Page 504 - Small Animal Internal Medicine, 6th Edition

476 PART III Digestive System Disorders

because they may contribute to the problem even when they severely ill dogs but are often absent in less severely affected
are not the principal cause. animals. Puppies infected in utero or before 8 weeks of age
VetBooks.ir Treatment may develop myocarditis. Rarely, parvoviral infection may
be associated with erythematous cutaneous lesions (ery-
An easily digested (so-called “bland”) diet (e.g., boiled potato
plus boiled skinless chicken) fed in multiple small feedings thema multiforme).
(see pp. 434-435) usually causes resolution of diarrhea in 1 Diagnosis
to 3 days. Once the diarrhea resolves, the diet can be gradu- Diagnosis is often tentatively made based on history and
ally changed back to the pet’s regular diet. physical examination findings. Neutropenia is suggestive but
neither sensitive nor specific for canine parvovirus enteritis;
Prognosis salmonellosis or any overwhelming infection can cause
The prognosis is usually excellent unless a young animal with similar leukogram changes. Furthermore, the neutropenia
minimal nutritional reserves becomes emaciated, dehy- may be very shortlived (i.e., < 12 hours). Regardless of
drated, or hypoglycemic. whether diarrhea occurs, infected dogs shed large numbers
of viral particles in the feces (i.e., >10 particles/g). Electron
9
microscopic evaluation of feces detects parvovirus, but
INFECTIOUS DIARRHEA CPV-1 (usually nonpathogenic except in neonates) is mor-
phologically indistinguishable from CPV-2. Detecting anti-
CANINE PARVOVIRAL ENTERITIS bodies to CPV appears useful for determining if vaccination
has been successful but not for diagnosis of acutely ill
Etiology
patients. Fecal polymerase chain reaction (PCR) testing is
Two types of parvoviruses infect dogs. Canine parvovirus-1 very sensitive and specific but must be performed at diag-
(CPV-1), also known as “minute virus of canines,” is a rela- nostic laboratories. Fecal “point-of-care” testing is consid-
tively nonpathogenic virus that sometimes is associated with ered the standard testing for most practices. There are
gastroenteritis, pneumonitis, and/or myocarditis in puppies different point-of-care methodologies (i.e., ELISA, immuno-
1 to 3 weeks old. Canine parvovirus-2 (CPV-2) is responsible chromatography, immunomigration). All are highly specific,
for classic parvoviral enteritis, and there now are at least but the sensitivity for both CPV-2b and CPV-2c is less than
three strains (CPV-2 a, b, and c). CPV-2 usually causes signs desired. Vaccination with a modified live parvoviral vaccine
5 to 12 days after the dog is infected via the fecal-oral route may cause a weak positive result for 5 to 15 days after vac-
by destroying rapidly dividing cells (i.e., bone marrow pro- cination. ELISA results may be negative if the assay is per-
genitors and intestinal crypt epithelium). formed too early in the clinical course of the disease (i.e.,
virus is not yet being shed in feces). Therefore, if faced with
Clinical Features a dog that seems likely to have parvoviral enteritis but is
The virus has mutated since it was first recognized, and the negative on the point-of-care test, the clinician should either
most recently recognized mutations may be more patho- repeat the test in 3 to 4 days or send feces to a diagnostic
genic in some dogs. CPV-2b and CPV-2c can also infect cats. laboratory for PCR testing. Shedding decreases rapidly and
Clinical signs depend on the virulence of the virus, size of may be undetectable by 10 to 14 days after infection, espe-
the inoculum, host’s defenses, age of the pup, and presence cially if the virus is being bound by fecal antibodies and/or
of other enteric pathogens and/or parasites. Doberman diluted by diarrhea. Rarely, clinically normal dogs and dogs
Pinschers, Rottweilers, Pit Bulls, Labrador Retrievers, and with chronic enteropathies will test positive; this may be due
German Shepherds may be more susceptible than other to asymptomatic infection or intestinal passage of the virus.
breeds. Viral destruction of intestinal crypts may produce A positive test result confirms the presumptive diagnosis
villus collapse, diarrhea, vomiting, intestinal bleeding, and of parvoviral enteritis. A negative result warrants consider-
subsequent bacterial invasion, but some animals have mild ation of diseases that can mimic parvovirus (e.g., salmonel-
or even subclinical disease. Many dogs are initially presented losis, intussusception). If the dog dies, there are typical
because of depression, hyporexia, and/or vomiting (which histologic lesions (i.e., crypt necrosis), and fluorescent anti-
can closely mimic foreign object ingestion) without diarrhea. body and fluorescent in situ hybridization techniques can
Diarrhea is often absent for the first 24 to 48 hours of illness establish a definitive diagnosis.
and may not be bloody if and when it does occur. Intestinal
protein loss may occur secondary to inflammation, causing Treatment
hypoalbuminemia. Vomiting is usually prominent and may Treatment of canine parvoviral enteritis is fundamentally the
be severe enough to mimic foreign body obstruction and/or same as for any severe, acute, infectious enteritis and depends
cause esophagitis. Damage to bone marrow progenitors may upon the clinical severity. Severely ill dogs need in-clinic
produce transient or prolonged neutropenia, making the treatment, whereas mildly affected animals can often be
animal susceptible to serious bacterial infection, especially if treated at home. Fluid and electrolyte therapy is crucial and
a damaged intestinal tract allows bacterial translocation is typically combined with antibiotics (Box 31.1). Most dogs
across the mucosa. Fever and/or SIRS are common in survive if they can be supported long enough. However, very