parvovirus attacks rapidly dividing cells including the bone marrow, intestinal

    lining and heart cells. The clinical signs are a result of this damage.

    ? The signs commonly take 2 forms:

    a) Puppies less than 8 weeks of age show a myocarditis often dying suddenly

    or go on to develop signs of congestive heart failure (in utero infection can

    also occur).

    b) In all ages parvovirus can cause severe gastrointestinal damage with acute

    vomiting (often resulting in oesophagitis) and diarrhoea usually with

    blood (intestinal bleeding). Fever and leucopenia are also usually present.

    Death will ensue if left untreated due to dehydration and endotoxaemia/

    septic shock. Other issues include bowel intussusception which should be

    ruled out where there is persistent vomiting.

    c) Diagnosis:

? History and clinical signs for example an unvaccinated puppy from a pet shop

    with bloody diarrhoea.

    ? Bloods for general haematology will often show reduced white blood cells

    (leucopenia/neutropenia).

    ? Biochemistry may show a hypoalbuminaemia due to protein loss through the

    intestines.

    ? ELISA (enzyme linked immunoassay) kits (also know as “SNAP” tests) are

    available to detect the viral antigen in the faeces. Care should be taken with

    the interpretation of these results as false positives may occur due to recent

    vaccination with live-modified virus especially in the previous 14 days. With

    more modern kits this cross reactivity appears less of a problem. Also a false

    negative could occur in the early stages of the disease so it would be wise to

    repeat the test a few days later if parvo is strongly suspected.

    d) Treatment As with Distemper treatment is supportive and symptomatic.

? Myocarditis: as the acute form usually results in sudden death there is no

    treatment. Congestive heart failure cases can have their lives prolonged with

    various heart/ pulmonary drugs, however, the long-term prognosis is

    extremely guarded. Drugs include:

    a) Bronchodilators e.g. Theophylline (“Nuelin”) at 20mg/kg by mouth 2-3

    times daily.

    b) Duirectics e.g. Frusemide (“Lasix”) at 1-2mg/kg by injection every 4-6

    hours initially followed 2mg/kg by mouth 2-3 times daily.

    c) Hypotensive agents e.g. Benazapril (“Fortekor”) at 0.25-0.5mg/kg once

    daily.

    d) Positive inotopes e.g. Pimobendan (“Vetmedin”) at 0.2-0.6mg/kg by

    mouth once daily.

? Enteric form: treatment is supportive as for Distemper using fluid therapy,

    antibiotics and anti vomiting and diarrhoeal drugs.

    a) If serum albumin concentration is less than 2g/dl then plasma

    should be administered (this will also give the patient antibodies

    which may be beneficial). If plasma is not available colloids such

    as “Dextran-70” or “Gelofusin” can be substituted but they are

    not as effective.

    b) In severe vomiting oesophagitis can occur this should be treated

    with Cimetidine or Ranitidine (as per Distemper) and Sucralfate

    “Antepsin” for <20kg give 500mg/dog and for >20kg give 1-

    2g/dog every 6-8 hours,

    c) Dogs who survive the initial infection may have permanent

    damage to their intestines, others show a full recovery.

    e) Prevention and Control:

     As with Distemper it is definitely a better idea to prevent the disease.

? VACCINATION is highly important and will be discussed later.

    ? Proper hygiene and isolation of any diseased puppies or dogs to reduce the

    spread of the disease is also important.

    a) An isolation unit specifically for infectious diseases should be set up. Limited

    staff should have access to this room and no bedding, feeding bowls etc

    should be allowed to leave. All animal treatments and exams should take

    place within this area and vets and assistants should wear gloves and aprons.

    b) A viricidal footbath should be present at the entrance to the room.

    c) As the virus is very persistent in the environment and resistant to many

    chemicals; special viricidal agents are used to clean the cages e.g. “Parvocide”,

    “Virkon” or Bleach at 1:49 dilution.

    d) Once a cage containing a Parvo or Distemper dog is empty at the SPCA these

    cages are cleaned daily for at least 3 days before allowing a new occupant as

    an extra precaution.

    ? Once the animal is discharged from hospital as the virus can be shed for up to

    2 weeks we advise the recovered animal to be kept away from any susceptible

    dogs during this period and to dispose of the faeces responsibly.

    ? We also advise clients if they have a puppy die from Parvo (or Distemper) not

    to introduce new dogs into the household for at least one month and

    preferably the new dog should have completed its vaccination course. Proper

    disinfection should be carried out and all bedding and feeding bowls etc

    disposed of.

    3. KENNEL COUGH (“CANINE INFECTIOUS TRACHEOBRONCHITIS”)

    a) Aetiology:

? Kennel cough is a syndrome associated with a number of different viruses

    including Canine Adenovirus 2 (CAV 2), Parainfluenza virus (PIV) and

    Bordetella bronchiseptica (bacteria).

    ? It is seen very commonly with kennelled animals in pet shops, boarding

    kennels, shelters and dog farms.

    ? It is thought to be related to stress; persistent barking and the presence of a

    high concentration of pathogens spread by close contract in air droplets.

    ? In nearly all cases the disease is self limiting with resolution of signs within 2

    weeks.

    b) Clinical signs:

    ? A harsh; sudden onset cough (sounds like something is stuck in the throat).

    Can be productive or not.

    ? Palpation of the trachea or pulling on collar at exercise often exacerbates the

    cough.

    ? Nasal discharge can also occur.

    ? Coughing can persist for up to 2-3 weeks. The dog is otherwise normal;

    systemic disease is not normally present.

    ? Kennel Cough occasionally will descend into the chest and cause a bacterial

    bronchopneumonia especially in young or immunocompromised patients.

    c) Diagnosis:

? From the clinical signs.

    ? History particularly environment e.g. a recent visit to kennels or groomers.

    d) Treatment:

    ? As the disease is usually self limiting some vets advocate not treating and just

    resting the dog.

    ? If coughing is severe; suppressants such as Butorphanol (“Torbugesic” or

    “Torbutrol”) at 0.05-0.1mg/kg by injection or 0.5-1mg/kg by mouth every 6-

    12 hours can be given. This is useful for non productive, dry coughs. An

    alternative cough suppressant is Hydrocodone bitartrate 0.25mg/kg every 8-12

    hours by mouth.

    ? The only justification to use antibiotics is against Bordetella (a bacteria), a

    good choice is Doxycycline 5-10mg/kg twice daily by mouth or

    Amoxycillin/Clavulanate (“Clavulox”) at 8.75mg/kg once daily by injection

    or 12.5-25mg/kg twice daily by mouth. Antibiotics should be continued for 5

    days after clinical signs have resolved or for a minimum of 10 days. ? If clinical signs have not resolved within 2-3 weeks further work up is needed

    e.g. x-rays and tracheal wash in case a bronchopneumonia or chronic

    bronchitis is developing.

    e) Prevention:

    ? VACCINATION: Good boarding kennels should require vaccination prior to

    entry. Most combination vaccines contain modified-live virus (Canine

    Adenovirus 2 (CAV 2) and Parainfluenza virus (PIV)) and are adequate for

    most dogs.

    ? Intranasal or injectable vaccines against Bordatella may be of use in kennels

    where there is an endemic problem or for frequently boarded animals. These

    vaccines will not eliminate the problem but instead will reduce the severity of

    the disease. Intranasal vaccines occasionally cause clinical signs (coughing)

    which are self limiting but could be disturbing to owners.

    ? Avoid overcrowding and poor hygiene in kennels and shelters.

    ? Kennels should also have separate feeding bowls and bedding and kennel

    keepers should observe good hygiene e.g. washing hands in between handling

    dogs.

    ? In an outbreak, isolation of clinical cases and thorough disinfection of kennels

    should be performed. Bringing in new dogs should be avoided.

    ? If an outbreak affects most of the kennel the whole kennel should be isolated.

4. CANINE VACCINES USED AT THE SPCA HONG KONG:

NOBIVAC DHPPiL = live Distemper, live CAV2 virus (active against hepatitis),

    inactivated Leptospirosis germs, live Parainfluenza and live attenuated Parvovirus.

    NOBIVAC DP = Live Distemper and live attenuated Parvovirus.

    ? The vaccines are usually started at 8 weeks of age. They can be given earlier if

    necessary in cases of high risk such as poor environment and low maternal

    immunity e.g. on puppy farms, certain breeds (Rottweilers).

    ? If necessary 3-4 vaccinations may be given.

    ? Due to the importance of maternal immunity (antibodies from pregnant bitches)

    passing to the puppies both pre (by transplacental) and post birth (via the

    colostrum) it is essential any breeding bitch should be fully and regularly

    vaccinated. Maternal immunity starts to fall anytime from 6-10 weeks.

    ? The second vaccination of the initial course should be given when the dog is at

    least 12 weeks of age so any maternal antibodies will not interfere with the

    immune response to the vaccination, this is particularly important with respect to

    Parvovirus.

    ? It is important to note that a minimum of 2 doses is required for primary

    vaccination.

    ? The regime adopted depends on what age the first vaccination is given:

Regime A: At 6 weeks DP ? 10 weeks DHPPiL ? 14 weeks DHPPiL

    Regime B: At 8 weeks DHPPiL ? 12 weeks DHPPiL +/- 16 weeks DP if high passive

    immunity is suspected (this is particularly important when considering Parvo).

    Regime C: At 10-12 weeks DHPPiL ? 14-16 weeks DHPPiL (or older).

    ? Immunity is not normally complete till 10-14 days after the second vaccination.

    ? In Hong Kong yearly boosters are required with a single dose of vaccine due to

    the higher disease risk compared to the UK or States.

NOBIVAC KC (Kennel Cough)

    ? Can be used in puppies from 2 weeks onwards.

    ? It is an intranasal vaccination against Bordatella bronchiseptica.

    ? The vaccine reconstitutes to 1ml of vaccine and 0.5ml is applied to each nostril.

? A single vaccination is all that is required at least 72 hours prior to exposure with

    regular vaccinations when at risk such as visiting a boarding kennel.

B. FELINE VIRAL DISEASES

? Cat Flu Complex

    ? Feline Panleucopaenia (FIE)

1. FELINE FLU COMPLEX

a) Aetiology:

    ? Cat flu is caused by a mixture of agents:

    a) Feline Viral Rhinotrachietis virus (FVR) also known as Feline

    Herpes Virus (FHV).

    b) Feline Calici virus (FCV)

    c) Chlamydophila felis and Bordetella bronchiseptica which are less

    commonly involved.

    ? Cat Flu is highly contagious spreading by airborne droplets and close contact.

    ? Feline Viral Rhinotrachietis (FVR) virus is easily killed outside the cat, where

    as Feline Calici (FCV) virus is more stable in the environment and can survive

    a few days.

    ? The disease is seen typically in kittens as maternal immunity wanes at around

    4-8 weeks, the source of infection can actually be the “carrier” mother.

b) Clinical signs

    ? Depend on the agent involved:

    a) Feline Viral Rhinotrachietis (FVR) virus is spread by upper respiratory

    tract secretions. It causes fever (pyrexia), depression, not eating

    (inappetance), rhinitis, trachietis, conjunctivitis and corneal ulceration plus

    pharyngitis and tonsillitis (salivation/ dysphagia). Discharges are normally

    serous but can become mucopurulent (green/ yellow) with Chlamydophila

    and secondary bacterial infections such as Bordetella.

    b) Feline Calici virus (FCV) virus is spread by upper respiratory tract

    secretions, urine and faeces. It causes mouth ulceration of the gums,

    tongue and throat, polyarthritis, upper respiratory tract disease or sub

    clinical infection.

    c) Chlamydophila results in a greenish/ yellow conjunctivitis is usually a

    secondary invader.

    d) Bordetella results in coughing and in young kittens pneumonia.

    ? Carrier states can develop with both viruses being shed intermittently after

    resolution of clinical signs especially following stress. This is very common

    with the Feline Viral Rhinotrachietis (FVR) virus with 80% of recovered cats

    being “carriers” the duration of the carrier state is not known but may last

    from weeks to years. Feline Calici (FCV) virus carriers will shed the virus

    continuously in saliva for several months though may eventually cease. ? Some cats are left with chronic sinusitis (due to either active viral infection or

    chronic damage to turbinates by Feline Viral Rhinotrachietis virus) or chronic

    gingivitis (due to Feline Calici virus).

    c) Diagnosis

? Is usually by the clinical signs and history.

    ? Other tests which due to expense and time are usually only performed in

    problem situations such as outbreaks in catteries include: a) Fluorescent antibody tests for Feline Viral Rhinotrachietis or Feline Calici

    virus on smears from conjunctiva, tonsils or pharynx.

    b) Virus isolation on pharyngeal, nasal and conjunctival swabs. c) Cultures taken from the oropharynx for Bordetella.

    d) Treatment As with all viral diseases treatment is supportive and symptomatic.

    ? Antibiotics to prevent or control secondary infection with bacteria. If

    Chlamydophila or Bordetella is suspected Doxycycline at 5-10mg/kg twice

    daily by mouth is the drug of choice for a minimum of 3 weeks. Otherwise

    Amoxicillin 22mg/kg twice daily can be given. It is very important to

    continue the antibiotics for 5 days after all clinical signs have gone. ? Mucolytics to help with nasal congestion e.g. Bromohexine at 1mg/kg once

    daily.

    ? Corneal ulcers resulting from Feline Viral Rhinotrachietis virus can be treated

    with topical anti-viral drugs such as trifluridine or idoxuridine one drop to

    each eye 5-6 times daily for no longer then 2-3 weeks. Other treatments

    includes antibiotic eye drops and topical atropine if mydriasis (a constricted

    pupil) is present to control pain.

    ? Severe nasal congestion can be treated with pediatric topical decongestants

    such as 0.25% phenylephrine. One drop is placed daily into each nostril for 3

    days. Treatment is then stopped for 3 days after which the 3 day course is

    repeated to prevent rebound congestion.

    ? Nebulisation for 15-20 minutes 2-3 times daily.

    ? Supportive therapy such as tempting to eat with strong smelling foods, fishy

    foods are good as is warming the food and making it soft. ? In cases of severe pharyngeal ulceration feeding is done via a stomach tube

    and special liquid concentrated diets.

    ? The disease is normally more severe in pedigree cats such as Persians or

    Scottish Folds.

    ? Chronic disease management includes avoiding stress, oral lysine 250mg/cat

    twice daily (for FVR infection) and long term antibiotics such as Doxycycline

    for 4-6 weeks.

    ? In a shelter environment as per other infectious diseases euthanasia is a

    sensible option for severely affected animals.

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