Respiratoryinfections arecommon in cats,especially inhigh-densitypopulationssuch as shelters,breedingcatteries, and feralcat colonies.A variety of viruses, bacteria,fungi, and protozoa cause these infections, whichnegatively impact feline health. While vaccines have greatlyreduced the incidence of serious respiratory disease in cats,they have not eliminated the highly contagious pathogensthat cause them.
Infections can occur in the upper and lower regions of therespiratory tract. The upper respiratory tract includes thenasal passages, sinuses, oral cavity, back of the oral andnasal cavity (pharynx), and the vocal folds (larynx). The lowerrespiratory tract includes the trachea, bronchi, and lungs(see Figure 1).
Symptoms of upper respiratory tract infections includeclear or colored discharge from the eyes or nose, coughing,sneezing, swelling of the mucous membranes around theeyes (conjunctivitis, see Figure 2), ulcers in the mouth,lethargy, and anorexia. In rare cases, cats may have troublebreathing.
Lower respiratory tract infections may cause coughing,lethargy, anorexia, and difficult or rapid breathing (whichshould not exceed 35 breaths per minute at rest).
FELINE HERPES VIRUS
Young and adolescent cats are mostsusceptible to this common infection.Up to 97% of cats are exposed to felineherpes virus in their lifetime, and the virus causes a lifelonginfection in up to 80% of exposed cats. Of these, up to 45%will periodically shed the virus, usually when stressed.
Clinical Signs
Commonly referred to as feline viral rhinotracheitis (FVR),herpes infection can cause upper respiratory signs (seethird paragraph above), ulcers on the cornea(keratitis), and fever.
Diagnosis
FVR is usually diagnosed by recognizing upper respiratorysigns in young or unvaccinated cats, or recurringconjunctivitis or keratitis in older cats, combined with theresults of various diagnostic tests. These tests includepolymerase chain reaction (PCR), which identifies viral DNA,and virus isolation tests that detect herpes by culturing thevirus from clinical samples.
Treatment
Multiple factors, including the severity of disease, areconsidered when deciding the best treatment for FVR. Inall cases, appropriate supportive care, such as maintainingadequate nutrition and hydration, is very important. Nasaldecongestants may be helpful in some cases. It is importantto note that the stress of giving medications may worsenbouts of keratitis and conjunctivitis that may otherwisesubside on their own.
In acute cases of infection in young cats, antiviral drugsmay help treat lesions on the cornea and upper respiratorysigns. Systemic antibiotics can also be used to control thesecondary bacterial infections that commonly occur withFVR. Recurring cases of keratitis or conjunctivitis can oftenbe managed with antivirals, drugs such as corticosteroids,and by limiting stress caused by crowded living conditions,surgeries, the introduction of new cats, or moving. Whilelysine supplementation is sometimes recommended, thistreatment is quite controversial. Several studies suggestthat lysine supplementation is not effective and mayactually worsen symptoms and promote shedding of thevirus.
Prognosis
Once infected, cats carry the infection for life and mayexperience recurring bouts of upper respiratory and eyedisease. While these flare-ups are often relatively mildand clear up on their own, infections can, in rare cases,lead to more significant illness and even death in cats withcoexisting health problems.
Prevention
Vaccination against feline herpes is recommended for allcats. Although current vaccines do not prevent infectionin all cases, they significantly decrease the severity ofdisease and the shedding of virus. This is beneficial to othersusceptible cats, particularly those living with the cat beingvaccinated.
FELINE CALICIVIRUS
Feline calicivirus is a highly contagious and common virusin cat populations worldwide. Approximately 10% of catshoused in small groups are infected, while up to 90% ofthose housed in more crowded conditions, such as inshelters and breeding catteries, may be infected.
Clinical Signs
While most cats infected with calicivirus develop upperrespiratory signs (see third paragraph above), theinfection may spread to the lower respiratory tract andcause pneumonia. Viral pneumonia may be exacerbatedby secondary bacterial infections of the lungs, resulting inincreased difficulty breathing. In rare cases, susceptible catsmay develop inflammation or ulcers in the mouth. Evenmore rarely, the more severe systemic form of the diseaseoccurs. This form is fatal in approximately two-thirds ofaffected cats. Systemic calicivirus often causes swellingof the head and limbs and crusting sores and hair losson the nose, eyes, ears, and footpads. Additionally, themouth and ears may become yellowish (jaundiced) dueto liver damage, and cats may experience bleeding in thegastrointestinal tract and under the skin. In rare cases, catsmay experience temporary limping when infected or afterreceiving a calicivirus vaccine.
Diagnosis
If oral ulcers and signs of acute upper respiratory diseasecause a veterinarian to suspect calicivirus infection, thediagnosis can be confirmed by a technique called reversetranscriptase polymerase chain reaction (RT-PCR), which candetect the genetic material of calicivirus in blood samplesor from swabs taken from the mouth or eyelids. Growingcalicivirus from clinical samples in the lab also confirms thediagnosis.
Treatment
Supportive care, including assurance of adequate hydrationand nutrition, is vital. This may be challenging, as painfullesions in the mouth may make eating and drinkinguncomfortable, and congested nasal passages can blockthe perception of food odors that stimulate the appetite.Non-steroidal anti-inflammatory drugs can minimize oralpain, and the nasal passages should be cleared usingdrugs to break down mucous, nebulization with saline, andregular wiping with a saline solution. A feeding tube thatbypasses the oral cavity may be recommended until orallesions subside.
Antibiotics may be used to combat secondary bacterialinfections in the mouth and respiratory tract. Unfortunately,available antiviral drugs are either ineffective or havesignificant side effects in cats. While some cats with severesystemic calicivirus infection have been reported to improvewhen given a combination of corticosteroids and interferon,the safety and effectiveness of this therapy needs morethorough testing before it can be routinely recommended.
Veterinarians may recommend that cats with chronic oralulcers receive rigorous dental cleaning, combined withimmune-modulating drugs, antibiotics, and pain-relievingmedications, but controlled studies to determine the besttreatment for this aspect of calicivirus infection are stillneeded.
Prognosis
The prognosis for cats with calicivirus infections dependsupon the severity of symptoms. Cats with uncomplicatedupper respiratory disease, pneumonia, or oral ulcers mayrecover in days or weeks, while those with severe systemicdisease have a much less favorable prognosis.
Prevention
Vaccination against feline calicivirus is recommended for allhealthy cats. Although the vaccine is not 100% protective, itdoes reduce the likelihood of severe disease. Vaccines donot, however, prevent shedding of this ubiquitous virus orcure cats that are already infected.
FELINE CHLAMYDIOSIS
Chlamydia felis is a bacterium that cannot survive outsideof its host and therefore requires close contact betweencats for transmission. Transmission occurs through eyesecretions. Infections occur most commonly in young catsand in cats housed at high density in shelters and breedingcatteries. Approximately 20% of cats with upper respiratorysigns and about 3% of healthy-looking cats carry C. felis.
Clinical Signs
Infected cats usually develop conjunctivitis with eyedischarge that is initially clear, but later contains mucousand has a yellowish, pus-like appearance. Rarely, infectedcats lose their appetite and become lethargic.
Diagnosis
The preferred method of verifying infection is the use ofPCR to identify C. felis DNA from eye swabs. The organismcan also be grown in the lab, but this technique is not assensitive as PCR. Unvaccinated cats can also be tested forC. felis antibodies.
Treatment
Antibiotics (e.g. doxycycline, amoxicillin/clavulanic acid)are generally effective in treating chlamydiosis in cats,with systemic treatment being more effective than topicalapplication to the eye.
Prognosis
The prognosis for infected cats that are appropriatelydiagnosed and treated is generally good.
Prevention
While vaccines are available, they do not prevent infection,but rather minimize the symptoms. Vaccination isrecommended for cats in multi-cat housing situations andthose in which C. felis has previously been diagnosed.
FUNGAL INFECTIONS
A number of fungal species can cause respiratory diseasein cats. The most common is Cryptococcus neoformans.Cats contract C. neoformans when they inhale fungalspores. The infection may remain within the nasal cavityor spread to other parts of the body, including the centralnervous system and the lower respiratory tract. Thisorganism is pervasive, and approximately 4% of all cats areasymptomatic carriers. Cats are approximately six timesmore likely to develop disease after exposure than dogs,and cats of all ages are equally susceptible. Bird droppingsand decaying plant matter provide an ideal environmentfor C. neoformans and may be sources of infection. Pigeons are frequent carriers. A closely related fungus, Cryptococcusgattii, causes very similar disease symptoms.
Clinical Signs
C. neoformans infections most commonly occur in thenasal form, in which cats develop nasal or facial swelling,sneezing, chronic nasal discharge that may becomebloody, and, ultimately, wounds that won’t heal or fleshypolyp-like growths in the nose and throat. Affected catsmay demonstrate changes in the tone of their vocalizations,and noisy breathing and snoring. They may also becomeanorexic and lose weight. If the infection spreads to thelungs, affected cats may demonstrate labored or rapidbreathing. C. neoformans infections can also affect thecentral nervous system and the skin, and in rare cases maybecome systemic and spread to multiple organs or systemsin the body.
Diagnosis
The preferred method of diagnosis is identification ofC. neoformans proteins in body fluids, ideally blood.Examining fluid samples, such as nasal discharge, under amicroscope (cytology) can also be helpful, as C. neoformanshas a characteristic microscopic appearance.X-rays, CT scan, or MRI may be recommended to determinehow deeply the fungus has invaded the bony structuresin the nose and sinuses and to monitor the response totherapy.
Treatment
While a number of anti-fungal drugs are used to treat C.neoformans infections, definitive guidelines regardingwhich should be used in specific cases are lacking. Insome cases, spread of infection to certain organs, suchas the brain, may alter therapeutic recommendations andoutcome.
Prognosis
The prognosis for cases diagnosed early in the diseaseand with no involvement of the central nervous system isgenerally favorable. One major factor influencing outcomesis compliance with therapy, which may last months to years.
Prevention
Since outdoor cats are exposed to C. neoformans morefrequently, keeping cats indoors minimizes the risk ofinfection.
OTHER FUNGI
A number of other fungi cause respiratory infections in cats,including Aspergillus fumigatus, Histoplasma capsulatum, andBlastomyces dermatiditis. Unlike C. neoformans infections,these organisms commonly spread to the lungs of affectedcats, causing pneumonia (see Figure 3) and difficultybreathing.
BORDETELLA BRONCHISEPTICA
B. bronchiseptica is a bacterium that commonly causesinfections of the upper respiratory tract of cats housed inhigh-density populations, such as in shelters and breedingcatteries. In these populations, approximately 5% of catswith signs of upper respiratory tract infections and 1.5%of cats that appear normal may harbor B. bronchiseptica.Infections spread through oral and nasal secretions, andcan cause symptoms ranging from mild to life-threatening.Infected dogs may spread the bacterium to cats, and invery rare cases, B. bronchiseptica may be transmitted topeople.
Clinical Signs
The clinical signs of infection vary from coughing, sneezing,and eye discharge that is mild and self-limiting to difficultybreathing, blue-tinged mucous membranes (cyanosis), anddeath. The more serious signs often occur in young catsthat develop lower respiratory tract infections, althoughthese may occur in older cats as well.
Diagnosis
Samples taken from the respiratory tract can be usedto grow B. bronchiseptica in the lab, or to detect B.bronchiseptica genetic material through PCR. Both of thesetests, however, may give negative results in infected cats.
Treatment
Antibiotic therapy (usually doxycycline) is the mainstay oftherapy, although supportive care, including assurance ofadequate nutrition and hydration, are very important inmanaging B. bronchiseptica infection in cats. Even in caseswith mild symptoms, antibiotics may be recommended toprevent a worsening of the infection.
Prognosis
Most cats with uncomplicated B. bronchiseptica infectionsrecover within 10 days of beginning antibiotic therapy.Without appropriate treatment, the disease may progressto varying degrees, from worsening upper respiratory signsto life-threatening pneumonia.
Prevention
A nasal vaccine is available, and while it is not considereda core vaccine for all cats, it should be considered for catsentering high-density housing situations. It should never beadministered to cats younger than four weeks, or to catsreceiving or scheduled to receive antibiotics. The vaccinemay cause mild upper respiratory signs in some cats.
OTHER INFECTIONS
A variety of other organisms can cause respiratoryinfections in cats, including some avian and canineinfluenza viruses, which cats can contract from humans anddogs, respectively. Avian influenza may also be transmittedfrom cats to humans. Other infectious organisms includeYersinia pestis (cause of the “Great Plague”), abacterium found primarily in rodents in thesouthwest U.S. that is transmitted by fleasand is potentially transmissible to humans;Toxoplasma gondii, a protozoan found inmany cats that can spread to humans; andPasteurella multocida, a normal bacteria ofthe feline respiratory system that may causesecondary infections.
Updated June 2018
