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Feline Infectious Peritonitis
Symposium on Feline Medicine
Feline Infectious Peritonitis John F. Timoney, Jr., M.V.B., Ph.D., MR.C.V.S.*
Feline infectious peritonitis is a highly fatal, chronic, and progressively debilitating disease of wild and domestic felidae. It has been reported in the United States, Europe, South Africa, and Australia; the incidence in the United States has been increasing since the 1950's.
ETIOLOGY The disease agent appears to be a corona virus which can replicate in leukocytes but which is extremely labile once removed from the cell. Experimental reproduction of the disease can be achieved by inoculation of tissues and cell-free extracts of infected cats. Cats can be infected per os as well as by parenteral inoculation. The virus is sensitive to ether, formalin (0.4 per cent), phenol (0.7 per cent), and heat (590 C. for one hour), and is resistant to freezing and thawing. The incubation period is unknown but may be several months.
EPIZOOTIOLOGY Young and very old cats are most often affected by the disease. Most cases of feline infectious peritonitis are observed in cats less than three years of age and there is no obvious sex or breed predisposition. Multiple cases of the disease in a household or cattery have been observed and indicate a degree of contagiousness. The morbidity rate appears to be low.
"Assistant Professor, Department of Microbiology, New York Stale College Veterinary Medicine. Cornell University. Ithaca, New York
Veterinary Clinics of North America- Vol. 6, No.3, August 1976
391
392
JOHN
F.
TIMONEY, JR.
CLINICAL SIGNS Feline infectious peritonitis has an insidious onset and often goes unnoticed until there is obvious abdominal distention or respiratory difficulty. The cat becomes progressively debilitated, depressed, and anorectic with a fever of 103 to 106° F. which drops shortly before death. The classic peritoneal form is characterized by effusions into the peritoneum and, less frequently , into the pleural cavity. This is known as the "wet" form of feline infectious peritonitis and cats so afflicted have a variable temperature and often develop liver failure in the terminal stages. The eyes and central nervous system are occasionally affected also. In the so-called "dry" form there is no accumulation of fluid and the presenting clinical signs are associated with involvement of the peritoneum, eyes, central nervous system, kidneys, or combinations of these organ systems. Affected cats are febrile and have progressive wasting. When eye involvement occurs, there is corneal edema, aqueous flare, iridocyclitis, retinal hemorrhages, and choroiditis.
CLINICAL PATHOLOGY The peritoneal and pleural effusions have the consistency of an egg white and clot after exposure to air. The protein content may be as
Table 1.
Clinical Pathologic Findings in Feline Infectious Peritonitis " DRY" FORM
"WET" FORM
Exudate Protein: 3.4-11.8 gm/ ml White blood cells: 1600-50,000/ cubic mm (mostly neutrophils) Specific gravity : 1.017-1.027 Dextrose: levels as in serum BLood Leukocytosis, moderate an e mi a Neutrophilia and lymphopenia Hype rprotein e mia (54% cases) H ypergammaglobulinemia Ele vated plasma fibrinogen (400 mg in 20% cases) Cel//m! N ervous S\'sll'lII Infreque ntly a'ffected
Rella! B ioI)"'.\' Not applicable
No exudate
Leukocytosis, moderate anemia Neutrophilia and lymphopenia Hype rproteinemia (71 % cases) Elevated plasma fibrinogen (400 mg in 20% cases) Elevated BUN CSF Protein: 90-2000 mg% White blood cells : 90-8000/cubic mm (mostly neutrophils) Necrotic "asculitis and pyogranulomatous re placement of re nal parenchyma
393
FELINE INFECTIOUS PERITONITIS
high as that of companion serum, the elevation being mostly in the gammaglobulin fraction. The clinical pathology findings in both wet and dry forms of the disease are summarized in Table I.
GROSS AND MICROSCOPIC PATHOLOGY The carcass is usually wasted and distended by a large amount of serum-like fluid in the abdominal cavity and possibly in the pleural cavity also. The serous surfaces are dull and granular in appearance (Fig. I) and the omentum is thickened and contracted. The dry form is characterized by multiple and pyogranulomatous necrotic foci on the surfaces and in the parenchyma of the abdominal organs, lungs, brain , and iris. Microscopically these lesions consist of neutrophils, macrophages, lymphocytes, and plasma cells congregated mostly around blood vessels which may show degenerative changes. These focal lesions are less common in the wet form of the disease but the same type of inflammatory cell infiltrate is found diffusely or focally in the fibrinous layer on the serous surfaces.
DIAGNOSIS The wet form of feline infectious peritonitis is readily diagnosed on the basis of a history of a chronic, febrile wasting syndrome with ascites, the exudate of which has a high concentration of protein, gammaglobulins, and many neutrophils. The dry form is clinically similar
Figure I. Appearance of abdominal viscera of Cal that died from the "weI" form of feline infectious peritonitis. There is e xtensive fibrinous peritonitis and the a bdominal cavity conlained a large volume of serum-like fluid. (Courtesy of Dr. F. Scott.)
394
JOHN
F.
TIMONEY, JR.
but is more difficult to diagnose because there is no characteristic exudate for examination. The eyes and/or central nervous system are involved in roughly 60 per cent of patients with this form and there is usually kidney enlargement. Kidney biopsy definitively reveals the nature of the condition. There is as yet no diagnostic test for the presence of infection by feline infectious peritonitis virus.
TREATMENT Symptomatic and supportive therapy may prolong life but is unlikely to cure the animal. A very few cats have apparently been cured by the oral administration of tylocine (80 mg per lb) daily in two doses, together with prednisolone (2 mg per lb) in divided doses daily, until clinical remission is noted seven or eight weeks later. Treatment is then continued for four weeks using half the previous drug dosages.
REFERENCES I. Ingram, P. L.: Feline infectious peritonitis and its differential diagnosis. J
Small Anim. Pract., 12:301,1971. 2. Pedersen, N. C., Holliday, T. A. , and Cello, R. M.: Feline infectious peritonitis. Am. Anim. Hosp. Assoc. Proc. , 41:147,1974. 3. Wolfe , L. G. , and Griesmer, R. A.: Feline infectious peritonitis: Review of gross and histopathologic lesions. JA .V.M.A., 158:987,1971. 4. Look, B. C., King, N. W. , Robinson, R. L., and McCombs, H. L.: Ultrastructural evidence for the viral etiology of feline infectious peritonitis. Vet. Path., 5:91 , 1968. Department of Microbiology New York State College of Veterinary Medicine Cornell University Ithaca, New York 14850
Feline Infectious Peritonitis John F. Timoney, Jr., M.V.B., Ph.D., MR.C.V.S.*
Feline infectious peritonitis is a highly fatal, chronic, and progressively debilitating disease of wild and domestic felidae. It has been reported in the United States, Europe, South Africa, and Australia; the incidence in the United States has been increasing since the 1950's.
ETIOLOGY The disease agent appears to be a corona virus which can replicate in leukocytes but which is extremely labile once removed from the cell. Experimental reproduction of the disease can be achieved by inoculation of tissues and cell-free extracts of infected cats. Cats can be infected per os as well as by parenteral inoculation. The virus is sensitive to ether, formalin (0.4 per cent), phenol (0.7 per cent), and heat (590 C. for one hour), and is resistant to freezing and thawing. The incubation period is unknown but may be several months.
EPIZOOTIOLOGY Young and very old cats are most often affected by the disease. Most cases of feline infectious peritonitis are observed in cats less than three years of age and there is no obvious sex or breed predisposition. Multiple cases of the disease in a household or cattery have been observed and indicate a degree of contagiousness. The morbidity rate appears to be low.
"Assistant Professor, Department of Microbiology, New York Stale College Veterinary Medicine. Cornell University. Ithaca, New York
Veterinary Clinics of North America- Vol. 6, No.3, August 1976
391
392
JOHN
F.
TIMONEY, JR.
CLINICAL SIGNS Feline infectious peritonitis has an insidious onset and often goes unnoticed until there is obvious abdominal distention or respiratory difficulty. The cat becomes progressively debilitated, depressed, and anorectic with a fever of 103 to 106° F. which drops shortly before death. The classic peritoneal form is characterized by effusions into the peritoneum and, less frequently , into the pleural cavity. This is known as the "wet" form of feline infectious peritonitis and cats so afflicted have a variable temperature and often develop liver failure in the terminal stages. The eyes and central nervous system are occasionally affected also. In the so-called "dry" form there is no accumulation of fluid and the presenting clinical signs are associated with involvement of the peritoneum, eyes, central nervous system, kidneys, or combinations of these organ systems. Affected cats are febrile and have progressive wasting. When eye involvement occurs, there is corneal edema, aqueous flare, iridocyclitis, retinal hemorrhages, and choroiditis.
CLINICAL PATHOLOGY The peritoneal and pleural effusions have the consistency of an egg white and clot after exposure to air. The protein content may be as
Table 1.
Clinical Pathologic Findings in Feline Infectious Peritonitis " DRY" FORM
"WET" FORM
Exudate Protein: 3.4-11.8 gm/ ml White blood cells: 1600-50,000/ cubic mm (mostly neutrophils) Specific gravity : 1.017-1.027 Dextrose: levels as in serum BLood Leukocytosis, moderate an e mi a Neutrophilia and lymphopenia Hype rprotein e mia (54% cases) H ypergammaglobulinemia Ele vated plasma fibrinogen (400 mg in 20% cases) Cel//m! N ervous S\'sll'lII Infreque ntly a'ffected
Rella! B ioI)"'.\' Not applicable
No exudate
Leukocytosis, moderate anemia Neutrophilia and lymphopenia Hype rproteinemia (71 % cases) Elevated plasma fibrinogen (400 mg in 20% cases) Elevated BUN CSF Protein: 90-2000 mg% White blood cells : 90-8000/cubic mm (mostly neutrophils) Necrotic "asculitis and pyogranulomatous re placement of re nal parenchyma
393
FELINE INFECTIOUS PERITONITIS
high as that of companion serum, the elevation being mostly in the gammaglobulin fraction. The clinical pathology findings in both wet and dry forms of the disease are summarized in Table I.
GROSS AND MICROSCOPIC PATHOLOGY The carcass is usually wasted and distended by a large amount of serum-like fluid in the abdominal cavity and possibly in the pleural cavity also. The serous surfaces are dull and granular in appearance (Fig. I) and the omentum is thickened and contracted. The dry form is characterized by multiple and pyogranulomatous necrotic foci on the surfaces and in the parenchyma of the abdominal organs, lungs, brain , and iris. Microscopically these lesions consist of neutrophils, macrophages, lymphocytes, and plasma cells congregated mostly around blood vessels which may show degenerative changes. These focal lesions are less common in the wet form of the disease but the same type of inflammatory cell infiltrate is found diffusely or focally in the fibrinous layer on the serous surfaces.
DIAGNOSIS The wet form of feline infectious peritonitis is readily diagnosed on the basis of a history of a chronic, febrile wasting syndrome with ascites, the exudate of which has a high concentration of protein, gammaglobulins, and many neutrophils. The dry form is clinically similar
Figure I. Appearance of abdominal viscera of Cal that died from the "weI" form of feline infectious peritonitis. There is e xtensive fibrinous peritonitis and the a bdominal cavity conlained a large volume of serum-like fluid. (Courtesy of Dr. F. Scott.)
394
JOHN
F.
TIMONEY, JR.
but is more difficult to diagnose because there is no characteristic exudate for examination. The eyes and/or central nervous system are involved in roughly 60 per cent of patients with this form and there is usually kidney enlargement. Kidney biopsy definitively reveals the nature of the condition. There is as yet no diagnostic test for the presence of infection by feline infectious peritonitis virus.
TREATMENT Symptomatic and supportive therapy may prolong life but is unlikely to cure the animal. A very few cats have apparently been cured by the oral administration of tylocine (80 mg per lb) daily in two doses, together with prednisolone (2 mg per lb) in divided doses daily, until clinical remission is noted seven or eight weeks later. Treatment is then continued for four weeks using half the previous drug dosages.
REFERENCES I. Ingram, P. L.: Feline infectious peritonitis and its differential diagnosis. J
Small Anim. Pract., 12:301,1971. 2. Pedersen, N. C., Holliday, T. A. , and Cello, R. M.: Feline infectious peritonitis. Am. Anim. Hosp. Assoc. Proc. , 41:147,1974. 3. Wolfe , L. G. , and Griesmer, R. A.: Feline infectious peritonitis: Review of gross and histopathologic lesions. JA .V.M.A., 158:987,1971. 4. Look, B. C., King, N. W. , Robinson, R. L., and McCombs, H. L.: Ultrastructural evidence for the viral etiology of feline infectious peritonitis. Vet. Path., 5:91 , 1968. Department of Microbiology New York State College of Veterinary Medicine Cornell University Ithaca, New York 14850