Page 914 - Clinical Small Animal Internal Medicine

852 Section 9 Infectious Disease

factor (TGF)‐beta. A CD4+‐mediated delayed‐type Conjunctivitis, nasal discharge, cough, and fever are classic
VetBooks.ir hypersensitivity and cytotoxic CD8+ T cells contribute signs. Respiratory infection may involve the lower respira-
tory tract with possible primary viral pneumonia.
to myelin loss in the chronic phase. Additionally, upregu-
lation of interferon‐gamma and IL‐1 may occur in
diarrhea may be present. Neurologic signs may be concur-
advanced lesions. Moreover, an altered balance between Secondary bacterial infection may occur. Vomiting and
matrix metalloproteinases and their inhibitors seems to rent with epithelial signs (i.e., respiratory disease, conjunc-
play a pivotal role for the pathogenesis of DL. tivitis, vomiting, diarrhea) with encephalitis caused by
Histologic manifestations include polioencephalitis direct viral replication. Alternately, neurologic disease may
and DL. The observations of p75 NTR ‐expressing bipolar occur several weeks after resolution of epithelial invasion.
Schwann cell‐like glia in CDV‐DL highlight the potential A significant amount of pathology results from the
of Schwann cell‐mediated remyelination and raise the host’s immune response to the virus, as well as the virus
hope for a beneficial regenerative process in CDV‐DL. itself. Seizures and myoclonus are two of the more com-
Though the central role of axonal damage as a triggering mon signs. The latter may affect limbs or manifest as
event is established in CDV‐DL, the role of macrophage chewing motion of the jaw. Ocular disease may also
polarization in CDV‐DL is currently unknown. In light occur. Lesions include anterior uveitis, optic neuritis,
of the fact that distinct macrophage responses have been and retinal detachment. Infection during pregnancy may
linked to axonal regeneration, degeneration, demyelina- lead to abortion or stillbirth. Puppies infected before
tion, and remyelination, the elucidation of a potential permanent dentition may have enamel hypoplasia.
macrophage polarization during CDV‐DL appears to Digital hyperkeratosis (“hard pad disease”) may be noted.
represent a promising field for future investigations and
the development of new treatment strategies.
Recovery from CDV depends on the host immune Diagnosis
response. A strong and effective cellular immune
response can eliminate the virus prior to infection of Diagnosis is established via virus identification in a clini-
parenchymal tissues, while weak and delayed cellular cal sample through use of reverse‐transcriptase poly-
and humoral immune responses lead to virus spread and merase chain reaction (PCR) of whole blood, a swab of
persistence, respectively. conjunctiva or tissue, cerebrospinal fluid (CSF), or urine.
When obtaining conjunctival scrapings, remove mucus
and tears and using a sterilized, blunt metal spatula or
Epidemiology dulled scalpel blade, repeatedly scrape the conjunctiva
until a small amount of tissue can be lifted. Apply the tis-
Canine distemper is a fatal disease of dogs with a world- sue to a slide and submit the slide to an outside lab for
wide distribution. With a mortality rate of around 50%, it immunofluorescence assay (IFA) testing. Urine is a good
is second only to rabies when it comes to virus‐induced source for PCR testing in patients with CDV encephalitis
fatality in dogs. after resolution of epithelial signs. CDV may be detected
in urine for a longer period than other sample types.
CDV detection in urine and CSF was equivalent in one
study of neurologic cases. Postmortem evaluation and
Signalment microscopic findings confirm infection. The specific
lesion of CDV is eosinophilic intranuclear/intracytoplas-
There is no breed or sex predilection. Animals <6 months mic inclusion bodies in glial cells, neurons, epithelial res-
are particularly vulnerable. piratory cells, and cells of the GI and urogenital tracts.
Virus isolation is the gold standard for diagnosis and is
useful in low levels of viral infection through observation
Clinical Signs of typical syncytial cell formation. Immunocytology can
be used to enhance the visibility of inclusion bodies by
Signs most often involve the respiratory tract. fluorescein‐conjugated CDV antibodies.
Gastrointestinal (GI) signs may also occur. Affected dogs
are listless and have a decreased appetite. In milder cases,
signs may be similar to other agents of canine infectious Treatment
respiratory disease complex. Subclinical infection with
shedding may also occur, depending on the level of host Treatment is supportive only (see Chapter 82). Antiviral
immunity. Systemic signs are most common in unvacci- medications are not routinely used or recommended. No
nated dogs (e.g., puppies) as maternal immunity wanes. single treatment is specific or uniformly successful.