Canine Respiratory Pathogens and Their Properties

VIRUSES

• Parainfluenza virus (CPiV)
• Adenovirus type 2 (CAV2)
• Distemper virus (CDV)
• H3N8 canine influenza virus (H3N8 CIV)
• H3N2 canine influenza virus (H3N2 CIV)
• Respiratory coronavirus (CRCoV)
• Pneumovirus (CnPnV)
• Canine herpes virus (CHV)

BACTERIA

• Bordetella bronchiseptica (Bordetella)
• Streptococcus zooepidemicus (Strep zoo)
• Mycoplasma cynos (M. cynos)

Incubation Period

The incubation period for the known bacterial and viral respiratory pathogens is 7 days or less. This short incubation period contributes to a rapid increase in number of dogs with kennel cough within a short period of time. The exception is CDV. The CDV incubation period is typically 2 weeks and this longer period causes delays in recognizing affected dogs and contributes to a slow insidious increase in number of dogs with kennel cough and progressive disease. Preclinical shedding occurs for all of the respiratory pathogens, meaning infected dogs are contagious before appearance of clinical signs.

Shedding Period

Most of the viral pathogens are shed in respiratory secretions for <14 days. The short shedding period contributes to feasibility of isolating affected dogs for 2 weeks before safely releasing back into the shelter population or to adoption groups or new owners. The exceptions are CDV, H3N2 CIV, Bordetella, Mycoplasma, and Strep zoo.

Here is a summary table of the CIRD pathogen properties. The incubation and shedding periods are included in the Canine Respiratory Infections in Shelters document.

Summary of Canine Viral CIRD Properties

	CAV2	CPiV	CDV	H3N8 CIV	H3N2 CIV	CRCoV	CnPnV	CHV
Pathogen type	DNA virus	RNA virus	RNA virus	RNA virus	RNA virus	RNA virus	RNA virus	DNA virus
Transmission route	direct contact, droplets, aerosols, fomites	direct contact, droplets, aerosols, fomites	direct contact, droplets, aerosols, fomites, feces, urine	direct contact, droplets, aerosols, fomites	direct contact, droplets, aerosols, fomites	direct contact, droplets, aerosols, fomites	direct contact, droplets, aerosols, fomites	direct contact, droplets, aerosols, fomites
Incubation period	≤1 wk	≤1 wk	2 wks	≤1 wk	≤1 wk	≤1 wk	≤1 wk	≤1 wk
Shedding period	<2 wk	<2 wk	wks-mos	<2 wk	≤3 wks	<2 wk	<2 wk	<2 wk
Persistent infection	no	no	no	no	no	no	no	yes

Summary of Canine Bacterial CIRD Properties

	Bordetella	M. cynos	Strep zoo
Pathogen type	gram-negative bacteria	bacteria w/o cell walls	gram-positive bacteria
Transmission route	direct contact, droplets, aerosols, fomites	direct contact, droplets, aerosols, fomites	direct contact, droplets, aerosols, fomites
Incubation period	≤1 wk	≤1 wk	≤1 wk
Shedding period (w/o antibiotics)	≤3 mo	weeks	weeks
Persistent infection	no	unknown (w/o antibiotics)	unknown (w/o antibiotics)

Duration of Virus Shedding and Clinical Disease for CIRD Viruses

Note: Click each graph to access the full-size version.

Most of the viral and bacterial respiratory pathogens cause subclinical infections in a proportion of exposed dogs. Subclinically infected dogs shed the pathogen in oronasal secretions, but the amount of shed pathogen is typically much smaller and for shorter periods of time. However, the inability to identify subclinically infected dogs ensures that more dogs are exposed by direct contact.

Transmission

The viral and bacterial respiratory pathogens are spread by contact with oronasal secretions from infected dogs. Sneezing and coughing generates large pathogen-containing droplets that spread within a 5-foot zone around the dog. Coughing also generates aerosols or fine mists that can spread within a 20-foot zone around the dog. The large droplets and aerosols are a major source of respiratory pathogen spread in a kennel. This is why clinically ill dogs should be promptly isolated from the population to decrease spread of infectious doses in the environment and to other dogs.

The typical shelter kennel layout contains rows of runs that are separated by concrete half-walls topped by chain link fencing. The doors are chain link. There may be two rows of runs facing each other separated by a 6-to 8-foot walkway. Droplets and aerosols generated by sneezing and coughing dogs can easily spread to other dogs in this setting.