Pathogenesis and Clinical Signs of Feline Calicivirus

Meghan Neal 

Feline Calicivirus (FCV) is a small, non-enveloped, single-stranded RNA virus. All members of the family Felidae can become infected with FCV. Young kittens and adult cats that go through a stressful event are most susceptible to infection. FCV is highly contagious and transmission occurs through aerosolized droplets from salivary, ocular or nasal secretions of infected cats. Susceptible cats get an infection through direct contact with another infected cat or environmental exposure via fomites, which can be carried to susceptible cats by a handler! It is also thought the FCV can be spread in urine and feces, but these are not major sources of infection.

The incubation period for FCV is 5-10 days. The virus replicates mainly in the oral and respiratory tissues, although some strains vary in their tissue tropism and pathogenicity. The virus may survive for weeks within the contaminated environment. FCV is shed continuously from infected cats and convalescent cats may harbor the virus for months. Many infected cats develop a carrier state and will continue to shed the virus intermittently or constantly. Carrier cats are an important source of infection as they may or may not show clinical signs of infection when they are actively shedding the virus. This carrier state may only last a few months, but in some cats it persists for life. Queens that are carriers can pass the infection to their newborn kittens.

There are many different strains of FCV resulting in a range of clinical signs that may be seen. Some strains induce salvation and ulceration of the tongue, hard palate, or nostrils; other strains induce pulmonary edema and interstitial pneumonia.  Certain strains of FCV are non-pathogenic. The most characteristic lesion of FCV is oral ulcerations. Ulcers begin as vesicles, typically on the margin of tongue, and then subsequently rupture with necrosis of the overlying epithelium. Healing of the ruptured ulcers takes 2-3 weeks. Fever, sneezing, ocular and nasal discharges also occur frequently.

Nasal discharge and vesicles & ulcers on the tongue of a cat infected with FCV.

(Photos Courtesy of Merck Animal Health)

Tongue ulcerative glossitis from a FCV case.

(Photo courtesy of Tufts University)

In-apparent infections or pneumonia may be occasionally seen with FCV infection. Pulmonary lesions are less common and are thought to be a result of initial inflammation of the bronchioles and alveoli. This causes acute pulmonary edema that then progresses to an exudative pneumonia and later a proliferative interstitial pneumonia. These lesions will result in dyspnea and altered lung sounds.

Radiographs of interstitial pneumonia.

(Photo courtesy of the Journal of Feline Medicine & Surgery)

Histopathology & gross pathology of interstitial pneumonia from a FCV case.

(Photos courtesy of Tufts University)

Some FCV strains can also cause an acute febrile lameness syndrome. Such strains produce a transient fever, alternating leg lameness, and pain on palpation of the joints. Lesions seen in the joints of cats with FCV-associated lameness include synovitis with thickening of the synovial membrane and an increase in quantity of synovial fluid within the joint. Unfortunately, vaccination does not protect against the strains that cause this lameness syndrome.

FCV has also been found in cats with lymphocytic-plasmacytic gingivitis and stomatitis. An acute febrile response, inappetence, and depression are common signs. Serous rhinitis and conjunctivitis also can occur.

Lymphocytic-plasmacytic stomatitis in a cat.

(Photo courtesy of Apex Dog and Cat Dentistry)

References:

“Feline calicivirus”

Alan D. Radford, Karen P. Coyne, Susan Dawson, Carol J. Porter and Rosalind M. Gaskell

Vet. Res. 38 (2) 319-335 (2007)

DOI: http://dx.doi.org/10.1051/vetres:2006056

“Feline Calicivirus Infection”

VCA Animal Hospitals

http://www.vcahospitals.com/main/pet-health-information/article/animal-health/feline-calicivirus-infection/4132

“Feline Respiratory Disease Complex”

The Merck Veterinary Manual

http://www.merckmanuals.com/vet/respiratory_system/respiratory_diseases_of_small_animals/feline_respiratory_disease_complex.html?qt=feline%20calicivirus&alt=sh

Subbiah, E. VM 8124 Veterinary Virology Course Notes, Feline Viruses. Spring 2013; Lecture 27.