Page 928 - Clinical Small Animal Internal Medicine

866 Section 9 Infectious Disease

Cross‐species infections frequently occur with influ- means of diagnosing infection. Serologic evaluations usu-
VetBooks.ir enza A viruses but adaptation to a new species is not ally require comparisons of paired sera to document sero-
conversion to confirm infection. CIV‐specific antibodies
common. Dogs are susceptible to infection with human
strains, normally without clinical illness or transmission
Hemagglutination inhibition assays are used to determine
to other dogs. It is not known why the H3 strains seem to can be detected as early as seven days after infection.
have adapted to the dog as a stable host, but it is possible antibodies specific for the H serotypes. However, conva-
that other strains could, with the appropriate mutations, lescent sera, in the absence of widespread exposure, can
evolve into true canine pathogens. In 2012, a novel H3N1 often be used to identify specific infection. Enzyme‐
human H1N1 and H3N2 reassortant virus was reported linked immunosorbent assay (ELISA) can be used to
to infect dogs subclinically in Korea but was not reported detect group‐specific antibodies for influenza A viruses.
to transmit from dog to dog. The group‐specific (not type‐specific) ELISA is based on
detecting specific antibody that binds to the nucleocapsid
protein, which coats the viral genome segments and is
Signalment highly conserved among all influenza A viruses.
Virus may be detected in samples collected with cotton
Any dog that has not developed immunity specific for or Dacron nasal swabs within four days after clinical
the H3N8 virus can be infected regardless of age, sex or signs are observed; that is, within seven days after infec-
breed. Being a highly contagious respiratory virus, the tion. Necropsy‐collected tissue from lungs or associated
length of time that a dog may remain in a shelter has lymph nodes may be used to detect virus. Diagnosis of
been associated with increased risk of infection with viral infection is often first determined using real‐time
CIV. With available vaccines and greater likelihood of reverse transcriptase polymerase chain reaction (PCR)
natural exposure, more animals will develop immunity of the gene that encodes the highly conserved matrix
and morbidity will likely decrease in all ages and breeds, protein in influenza virion. A positive PCR result may be
and both sexes. followed by viral isolation (after up to three passages)
using Madin–Darby canine kidney cells or embryonated
chicken eggs in order to determine the H and N subtypes
of the isolated virus.
History and Clinical Signs Subtyping the H and N of the viral isolates can also be
determined by laboratories that have the tools for
Clinical history is indistinguishable from other respira- sequencing the viral genome. The hemagglutination
tory diseases of dogs and resembles influenza infections inhibition assay is often used to determine the serotype
in other animals. Morbidity may be expected to be at of CIV strains in the US. Antibodies that react with virus
least 60%, but it has been reported that as many as 80% of inhibiting red blood cell agglutination of CIV serotype
infected animals may develop clinical signs of infection. standards can be used to inhibit agglutination and thus
Between two and four days following infection, dogs may identify the H subtype of the CIV isolate.
present with clinical illness, such as fever, sneezing,
dyspnea, anorexia, depression and coughing, and ocular
and nasal discharge that can become mucopurulent. Therapy
Illness, especially coughing, may continue for 10–30
days post infection. The mortality is generally low. A Supportive therapy may be necessary to provide opti-
minority of infected dogs will develop pneumonia with mum conditions for the immune system to respond,
tracheitis and bronchitis. Complications of secondary eliminating infection and reducing the severity of clinical
infections from bacteria or mycoplasma may exacerbate signs. Oxygen, intravenous fluids, and nebulization with
lung involvement, such as hemorrhage in the lungs, coupage may be needed for dogs with pneumonia. Good
mediastinum and pleural cavity, and greater mortality. nutrition and basic biosecurity measures that include
disposable or dedicated protective clothing and the use
of kennel‐approved disinfectants can help to prevent
Diagnosis viral spread. Soap and water hand washing which
destroys the bilipid envelope membrane of influenza
Because clinical illness is similar to that of other respira- viruses is highly effective in inactivating the virus.
tory illnesses in dogs, CIV involvement must be diag- Isolation of infected or suspected infected animals may
nosed by detection of viral antigen, viral RNA or the protect dogs not exposed to the virus or vaccine although
presence of specific antibody. Because of the short dura- exposure is difficult to assess since infection occurs prior
tion of virus infection, serology may be a more reliable to the appearance of clinical illness.