FELINE VIRAL DISEASES J. Thorsen*

IN A DISCUSSION of feline viral diseases, there with contaminated surroundings, or by fleas are three topics of primary importance; feline that have fed on an infected cat. The virus sur- panleukopenia, feline viral rhinotracheitis and vives for long periods of time outside the host, feline pneumonitis. This last disease is actually and premises remain contaminated for three or bacterial, but the causative agent has long been four months after the departure of an infected referred to as a virus, and still remains within cat. the province of the virologist. Other virus The viral etiology of the disease has been diseases that occur sporadically in cats are recognized for 40 years (18) but only recently rabies and pseudorabies. Many other viruses has any information accumulated about the have been isolated from cats, not always in virus. In 1964, a virus was isolated from a association with definite clinical syndromes. leopard cub with panleukopenia symptoms and cultivated in kitten kidney cell cultures FELINE PANLEUKOPENIA (11). The virus produced a cytopathic effect The most important disease of cats, world- consisting of transient intranuclear inclusions, wide, is panleukopenia, also known by various visible in stained cell culture preparations. The synonyms including feline enteritis, feline ag- cell-cultured virus produced panleukopenia ranulocytosis and feline distemper. Clinically, symptoms in susceptible cats. The virus is a the disease is characterized by depression, de- small DNA virus, about 20 m,u in diameter, hydration, diarrhea, anorexia, vomition and a with cubic symmetry, tentatively classified as biphasic temperature curve (18). Respiratory a member of the Parvovirus group. An inter- signs are not a feature of uncomplicated pan- esting property of this group of viruses is their leukopenia infection. The symptom after which affinity for cells in active mitosis (14). In ceDl the disease is named is a marked decrease in cultures, the degree of cytopathic effect caused the total leukocyte count (10), particularly by the virus is proportional to the mitotic neutrophils although leukopenia is not pecu- activity of the cells (12). In mature animals liar to feline panleukopenia. Total white blood this preference for mitotically active cells leads cells may fall to 500 per cu mm or lower. to destruction of actively dividing cells in the Counts below 5,000 to 6,000 are considered bone marrow and lymphopoietic tissue or in significant, especially if neutropenia is pro- the intestinal epithelium. Infection of pregnant nounced. dams leads to virus attack on the actively di- Mortality from panleukopenia is approxi- viding cells of the fetus, resulting in resorption, mately 90% in young kittens, falling to 50 or mummification, stillbirths, abortion, and in the 60% in older cats. Treatment should include condition known as feline ataxia in newborn fluid therapy to combat dehydration, whole kittens (13, 14). Feline ataxia is due to the blood transfusions, and antibiotics to control action of the virus on the dividing cells of the secondary bacterial invasion. Vitamin B com- germinal layer in the cerebellum. Recovered plex, ascorbic acid and, during the recovery dams may be virus carriers, with varying de- period, vitamin A are also recommended. Medi- grees of reproductive failure. cation to control vomiting and diarrhea may Panleukopenia vaccines have been prepared be useful. Strict isolation and sanitation are by inactivating tissue origin virus. Vaccination obviously important. of cats with either panleukopenia vaccine or Panleukopenia virus affects various members mink enteritis vaccine will produce a service- of the family Felidae, and also raccoons. The able immunity, due to their close antigenic re- virus of mink enteritis is regarded as either a lationship. The introduction of inactivated close antigenic relative or a strain of feline pan- tissue culture origin vaccines represents an leukopenia virus. Transmission of panleuko- improvement, since these vaccines should con- penia virus may be by direct contact, contact tain less host protein and probably less forma- lin than tissue origin vaccines. Tissue culture Division of Virology, Ontario Veterinary Col- are lege, University of Guelph, Guelph, Ontario. vaccines containing live attenuated virus This paper was presented at the 58th Annual also available, and should produce an excellent Summer Convention of the Alberta Veterinary antibody response in vaccinated animals. Medical Association. Supported in part by the Other viruses cytopathic in kitten kidney Ontario Department of Agriculture and Food. cell cultures have been isolated from the spleen 18 CAN. VET. JOUR., vol. 11, no. 1, January, 1970 FELINE VIRAL DISEASES of cats, among them viruses designated as FPL nasal swabs or from mucosal scrapings, and (4), KCD (9) and F20 (2). Some of these grows with cytopathic effect in kitten kidney have been regarded as panleukopenia virus, cell cultures. but serological studies have not shown any anti- In treatment, antibiotic therapy to control genic relationships. Experimental infections secondary bacterial infection is advisable. Par- with these viruses do not result in panleuko- enteral tetracyclines would be the antibiotics of penia. FPL virus does have a potentiating effect choice, in the event that the condition is actually on panleukopenia virus, and the symptoms and feline pneumonitis. Other treatment consists of mortalitv resulting from combined infection removal of crusted nasal and ocular discharges, more closely resemble field cases of panleuko- administration of nose drops, and antibiotic penia than those caused by panleukopenia virus ophthalmic ointments, and fluid therapy with alone (3). This agrees with recent experiments balanced electrolytes in cases of severe emacia- in germ-free cats, in which infection with pan- tion and dehydration. The prospects for devel- leukopenia virus is not as severe as in normal opment of an effective feline rhinotracheitis cats (17), indicating that the microbial flora vaccine are not good. Since recovery from of the cat has a bearing on the severity of natural infection does not produce durable symptoms. immunity, revaccination at frequent intervals A condition closely resembling panleuko- would be necessary. penia clinically, and producing a similar degree of leukopenia, is necrotic colitis. Necrotic colitis FELINE PNEUMONITIS usually occurs in older cats which presumably Feline pneumonitis, another important respir- have developed immunity to panleukopenia by atory disease of cats, is caused by a bacteria, a vaccination or exposure. The etiology has not member of the genus Chlamydia or Bedsonia, been definitely established. Coliform enteritis the names now in common use for the group. in cats also produces leukopenia, but with a These agents are obligate intracellular parasites, marked neutrophilia. have long been referred to as basophilic viruses, and are still generally regarded as viro- FELINE VIRAL RHINOTRACHEITIS logical problems. An important respiratory pathogen of cats The feline pneumonitis agent was isolated is feline rhinotracheitis virus. Virological and in 1944, from cats with symptoms of respira- serological surveys indicate that the virus is tory disease (1). The agent is fairly resistant widespread in domestic cat populations. Feline to environmental influences. Transmission rhinotracheitis is a highly contagious disease among cats is by contact with nasal and ocular of cats of all ages, characterized by fever, secretions and by aerosol. Recovered animals sneezing, excess lacrimation, nasal discharge, may be carriers of the agent, and the condition anorexia and depression (7). The nasal and may be reactivated by stress. ocular discharges tend to become mucopurulent The symptoms of feline pneumonitis include early in the course of the disease. Another fre- increased lacrimation, conjunctivitis, muco- quent sign is ulcerative glossitis, especially of purulent discharge from the eyes and nose, the tip and edges of the tongue. The disease and sneezing and coughing. Fever is not a fea- varies widely in severity, and is generally most ture of pneumonitis. The condition varies con- severe in young animals in which severe fatal siderably in severity and duration. Anorexia dehydration and emaciation may result. may occur in severe cases, and weight loss is Feline rhinotracheitis virus, a herpesvirus, marked in longstanding cases. is not highly resistant to external environmental The lesions occur mainly in the respiratory factors, and does not persist for long periods tract, and include redness, swelling and exuda- outside the host. Transmission is mainly by tion of the nasal mucus membranes and the aerosol from sneezing. As with other herpes- conjunctiva, and inflammation of the larynx viruses, rhinotracheitis virus may persist as a and trachea. There may be areas of consolida- latent infection in recovered cats, with reacti- tion in the lungs, usually in the anterior lobes. vation during periods of stress. Stained sections will show large inclusion Clinical diagnosis of rhinotracheitis is based bodies in the cytoplasm of infected cells. on symptoms of sneezing and nasal and ocular Clinically, it is impossible to differentiate discharges, but these symptoms are common feline pneumonitis from other viral upper res- to infections with a variety of agents. Post piratory infections of cats. The agent can be mortem diagnosis depends on finding the typi- isolated and cultivated in embryonated eggs cal eosinophilic intranuclear inclusions in res- and cell cultures. In cell cultures, it is readily piratory and conjunctival epithelium, and in differentiated from feline rhinotracheitis virus the tonsils. The virus can be recovered in by the large basophilic cytoplasmic inclusions, 19 CANADIAN VETERINARY JOURNAL as opposed to the eosinophlic intranuclear in- and enteritis. Ulcers and diphtheritic mem- clusions of rhinotracheitis virus. branes occur on the larynx and trachea, and Tetracyclines are specific for treatment of pneumonia may develop from inhalation of pneumonitis and chloramphenicol may also be necrotic material from the larynx and trachea. of value. The infective agent is resistant or Antibiotics and fluid therapy are recommended, rapidly becomes resitant to other antibiotics. as well as feeding with a dose syringe. Local treatment of nasal and ocular lesions, A brief review of rabies in the cat is appro- and fluid therapy may also be indicated. Re- priate to a discussion of feline viral diseases. covery from pneumonitis confers immunity of The incidence of rabies is markedly lower in short duration, and modifies subsequent at- cats than in dogs in this country, although this tacks. Vaccines have been developed by attenu- is not so everywhere They are not very effi- ating the agent through serial passages in cient transmitters of infection, possibly due to embryonated eggs. The degree and duration a relatively short period of virus excretion, of immunity conferred by these vaccines have three or four days. The incubation period of not been clearly established. The value of vac- rabies in cats varies from two weeks to two cination also depends on the prevalence of months, and once signs appear, most cats die feline pneunionitis in an area relative to other within four or five days. The available evidence primary respiratory pathogens of cats. indicates that the mortality in affected cats is 100%. OTHER CONDITIONS AND AGENTS The majority of cases of rabies in cats are Another member of the Bedsonia family of the furious type. The prodromal phase is causes a specific conjunctivitis in cats of all ages marked by personality changes, increased irri- (20). The agent shares antigens with the feline tability, and a tendency to hide. This is fol- pneumonitis agent but does not cause respira- lowed by a vicious stage of biting and scratch- tory symptoms in cats. The condition can be ing, accompanied by a voice change due to diagnosed by demonstrating cytoplasmic in- laryngeal paralysis. The next stage is one of clusion bodies in Giemsa-stained conjunctival ascending paralysis, encephalitis and death. scrapings. Tetracycline or chloramphenicol oph- Dumb rabies follows a similar progression, but thalmic ointments appear to be effective in without the vicious stage. treatment. The agent may be present as a A variety of other conditions may mimic mixed infection with a Mycoplasma species. some of the signs of rabies, among them toxo- Many other viruses have been isolated from plasmosis, thiamine deficiency, lead and strych- cats with upper respiratory infection. A recent nine poisoning, and prostration from panleuko- review by Crandell and York (8) indicates penia and infectious anemia. A history of sud- that many of these agents do not produce the den vicious attacks on humans, accompanied by typical cytopathic effects of rhinotracheitis a change of voice and followed by paralysis virus or the pneumonitis agent. Further studies leaves little doubt of the diagnosis. In suspi- on the characterization and antigenic relation- cious cases, and for confirmation, the brain ships of these agents are required. Agents iso- should be submitted for laboratory examination. lated from cats with respiratory symptoms by Rabies vaccination of cats should be carried Burki were first classified as picornaviruses (5), out at three or four months of age, and at but subsequent studies have led to some doubt regular intervals thereafter. Either high egg as to their taxonomic position (21). The viruses passage chick embryo vaccine or some of the associated with feline influenza, a severe res- cell culture virus vaccines are recommended piratory infection of cats in England, were first for use in cats. tentatively identified as adenoviruses (16), Pseudorabies, or Aujeszky's disease, infre- but it now appears that they may more closely quently affects cats, and causes some of the resemble rhinoviruses. same symptoms as rabies, including behavior Any of the upper respiratory infections of changes and a tendency to hide. Pharyngeal cats may be followed by a chronic rhinitis and paralysis and anorexia commonly occur. The sinusitis. Mycoplasma species have been iso- classical symptom is intense pruritis. Progres- lated from some of these cases (6), and long sive paralysis does not occur. Sugar appears in term treatment with tylosin tartrate may be the urine of affected cats prior to death, and effective. Another suggested treatment is tre- may be of value in establishing a diagnosis. phining of the sinuses. There are reports of an Diagnosis can be confirmed by virus isolation. apparently specific entity of unknown etiology, The rat is probably the usual source of which may follow respiratory infection in cats, Aujeszky's virus infection for cats. European known as necrotic laryngo-enteritis (15, 19). outbreaks have been traced to feeding cats un- Signs are fever and severe laryngitis, tracheitis cooked pork scraps from infected pigs. 20 FELINE VIRAL DISEASES

Infectious feline peritonitis is a condition of feline cytopathogenic viruses and feline pan- unknown etiology, possibly viral, affecting leukopenia virus. Am. J. vet. Res. 22: 374. mainly cats under two years of age, with close 1961. 4. BOLIN, V. S. Cultivation of panleukopenia to 100% mortality. The course of the disease virus in tissue culture. Virology 4: 389. 1957. varies from seven to ten days in acute cases up 5. BiURm, F. Picornaviruses of cats. Arch. ges. to six weeks in chronic cases. The signs in acute Virusforsch. 15: 690. 1965. cases include fever (104°-106 ), anorexia, 6. COLEGRAvE, A. J., B. INGHAM and J. M. INGLIS. dehydration and occasional gastrointestinal up- Chronic rhinitis in cats. Vet. Rec. 76: 67. 1964. set. Abdominal enlargement is not a feature 7. CRANDELL, R. A. and F. D. MAURER. Isola- of acute cases. In more chronic cases, the tion of a feline virus associated with intranu- symptoms include fever, ascites, anorexia, de- clear inclusion bodies. Proc. Soc. exp. Biol. pression and weight loss. Other occasional Med. 97: 487. 1958. signs are vomition, diarrhea, icterus, sneezing, 8. CRANDELL, R. A. and C. J. YoRK. New feline viruses: a review of their designations and sig- coughing and pleural effusions. Treatment has nificance. Can. J. comp. Med. 30: 256. 1966. not been very successful. Broad spectrum anti- 9. FASTIER, L. B. A new feline virus isolated biotics have no effect on the condition. Paren- in tissue culture. Am. J. vet. Res. 18: 382. teral fluid therapy prolongs the course of the 1957. condition, but does not affect the outcome. 10. HAMMON, W. McD. and J. F. ENDERS. A Post mortem lesions include severe periton- virus disease of cats principally characterized itis; excessive yellowish or brownish fluid in by aleucocytosis, enteric lesions and the presence of intranuclear inclusion bodies. the abdominal cavity, and varying amounts of J. exp. Med. 69: 327. 1939. fibrin on the abdominal viscera. Focal necrosis 11. JOHNSON, R. H. Isolation of a virus from a is observed in the liver and spleen. Males may condition simulating panleucopenia in a leo- show a fibrino-purulent periochitis. pard. Vet. Rec. 76: 1008. 1964. 12. JOHNSON, R. H. Feline panleucopenia virus. SUMMARY II. Some features of the cytopathic effects in feline kidney monolayers. Res. vet. Sci. 6: The virus diseases of importance in cats are 472. 1965. discussed, as well as viruses of uncertain sig- 13. JOHNSON, R. H., G. MARGOLIs and L. KILHAM. nificance, and some conditions of uncertain Identity of feline ataxia virus with feline pan- etiology. Diseases caused by Chlamydia are leucopenia virus. Nature 214: 174. 1967. included, since this group of organisms is still 14. KILHAM, L. and G. MARGOLIs. Viral etiology considered to be within the province of the of spontaneous ataxia of cats. Am. J. Path. 48: virologist. 991. 1966. 15. KREMBs, J. and 0. SEIFRIEM. Laryngo-En- teritis infectiosa, eine in Deutschland bisher RESUME unbekannte, verlustreiche Katzenseuche. Tier- 1Rtude des affections virales importantes chez arztl. Rdsch. 42: 377. 1936. le chat ainsi que des virus a role incertain, et de 16. PRIEcY, S. E. and J. PRYDIE. Feline influenza. quelques affections dont l'etiologie est douteuse. Vet. Rec. 75: 86. 1963. L'expose comprend les maladies causees par 17. ROHOVSKY, M. W. and R. A. GRIESEMER. En Experimental feline infectious enteritis in the Chlamydia. effet, on considere toujours que germfree cat. Pathologia vet. 4: 397. 1967. ce groupe de microorganismes fait partie du 18. VERGE, J. and N. C. R. CHRUSTOFORONI. La domaine de la virologie. gastro-enterite infectieuse des chats est-elle due a un virus ifitrable? C. r. Seanc. Soc. Biol. REFERENCES Paris. 99: 312. 1928. 1. BAKER, J. A. A virus causing pneumonia in 19. WINTER, E. C. Infectious laryngo-enteritis of cats and producing elementary bodies. J. exp. cats. Vet. Rec. 48: 1146. 1936. Med. 79: 159. 1944. 20. YERASIMIDES, T. G. Isolation of a new strain 2. BITTLE, J. L., C. J. YoRK, J. W. NEWBERNE of feline pneumonitis virus from a domestic and M. MARTIN. Serological relationships of cat. J. infect. Dis. 106: 290.1960. new feline cytopathogenic viruses. Am. J. vet. 21. ZWILLENBERG, L. 0. and F. BURKi. On the Res. 21: 547. 1960. capsid structure of some small feline and 3. BITTLE, J. L., J. B. EMERY, C. J. YORK and bovine RNA viruses. Arch. ges. Virusforsch. J. K. MCMILLEN. Comparative study of 19: 373. 1966.

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