Respiratory Infections

The signs differ somewhat between dogs and cats, though both species can progress from mild upper respiratory infection to serious lower respiratory disease (pneumonia) without proper care.

Dogs (kennel cough / CIRDC):

• Sudden-onset dry, honking cough — often forceful enough to sound like the dog is trying to expel something from its throat
• Reverse sneezing — a rapid, snorting inhalation that alarms owners but is typically benign
• Mild nasal discharge
• Otherwise normal behavior, appetite, and energy in mild cases
• Fever, lethargy, thick purulent nasal discharge, and labored breathing — warning signs that infection has extended to the lungs (bacterial bronchopneumonia)

Cats (feline upper respiratory infection):

• Sneezing, sometimes in violent fits
• Watery to thick nasal and eye discharge — discharge that becomes yellow-green suggests secondary bacterial infection
• Conjunctivitis (eye inflammation) — redness, squinting, and discharge; herpesvirus can cause corneal ulcers (painful erosions on the eye surface) that must be treated promptly to prevent permanent damage
• Open-mouth breathing or loud congestion — significant concern in cats, who are obligate nasal breathers
• Reduced appetite caused by loss of smell from nasal congestion
• Oral ulcers (sores in the mouth) — more characteristic of calicivirus infection

Most respiratory infections are caused by a combination of pathogens rather than a single organism:

Canine infectious respiratory disease complex (CIRDC) — dogs:

• Bordetella bronchiseptica — a bacterial pathogen; the primary target of the Bordetella (kennel cough) vaccine
• Canine parainfluenza virus — a common viral co-pathogen included in the core DA2PP vaccine
• Canine influenza virus (CIV) — H3N2 and H3N8 strains; highly contagious in dog-dense environments; separate vaccine available
• Mycoplasma cynos, adenovirus type 2, and others can be co-infecting agents in severe cases

Feline upper respiratory infection — cats:

• Feline herpesvirus-1 (FHV-1, also called feline viral rhinotracheitis) — causes the most severe URI; cats that recover typically become latent carriers and can shed virus during stress
• Feline calicivirus (FCV) — causes oral ulcers and can range from mild to, in rare virulent systemic strains, rapidly fatal
• Both viruses are included in the core FVRCP vaccine
• Secondary bacterial infections (Bordetella, Chlamydophila felis, Mycoplasma) commonly complicate viral URI

Risk factors for both species: recent boarding, daycare, grooming, or shelter exposure; young age (puppies and kittens most vulnerable); overcrowded or poorly ventilated environments; incomplete vaccination; stress; or concurrent illness that suppresses immune function.

Many cases of kennel cough and feline URI are diagnosed clinically — the history of exposure and the characteristic signs are usually sufficient to guide initial treatment. More thorough testing is reserved for severe, prolonged, or non-responsive cases:

• Physical examination: assessment of respiratory rate, effort, and lung sounds; tracheal sensitivity (a kennel-cough dog typically coughs when the trachea is gently palpated); eye and mouth exam for ulcers or ocular involvement
• Thoracic radiographs (chest X-rays): essential when breathing is labored, when fever is present, or when coughing has not improved after 7–10 days — rules in or out pneumonia, which changes management significantly
• PCR respiratory panel: a swab-based molecular test that identifies the specific pathogen(s) responsible; most useful in outbreak situations, refractory cases, or when an unusual agent is suspected
• Complete blood count and chemistry: helps distinguish a mild viral infection from a bacterial pneumonia with systemic illness

Treatment is matched to the severity of illness:

• Supportive care for mild cases: rest, hydration, a quiet environment, and minimizing exercise to reduce coughing triggers. A cool-mist humidifier or brief steam-room exposure (a steamy bathroom) can ease congestion in cats
• Airway hygiene: gently wiping nasal and eye discharge with a warm damp cloth prevents crusting and secondary infection; cats that stop eating because they cannot smell their food may benefit from warming food to enhance its aroma
• Antibiotics: prescribed when there is evidence of secondary bacterial infection — purulent discharge, fever, documented pneumonia on X-ray, or failure to improve in 7–10 days. Antibiotics are not indicated for uncomplicated viral upper respiratory infections
• Antiviral therapy (cats with herpesvirus): oral famciclovir (an antiviral medication) reduces the severity and duration of active FHV-1 flares; topical antiviral eye drops are used for corneal ulcers
• L-lysine: an amino acid supplement traditionally used to suppress herpesvirus replication in cats; evidence for its benefit is mixed, though it is generally safe
• Hospitalization and oxygen therapy: for patients with bacterial pneumonia, severe dyspnea (labored breathing), or inability to maintain hydration and nutrition on their own

Prevention: the Bordetella vaccine (intranasal, oral, or injectable) significantly reduces the severity of kennel cough and is recommended for dogs with any boarding, daycare, or dog-park exposure. FVRCP is a core cat vaccine that protects against feline herpesvirus and calicivirus. Canine influenza vaccination is recommended for high-risk dogs in affected geographic areas.

Mild kennel cough in a healthy adult dog — a honking cough but otherwise normal behavior and appetite — can often be monitored at home for a few days. However, schedule an appointment promptly if your dog's cough is accompanied by fever, lethargy, reduced appetite, or labored breathing — these suggest pneumonia rather than simple kennel cough. For cats, open-mouth breathing, significant eye involvement, corneal ulcers, or anorexia lasting more than a day or two always warrant an evaluation. Kittens with feline URI need early attention because congestion can prevent them from nursing or eating, and rapid dehydration is a real risk in young cats. Dr. Diaz and our team at Dog & Cat Hospital Calabasas can assess the severity, confirm whether chest films are needed, and tailor a treatment plan that gets your pet back to normal as quickly as possible. Book an appointment today.