Canine Parvovirus: Current Perspective

Abstract

Canine parvovirus 2 (CPV-2) has been considered to be an important pathogen of domestic and wild canids and has spread worldwide since its emergence in 1978. It has been reported from Asia, Australia, New Zealand, the Americas and Europe. Two distinct parvoviruses are now known to infect dogs-the pathogenic CPV-2 and CPV-1 or the minute virus of canine (MVC). CPV-2, the causative agent of acute hemorrhagic enteritis and myocarditis in dogs, is one of the most important pathogenic viruses with high morbidity (100%) and frequent mortality up to 10% in adult dogs and 91% in pups. The disease condition has been complicated further due to emergence of a number of variants namely CPV-2a, CPV-2b and CPV-2c over the years and involvement of domestic and wild canines. There are a number of different serological and molecular tests available for prompt, specific and accurate diagnosis of the disease. Further, both live attenuated and inactivated vaccines are available to control the disease in animals. Besides, new generation vaccines namely recombinant vaccine, peptide vaccine and DNA vaccine are in different stages of development and offer hope for better management of the disease in canines. However, new generation vaccines have not been issued license to be used in the field condition. Again, the presence of maternal antibodies often interferes with the active immunization with live attenuated vaccine and there always exists a window of susceptibility in spite of following proper immunization regimen. Lastly, judicious use of the vaccines in pet dogs, stray dogs and wild canids keeping in mind the new variants of the CPV-2 along with the proper sanitation and disinfection practices must be implemented for the successful control the disease.

Full text

REVIEW ARTICLE
Canine Parvovirus: Current Perspective
S. Nandi •Manoj Kumar
Received: 25 May 2009 / Accepted: 22 November 2009 / Published online: 3 September 2010
ÓIndian Virological Society 2010
Abstract Canine parvovirus 2 (CPV-2) has been con-
sidered to be an important pathogen of domestic and wild
canids and has spread worldwide since its emergence in
1978. It has been reported from Asia, Australia, New
Zealand, the Americas and Europe. Two distinct parvovi-
ruses are now known to infect dogs—the pathogenic CPV-
2 and CPV-1 or the minute virus of canine (MVC). CPV-2,
the causative agent of acute hemorrhagic enteritis and
myocarditis in dogs, is one of the most important patho-
genic viruses with high morbidity (100%) and frequent
mortality up to 10% in adult dogs and 91% in pups. The
disease condition has been complicated further due to
emergence of a number of variants namely CPV-2a, CPV-
2b and CPV-2c over the years and involvement of domestic
and wild canines. There are a number of different sero-
logical and molecular tests available for prompt, specific
and accurate diagnosis of the disease. Further, both live
attenuated and inactivated vaccines are available to control
the disease in animals. Besides, new generation vaccines
namely recombinant vaccine, peptide vaccine and DNA
vaccine are in different stages of development and offer
hope for better management of the disease in canines.
However, new generation vaccines have not been issued
license to be used in the field condition. Again, the pres-
ence of maternal antibodies often interferes with the active
immunization with live attenuated vaccine and there
always exists a window of susceptibility in spite of
following proper immunization regimen. Lastly, judicious
use of the vaccines in pet dogs, stray dogs and wild canids
keeping in mind the new variants of the CPV-2 along with
the proper sanitation and disinfection practices must be
implemented for the successful control the disease.
Keywords Canine parvovirus Hemorrhagic enteritis 
Myocarditis Minute virus of canine Vaccination
Introduction
Canine parvovirus 2, the causative agent of acute hemor-
rhagic enteritis and myocarditis in dogs, is one of the most
important pathogenic viruses. It is a highly contagious and
often fatal disease. CPV-2 was first recognized in 1977 and
since then it has been well established as an enteric path-
ogen of dogs throughout the world with high morbidity
(100%) and frequent mortality up to 10% [2,6]. CPV is
believed to have originated as a host range variant from
feline panleucopenia virus (FPV), include a direct mutation
from FPV, a mutation from a FPV vaccine virus and the
adaptation to the new host dog via non-domestic carni-
vores, like mink and foxes. The disease is characterized by
two prominent clinical forms (i) enteritis with vomition and
diarrhea in dogs of all ages [1,99] (ii) myocarditis and
subsequent heart failure in pups of less than 3 months of
age [30]. The virus was named CPV-2 in order to differ-
entiate it from a closely related parvovirus of canine known
as CPV-1 or minute virus of canine (MVC). MVC, a
completely different parvovirus, had not been associated
with natural disease until 1992. MVC may cause pneu-
monia, myocarditis and enteritis in young pups or trans-
placental infections in pregnant dams, with embryo
resorptions and fetal death [10]. About 30 confirmed cases
S. Nandi (&)M. Kumar
Virology Laboratory, Centre for Animal Disease Research and
Diagnosis (CADRAD), Indian Veterinary Research Institute
(IVRI), Izatnagar 243122, UP, India
e-mail: snandi1901@yahoo.com
M. Kumar
e-mail: manojvet1901@yahoo.com
123
Indian J. Virol. (Jan-June 2010) 21(1):31–44
DOI 10.1007/s13337-010-0007-y

of CPV-1 have been reported in USA, Sweden, Italy,
Germany and more recently in Japan [52,74]. The CPV-2
infections have been emerged to be a problem in dogs in
recent times around the world. The disease has also been
reported in high proportions in dogs in India with high
level of casualties even in vaccinated populations. The
disease is highly infectious and is spread from dog to dog
by direct or indirect contact with their faeces. Over the
years, a number of diagnostic assays both serological and
molecular have been developed for prompt, precise and
sensitive diagnosis of the disease. Again, both inactivated
and live attenuated CPV vaccines both as monovalent and
along with vaccines against other diseases have been
developed and used for the control of the disease. How-
ever, in spite of proper vaccination of animals, vaccines
failures have been reported due to presence of maternal
antibodies and emergence of new variants. So, this review
on CPV is aimed to provide detailed informations about the
disease including diagnosis, immunoprophylaxis, treat-
ment, etc. for the scientific fraternity, students, teachers,
diagnosticians, practitioners, pet owners, kennel club
owners, pet shop owners, defense personnel and lastly the
general public so that it can be managed and controlled in a
highly scientific and efficient manner [7].
Etiology
‘Parvo’ means small (Latin), canine parvovirus belongs to
genus Parvovirus and family Parvoviridae. The genome is
a single stranded negative sense DNA having size of
5.2 Kb [54] in length which has two promoters resulting in
the expression of three structural (VP1, VP2 and VP3) and
two non-structural proteins (NS1 and NS2) through alter-
nate splicing of the viral mRNAs. VP2 (64 kDa) is an
NH2-terminally truncated form of VP1 (84 kDa) and is the
major component of the capsid. VP3 is derived from VP2
by posttranslational proteolytic cleavage and is present
only in complete (DNA-containing) virions. Empty parti-
cles do not contain VP3 protein. Trypsin treatment of full
particles cleaves VP2 to VP3 protein. CPV-2 has icosa-
hedral symmetry, 25 nm in diameter and nonenveloped
with a linear, single stranded DNA genome. The crystal
structures of CPV-2 have been determined and their basic
capsid organizations are similar. The 60 protein subunits,
of which about 5–6 copies of VP1 and 54–55 copies of VP2
that make up the capsid have a common structure, arranged
with T =1 icosahedral symmetry [90]. There is some
evidence that the VP1 terminus is internal and may help
neutralize the DNA. The main structural motif is an eight-
stranded, antiparallel b-barrel, which also has been found
in most other viral capsid structures. The b-barrel motif
contains only approximately one-third of the amino acid
composition of VP2, the major structural protein in most
parvovirus that comprises about 90% of the capsid [12].
The remaining two-thirds is present as large loops con-
necting the strands of the b-barrel. The loops form much of
the capsid surface, onto which a number of biologic fea-
tures, such as host species and tissue tropism, receptor
binding and antigenic properties have been structurally and
genetically mapped [66,70]. Replication occurs in the
nucleus of dividing cells and infection leads to large
intranuclear inclusion bodies. Other characteristic features
of the parvoviral capsid include spike like protrusions at
the icosahedral threefold axes, a 15-A
˚canyon-like
depression about the fivefold axes and a dimple-like
depression at the icosahedral twofold axes. Antigenic
regions have been mapped to the threefold protrusion
whereas the twofold depression has been implicated in the
attachment of host cell factors [54]. The particle has a
molecular weight (MW) of 5.5 to 6.2 910
6
Da. Approx-
imately 50% of the mass is protein, and the remainder is
DNA. Because of the relatively high DNA-to-protein ratio,
the buoyant density of the intact virion in cesium chloride
(CsCl) is 1.39–1.42 g/cm
3
. Finally, the sedimentation
coefficient of the virion in neutral sucrose gradients is
110–122 S [54,69].
Emergence of Canine Parvovirus Strains
and its Distribution
During the early 1970s, a new infectious disease of pups,
characterized by either gastroenteritis or myocarditis, was
observed worldwide. A small, round, non-enveloped virus
was observed by electron microscopy in stool specimens
and in tissues of affected animals. Subsequently, a novel
parvovirus was isolated both in canine and feline cell
cultures [1,8,41]. The virus was named CPV-2. It was
speculated that CPV-2 might have emerged at least
10 years before the clinical disease was recognized [84]. It
was deduced that beneficial mutations (to the virus) had
accumulated during that period until a virus emerged from
an unknown source that infected a new host (the dog) and
acquired the ability to spread [84]. After a period of
adaptation, the virus became highly infectious for dogs,
resulting in the pandemic that became evident in
1978–1979. The rapid rate at which parvoviruses accu-
mulate mutations in vivo similar to observations made in
studies on CPV-2 vaccinal virus, where mutations were
found to accumulate rapidly during passage in tissue cul-
ture [3,84].
CPV-2 and FPV are significant pathogens for domestic
dogs and cats as well as for various wild carnivore species.
32 S. Nandi, M. Kumar
123

CPV-2 and FPV are grouped along with other viruses such
as mink enteritis virus (MEV), raccoon parvovirus (RPV),
raccoon dog parvovirus (RDPV) and blue fox parvovirus
(BFPV) in the so-called feline parvovirus subgroup [89].
Phylogenetic analysis revealed that all CPV variants were
descended from a single ancestor which emerged during
the mid-1970s, which was closely related to the long-
known feline panleukopenia virus (FPV) which infects
cats, minks, and raccoons but not dogs or cultured dog cells
[91]. There is more than 98% sequence homology and as
few as six coding nucleotide differences in the VP2 gene at
positions 3025, 3065, 3094, 3753, 4477 and 4498 [93]. The
biological effects of these few genomic changes were
sufficient for CPV-2 to acquire canine host range, but lost
the ability to replicate in feline host [92]. Two differences
at VP2 residues 93 from Lys to Asn and 323 from Asp to
Asn between FPV and CPV could introduce the canine host
range, a CPV-specific antigenic epitope [13]. Despite the
close relationship to FPV, CPV type 2 isolates did not
replicate in cats, and this host range was determined at least
in part by VP2 residues 80, 564, and 568 which are in close
proximity in the capsid structure [94].
Nucleotide substitutions in CPV-2 continued to be
observed, but their biological significance is not known. In
1979, a CPV variant (CPV type 2a) emerged that spread
worldwide within 1 year due to antigenic drift and replaced
the CPV type 2 strains. CPV type 2a contained five sub-
stitutions in the capsid sequence compared to CPV type 2,
including changes of VP2 residues 87 from Met to Leu,
300 from Ala to Gly, and 305 from Asp to Tyr [70]. CPV
type 2a isolates were antigenically different from CPV type
2 and also infected and caused disease in cats [94]. An
antigenic variant of CPV type 2a (CPV type 2b) was rec-
ognized in 1984, and it differed in an antigenic epitope as a
result of the substitution of VP2 at residue 426 from Asn to
Asp and at residue 555 from Ile to Val [68]. These CPV-2a
and CPV-2b are the predominant strains currently circu-
lating in the different dog population, and have completely
replaced the original CPV-2 virus worldwide [70,94]. Both
the antigenic types coexist in different ratio in dog popu-
lations around the world. The regaining of feline host range
by CPV-2a and CPV-2b was likely to be a selective
advantage of the virus [94].
In 2000, another mutant called CPV-2c was reported in
dogs from Italy and it differs from CPV-2b by one amino
acid at 426 position from Asp to Glu [7] and subsequently
from Vietnam, Spain, United Kingdom, South America,
North America, Portugal and India [20,55,59]. The
mutation Glu-426 affects the major antigenic region loca-
ted over the three-fold spike of CPV-2 capsid. Monoclonal
antibodies have been developed and used for detection of
different novel mutants of CPV-2 [55]. In addition,
sequence analysis of recent CPV-2a isolates has revealed a
reversion at position 555 to the sequence of FPV/CPV-2,
Ile to Val. This mutation restricts the differences among the
antigenic variants CPV-2a, 2b and 2c to only one amino
acid at position 426, which are Asn in CPV-2a, Asp in
CPV-2b and Glu in the CPV-2c. Most CPV-2 strains
spreading currently in Italy differ only in this residue [20].
There is no evidence that CPV-2c is a more serious threat
to either shelter or owned dogs than the other CPV strains.
It is not possible to distinguish CPV-2c from CPV-2b or 2a
isolates based on clinical signs. CPV-2c causes similar
clinical signs as the previously known strains, including
mucoid or hemorrhagic diarrhea, leukopenia, and lym-
phopenia [33,40]. Although a few reports suggest that
CPV-2c may cause more severe clinical signs and mortality
particularly in adult dogs than type 2a and 2b, others
describe less-severe disease and lower mortality rates in
CPV-2c infected dogs [39].
Incidence
Canine parvovirus infection occurs worldwide in domestic
dogs and other members of the dog family. Incidence is
higher in animal shelters, pet stores, and breeding kennels.
CPV can affect dogs at any age. Severe infection is most
common in puppies between 6 weeks and 4 months old.
All breeds of dogs are susceptible. The crossbreds are less
susceptible in comparison to pure breeds like Rottweilers,
Doberman Pinchers, English Springer Spaniels and Ger-
man Shepherd, the exception to this being Toy Poodles and
Cocker Spaniels [35]. CPV affects only dogs, and cannot
be transmitted to humans or other species. If a dog survives
the first 4 days, they will usually recover rapidly and
become immune to the virus for life. Most puppies die
without medical treatment. The CPV infection is more
severe in young puppies especially those younger than
3 months of age [2,38]. All infected dogs may not nec-
essarily exhibit clinical manifestations but they may shed
the virus in feces during the acute phase of enteric fever
and show significant rise in the serum antibody titers [86].
The different antigenic variants of CPV-2 are prevalent
in varying proportion in different countries. The prevalence
of CPV-2b has been reported by various authors in several
countries namely Brazil [71], USA [69], Japan [32],
Switzerland [95] and South Africa [87]. Contrastingly,
CPV-2a was found to be the prevalent antigenic type in
France, Taiwan and Italy [13,48]. However both CPV-2a
and CPV-2b have been found to be distributed in equal
proportion in Spain [18] and U.K. [28]. CPV-2c has also
been found in Vietnam [55], Spain [20], United Kingdom
[22], South America [72], North America [40].
CPV-2 for the first time was isolated in India in 1982
[76]. After that, a large number of CPV outbreaks have
Canine Parvovirus: Current Perspective 33
123

been reported from different parts of India. The incidence
of CPV-2 variants in dogs were reported from different
states viz. Kerala [24], Assam [73], Tamil Nadu [78],
Orissa [4], West Bengal [5], Pondicherry [65], Haryana
[79] and Uttar Pradesh [59,60,54]. The prevalence of
CPV-2a has been documented in 2001 in India [62]. It was
also found that CPV-2b variants are more common in
Northern India especially in Bareilly region compared to
CPV-2a [57,60,64]. However, these observations were in
contrast with the findings of a researcher [14] who reported
that CPV-2a is the major antigenic variant prevalent in
Southern and Central India, based on VP2 gene sequences.
Further, based on VP2 gene sequences, it was revealed that
the Indian isolates formed a separate lineage distinct from
the South East Asian isolates and the canine parvovirus
isolates in India appear to have evolved independently
without any distinct geographical patterns of evolution
[14]. Occurrence of CPV-2c was first reported in India in
2010 [59] based on the sequence analysis of CPV-2b
positive sample. Its presence in India supports the
assumption that CPV-2c is reaching a worldwide distri-
bution and provides new information to understand the
evolution of antigenic variants of CPV-2 [59].
Transmission
Canine parvovirus spreads through oral contact with
infected faeces or contaminated surfaces (e.g., soil, shoes,
dog toys etc.). The source of CPV infection is faecal waste
from infected dogs. It has been diagnosed wherever groups
of dogs are found: dog shows, obedience trials, breeding
and boarding kennels, pet shops, animal shelters, parks and
playgrounds [6]. Dogs that are confined to a house or yard
and are not in contact with other dogs have much less
chance of exposure to CPV. It’s easily transmitted via the
hair or feet of infected dogs and also by contaminated
objects such as cages or shoes. CPV is hardy and can
remain in faeces-contaminated ground for 5 months or
more if conditions are favorable. The faeces of infected
dogs contaminate the places such as Veterinary hospitals,
pet shops, boarding kennels and commercial breeding
establishments. These contaminated premises serve as
source of secondary infection to the susceptible canine
population [38].
Pathogenesis
The virus enters the body through the mouth as the puppy
cleans itself or eats food off the ground or floor. There is a
3–7 day incubation period before the puppy seems obvi-
ously ill. Upon entering into the body, it replicates to large
numbers in the lymph nodes [86]. After a couple of days,
significant amounts of virus have been released free into
the bloodstream. Over the next 3–4 days, the viruses go to
new organs containing the rapidly dividing cells like the
bone marrow and the delicate intestinal cells and form
large eosinophilic intranuclear inclusion bodies. Within the
bone marrow, the virus is responsible for destruction of
young cells of the immune system and then knocking out
the body’s best defense mechanism. The virus causes most
devastating effects in the gastro-intestinal tract. Canine
parvoviral infections are characterized by a drop in white
blood cell count due to the bone marrow infection.
It is in the GI tract where the heaviest damage occurs.
The normal intestine possesses little finger-like protrusions
called ‘‘villi.’’ Having these tiny fingers greatly increases
the surface area available for the absorption of fluid and
nutrients. To make the surface area available for absorp-
tion, the villi possess ‘‘microvilli’’ which are microscopic
protrusions. The cells of the villi are relatively short-lived
and are readily replaced by new cells. The source of the
new cells is the rapidly dividing area at the foot of the villi
called the Crypts of Lieberkuhn [50,67]. It is right at the
crypt where the parvovirus strikes. Without new cells
coming from the crypt, the villus becomes blunted and
unable to absorb nutrients and diarrhea results. The barrier
separating the digestive bacteria from the blood stream
breaks down. The diarrhea becomes bloody and bacteria
can enter the body causing widespread infection. The virus
kills one of two ways, diarrhea and vomiting lead to
extreme fluid loss and dehydration until shock and death
result. Loss of the intestinal barrier allows bacterial inva-
sion of potentially the entire body.
Symptoms of Canine Parvovirus
Canine parvovirus (CPV) is the most dangerous and con-
tagious virus that affects unprotected dogs. When it was
first discovered in 1978, most of the puppies under
5 months old and 2–3% of older dogs died from CPV. CPV
infection is now considered most threatening to puppies
between the time of weaning and 6 months of age. Adult
dogs can also contract the virus, although it’s relatively
uncommon.
Diarrhoea occurs in dogs of any age but appears in
serious proportions in pups. Dogs with enteritis act like
they are in extreme pain. Early symptoms are depression,
loss of appetite, vomiting, high fever and severe diarrhea
(Fig. 1). There is slight rise of temperature in the initial
stage of the disease but gradually turn to subnormal level
with advancement of vomiting and diarrhoea [42]. There is
no consistent character of the stool, it may be watery,
yellow in color or tinged with frank blood in severe cases.
34 S. Nandi, M. Kumar
123

Rapid dehydration is a danger, and dogs may continue to
vomit and have diarrhoea until they die, usually 3 days
after onset of symptoms. The course of illness is also
highly variable depending on the infectious dose of the
virus and clinical signs usually develop from 3 to 5 days
following infection and typically persist for 5–7 days [25].
The morbidity and mortality vary according to the age of
the animals, the severity of challenge and the presence of
intercurrent disease problems. Puppies can die suddenly of
shock as early as 2 days into the illness [86].
The second form of CPV is cardiac syndrome, or
myocarditis, which can affect puppies under 3 months old
[2]. Within an infected litter, 70% pups will die in heart
failure by 8 weeks of age and the remaining 30% will have
pathological changes which may result in death many
months or even years later. The most dramatic manifesta-
tion of CPV-2 myocarditis is the sudden death in young
pups usually about 4 weeks of age [51]. The collapsed
dying pup may have cold extremities, pale mucosae and
show gasping respiration or terminal convulsions. Acute
heart failure with respiratory distress occurs in pups
between 4 and 8 weeks of age. Subacute heart failure
occurs in older pups usually 8 weeks or more. They are
tachypnoeic or dyspnoeic especially on exercise. The
abdomen is swollen with hepatomegaly and ascitic fluid is
blood tinged [11]. There is tachycardia, sometimes with
arrhythmias and a weak pulse. Most animals die due to
cardiogenic shock. However, if the animal survives it will
suffer from chronic myocardial and circulatory complica-
tions [30,77]. There is no diarrhoea because the virus
multiplies rapidly in muscle cells of the immature heart.
Pathological Changes
The pathological changes produced by CPV reflect the
requirement of the virus for dividing cells. The macro-
scopic lesions of CPV infection are highly variable and
relatively non-specific. In the enteric disease, lesions may
be distributed segmentally in the gastrointestinal tract. The
lesions usually affect the jejunum and ileum but not the
duodenum and colon. Affected segments may be somewhat
flaccid with subserosal hemorrhage or congestion [77]. The
lumen of the intestine is often empty but may contain
variable watery ingesta. The mucosal surface is often
congested but devoid of exudates. Mesenteric lymph nodes
are frequently enlarged and edematous. Multifocal pete-
chial hemorrhages are often seen within the cortex of a cut
section of affected lymph nodes during acute stage of the
disease and leucopenia is also common. Thymic cortical
necrosis and atrophy are common findings in young dogs
[16,30,77].
In cases of parvoviral myocarditis, gross lesions include
cardiac enlargement with prominent dilatation of the left
atrium and ventricle. The lungs often do not collapse when
cut although white frothy fluid may be present in the tra-
chea and bronchi. Evidence of pulmonary edema and
passive congestion of the liver is often present, with the
variable degree of ascites and pleural effusion. The ven-
tricular myocardium frequently contains visible white
streaks associated with the presence of a cellular infiltrate.
Some pups may die from chronic decompensating left
sided heart failure weeks or months after some of their
littermates died suddenly with acute myocarditis. Pul-
monary hypertension and myocardial dilation with scarring
is often regarded as the cause of delayed death [30].
Histopathology
Microscopic lesions associated with CPV infection are
initially confined to areas of proliferating cell population.
In the enteric form of the disease, the early lesions consist
of necrosis of the crypt epithelial cells [16]. Crypt lumenae
are often dilated, lined by attenuated epithelium and filled
with necrotic debris. There may be occasional intranuclear
eosinophilic inclusion bodies in intact crypt epithelial cells.
The villi and lamina propria may collapse completely as a
result of the loss of crypt epithelium and the failure to
replace sloughed villous epithelial cells. These lesions may
be extensive or diffuse. Loss of digestive epithelium and
absorptive surface area presumably results in diarrhoea
caused by combined effect of maldigestion and malab-
sorption. Death may follow as a result of dehydration,
electrolyte imbalance, endotoxic shock or secondary
septicemia.
The regeneration of intestinal epithelial cells has been
reported even in fatal cases. The remaining intestinal crypts
are elongated and lined by hyperplastic epithelium with a
high mitotic index. The shortened villi are covered by
immature epithelial cells and adjacent villi are often fused.
Necrosis and depletion of small lymphocytes is seen in
Fig. 1 A case of canine parvovirus infection with severe diarrhea and
vomiting undergoing treatment
Canine Parvovirus: Current Perspective 35
123

Peyer’s patches, the germinal centers of mesentric lymph
nodes, and in splenic nodules early in the course of
infection [16]. Diffuse cortical necrosis of the thymus
occurs in young dogs, with an associated loss in thymic
mass. Later in the disease, there is evidence of regenerative
lymphoid hyperplasia.
Canine Parvovirus Variants in Wild Animals
CPV-2 is closely related to FPV with more than 98%
genome homology, and as few as six coding nucleotide
differences in the VP2 protein positions: 3025, 3065, 3094,
3753, 4477, 4498 [69,70]. The biological effects of these
few genomic changes were enormous, in that CPV-2
acquired the canine host range, but lost the ability to rep-
licate in cats [93]. The host ranges of CPV-2 and FPV are
complex and differ in vitro and in vivo. FPV replicates in
feline cells in vitro and in cats in vivo, but does not infect
canine cells in vitro and shows only a restricted tissue
spectrum in vivo. CPV-2 does replicate in canine and feline
cells in vitro, but the in vivo replication is restricted to
canides [37,94]. No feline host has ever been described to
be susceptible to CPV-2, although it replicates to low titers
in mink which is a mustelid, after experimental inoculation
[68]. After its emergence CPV spread to most populations
of domestic and wild carnivores. In 1976, reports from
Belgium and the Netherlands indicated that the virus had
spread throughout the world infecting wild and domestic
canids [92,94]. Clinical signs of parvovirus disease were
observed in captive and free-ranging coyotes and DNA
sequence analysis of the VP2 gene showed the virus to be
CPV-2. Raccoons, in contrast, were shown to be resistant
to CPV-2 infection [93].
Serologic prevalence, infection or clinical signs of dis-
ease due to CPV viruses were found in jackals (Canis
aureus,Canis adustus,Canis mesomelas), grey foxes
(Urocyon littoralis), the San Joaquin kit fox, Asiatic rac-
coon dogs (Nyctereutes procyonoides) and the crab eating
fox (Cerdocyon thous) in the Kenya [25,89]. Canine par-
vovirus infections were reported in farmed raccoon dogs
and confirmed to be CPV-2 by DNA sequence analysis of
the VP2 gene [93]. CPV-2a and CPV-2b DNA sequences
were recovered from six of nine cheetahs, as well as from
one Siberian tiger, all showing clinical symptoms of par-
vovirus disease [88]. The very high prevalence of CPV-2a/
2b infections in large cats compared to domestic cats may
suggest a higher susceptibility of the species for these virus
types [88]. Since vaccination of domestic cats and dogs is
very effective in preventing disease, parvovirus vaccination
of all domestic and non-domestic carnivores at risk of
infection is highly recommended. CPV-2c type viruses
have been isolated from leopard cats but not from domestic
cats in the same area. Phylogenetic analysis indicated that
CPV-2c(a) and CPV-2c(b) have been evolved from CPV-
2a and CPV-2b to adapt to leopard cats and lost neutral-
izing epitopes compared to former serotypes CPV-2a and
CPV-2b [37].
Diagnosis
A presumptive diagnosis of CPV enteritis can be made
based on the clinical signs such as depression, vomiting,
diarrhoea, anorexia and fever. The tests should be per-
formed on any dog with diarrhoea that is also exhibiting
signs of systemic disease: vomiting, lethargy, fever, loss of
appetite, dehydration or dogs with unusually copious,
smelly/bloody diarrhoea, or any dog with known exposure
to parvovirus within the preceding 14 days of developing
diarrhoea.
The diagnostic tests which were employed earlier
include HA (Haemagglutination) [9], Electron Microscopy
(EM) [8], virus isolation using in MDCK, CRFK or A 72
cell line [2], Enzyme Linked Immunosorbent Assay
(ELISA) [53], Latex Agglutination Test (LAT) [1], Fluo-
rescent Antibody Test (FAT), CIE test [76], Virus neu-
tralization test, PCR and RE digestion [56,71], real time
PCR [19], loop-mediated isothermal amplification (LAMP)
[34], nucleic acid hybridization or dot blot, in situ
hybridization, nucleic acid sequencing etc. [15,59], but
they have varying degree of sensitivity and specificity and
sometimes yielding false positive cases.
Haemagglutination (HA) Assay
The HA is simple and rapid test for detecting CPV in
faeces and this test was performed using porcine, rhesus
monkey or feline RBC’s [9]. The viral HA titer commonly
ranges between 128 and 10,240, between PI days 4 and 7,
or when the signs of enteritis commence. The HA activity
generally ceases between PI days 7 and 9 [9]. Though it is
less sensitive than virus isolation in A-72 cell line, HA test
on stool samples is rapid and simple to perform. The
nonspecific HA titer (\32) is common but it may be
reduced by brief treatment of samples with fluorocarbon
(Genetron, Freon 113) or CHCl
3
(10% V/V). A modifica-
tion of the HA test involves the adsorption of the CPV in
faecal samples onto RBCs at 4°C. Antigen is eluted from
cells at 37°C and tested for HA activity [63]. Although HA
test is sensitive, relatively simple and inexpensive to per-
form, it has several disadvantages, including requirement
of a continuous source of RBC, and the need to monitor the
specificity of the low titred reactions with HA inhibition
assay [17,53]. HI test has also been used most frequently
for the detection of CPV [43]. The antibody can be
36 S. Nandi, M. Kumar
123

detected by HI after oral infection on PI day 3 or 4 and with
a high titre ([640) by PI day 7 [17].
HA test can be performed by employing erythrocyte
from various species as swine, sheep, goat, poultry and
dogs. Among the erythrocyte of different species, pig RBCs
showed the characteristic haemagglutination. Erythrocyte
from other species does not give specific haemagglutination
[17,43]. The HA test can be performed by incubating the
plates at various temperature such as 4°C, 25 and 37°C and
the best results were found at 4°C followed by at 25°C and
least titre at 37°C[43]. Apart from this, various buffer
system have been evaluated for HA test such as normal
saline solution (0.9% NSS), phosphate buffer solution with
BSA (15 mM PBS ?0.1% BSA) and phosphate buffer
saline solution (PBSS) (15 mM PBS ?0.9% NSS) etc. The
optimum results were obtained with PBS followed by PBS
with BSA and PBSS in a pH range of 4–6 but the results of
all three systems were comparable [17,43].
Electron Microscopy
During acute illness, parvoviral virions are readily dem-
onstrated in faeces by negative staining and use of electron
microscopy [8,50]. Specific identification of CPV may be
made using IEM, employing antibodies to CPV or FPV [8].
Isolation of CPV
A number of primary cell cultures and cell lines like
MDCK (Madin-Darby Canine Kidney) or CRFK (Crandell
Feline Kidney) support replication of CPV and virus could
be isolated from the cases of CPV induced myocarditis and
enteritis. The cell culture adapted virus will enable the
biochemical and molecular characterization of the CPV
isolates [2,6]. A canine cell line (A-72) deserves special
mention because it has proved to be particularly useful for
CPV isolation from field materials. The A-72 cell line was
established from a canine S/C tumour and it has maintained
a fibroblastic appearance for more than 135 serial passages.
This line proved to be particularly useful for isolation and
growth of CPV because CPE were pronounced on initial
culture or after one additional passage. The sizes of the
plaques produced by CPV under methyl cellulose or aga-
rose overlay media vary from 0.4 to 1.5 mm in diameter.
Since the original tissues for culture were derived from an
uncharacterized tumour, A-72 cells should not be used for
vaccine virus production [9].
ELISA
This test is based on the antigen–antibody reactions with
specific MAbs fixed on plastic, nitrocellulose membranes,
latex or gold particles [96]. The tests are rapid, relatively
cheap and can be performed in any veterinary clinic.
Recently an ELISA test, using monoclonal antibodies was
reported for the detection of CPV antigen in faeces as little
as 1.5 ng of virus [53]. The double sandwich ELISA is a
rapid, simple, sensitive and suitable test over ELISA for
routine diagnostic use for detection of CPV antigen in
canine faeces. The ELISA test has become the most
common test for parvovirus in puppies [97].
Polymerase Chain Reaction
Recently the PCR technique has been increasingly used as
a tool for the diagnosis of canine parvoviral infection
[45,51]. It has been widely applied to provide rapid, sen-
sitive and accurate diagnosis of the disease. The PCR has
been found to detect fewer particles of CPV-2 than other
tests like HA and ELISA (Fig. 2). The PCR can now be
used to differentiate the different mutants of CPV-2 using
the primers specific for particular mutants [71]. To increase
the sensitivity and specificity of the reaction, the nested
PCR has been employed [31]. The conventional PCR could
detect 10 fg of viral replicative form (RF) DNA on agarose
gel electrophoresis, whereas as little as 100 ag of the RF
DNA was detected by the nested PCR, which was shown to
be 100 times more sensitive than the single PCR [31]. The
number of the genome copy in positive samples was esti-
mated about 10
9
–10
11
/g of faeces by the conventional PCR
and 10
11
–10
13
/g of faeces by the nested PCR. Thus, the
nested PCR seems to be a sensitive, specific and practical
method for the detection of CPV in faecal samples [31,71].
A touch-down protocol was used which enabled the
specific amplification of virion DNA from faeces after a fast
and simple boiling pretreatment. The sensitivity of PCR
was as high as 10 infectious particles per reaction which
corresponds, to a titer of about 10 infectious particles per
gram of unprocessed feces. This renders the PCR about 10
to 100-fold more sensitive than electron microscopy [82].
The PCR followed by RFLP and sequencing have
been used for typing the CPV strains [44]. On amplifying
VP1/VP2 gene (*2.2 kb) and its RE digestion with HpaI
and RsaI, it can differentiate between original CPV-2 type
and CPV-2a/2b type. Also, RE digestion of amplicon
employing AluI can differentiate between CPV-2a and
CPV-2b type [44]. The typing of field samples using PCR
followed by RsaI based RFLP showed that the vaccine
strain used in India are CPV-2 type while field isolates are
either of CPV-2a/2b type [79]. The results are in accor-
dance with the other workers who found the same differ-
ence between field and vaccine strain of CPV employing
PCR based differentiation [57,71]. CPV-2c variant can be
identified by MboII digestion of PCR products of CPV-2b
positive samples [7].
Canine Parvovirus: Current Perspective 37
123

Real Time PCR
Real time PCR (RT-PCR) employing the TaqMan assay
has been used for the detection of CPV-2 DNA in the
sample [19]. The minor groove binder (MGB) probe
technology was applied to obtain rapid and unambiguous
identification of the viral type [21]. MGB probes are short
TaqMan probes conjugated with molecules that form
hyper-stabilized duplexes with complementary DNA,
allowing reduction in length of the probe and an increase in
specificity [21]. MGB probes are, therefore, an attractive
tool for revealing single nucleotide polymorphisms in the
capsid protein gene between CPV types 2a and 2b and CPV
types 2b and 2c. Recently, SYBR Green based real time
PCR has been developed for detection and quantitation of
CPV-2 variants in faecal samples of dogs employing pri-
mer set pCPV-2RT (forward 50-CAT TGG GCT TAC CAC
CAT TT-30and reverse 50-CCA ACC TCA GCT GGT
CTC AT-30) based on the sequences of VP2 gene and
produce a PCR product 160 bp [46]. The advantage of the
real time PCR is that there is no need to analyse the PCR
product by agarose gel electrophoresis. Everything will be
graphically shown on the monitor of the computer. Another
advantage is that amount of the DNA present in the sample
can be quantitated [19].
Detection of CPV in Fecal Samples Using LAMP
The Loop Mediated Isothermal Amplification of DNA
(LAMP) method was applied for the detection of CPV
genomic DNA. A set of four primers, two outer and two
inner, were designed from CPV genomic DNA targeting
the VP2 gene. The optimal reaction time and temperature
for LAMP were determined to be 60 min and 63.8°C
respectively. The relative sensitivity of LAMP was 100%
and the relative specificity was 76.9%. The detection limit
of the LAMP method was 10
-1
median tissue culture
infective doses (TCID
50
)/ml [34].
Nucleic Acid Hybridization/Dot Blot
In this process the DNA is extracted from the stool samples
or cell culture supernatant inoculated with the sample or
stool sample suspected for canine parvovirus and charged
on the nitrocellulose paper or nylon membrane. The DNA
is then subjected to hybridization with CPV-specific probe
either radio-labelled or biotin labeled. In the positive case
there will be development of band in the X-ray film after
autoradiography in case of radio-labelled probe or colour
in the nitrocellulose paper in case of non-radio-labelled
probe [15].
Detection of Canine Parvovirus by In situ Hybridization
This technique was developed to detect viral replication in
tissue sections obtained from CPV-infected animals. In this
method identification of CPV-specific nucleic acid was
done. A CPV-specific DNA probe was produced by PCR
amplification of a genome segment encoding capsid pro-
teins VP-1 and VP-2 and was used for knowing the dis-
tribution of CPV specific nucleic acid in tissue specimens
obtained from infected dogs [98].
Nucleic Acid Sequencing
The PCR product as it is or cloned in the suitable cloning
vector can be sequenced using the suitable primer with the
help of automated DNA sequencer for typing of CPV strains.
The sequence is analysed using the appropriate software.
This is an important technique to know with certainty the
particular variant of the CPV present in the field sample.
Both the nucleotide and amino acid sequence data can also
be used to know the percent homology and for phylogenetic
analysis of CPV-2 isolates from different geographi-
cal regions [58]. Based on sequence analysis CPV-2a and
CPV-2b type could be differentiated and none of the isolates
were belonging to original CPV-2 type [14]. In a further
study, field isolate as well as vaccine strain of CPV were
sequenced and it was found that vaccine strains are of CPV-2
type and field isolate of CPV-2b type [61] (Fig. 3). CPV-2c
variants have been reported from various countries based on
the nucleotide sequence analysis [40,59].
Immunization
The biggest problem in protecting a puppy against canine
parvovirus infection ironically stems from the natural
mechanism of protection that has evolved. Puppies obtain
Fig. 2 Amplification of part of the VP2 gene of the CPV-2 variants
by PCR employing primers pCPV-2 (F) 50-GAA GAG TGG TTG
TAA ATA ATA-30(21 mer) and pCPV-2 (R) 50-CCT ATA TCA
CCA AAG TTA GTA G-30(22 mer) [57]. MMarker, 1–6 =681 bp
amplicon amplified by PCR, 7=negative control
38 S. Nandi, M. Kumar
123

their immunity from their mother’s first milk, the colostrum,
on the first day of life.There is a strong correlation between
HI or serum neutralizing antibody titers and resistance to
infection with CPV. The HI test has been useful to measure
antibodies which correlated well with immunity. The HI
titre 1:80 or more is considered protective but HI titre of
1:40 is not protective but interferes with active immuniza-
tion against CPV-2 in dogs. The highest rate of infection is
reported in pups older than 6 weeks of age. As with other
infectious diseases of dogs, puppies from immune bitches
are protected for the first week of life by maternal antibodies
which are acquired via the colostrums. Successful immu-
nization with most vaccines can be accomplished with a
high degree of confidence only in seronegative pups, or in
pups with very low antibody titers. Maternal antibodies are
acquired during the initial 2–3 days of life and then decline,
with an average half life of about 9–10 days. There is a
critical period where maternal antibodies are no longer
present in sufficient quantity to confer protection. But 90%
of the pups from vaccinated populations respond to vac-
cines at 12 weeks of age [75,91].
Vaccination of dogs is generally performed using mul-
tivalent vaccines, which contain CDV, CPV, leptospira
bacterin and inactivated rabies virus. Monovalent CPV-2
vaccines are also available, some of them containing very
high titer virus (10
7
TCID
50
) and widely recommended for
initial vaccination of pups. About 60% of all puppies se-
roconverted after a single vaccination either at 6 weeks of
age with a CPV monovalent vaccine or at 8 weeks of age
with a multivalent vaccine. At 12 weeks of age another
shot is given when all pups had received 2–3 inoculation at
this age but nearly 10% pups still had not been sero-con-
verted. The principal reason for the non-responders was the
persistence of interfering levels of maternal antibodies.
None of the vaccines tested were capable of breaking
through a maternal antibody titer of 1:160 or higher,
regardless whether the vaccines were high tittered or not
[75,91]. If it is necessary to develop an individual vacci-
nation schedule, determination of the antibody titer of one
or two pups in the litter could be determined at 5 or
6 weeks of age, then vaccination of the litter may be cal-
culated on the basis of titer. Vaccination is likely to be
successful when the maternal antibody titer has declined to
less than 1:10 [80].
There have been concerns expressed over the efficacy of
canine parvovirus vaccines which are based on the original
type 2 strain [49,91]. The reports of gastroenteritis sub-
sequent to vaccination are related to infection with CPV
field strains shortly before or after the vaccine adminis-
tration [23]. It has previously been demonstrated that a type
2 vaccine is able to provide protection against type 2a and
2b field isolates [27]. The emergence of the 2c variant
naturally raises the question of whether the CPV-2 vac-
cines can provide protection against this new variant also.
The research to date also showed that all currently avail-
able vaccines based on CPV-2 and CPV-2b protect against
all known strains of CPV, including the newer CPV-2c
strain [81,85]. In India, most of the vaccines marketed are
based on the CPV-2 isolated about 30 years ago [57,61].
However, CPV-2a/2b/2c has recently replaced the CPV-2
incidence in dogs in most of the parts of the world
including India. There are reports of gastroenteritis in
vaccinated dogs and this may be due to CPV-2 is not
capable enough to provide full protection against the new
strains [79]. It is better to use homologous vaccines that use
CPV-2a or CPV-2b mutants depending on the prevalence
of disease in different places to control the disease.
Killed and Modified CPV Vaccine
First, a killed CPV vaccine and more recently live and
recombinant vaccine have been developed in the search of
Fig. 3 Phylogenetic analysis
based on nucleotide sequence of
VP1/VP2 gene of two Indian
isolates [CPV-Bhopal (BHO)
and CPV-IVRI] and two
vaccine strain [Nobivac (NOBI)
and Parvovirus vaccine (PVV)]
and their comparison with
several published nucleotide
sequences of canine parvovirus
employing using MegAlign
programme of DNASTAR Inc,
USA, Software. Both the
isolates are of CPV-2b type and
both the vaccine strains are
found to be CPV-2 type [61]
Canine Parvovirus: Current Perspective 39
123

a product of improved potency. However, no vaccine has
proved to be of high efficacy in the face of maternally
derived antibodies (MDA), hence a pup’s primary vacci-
nation cannot be completed before 16 weeks [50]. In CPV
infection live virus vaccines offer a longer duration of
immunity than killed vaccines as in other diseases [80].
None of the currently available vaccines circumvent
maternally derived immunity as effectively as does virulent
CPV although MLV-CPV vaccines can overcome a higher
concentration of maternally derived antibodies than vac-
cine containing inactivated virus [26]. MLV vaccine using
highly attenuated CPV are more susceptible to maternal
antibody induced suppression of active immunization than
less attenuated strains. Another way of overcoming the
interference of maternal antibodies with CPV vaccine is by
using MLV-CPV of high antigenic mass [85].
Recombinant Vaccine
Recombinant vaccine containing the baculovirus expressed
VP2 protein was found to be structurally and immuno-
logically indistinguishable from authentic VP2. The
recombinant VP2 also shows the capability to self assem-
bles, forming virus like particles similar in size and
appearance to CPV virions. The VP2 protein at the rate of
10 lg was able to elicit good protective response as mea-
sured by ELISA and shown to be better than commercially
available inactivated CPV vaccine in terms of immune
response. The expressed VP2 was used along with the Quil
A (50 lg/animal), alumina or both adjuvants on 0 and
28 days to improve the immunogenicity of the vaccine at
different doses (10, 25, 50 and 100 lg). All the vaccinated
dogs maintained the protective antibody response up to
6 days observation period and withstood challenge virus
infection 42 days after the booster doses [47].
DNA Vaccine
The prokaryotic vector harboring the genes coding for the
structural proteins of the canine parvovirus have shown the
encouraging results. The dogs immunized with the DNA
vaccines withstood the challenge with virulent canine
parvovirus. However, the DNA vaccines still is in the
experimental stage and not yet licensed to be used in the
field condition [29].
Peptide Vaccine
The N-terminal domain of the major capsid protein VP2 of
canine parvovirus was shown to be an excellent target for
development of a synthetic peptide vaccine. Several pep-
tides based on this N-terminus were synthesized to estab-
lish conditions for optimal and reproducible induction of
neutralizing antibodies in rabbits. Within the N-terminal 23
residues of VP2, two sub sites able to induce neutralizing
antibodies. The shortest sequence sufficient for neutral-
ization induction was nine residues. Peptides longer than
13 residues consistently induced neutralization, provided
that their N-termini were located between positions 1 and
11 of VP2. The orientation of the peptides at the carrier
protein was also of importance, being more effective when
coupled through the N-terminus than through the C-ter-
minus to keyhole limpet hemocyanin. This means that the
presence of amino acid residues 2–21 (and probably 3–17)
of VP2 in a single peptide is preferable for a synthetic
peptide vaccine [36].
Therapy
The restoration of the electrolyte and fluid balance is the
most important goal of therapy [99]. The affected dog
should be put under broad spectrum antibiotic umbrella
(ampicillin, chloramphenicol, erythromycin, gentamycin,
etc.) Norfloxacin and nalidixic acid have been proved to be
effective against canine haemorrhagic gastroenteritis [41].
Symptomatic treatment with steroid, broad spectrum anti-
biotic, fluid and electrolyte may save the life of the animal.
As soon as the problem is recognized, fluid therapy should
be started. Supplementation of these fluids with bicarbon-
ate may be recommended. Metabolic acidosis develops if
the diarrhoea is severe and potassium supplementation in
the form of KCl may be necessary to maintain electrolyte
balance. All oral intakes must be withheld in case of severe
vomiting and should be given parenterally [99]. During the
early phase of the disease, the application of hyperimmune
serum may help to reduce the virus load and render the
infection less dramatic. Such treatment has been shown to
reduce the mortality and shorten the length of the disease
however hyperimmune serum is difficult to obtain. In case
of vomiting, chlorpromazine or metaclopromide (Reglan),
out of which Reglan can be given at 0.5 mg/kg body
weight parenterally at 8 h interval. To correct the gastric
problem cimetidine, ranitidine, famotidine and to check
diarrhoea, loparamide or bismuth subnitrate or other
astringent preparations may be given [42]. A dog with
persistent vomiting should not be given any food until the
diarrhoea and vomiting subsides.
Prevention and Control
As the canine parvovirus is not enveloped, it is especially
hardy in the environment. It is able to overcome winter
freezing temperatures in the ground outdoors and many
household disinfectants are not capable of killing it
40 S. Nandi, M. Kumar
123

indoors. Infected dogs shed virus in their stool in gigantic
amounts during the 2 weeks following exposure. A typical/
average infectious dose for an unvaccinated dog is 1000
viral particles. An infected dog sheds 35 million viral par-
ticles (35,000 times the typical infectious dose) per ounce of
stool [83]. Indoor decontamination: Indoors, virus loses its
infectivity within 1 month; therefore, it should be safe to
introduce a new puppy indoors 1 month after the active
infection has ended. Outdoor decontamination: freezing is
completely protective to the virus. If the outdoor is con-
taminated and is frozen, one must wait for it to thaw out
before safely introducing a new puppy. Shaded areas should
be considered contaminated for 7 months. Areas with good
sunlight exposure should be considered contaminated for
5 months. Although most disinfectants cannot kill it, chlo-
rine bleach is quite effective in the ratio of 1 part bleach and
30 parts water. There is no way to completely disinfect
contaminated dirt and grass, although sunlight and drying
has some effect [35]. Mechanical decontamination through
irrigation may also be helpful, but the area must be allowed
to dry thoroughly between applications. Potassium per-
oxymonosulfate has relatively good activity in the face of
organic matter, and can be sprayed on contaminated areas
using a pesticide sprayer or other applicator [83].
Conclusion
In summary, parvovirus is a very common problem of
canines and is a huge killer of puppies. Due to its ability to
be transmitted through hands, clothes, and most likely
rodents and insects, it is virtually impossible to have a
kennel that will not eventually be exposed to the disease.
Modified live vaccines are safe and effective, but despite
the best vaccination protocol, all puppies will have a
window of susceptibility of at least several days where they
will be at risk. In addition, the newer CPV-2c strain pre-
sents new challenges as the current vaccines may not be as
effective in providing protection against it. Again, com-
mercially available FPV or CPV-2 based vaccines might
also protect animals from the new virus infection. How-
ever, if the new virus gains wider host ranges, deadly
outbreaks could be observed like first emergence of CPV-2
in dogs. In that case, recent isolates need to be investigated
to anticipate and assess the risk caused by newly emerging
viruses. Further the homologous vaccine based on current
or newer variant should be made ready to tackle the dis-
ease. Also, zoo sanitary measures should be employed to
prevent the disease in wild animals.
Although potent and efficacious live attenuated and
inactivated vaccines are available in India but large num-
bers of cases are diagnosed by HA, HI, ELISA or PCR,
mostly from the unvaccinated dogs as the stray dogs
usually are not vaccinated against the disease and they
remain carrier of the virus and source of infection to other
susceptible dogs. Extensive studies must be undertaken to
know the molecular epidemiology of the canine parvovirus
infections in different canine species and the variants of the
CPV involved in the outbreak of the disease. The necessary
preventive measures must be undertaken to immunize the
susceptible dogs including the stray dogs with the potent
and efficacious vaccines against the disease to check the
spread of the disease. Prompt symptomatic treatment, res-
toration of fluid and antibiotics to prevent bacterial infec-
tion by a veterinarian will increase survivability in infected
puppies but vaccination program should be considered the
best way to control the disease in dog.
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