Page 1515 - Small Animal Internal Medicine, 6th Edition

CHAPTER 96 Polysystemic Viral Diseases 1487

antibody in the CSF had to be produced locally and is con- populations. Care should be taken to avoid transmission by
sistent with CNS CDV infection. If increased CSF protein contaminated fomites (see Chapter 93). All puppies should
VetBooks.ir concentrations, mononuclear pleocytosis, and antibodies be administered at least three CPV-2, CAV-2, and CDV-
containing vaccines, every 3 to 4 weeks, between 6 and 16
against CDV are detected in a CSF sample not contaminated
with peripheral blood, a presumptive diagnosis of CDV
of age (see Chapter 93). Administration of a final dose at
encephalitis can be made. weeks of age, with the last booster administered at 16 weeks
Definitive diagnosis of CDV infection requires demon- 18 to 20 weeks of age should be considered for dogs resid-
stration of viral inclusions by cytologic examination, direct ing in high-risk environments. Modified-live CDV vaccines
fluorescent antibody (DFA) staining of cytologic or histo- and the recombinant CDV (rCDV) vaccine are considered
pathologic specimens, histopathologic evaluation, virus iso- effective by the AAHA task force (https://www.aaha.org/
lation, or reverse transcriptase polymerase chain reaction guidelines/canine_vaccination_guidelines.aspx). The rCDV
(RT-PCR) documentation of CDV RNA in peripheral blood, vaccine can be used to break through maternal antibodies
CSF, or conjunctival scrapings. Viral inclusions are rarely that can block CDV vaccines. In one recent study, almost
found in erythrocytes, leukocytes, and leukocyte precursors all vaccinated dogs in a shelter achieved protective serum
of infected dogs. Inclusions are generally present for only 2 antibody titers within 13 to 15 days after receiving a modi-
to 9 days after infection and therefore often are not present fied live CDV vaccine (Litster et al., 2012a). Vaccines should
when clinical signs occur. Inclusions may be easier to find be boosted at 1 year of age. After the 1-year booster, repeat
in smears made from buffy coats or bone marrow aspirates boosters are not needed again for a minimum of 3 years
than in those made from peripheral blood. Viral particles and protection after challenge has been documented for
can be detected by DFA in cells from the tonsils, respiratory more than 4 years (Jensen et al., 2015). Serologic studies
tree, urinary tract, conjunctival scrapings, and CSF for 5 to have shown that vaccination induces long-term protection
21 days after infection. In areas molecular assays are expen- against CDV (Killey et al., 2018).
sive or not available, DFA assays can be performed with a Disease from CDV infection has occurred in some vac-
moderate sensitivity (79%) when compared with molecu- cinated dogs and rarely is attributed to modified-live virus
lar assays (Athanasiou et al., 2018). However, false-positive vaccination. Clinical disease in vaccinated dogs develops if
results have been detected occasionally in DFA performed the host was immunocompromised, infected with the virus
on conjunctival cells from specific pathogen-free puppies, so before vaccination, had vaccine-suppressive levels of mater-
results of these tests should be interpreted cautiously (Burton nal antibodies, or was incompletely vaccinated. Alternately,
et al., 2008). Recent administration of modified-live CDV- the vaccine may have been inactivated by improper handling
containing vaccines can lead to positive results in DFA and or may not have protected against all field strains of CDV
some RT-PCR assays so vaccination history is important to (Anis et al., 2018). Distemper virus encephalitis develops
consider with assessing the results of these assays. It is pos- after modified-live vaccination of some dogs co-infected
sible to differentiate wild strains and vaccine strains of CDV with canine parvovirus; administration of modified-live
by RT-PCR; veterinarians should ask the preferred service CDV vaccines should be delayed in dogs with clinical signs
laboratory whether the assay being used can provide this of disease consistent with parvovirus infection. Mild, tran-
discrimination (Yi et al., 2012). sient thrombocytopenia can be induced by modified CDV
vaccination but has not been associated with spontaneous
Treatment bleeding unless the patient has an underlying subclinical
Although a number of substances like ribraviron, interferon coagulopathy. No proven public health risks are associated
alpha, and caffeic acid inhibit CDV in vitro, therapy for CDV with CDV.
infection is nonspecific and supportive (Carvalho et al., Serum antibody titers that predict resistance to challenge
2014). Secondary bacterial infections of the gastrointestinal with CDV are known. Samples can be submitted to a vali-
tract and respiratory system are common and, if indicated, dated laboratory for assessment of vaccination needs. Alter-
should be treated as indicated. Anticonvulsants are admin- nately, in some countries, assays designed to be used in the
istered as needed to control seizures (see Chapter 62), but clinic are available and have been used to assess animals for
chorea myoclonus has no known effective treatment. Gluco- CDV susceptibility in outbreak situations or for individual
corticoid administration may be beneficial in some dogs pet dogs (Gray et al., 2012; Litster et al., 2012ab). Some vac-
with CNS disease from chronic CDV infection, but it is cinated dogs are negative for CDV antibodies 3 years after
contraindicated in acutely infected dogs. The prognosis for vaccination, depending on the assay used (Mahon et al.,
dogs with CNS distemper is poor. 2017). These findings support the use of serology in deter-
mining CDV vaccination need, which can be used yearly in
Prevention and Zoonotic Aspects lieu of vaccination to determine when the titer goes below
The CDV survives in exudates only for approximately 1 hour protection levels. Serology can also be used to determine
at body temperature and 3 hours at room temperature and areas within a community that are the likely source of dogs
is susceptible to most routine hospital disinfectants. Dogs in CDV outbreaks and drive targeted vaccination programs
with gastrointestinal or respiratory signs of disease should and lessen the potential for local outbreaks (Spindel et al.,
be housed in isolation to avoid aerosolization to susceptible 2018).