Feline Respiratory Infections: Causes, Transmission, and Zoonotic Risk

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-06-06

Key Takeaways

• Bacterial pathogens, including _Bordetella bronchiseptica_, _Chlamydia felis_, and _Mycoplasma_ species, are significant contributors to feline respiratory disease, acting as primary invaders or secondary opportunists that exacerbate viral infections.
• Transmission occurs through direct contact with infected secretions, aerosolized droplets from coughing/sneezing, and fomite contamination, with kittens and immunocompromised adults being at highest risk.
• Diagnostic approaches integrate clinical signs with laboratory methods such as bacterial culture, antimicrobial sensitivity testing, and multiplex PCR panels for definitive pathogen identification.
• Treatment necessitates targeted antimicrobial therapy guided by culture and sensitivity, with doxycycline being a common first-line choice for _B. bronchiseptica_, _C. felis_, and _Mycoplasma_ infections.
• Zoonotic risk is primarily associated with _Bordetella bronchiseptica_ and _Pasteurella multocida_, posing a greater concern for immunocompromised individuals through direct contact or bites/scratches.
• Prevention strategies include core vaccinations against common viral triggers, environmental management (ventilation, disinfection), and quarantine protocols for newly introduced cats.

Introduction

Feline upper respiratory tract infections represent a complex disease syndrome with multifactorial etiology involving viral, bacterial, and mycoplasmal pathogens [<a href="#ref-1">1</a>]. While viral agents such as feline herpesvirus type 1 (FHV-1) and feline calicivirus (FCV) are frequently incriminated as primary initiators, bacterial pathogens play critical roles as primary invaders or secondary opportunists that exacerbate clinical disease [<a href="#ref-2">2</a>]. Understanding the bacterial component of feline respiratory infections is essential for appropriate antimicrobial stewardship, accurate diagnosis, and management of zoonotic risk [<a href="#ref-3">3</a>]. This article provides a detailed examination of bacterial causes, transmission dynamics, clinical implications, and the zoonotic potential of feline respiratory pathogens.

Etiology of Bacterial Respiratory Infections in Cats

Bordetella bronchiseptica

_Bordetella bronchiseptica_ is a Gram negative, aerobic coccobacillus that colonizes the ciliated respiratory epithelium of cats and other mammalian hosts [<a href="#ref-1">1</a>, <a href="#ref-4">4</a>]. It is a primary pathogen in feline respiratory disease, particularly in high density housing environments such as shelters and breeding catteries [<a href="#ref-2">2</a>]. The organism expresses adhesins including filamentous hemagglutinin and fimbriae that facilitate binding to ciliated cells [<a href="#ref-4">4</a>]. _B. bronchiseptica_ produces a tracheal cytotoxin that disrupts ciliary function and a dermonecrotic toxin that contributes to epithelial damage [<a href="#ref-1">1</a>].

Chlamydia felis

_Chlamydia felis_ (formerly _Chlamydophila felis_) is an obligate intracellular Gram negative bacterium that primarily causes conjunctivitis in cats [<a href="#ref-2">2</a>]. Although its role in lower respiratory disease is less pronounced, it can contribute to rhinitis and sneezing, particularly in young kittens [<a href="#ref-1">1</a>]. The organism replicates within cytoplasmic inclusions of conjunctival epithelial cells and induces an inflammatory response characterized by neutrophil infiltration.

Mycoplasma Species

Several _Mycoplasma_ species, including _Mycoplasma felis_ and _Mycoplasma gateae_, are associated with feline upper respiratory disease [<a href="#ref-2">2</a>, <a href="#ref-3">3</a>]. Mycoplasmas are cell wall deficient bacteria that adhere to respiratory epithelial cells and induce ciliostasis and inflammation [<a href="#ref-1">1</a>]. They are frequently isolated concurrently with viral or other bacterial pathogens and are considered opportunistic secondary invaders [<a href="#ref-2">2</a>].

Other Bacterial Pathogens

How Do Cats Get Respiratory Infections

Transmission of bacterial respiratory pathogens occurs via direct contact with infected secretions, fomite exposure, and aerosolization over short distances [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>]. Kittens and immunocompromised adults are at highest risk [<a href="#ref-3">3</a>].

Transmission Routes

1. Direct contact: Nose to nose contact, mutual grooming, and sharing food bowls facilitate pathogen transfer [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>].
2. Aerosol droplets: Sneezing and coughing generate droplet nuclei that can transmit _B. bronchiseptica_ and _Mycoplasma_ over distances up to 1 to 2 meters [<a href="#ref-2">2</a>].
3. Fomites: Bedding, litter boxes, and human hands can carry viable bacteria for hours to days [<a href="#ref-1">1</a>, <a href="#ref-3">3</a>].
4. Vertical transmission: Queens shedding _C. felis_ during parturition can infect newborn kittens [<a href="#ref-2">2</a>].

Risk Factors

Crowded shelters, multicat households, poor ventilation, and concurrent viral infections (FHV-1, FCV) increase the likelihood of bacterial respiratory infection acquisition [<a href="#ref-3">3</a>, <a href="#ref-4">4</a>]. Stress induced by weaning, transport, or surgery elevates cortisol levels and suppresses mucosal immunity, facilitating bacterial colonization [<a href="#ref-1">1</a>].

Are Cat Respiratory Infections Dangerous

Severity of bacterial respiratory infections ranges from mild self limiting conjunctivitis to life threatening pneumonia [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>]. In otherwise healthy adult cats, uncomplicated infections typically resolve within 7 to 14 days with supportive care [<a href="#ref-3">3</a>]. However, several factors increase danger.

Complications

• Chronic rhinosinusitis: Persistent inflammation after acute infection leads to turbinate destruction and secondary bacterial colonization [<a href="#ref-1">1</a>, <a href="#ref-4">4</a>].
• Aspiration pneumonia: Nasal discharge and altered swallowing reflexes predispose to inhalation of food or water [<a href="#ref-2">2</a>].
• Neonatal mortality: Kittens infected with _B. bronchiseptica_ or _C. felis_ may develop severe bronchopneumonia with mortality rates exceeding 50% in untreated litters [<a href="#ref-3">3</a>].
• Systemic dissemination: _Pasteurella multocida_ can cause septicemia in neonates [<a href="#ref-1">1</a>].

Disease Severity Indicators

Diagnostic Approaches

Accurate diagnosis requires integration of clinical signs, cytology, culture, and molecular methods [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>].

flowchart TD
 A["Cat with respiratory signs"] --> B["Clinical examination"]
 B --> C{"Nasal/ocular discharge?"}
 C -->|"Yes"| D["Swab for cytology and PCR"]
 C -->|"No"| E["Radiography if dyspnea"]
 D --> F["Cytology: neutrophils, intracellular bacteria?"]
 F --> G["Culture and antimicrobial sensitivity"]
 F --> H["PCR panel: FHV-1, FCV, C. felis, B. bronchiseptica, Mycoplasma"]
 E --> I["Alveolar pattern?"]
 I --> J["Transtracheal wash for culture"]
 G & H & J --> K["Targeted antimicrobial therapy"]

Sample Collection

Deep nasal or oropharyngeal swabs are preferred for bacterial culture and PCR [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>]. Conjunctival swabs are optimal for _C. felis_ detection [<a href="#ref-3">3</a>]. Samples should be placed in transport medium and processed within 24 hours [<a href="#ref-4">4</a>].

Laboratory Methods

• Bacterial culture: Selective media (MacConkey agar for _B. bronchiseptica_, enriched chocolate agar for _C. felis_) [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>].
• PCR assays: Multiplex panels detect FHV-1, FCV, _C. felis_, _B. bronchiseptica_, and _Mycoplasma felis_ with high sensitivity and specificity [<a href="#ref-2">2</a>, <a href="#ref-3">3</a>].
• Serology: Limited utility for bacterial pathogens; antichlamydial antibody testing may aid diagnosis in chronic cases [<a href="#ref-4">4</a>].

Treatment Principles

Antimicrobial therapy should be guided by culture and sensitivity results when possible [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>].

First Line Antimicrobials

Supportive care includes humidification, nasal clearance, appetite stimulation, and fluid therapy [<a href="#ref-1">1</a>, <a href="#ref-4">4</a>]. Corticosteroids are contraindicated during active bacterial infection [<a href="#ref-2">2</a>].

Is Cat Respiratory Infection Contagious to Humans

Zoonotic potential varies by pathogen. Most feline bacterial respiratory agents have low to moderate zoonotic risk, primarily affecting immunocompromised individuals [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>].

Zoonotic Pathogens of Concern

• _Bordetella bronchiseptica_: Documented transmission from cats to immunocompromised humans, including cases of pneumonia in HIV positive patients and neutropenic individuals [<a href="#ref-1">1</a>, <a href="#ref-3">3</a>]. Healthy adults rarely develop disease [<a href="#ref-2">2</a>].
• _Pasteurella multocida_: Commonly transmitted via bites or scratches; can cause wound infections, cellulitis, and occasionally respiratory disease in humans [<a href="#ref-1">1</a>, <a href="#ref-4">4</a>].
• _Chlamydia felis_: Rarely causes human conjunctivitis; reported in immunocompromised individuals after direct ocular contact with infected cat secretions [<a href="#ref-2">2</a>, <a href="#ref-3">3</a>].
• _Mycoplasma felis_: No confirmed zoonotic transmission; considered host specific [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>].

Risk Mitigation

Immunocompromised individuals should avoid contact with cats showing respiratory signs, practice hand hygiene after handling, and wear gloves when cleaning ocular or nasal discharge [<a href="#ref-3">3</a>, <a href="#ref-4">4</a>].

Prevention and Control

• Vaccination: Core vaccines for FHV-1 and FCV reduce viral predisposing factors; intranasal _B. bronchiseptica_ vaccine is available for high risk cats [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>].
• Environmental management: Adequate ventilation, disinfection with quaternary ammonium compounds, and reduced stocking density in shelters [<a href="#ref-2">2</a>, <a href="#ref-3">3</a>].
• Isolation: Newly introduced cats should be quarantined for 14 days [<a href="#ref-1">1</a>].

Conclusion

Bacterial pathogens contribute significantly to feline respiratory infections, either as primary agents or as secondary invaders following viral infection. Understanding transmission routes, clinical progression, and diagnostic pathways enables effective management and reduces zoonotic risk. The question "how do cats get respiratory infections" is answered through a combination of direct contact, aerosol, and fomite transmission. The danger of these infections depends on host factors and pathogen virulence, with severe outcomes in kittens and immunocompromised adults. Regarding zoonotic risk, _B. bronchiseptica_ and _Pasteurella multocida_ represent the principal concerns, particularly for immunocompromised human contacts.

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References

Disclaimer: This article is for educational and informational purposes only. It is not intended to substitute for professional veterinary advice, diagnosis, treatment, or regulatory guidance. Always consult a licensed veterinarian or qualified specialist regarding animal health, disease diagnosis, and therapeutic decisions.