PARVOVIRUS INFECTION PARVOVIRUS INFECTION IN DOGSIN DOGS

•Introduction Introduction EtiologyEtiology•PathogenesisPathogenesis•Signs & SymptomsSigns & Symptoms•DiagnosisDiagnosis•TreatmentTreatment•Prevention & ControlPrevention & Control•Etiology/ EpidemiologyEtiology/ Epidemiology•EvolutionEvolution•Helpful LinksHelpful Links•ReferencesReferences

IntroductionIntroduction

• Relatively new disease that struck the canine population in 1978.

• Charcterized by vomiting and bloody diarrhoea in young pups.

• Virus has a selective effect on the most rapidly dividing cells of the body.

• The lining of the small intestine and the cells of the bone marrow are most severely affected

EtiologyEtiologyParvovirus of Parvoviridae familyParvovirus of Parvoviridae family

Family Parvoviridae

Subfamily Parvovirinae(birds & mammals)

Subfamily Densovirinae(insects)

Genus Parvovirus*(CPV)*

Genus Erythrovirus(B19V)

Genus Dependovirus(AAV)

Genus Densovirus

Genus Iteravirus

Genus Contravirus

Source for pictures: http://viperdb.scripps.edu/gallery_maker.php

Genus DensovirusGenus Parvovirus

General Characteristics of Family General 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

Source for pictures:http://www.virology.net/Big_Virology/BVDNAparvo.html

Diagram source:http://web.uct.ac.za/depts/mmi/stannard/linda.html

EM of canine parvovirus

X-ray crystallographyof canine parvovirus

Icosahedron

General Characteristics of Family General Characteristics of Family ParvoviridaeParvoviridae

GenomeGenome• 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.

Diagram source: http://servet.uab.es/avillaverde/Caan/data/figs/3-9.htm

Parvovirus TypesParvovirus Types• The 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 ever-changing virulence of this bug.

Specific Types• CPV-1: a.k.a. 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). [Schwartz et al.]

• CPV-2: This emerged suddenly in 1978, most likely from FPV, to cause gastroenteritis in adult dogs and myocarditis in very young pups. After ‘jumping the species barrier’ from FPV, CPV-2 was further selected for growth within dog cells, making dogs a better and natural host [Strauss p 276].

• CPV-2 mutated and evolved again in 1979 to give us CPV-2a , in 1984 to produce CPV-2b, and finally CPV-2c most recently in Italy, Vietnam, and Spain [Decaro et al.].

Canine Parvovirus PathogenesisCanine Parvovirus Pathogenesis(CPV-2)(CPV-2)

• 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.

Canine Parvovirus PathogenesisCanine Parvovirus PathogenesisDilated crypt epithelium

Acute hemorrhagic enteritis

Source for pictures:http://w3.vet.cornell.edu/nst/nst.asp?Fun=Home

Source for drawings:http://www.veterinarypartner.com/Content.plx?P=A&C=189&A=581&SourceID=

Signs & SymptomsSigns & Symptoms• Signs 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 [Merck].

• 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!

DiagnosisDiagnosis

• Extensive history based upon clinical signs

• Positive fecal ELISA result to confirm• Newest 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. The following are some common practices performed in veterinary offices or laboratories:

Diagram source: http://www.clinical-virology.org/pages/cvn/sp_gp/cvn_gp_how.html

DiagnosisDiagnosisNewest 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 parvoDNA 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 [ Decaro, N. et al.]. 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.” [Costantina, D. et al.].

EM 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. The WSVL currently uses EM for diagnosis of parvovirus but it is also developing a PCR test for typing of the virus.

TreatmentTreatment

Supportive care

• replace lost fluids & monitor electrolyte levels

Control vomiting

• withhold food and water• if persistent, the compound metoclopramide

can be administered [Merck].• once vomiting has subsided, a bland diet

such as cottage cheese and rice will suffice• Gradually reintroduce regular diet

Antibiotic therapy• in the most severe cases, such as

bacteriemia and septicemia, antibiotics should be administered with a broad spectrum series [Merck].Note: Prevention and control of the virus is the most

effective means of treatment.

Prevention & ControlPrevention & 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 [Mar Vista Animal Medical Center].

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 [Merck].

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.

Etiology/ EpidemiologyEtiology/ 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 a limbo period of decreased antibody protection from the mother and the inadequate vaccination protection for the young pups [Merck].

• 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 [Merck].

• Mortality rate is variable: 16-48% [Merck].

“Canine parvovirus disease is currently the most common infectious disorder of dogs in the United States.”

[Pet education.com]

EvolutionEvolution

The evolution of Canine Parvovirus is perhaps one of

the most important, and closely studied, evolutionary

pathway in diagnostic virology. This evolutionary

map shows in detail how the current strains of Canine

Parvovirus (CPV-2a and CPV-2b) came into being.

Diagram source: Uwe Truyen (Veterinary Microbiology)

EvolutionEvolution• Prior to the emergence of Canine Parvovirus, this virus infected the cat

(Feline panleukopenia virus or FPLV) and mink (Mink enteritis virus or MEV).

• A mutation of just 2 amino acids enabled FPLV to evolve and make a leap between species.

• At least 11 conserved nucleotide differences (7 nonsynonymous and 4 synonymous changes) were seen between CPV-2 isolates and FPLV-type viruses in the capsid VP2 sequence. However, CPV and FPLV isolates differ in <2% of their genomic DNA sequences.

• In 1978, CPV-2 appeared, quickly spreading worldwide within a couple of months, infecting and killing thousands of dogs. This strain of parvovirus could not replicate well in cats.

• Discovered some years later in 1983, a virus isolated from Artic Fox from Finland (Blue Fox Parvovirus or BFPV ), while being essentially the same as MEV-2, had three synonymous nucleotide changes in the VP2 gene that were specific for the canine sequence. This suggests that BFPV may have been an evolutionary intermediate between FPLV and MEV, and CPV-2.

EvolutionEvolution• With the introduction of vaccines, dogs started to develop immunity to CPV-2.

This forced the virus to mutate once again.

• The new antigenic type, CPV-2a, became the more commonly seen strain by 1981. CPV-2 was rarely seen after this point in time. This marked the death of the original Canine parvovirus strain.

• The new strain of CPV-2a differed from CPV-2 in that it had lost at least one epitope recognized by monoclonal antibodies (MAbs) and gained a new specific epitope.

• In 1984, yet another new antigenic type, CPV-2b appeared. This strain overtook CPV-2a as the parvovirus dogs are most commonly infected with in the United States.

• Both these antigenic types, CPV-2a and CPV-2b replicate effectively in cats. In fact, domestic cats and wild felines both present with these viruses today.

• The newest antigenic type is CPV-2c. This strain, discovered in 1997, has only been found in Leopard cats. The virulence of CPV-2c in dogs has yet to be determined.

Helpful LinksHelpful Links• http://www.workingdogs.com/parvofa

q.htm• http://www.avma.org/careforanimals/

animatedjourneys/pethealth/canine.asp#4

• http://www.avma.org/communications/brochures/canine_parvo/parvo_brochure.asp

• http://www.veterinarypartner.com/Content.plx?P=A&C=&A=1199&SourceID

• http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB

• http://www.marvistavet.com/html/canine_parvovirus.html

• http://www.cpvh.com/Articles/39.html• http://www.peteducation.com/article.

cfm?cls=2&cat=1554&articleid=4• http://www.cdc.gov/• http://viperdb.scripps.edu/links.php

ReferencesReferences

Costantina, D. et al. “Canine Parvovirus Infection: Which Diagnostic Test for Virus?” Journal of Virological Methods 126 (2005): 179-185.

Decaro, N et al. “Occurrence of Severe Gastroenteritis in Pups After Canine Parvovirus Vaccine Administration: A Clinical and Laboratory Diagnostic Dilemma.” Vaccine (2006), doi:10.1016/j.vaccine.2006.10.020

Ikeda, Y. et al. “Feline Host Range of Canine Parvovirus: Recent Emergence of New Antigenic Types in Cats.” Immerging Infectious Diseases, Vol. 8, No.4 (2002): pp 341-346.

Kahn, Cynthia M. ed. The Merck Veterinary Manual 9th edition. Whitehouse Station: Merck & Co, 2005.

Parrish, C.R, et. al. “Rapid Antigenic-Type Replacement and DNA Sequence Evolution of Canine Parvovirus.” Journal of Virology, Vol. 65, No. 12 (1991): pp. 6544-6552.

Schwartz, D., B. Green, L.E. Carmichael and C.R. Parrish. “The Canine Minute Virus (minute virus of canines) is a Distinct Parvovirus That is Most Similar to Bovine Parvovirus.” Virology 302 (2002), pp. 219–223.

Strauss, James H., and Ellen G. Strauss. Viruses and Human Disease. San Diego: Academic Press, 2002.

Truyan, Uwe. “Evolution of Canine Parvovirus-A Need for New Vaccines.” Veterinary Microbiology 117 (2006): 9-13.

Web references:“Canine Parvovirus.” Mar Vista vet.com. 2000. Mar Vista Animal Medical Center. 11 Dec.

2006http://www.marvistavet.com/html/body_vaccination_options_prevention.html.

“Parvovirus.” Pet Education.com. 2006. Drs. Foster & Smith, Inc. 11 Dec. 2006http://www.peteducation.com/article.cfm?cls=2&cat=1554&articleid=4.