Parvo virus Infection in Dog & its Therapeutic

Management

Presented By: Dr.Bibhu Ranjan DasAdm. No.-03/VCME/10

Canine ParvovirusCanine Parvovirus IntroductionIntroduction EpidemiologyEpidemiology Family Characteristics & Structure Family Characteristics & Structure Parvovirus TypesParvovirus Types PathogenesisPathogenesis Sign & SymptomsSign & Symptoms DiagnosisDiagnosis TreatmentTreatment Prevention & ControlPrevention & Control

IntroductionFamily Parvoviridae

Family Parvoviridae

Subfamily Parvovirinae(birds & mammals)

Subfamily Densovirinae(insects)

Genus Parvovirus*(CPV)*

Genus Erythrovirus(B19V)

Genus Dependovirus(AAV)

Genus Densovirus

Genus Iteravirus

Genus Contravirus

Genus Densovirus

Genus Parvovirus

Epidemiology

Canine parvovirus is an extremely hardy bug that is able to withstand harsh environmental conditions and common disinfectants.Highly contagious. Mainly affects young puppies that are 6-20 wks old due to decreased antibody protection from the mother and the inadequate vaccination protection for the young pups.Adult dogs may be asymptomatic carriers and shed the virus periodically.Certain breeds seem to be particularly susceptible: Rottweilers, German Shepherds, Doberman Pinschers, and American Pit Bull Terriers.Mortality rate is variable: 16-48%

General Characteristics of Family Characteristics of Family ParvoviridaeParvoviridae

MorphologyMorphology

• Virion is non-enveloped

• Nucleocapsids are 18-26 nm in diameter

• Symmetry is icosahedral with capsids (protein coat surrounding DNA) made up of 60 molecules of overlapping capsid proteins designated: VP1, VP2, & VP3

• Surface projections appear as small, rough spikes

EM of canine parvovirus

X-ray crystallographyof canine parvovirus

Icosahedron

General Characteristics of Family Parvoviridae

Genome• DNA is single-stranded (– sense or a combination of both + and

-), linear, and ~5Kb long.• Palindromic sequences (100-300 nucleotides long) form a

hairpin structure, which is important for initiation of replication.

Palindromic sequences resulting in hairpin structure.

Parvovirus TypesThe genus Parvovirus contains viruses that are some of the smallest and hardiest of bugs, able to survive in a wide range of climatic conditions in nature.These viruses also have a variable host range, infecting many different mammal & bird species in which the viruses have been named accordingly: Canine Parvovirus (CPV), Feline Parvovirus (FPV), Porcine Parvovirus (PPV), Bovine Parvovirus (BPV), Goose Parvovirus (GPV), etc., etc.CPV in particular is an example of an emerging virus due to its recent appearance (1970’s) and rapid spread throughout the world.The evolutionary capabilities of this virus has produced many types to date and is related to the virulence of this bug. ever-changing

Specific Types

CPV-1: canine minute virus (CMV). This is the first described canine parvovirus in late 60’s / early 70’s that is associated with fetal viral infections, that leads to reproductive failure and neonatal respiratory disease. It may also produce enteritis in puppies and older dogs. However, it has been shown by DNA sequencing to be more closely related to bovine parvovirus (BPV) than canine parvovirus today that is descended from feline parvovirus (FPV).

• CPV-2: • This emerged suddenly in 1978

• 'Parvo' is a highly contagious disease characterized by diarrhea that is often bloody.

• Prior to 1980, most canine parvovirus that caused disease was Type 2 (CPV-2). After 1980, CPV-2 was replaced by CPV-2a became more common and in 1986,another variation called CPV-2b appeared. In the past few years, a new strain, CPV-2c has been detected. Today, CPV-2b has largely replaced the previous strains as the most common parvovirus causing disease in the dog

Life cycle of Parvovirus

Canine Parvovirus Pathogenesis

Incubation: 3-8 days, with shedding of the virus beginning on the 3rd day, before the appearance of clinical signs.

Transmission is either through direct contact with infected dog’s feces, or indirectly through fecal-contaminated fomites. The virus may be shed up to 3 weeks following infection and may survive up to 9 months in a contaminated area.

Following inhalation or ingestion, the virus will initially replicate within the lymphoid tissues of the oropharynx region.

Now in the bloodstream, the virus will seek out rapidly dividing cells such as: bone marrow cells, lymphopoietic cells, and intestinal epithelium, leading to viremia and further replication and lysis of these host cells.

Tropism for intestinal epithelium leads to collapse of intestinal villi, epithelial necrosis, and hemorrhagic diarrhea—clinical signs of gastroenteritis.

Depletion of lymphocytes and compromised gastrointestinal system may lead to bacteremia by normal gut flora, i.e. Escherichia coli, which can be fatal.

PathogenesisPathogenesis

• TonsilsTonsils• Replicates in Lymphocytes

• in the next 3-4 days

Cell lysis Cell lysis Viremia Viremia

Bone MarrowBone MarrowStem cells

GITGIT

MyocarditisMyocarditis

Dilated crypt epithelium

Acute hemorrhagic enteritis

Hemorrhagic enteritisVilli become blunted and

unable to absorb nutrients

Barrier to GIT flora is broken down

Mechanism of Death

1. Diarrhea and vomiting

extreme dehydration SHOCK

2. Loss of intestinal barrier

bacterial invasion SEPTIC SHOCK

Signs & SymptomsSigns and symptoms are related to usually 2 disease presentations: gastroenteritis and myocarditis. Myocarditis however is rarely an issue currently due to immunization practices in the mothers.

Initial signs of CPV infection: depression, fever, anorexia, vomiting, and severe diarrhea. Feces may be yellowish gray due to the presence of mucus. The feces may also contain blood due to the onset of hemorrhagic enteritis.

Dehydration is also common due to the rapid loss of fluids from vomiting and loose stools. Some very unfortunate puppies may experience projectile, bloody diarrhea and vomit until their deaths (48-72 hrs following obvious signs).

CPV infections have been misdiagnosed, unfortunately due to the similarities in symptoms to parasitic infections, stress colitis, or perhaps the dog’s last meal was disagreeable.

So, the correct diagnostic tools are crucial to prevent the deaths of such young pups.

Diagnosis

Extensive history based upon clinical signsPositive fecal ELISA result to confirmNewest diagnostic tools

ELISA (Enzyme-Linked Immunosorbent Assay)

The ELISA test is the most efficient test to use. It takes only 15 minutes and can be easily performed in the veterinary office.

However, ELISA is a very sensitive test and can be influenced by some different factors such as recent vaccination and onset of clinical signs, giving false positive or false negative results.

Testing is the only way that you will know for certain if you have a parvovirus problem. Testing is the only way that you will know for certain if you have a parvovirus problem.

The following are some common practices performed in veterinary offices or laboratories:

DiagnosisNewest Diagnostic Tools

PCR: Parvovirus PCR testing has been shown to be a very effective and sensitive way to detect canine parvovirus. Dogs that have been experimentally exposed to parvo had positive fecal PCR results from day three to day fourteen after exposure. This gives you a much bigger window of opportunity to diagnose the virus. The PCR test will also find the presence of fecal parvo. DNA even when an antigen test (ELISA) showed a negative result.

Real-time PCR is the newest technology using a minor groove binder (MGB) probe assay to specifically identify CPV-2 vaccine strains and field strain types (2a, 2b, and 2c). It is based on the TaqMan technology, and this real-time PCR has been proven to be even more specific, sensitive, and reproducible than other conventional methods such as: hemagglutination assays,immunochromatographic tests, viral isolation, and even gel-based PCR.

Other advantages compared to conventional PCR:

Less time-consuming, less chance of carry-over contamination.However, the molecular assays, especially the real-time PCR method, require expensive equipment, reagents and specialized operators; thus, their use as tests for the veterinary practice is not feasible. Nevertheless, there are efforts by several companies to adapt molecular methods to clinical practice, taking advantage of microchip technology that would reduce the cost and size of the equipment necessary for on site testing.

Electron microscopy :

Electron microscopy is another vital diagnostic tool utilized to view the morphological characteristics of extremely small organisms, like parvoviruses, when standard microscopy will not suffice. Even with all the newest forms of diagnostic methods, EM is still extensively used as a reference technique, especially in cases of specimens expected to contain high concentrations ofthe virus in diarrheic stool samples.

Haemagglutination (HA)Haemagglutination (HA)

virus No virus

HaemagglutinationHaemagglutination

Dilution

2 4 8 1632 64128256512

prozone titre

1024 Novirus

Comparison of sensitivityComparison of sensitivity

dilution0 1/10 1/1001/1000..…….. 10-7

IDEXX

Virus isolation

HA 1/8192 (HA titre during peak clinical signs

is 1,000 -10,000)

Haemagglutination inhibition Haemagglutination inhibition (HAI)(HAI)

• heat to inactivate complement in serum

• adsorb to RBC, then remove

• dilute (1/20, 1/40 etc)

• add virus

• incubate

• add RBC

• incubate

HAIHAISerumdilution

1/201/401/801/1601/3201/6401/1280

-ve control

1 wk8 wksVirusHA

Differential Diagnosis

Canine Distemper Infectious Canine Hepatitis Canine Coronavirus Salmonellosis Campylobacteriosis Gastroenteritis (HGE) Toxicosis

Treatment There is no specific therapy to eliminate the virus.

Most dogs recover with appropriate supportive care directed to restoration of fluid balance.

Oral electrolyte solutions may be used in mildly dehydrated dogs without a history of vomiting.

More severely affected dogs should receive IV fluid therapy (lactated Ringer’s and 5% dextrose with additional potassium chloride [10-20 mEq/L]) to counter dehydration and maintain fluid balance. Monitoring of electrolyte changes is advisable.

Most dogs that survive the first 2-3 days of disease recover. Persistent vomiting can be controlled with metoclopramide, 0.2-0.5 mg/kg, PO or SC, qid, or 1-2 mg/kg/day, slow IV). Routine use of antibiotics is discouraged. More severe cases (eg, dogs with severe blood loss, fever, or loss of intestinal integrity) are predisposed to bacteremia and septicemia. In these cases, a combination of either ampicillin or a first- or second-generation cephalosporin, plus an aminoglycoside or enrofloxacin, provide broad-spectrum coverage. Food and water should be withheld until vomiting has subsided. After this, small amounts of a bland diet (eg, cottage cheese and rice or a commercially available prescription diet) should be offered frequently. A small volume of warm, salted meat broth should be given concurrently. If GI signs recur after feeding, the dog should be fasted for an additional 12-24 hr before feeding again. The dog’s regular diet can be gradually reintroduced.

A somewhat controversial study has just been published in the Journal of Veterinary Emergency and Critical Care (Savigny et al 2010). The study looked at the use of Tamiflu (oseltamivir) for the treatment of parvovirus infection in dogs. Parvaid is an all natural organic nutraceutical which aids in the treatment of the deadly Parvo Virus. The treatment is high in vitamin C and other antioxidants that are important in combating severe health situations, and in addition, it is soothing to the digestive system and the mucous membranes. Generally, Parvaid is to be given to the dog orally 3 to 4 times daily. The correct dosage amount will depend upon the dog's weight and size. Parvaid is most commonly used to treat puppies and dogs with Parvo.

Cont.....

Prevention & Control1. Vaccination2. Decontamination3. Isolation

VaccinationThe most important form of prevention is to vaccinate against CPV-2a and CPV-2b. The most effective vaccination available is the live-attenuated canine parvo. It is most important to vaccinate puppies, however adult dogs that have been continuously vaccinated are at low risk and may not need to be vaccinated so often. To protect puppies from infection, a series of vaccine shots should be given every 2-4 weeks until they are 16 weeks old. By that time the maternal antibodies will have gone and the vaccine will be able to take affect.

DecontaminationThe only absolutely effective disinfectant is bleach at a 1:30 dilution. Use to disinfect hands, clothing, food and water bowls, toys, anything that the puppy may come into contact with, or has regular contact with.

IsolationInfected animals must be isolated from healthy animals to prevent the spread of the virus. Places of high risk are dog shows, field trials, boarding kennels and public spaces reserved for dogs.

Maternal Antibodies

• Critical period and vaccine response varies with the individual – Dams antibody level

– First born, aggressive pups• More colostrum Higher MA

Vaccine Failure

• Ineffective Vaccine – Inappropriate storage– Inappropriate administration– Low titer vaccine

• Immunogenicity and Serological response– Virulence of parent viral strain– Method and level of virus attenuation– Amount of attenuated virus in each dose– No vaccine produces 100% immunity

• Health Status– Fever– Immunocompromised animals

• Client Compliance– Recommended vaccination schedule

• Breed– A disproportionate number of Rottweilers that have

been properly vaccinated will develop parvo

• The primary cause of failure of canine parvovirus vaccines is an interfering level of maternal antibody against the canine parvovirus.

• Maternal antibodies are the antibodies present in the mother's milk during the first 24 hours after the puppy‘s birth.The age at which puppies can effectively be immunized is proportional to the titer of the mother and the effectiveness of transfer of maternal antibody within those first 24 hours.

• High levels of maternal antibodies present in the puppies bloodstream will block the effectiveness of a vaccine.

• When the maternal antibodies drop to a low enough level in the puppy, immunization by a commercial vaccine will work.

• The complicating factor is that there is a period of time from several days to several weeks in which the maternal antibodies are too low to provide protection against the disease. This period is called the window of

susceptibility. This is the time when despite being vaccinated, a puppy can still contract parvovirus. The length and timing of the window of susceptibility is different in every puppy in every litter.

• At six weeks of age, 25% of the puppies could be immunized. At 9 weeks of age,40% of the puppies were able to respond to the vaccine. The number increased to 60% by 16 weeks, and by 18 weeks of age,95% of the puppies could be immunized.

• The recommended protocol is to vaccinate puppies against parvovirus beginning at 6-8 weeks of age, and revaccinating every 3 weeks until the puppy is 16-20 weeks of age. A booster is given at one year of age and every 1-3 years thereafter.

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