ISRAEL JOURNAL OF VETERINARY MEDICINE Vol. 54 (2), 1999 A SEROEPIDEMIOLOGICAL STUDY OF FELINE CORONAVIRUS, FELINE IMMUNODEFICENCY VIRUS AND FELINE LEUKEMIA VIRUS AMONG CATS IN ISRAEL G. Baneth1, P. H. Kass2, D. Steinfeld1 and M. Besser1 1. School of Veterinary Medicine, Hebrew University of Jerusalem, Israel 2. Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, California. Summary The prevalence of antibodies to feline coronavirus (FCoV), feline immunodeficency virus (FIV), and feline leukemia virus (FeLV) antigenemia was examined in 180 Israeli cats. FCoV antibodies were detected in 60% of the cats, with the highest prevalence among cats from animal shelters, followed by feral cats and client-owned cats. Antibodies to FIV were detected in 12% of the cats, while FeLV antigenemia was found in only 4%. FCoV seropositivity was significantly associated with nasal discharge and negatively correlated with age, with the highest prevalence in cats 1 year old and a drop of approximately 18% in the prevalence odds of seropositivity for each additional year. FIV antibodies were significantly associated with gingivitis, and the prevalence odds of FIV seropositivity rose with age up to 8 years, when the odds was approximately 7-fold greater than in 1 year old cats. No statistical association was found between FCoV, FIV, and FeLV infections. Introduction Feline coronavirus (FCoV), feline immunodeficency virus (FIV) and feline leukemia virus (FeLV) are 3 of the most important viral pathogens of domestic cats. FeLV and FIV both induce an immunosupression that leads to the development of secondary infections by opportunist microorganisms, haematopoeitic tumors and anaemia (1,2). FCoV may cause enteritis and upper respiratory tract disease, and in a small percentage of infections may progress to fatal feline infectious peritonitis (FIP)(3). Although FCoV, FIV and FeLV have been reported from many areas of the world, the seroprevalence of these viruses varies among different geographic locations (4-10). The aims of this study were to assess the infection rate of cats from Israel with FCoV, FIV and FeLV, and to explore possible associations between infection, signalment, clinical signs and co-infection among the 3 viruses examined. Materials and Methods Blood samples Blood samples were taken by jugular or cephalic venipuncture into heparinized tubes. Plasma was separated by centrifugation at 100 x g for 10 minutes, and samples were stored at -200C until tested. Cats The cats sampled were classified into 3 groups representing the type of environment in which the cat lived: animal shelters, feral cats and client-owned cats. Age, sex, spayed/intact status, and the presence of clinical signs of disease were also recorded. The ages of clientowned cats were determined from the patient's records. Ages of cats at animal shelters and feral cats were estimated on the basis of a combination of the facility's records and/or a dental and clinical examination. Cats were sampled from 4 different cities in Israel: Jerusalem, Haifa, Tel Aviv and Beer Sheva. In addition, plasma from sick client-owned patient cats referred to the Hebrew University Veterinary Teaching Hospital (VTH) was also included in the study. Diagnostic tests A commercial enzyme-linked immunosorbent assay (ELISA) (PetCheck ® FeLV test kit, IDEXX Laboratories, Westbrook, Maine) was used to test samples for FeLV p27 antigen. The PetCheck® Anti-FIV test kit (IDEXX Laboratories, Westbrook, Maine) was employed to detect antibodies against FIV. Anti-FCoV antibodies were detected using the Immunocomb® test kit (Biogal, Israel). This test is based on FIP-1 type antigen and reacts with feline coronavirus antigen in general. The Immunocomb® test has recently been recommended as having a high degree of correlation with the indirect fluorescent antibody test (IFAT) for FCoV as performed in the Feline Virus Unit at the University of Glasgow (11). Statistical analysis Prevalence odds ratios (POR) were calculated by exact logistic regression as cross-sectional measures of association between disease status and putative risk factors. P-values of the null hypothesis (i.e., POR=1) less then 0.05 were considered statistically significant. Results A total of 180 cats were included in the study, of which 39% were feral cats, 32% originated from animal shelters belonging to the Society for Prevention of Cruelty to Animals (SPCA), and 29% were client-owned sick cats admitted to the VTH for veterinary care (Table 1). FIV+ FeLV+ FCoV Gender Male 13.7 (14/102) 3.9 ( 4/102) 53.5 ( 46/86) 9 (7/78) 3.8 (3/78) 68.1 (47/69) 11.7 (21/180) 3.9 (7/180) 60 (93/155) 0- < 1 3.1 (1/32) 3.1 (1/32) 75 (21/28) 1- < 2 4.26 (2/47) 4.3 (2/47) 67.4 (31/46) 2- < 3 15.4 (4/26) 3.9 (1/26) 64 (16/25) Female Total Age groups (years) 3- < 4 19 (4/21) 0 (0/21) 70.6 (12/17) 4- < 5 20 (3/15) 6.7 (1/15) 60 (6/10) >= 5 19 (7/37) 5.4 (2/37) 22.2 (6/27) Total 11.8 (21/178) 3.9 (7/178) 60.1 (92/153) (3/28) 0 (0/28) 76.5 (13/17) (18/152) 4.6 (7/152) 58 (80/138) Spay/neuter status Neutered Intact 10.7 11.8 Source Feral 11.4 (8/70) 4.3 (3/70) 60.3 (41/68) Animal shelters 5.17 (3/58) 1.7 (1/58) 83.3 (45/54) 5.8 (3/52) 21.2 (7/33) Client owned 19.23 (10/52) Origin Jerusalem 0 (0/30) 3.3 (1/30) 81.5 (22/27) Haifa 10.7 (3/28) 0 (0/28) 85.2 (23/27) Tel Aviv 10.8 (8/74) 4 (3/74) 60.9 (42/69) Beer Sheva 14.8 (4/27) 17.4 (2/27) 19.2 (5/26) VTH 28.6 (6/21) 4.8 (1/21) 16.7 (1/6) Nasal discharge 0 (0/13) 0 (0/13) 100 (13/13) Gingivitis 55 (5/11) 0 (0/11) 55.6 (5/9) Assosiation with other diseases FIV+ 0 (0/21) FeLV + 0 (0/7) FCoL + 8.6 (8/93) 53.3 (8/15) 28.6 (2/7) 2.2 (2/93) - Prevalence (%) of FIV antibodies, FeLV antigenemia and FCoV antibodies among cats from Israel. In parentheses: number of cats (numerator equals number of positives in the specific category; denominator equals total number of cats tested in the category). Table 1 Of the clinical findings noted on physical examination, nasal discharge found in 13 cats and gingivitis in 11 were the two most common symptoms recorded. These were statistically analyzed for association with other parameters. In total, FeLV antigen was detected in plasma samples from 4% of the cats, 12% were seropositive for FIV and 60% seropositive for FCoV (of 155 tested for FCoV). Co-infection with FIV and FCoV was found in 8 (5%) of the cats and FeLV with FCoV was found in 1 (1%) cat. No cats were co-infected with FIV and FeLV. Logistic regression analysis indicated that for FCoV infection, a significant negative linear trend was found between the cat 's estimated age in years and coronavirus antibodies. For each additional year of age in the cat the prevalence odds of coronavirus positivity fell approximately 18% (POR = 0.82; 95% confidence interval (95% CI) = 0.68-0.99) (Fig. 1). Fig. 1 - Prevalence of antibodies for feline coronavirus (FCoV) and feline immunodeficency (FIV) virus among Israeli cats of six age groups. The prevalence of coronavirus antibodies was higher in feral cats than patient cats (POR=1.52; 95% CI = 1.20-1.85), and was significantly higher in animal shelter cats than patients cats (POR=8.29; 95% CI = 2.33-29.45). The presence of coronavirus antibodies was strongly associated with the prevalence odds of nasal discharge (POR=8.39, 95% CI = 1.18(). For each additional year of age in a cat’s life the prevalence odds of nasal discharge fell approximately 43% (POR=0.57, 95% CI= 0.30-0.94). For FIV infection, the prevalence odds of positive serology rose with age up to 8 years, when the odds was approximately 7-fold greater than in 1 year old cats (POR=6.79; 95% CI =2.9015.89). After 8 years the prevalence odds began to decline in the population of cats studied. After accounting for the association between estimated age and FIV prevalence, there was no evidence to suggest that the source of the cat had any residual association with FIV prevalence. FIV seropositivity was strongly associated with the prevalence odds of gingivitis (POR=12.16, 95% CI = 1.86-99.66). Only 7 cats were positive for FeLV, too few a number for reliable or precise inferences about the role of putative risk factors on seropositivity. In all, no statistical relationship was found between seropositivity with any of the 3 viruses and gender (male/female), neuter/spay status, city of origin, and co-infection with another virus tested Discussion The main findings from this study are that while the prevalence of FcoV and FIV antibodies is high in the cats tested from Israel, FeLV antigenemia is rarer and was found in only 4% of the samples. The prevalence found for FIV and FeLV differ from those in most countries in Western and Central Europe where FeLV seems to be more prevalent than FIV (5,8), and from Britain where the seroprevalence for both infections was found roughly similar among sick cats (18-19%) and among healthy ones (5-6%) (4). The prevalence in cats from Israel follows the same pattern as cats in Norway (7) and free-ranging cats from Finland (6) where FIV is more prevalent than FeLV. Interestingly, the prevalence of FeLV among stray and privately owned cats in Beirut, Lebanon, which neighbours Israel to the north, was only 3.1% (12), roughly similar to the findings from Israel. The reasons why a low incidence of FeLV is found in some geographic locations are unknown. The differences in the prevalence of FeLV reported in surveys from various countries could be accounted for by several possible explanations including: genetic resistance to infection in some populations or breeds, the effect of climate conditions on the transmission of the virus, behavioural differences among cats in different areas affecting disease transmission, and the presence of less virulent viral strains that successfully establish an infection in a smaller percentage of exposed cats. None of these theories has been shown to be responsible for a lower or higher incidence of FeLV in a certain region. Another possible explanation is if FeLV spread from where the virus initially appeared to other regions through importation of infected animals or natural migration, than perhaps there are still some cat populations to which the disease has not yet spread, or in which the virus is gradually spreading but still has a low prevalence. An important finding for veterinarians in Israel that emerges from this study is that every fifth cat above 3 years of age in this survey was positive for FIV. FIV should certainly be high on the list of differential diagnoses when clinical signs compatible with this disease are observed in cats presented for medical care. Most studies on FIV that compared the prevalence of disease in sick and healthy cats have reported a higher incidence in sick cats (4,7,10,13,14). Although in the present study the differences in prevalence of FIV among client-owned sick cats (19%) and feral and animal shelter cats (11% and 5% respectively) were not statistically significant, a trend of a higher prevalence among sick cats can be seen and could have possibly been significant if the number of animals in the study was larger. The significant association between gingivitis and FIV infection found in this study can be explained by secondary infection of the oral cavity commonly found in immunosupressed cats with FIV (13,15). Due to the close antigenic relation of Feline Enteric Corona Virus (FECV) strains with FIP strains no serological test developed to date can distinguish between these related infections (16). Furthermore, studies analyzing gene sequences from FECV and FIP strains have indicated that local isolates of FECV and FIP are more closely related than strains of FIP from different geographic locations (17). These findings support the hypothesis made earlier by Pedersen and colleagues (18) that FIP arises from spontaneous mutations in some of the cats infected with FECV. A longitudinal study from Britain revealed that about 5-10% of cats seropositive for FCoV will develop fatal FIP (19). If these findings can be universally applied, than FIP should be present among a subset of the FCoV positive animals in this study, probably in less than 6% of the cats sampled. Our findings that the seroprevalence of FCoV decreased with estimated age from 75% in cats younger than 1 year to 22% in cats above 5 years old, and that the prevalence of this infection was highest among cats from animal shelters followed by feral cats and significantly less prevalent in client-owned cats, are in agreement with findings of other workers. FCoV infection has been reported to be highly prevalent in young cats living in catteries under conditions where many cats are concentrated and share the same food sources and litter facilities (20). Such conditions are present in animal shelters included in this study. In contrast to the high frequency of FCoV antibodies among young cats (< 4 years) in the present study, the prevalence of FIV infection in the same group of cats increased until the age of 8 years. The drop in prevalence of FIV antibodies after that age could be explained by the possibility that after 8 years, the number of cats that die of FIV following a prolonged course of infection with this virus exceeds the number of cats that acquire the disease. The significant association between nasal discharge and FCoV antibodies found in this study is probably due to upper respiratory tract infections often found in cats infected with coronavirus (4). No significant association linking infections with FCoV and FIV or FeLV in this study was found. Although this may be a result of the relatively small sample of cats included in the survey, the findings of no apparent epidemiologic relationship between infection with FIV and FeLV are in agreement with those from other studies on cats from North America, Japan and Britain (4,13,15). Additionally, Lutz and colleagues (5) who compared the seroprevalence of FCoV with FIV and FeLV in cats from Switzerland did not present evidence for an epidemiologic association between these three infections. The reason for the lack of apparent relationship between FIV and FCoV could be due to the different routes of infection and typical environment in which transmission takes place. FIV is transmitted mainly by bite wounds during aggressive behavior between cats that are allowed to roam freely and often engage in defending their territories (22), while FCoV is chiefly transmitted by exposure to excretions containing infective virus which occurs intensively in catteries and multiple cat households where many cats share the same premises, food and litter boxes (20). Cats kept indoors in stable social structures often keep a hierarchy where little aggression is demonstrated. In conclusion, the seroepidemiological findings from this study have demonstrated that FIV and coronavirus are important feline pathogens in Israel. While FCoV infection affected mainly young cats that were not client-owned and had a high prevalence of nasal discharge, FIV was found mostly in middle aged to older cats with a high prevalence of gingivitis. Acknowledgments The authors thank Lea Graziani, Maria Griber, Drs. Zvi Galin, Sergei Weinstein and Tamar Ben Zvi for their help in obtaining blood samples. We thank IDEXX laboratories and Biogal laboratories for donating the test kits used in this study. References 1. Cotter, S.M.: Feline leukemia virus infection. In: Greene, C.E. (Ed.) Infectious Diseases of the dog and Cat. 2nd edn. W.B. Saunders, Philadelphia. pp 71-83, 1998. 2. Sellon, R.K. Feline immunodeficiency virus. In: Greene, C.E. (Ed.) Infectious Diseases of the dog and Cat. 2nd edn. W.B. Saunders, Philadelphia. pp. 84-96, 1998. 3. Addie, D.D. and Jarret, O. Feline Coronavirus Infection. In: Greene, C.E. (Ed.) Infectious Diseases of the dog and Cat. 2nd edn. W.B. Saunders, Philadelphia. pp 58-69. 1998. 4. Hosie, M.J., Robertson, C. and Jarret, O.: Prevalence of feline leukaemia virus and antibodies to feline immunodeficiency virus in cats in the United Kingdom. Vet. Rec. 128: 293-297, 1989. 5. Lutz, H., Lehman, R., Winkler, G., Kottowitz, B., Dittmer, A., Wolfensberger, C. and Arnold, P.: Feline immunodeficiency virus in Switzerland: clinical aspects and epidemiology in comparison with feline leukemia virus and coronaviruses. Schweiz. Arch. Tierheilkd. 132: 217-225, 1990. 6. Sukura, A., Salminen, T. and Lindberg, L.A.: A survey of FIV antibodies and FeLV antigens in free-roaming cats in the capital area of Finland. Acta Vet. Scand. 33: 9-14, 1992. 7. Ueland, K. and Lutz, H.: Prevalence of feline leukemia virus and antibodies to feline immunodeficiency virus in cats in Norway. J. Vet. Med. B. 39: 53-58, 1992. 8. Braley, J.: FeLV and FIV: survey shows prevalence in the United States and Europe. Feline Pract. 22:25-28, 1994. 9. Lin, J.A., Cheng, M.C., Inoshima, Y., Tomlonaga, K., Miyazawa, T., Tohya, Y., Toh, K., Lu, Y,S. and Mikami T.: Seroepidmiological survey of feline retrovirus infections in cats in Taiwan 1993 and 1994. J. Vet. Med. Sci. 57: 161-163, 1995. 10. Malik, R., Kendall, K., Cridland, J., Coulston, S., Stuart, A.J., Snow, D. and Love, D.N.: Prevalences of feline leukemia virus and feline immunodeficiency virus in cats in Sydney. Aust. Vet. J. 75: 323-327, 1997. 11. Addie, D.D.: The diagnosis and prevention of FIP and recent research into feline coronavirus shedding. Proceedings of the 8th Annual Congress of the European Society of Veterinary Internal Medicine, Vienna, Austria. pp 110-117, 1998. 12. Deeb, B.J. and Sufan, M.M.: Feline leukemia virus antigen in cats from Beirut, Lebanon. Vet. Rec. 118: 209-210, 1986. 13. Ishida, T., Washizu, T., Toriyabe, K., Motoyoshi, S., Tomoda, I. and Pedersen N.C.: Feline immunodeficiency virus infection in Japan. J. Am. Vet. Med. Assoc. 194: 221-225, 1989. 14. Grindem, C.B., Corbett, W.T., Ammerman, B.E. and Tompkins, M.T.: Seroepidemiologic survey of feline immunodeficiency virus infection in cats of Wake County, North Carolina. J. Am. Vet. Med. Assoc. 194: 226-228, 1989. 15. Yamamoto, J.K., Hansen, H., Ho, E.W., Morishita, T.Y., Okuda, T., Sawa, T.T., Nakamura, R.M. and Pedersen , N. C.: Epidemiologic and clinical aspects of feline immunodeficiency virus infection in cats from the continental United States and Canada and possible mode of transmission. J. Am. Vet. Med. Assoc. 194: 213-220, 1989. 16. Pedersen, N.C.: The history and interpretation of feline coronavirus serology. Feline Pract. 23: 46-51,1995. 17. Vennema, H., Poland, A., Floyd, K and Pedersen, N.C.: A comparison of the genomes of FECV's and FIPVs and what they tell us about the relationship between feline coronaviruses and their evoulution. Feline Pract. 23: 40-44, 1995. 18. Pedersen, N.C., Boyle, J.F. and Floyd K.: An enteric coronavirus infection of cats and relationship to feline infectious peritonitis. Am. J. Vet. Res. 42: 368-377, 1981. 19. Addie, D.D., Toth, S., Murray G.D. and Jarret, O.: Risk of feline infectious peritonitis in cats naturally infected with feline coronavirus. Am. J. Vet. Res. 56: 429-434, 1995. 20. Pedersen, N.C.: Coronavirus diseases (coronavirus enteritis,feline infectious peritonitis). In: Holzworth, J. (Ed.): Diseases of the Cat. W.B. Saunders, Philadelphia, pp. 193-214, 1987. 21. Addie, D.D. and Jarret, O.: A study of naturally occurring feline coronavirus infection in kittens. Vet. Rec. 130:133-137, 1992. 22. Pedersen, N.C., Yamamoto, J.K., Ishida, T. and Hansen, H.: Feline Immunodeficency Virus Infection. Vet. Immunol Immunolopathol. 21:111-129, 1989.