- Email: [email protected]
A review of feline leukemia virus and feline immunodeficiency virus seroprevalence in cats in Canada
Veterinary Immunology and Immunopathology 143 (2011) 243–245
Contents lists available at ScienceDirect
Veterinary Immunology and Immunopathology journal homepage: www.elsevier.com/locate/vetimm
Mini review
A review of feline leukemia virus and feline immunodeficiency virus seroprevalence in cats in Canada Susan Little ∗ Bytown Cat Hospital, 422 McArthur Ave., Ottawa, Ontario K1K 1G6, Canada
a r t i c l e
i n f o
Keywords: Feline FeLV seroprevalence FIV seroprevalence
a b s t r a c t Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are common and important infectious diseases of cats in Canada. Prevalence data are necessary to define prophylactic, management, and therapeutic measures for stray, feral and owned cats. Recently, comprehensive data on the seroprevalence of retrovirus infections of cats in Canada have become available and are reviewed. Further investigation into geographic variations in retrovirus seroprevalence within Canada is warranted, and may provide information to improve recommendations for testing and prevention. As well, more information is needed on FIV subtypes in Canada to improve diagnostics and vaccines, as well as to provide information on disease outcomes. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Seroprevalence of FeLV and FIV in Canada
Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are retroviruses causing two of the most common and important infectious diseases of cats. Diseases associated with FeLV and FIV may affect any organ, and include lymphoma, blood dyscrasias, central nervous system and ocular disease, gingivostomatitis, and secondary and opportunistic infections. Organizations such as the American Association of Feline Practitioners (Levy et al., 2008) and the European Advisory Board on Cat Diseases (Hosie et al., 2009; Lutz et al., 2009) have published guidelines for prevention and management of FeLV and FIV infections. Prevalence data are necessary to define prophylactic, management, and therapeutic measures for stray, feral and owned cats. Recently, comprehensive data on the seroprevalence of retrovirus infections of cats in Canada have become available.
The seroprevalence of FeLV and FIV infection in a variety of North American cat populations has been described in several publications, but until recently the available data applied predominantly to the United States. Presented here is a summary of FeLV and FIV seroprevalence for Canadian cats (Table 1). Yamamoto et al. (1989) evaluated the epidemiologic features of FIV infection, and categorized cats as high risk (n = 2254) or healthy with low or unknown risk (n = 511). In the high risk group, 14% were FIV seropositive compared to 1.2% in the healthy group. Further, in the high risk group, FIV seropositivity was more likely in males than females, in cats over 6 years of age than younger cats, and in free-roaming cats than confined cats. In the high risk group, FeLV seroprevalence among 1609 cats was 13%; 42 cats were reported to be from Canada, but no specific location was given. FIV seroprevalence was 19% among the Canadian cats. Within the healthy, low or unknown risk group of cats, 352 were reported to be from Canada, but no specific location was indicated. FIV seroprevalence for the healthy group as a whole was 1.2%, with no breakdown for origin from Canada versus the United States. More recently Levy et al. (2006), evaluated seroprevalence of FeLV and FIV among North American cats as well as
∗ Tel.: +1 613 741 2460; fax: +1 613 741 8463. E-mail address: [email protected] 0165-2427/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.vetimm.2011.06.018
244
S. Little / Veterinary Immunology and Immunopathology 143 (2011) 243–245
Table 1 Summary of FeLV and FIV seroprevalence studies in Canada. Study
Population Tested
Yamamoto et al. (1989)
Provinces not given High risk (n = 42) Low risk (n = 352) Atlantic Canada (90.5% PEI) PEI Adult feral males (n = 65) Adult feral females (n = 74) Ottawa Urban strays (n = 74) Owned cats (n = 152) AB, BC, NF, NS, ON, QC, SK (n = 325) All Canadian provinces (n = 11,144) NF shelter cats (n = 591) SK, MB, AB (n = 1205)
Hitt et al. (1992) Gibson et al. (2002)a
a
Little (2005)
Levy et al. (2006)a Little et al. (2009)a , b
Berghuis (2009)a Ravi et al. (2010)a a b
FIV
FeLV
19% 1.2% 7.6%
n/a n/a n/a
13.8%
7.7%
2.7%
5.4%
23% 5.9% 3.1%
6.7% 2.6% 2.5%
4.3%
3.4%
2.5%
6.1%
5.5%
3.5%
Testing performed with SNAP Combo FeLV antigen/FIV antibody, IDEXX Laboratories, Westbrook, Maine, USA. Testing performed with PetChek FIV antibody and FeLV antigen ELISA, IDEXX Laboratories, Westbrook, Maine, USA.
risk factors for seropositivity in a large prospective crosssectional survey. In this study, 18,038 cats were tested at 345 veterinary clinics (n = 9970) and 145 animal shelters (n = 8068). In this population of cats, seroprevalence of FeLV was 2.3% and seroprevalence of FIV was 2.5%, while 0.3% of cats were co-infected. The risk of seropositivity for either virus was higher in adult cats (>6 months) than juveniles, and in males than females. Other risk factors were access to outdoors and concurrent illness. The highest risk for retrovirus infection was associated with being sick and feral, followed by being sick with access to outdoors. The study included data on 325 cats from 7 Canadian provinces (AB, BC, NF, NS, ON, QC, SK), with 2.5% FeLV- and 3.1% FIVseropositivity among them. Little et al. (2009) conducted the first Canadian study of FeLV and FIV seroprevalence and risk factors. Signalment, lifestyle factors, and test results for FeLV antigen and FIV antibody were analyzed for 11,144 cats from the 10 Canadian provinces. More cats were tested at veterinary clinics (n = 9588) than at animal shelters/rescue organizations (n = 1556). Results showed seroprevalence for FeLV antigen was 3.4% and seroprevalence for FIV antibody was 4.3%. Fifty-eight cats (0.5%) were seropositive for both viruses. Significant risk factors for infection were age (>6 months), presence of current illness, and access to outdoors. FeLV seropositivity was highest in intact females (7.3%) and intact males (7.1%) and FIV seropositivity was highest in intact males (7.4%). An inactivated dual-subtype vaccine against FIV became available in Canada in 2003; however, FIV vaccination status was not recorded or known for cats in this study. It was assumed that veterinarians would be unlikely to test cats for FIV if they were known to be vaccinated, and that the population of cats tested by shelters and rescue groups is unlikely to have a high rate of FIV vaccination. Therefore, it seems likely that bias of FIV
prevalence estimates caused by vaccination in this study would be minimal. Other studies have evaluated seroprevalence of FeLV and FIV in specific populations of Canadian cats. Hitt et al. (1992) evaluated sera (n = 671) submitted to a diagnostic laboratory in Atlantic Canada, with 90.5% of samples from Prince Edward Island. FIV seroprevalence was 7.6%, and higher rates correlated with increased age and intact male status. FeLV seroprevalence was not reported. Of cats trapped in a neuter and release program in Prince Edward Island (n = 185), Gibson et al. (2002) found 6.5% and 7.6% were seropositive for FeLV antigen and FIV antibody, respectively. All kittens (n = 46) were negative for both viruses, and seroprevalence of FeLV was higher in adult males than adult females. Three male cats (1.6%) were seropositive for both FeLV and FIV. Little (2005) evaluated seroprevalence in 246 cats from three demographic populations in Ottawa, Ontario. Seroprevalence of FIV was highest in urban stray cats (23%) and lower in client-owned cats (5.9%) and in a feral cat colony (5%). The same groups of cats had 6.7, 2.6 and 0% seroprevalence of FeLV, respectively. Two male cats (0.8%) were seropositive for both FeLV and FIV infection. In a study of Newfoundland cats predominantly from shelters (n = 591), Berghuis (2009) found seroprevalence of 6.1% and 2.5% for FeLV and FIV, respectively. Coinfection was uncommon (0.1%). The majority of retrovirus positive cats were unneutered males with access to outdoors and signs of ill health. In a retrospective study of 1205 samples from Saskatchewan, Manitoba and Alberta, Ravi et al. (2010) found seroprevalence of FeLV and FIV was 3.5% and 5.5%, respectively. Coinfection was uncommon (0.66%), and males had higher rates of seroprevalence than females. FIV infection was also significantly associated with illness (bite wounds,
S. Little / Veterinary Immunology and Immunopathology 143 (2011) 243–245
lethargy, and inflammatory oral disease) and increasing age. Scant data exist on the prevalent FIV subtypes in Canada. A study of 35 FIV isolates from Ontario by Reggeti and Bienzle (2004) identified subtype A as the most common (23/35), even though subtype B was most common in the eastern and central United States. Also, 7 cats with subtype B, 1 cat with subtype C, and 4 cats with A/B or A/C inter-subtype recombinants were identified in the Canadian study. 3. Conclusion Retrovirus infections across Canada appear to be slightly more common than in the United States. FIV infection is more frequent than FeLV infection, co-infection is relatively uncommon, and factors such as sample origin, cat sex and outdoor access appear to influence infection rates. Further investigation into geographic variations in retrovirus seroprevalence within Canada is warranted, and may provide information to improve recommendations for testing and prevention. As well, further investigation of FIV subtypes in Canada is necessary not only for developing molecular assays, but also for possible vaccine design and understanding of subtype association with disease outcomes. Although testing for FeLV and FIV has been readily available in Canada for many years and vaccines against FeLV have been in widespread use for at least 15 years, feline retroviral infections remain common in Canada. Increased awareness of seroprevalence data and available guidelines for feline retrovirus testing and management among veterinarians, shelters, and pet owners may help improve testing and vaccination rates. Conflict of interest All authors declare that there is no conflict of interest.
245
References Berghuis, L., 2009. The prevalence of feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) in shelter cats of Newfoundland. B.Sc. (Honors) Thesis, Memorial University of Newfoundland. Gibson, K., Keizer, K., Golding, C., 2002. A trap, neuter, and release program for feral cats on Prince Edward Island. Can. Vet. J. 43, 695–698. Hitt, M., Spangler, L., McCarville, C., 1992. Prevalence of feline immunodeficiency virus in submissions of feline serum to a diagnostic laboratory in Atlantic Canada. Can. Vet. J. 33, 723–726. Hosie, M.J., Addie, D., Belak, S., Boucraut-Baralon, C., Egberink, H., Frymus, T., Gruffydd-Jones, T., Hartmann, K., Lloret, A., Lutz, H., Marsilio, F., Pennisi, M.G., Radford, A.D., Thiry, E., Truyen, U., Horzinek, M.C., 2009. Feline immunodeficiency ABCD guidelines on prevention and management. J. Feline Med. Surg. 11, 575–584. Levy, J., Crawford, C., Hartmann, K., Hofmann-Lehmann, R., Little, S., Sundahl, E., Thayer, V., 2008. 2008 American Association of Feline Practitioners’ feline retrovirus management guidelines. J. Feline Med. Surg. 10, 300–316. Levy, J.K., Scott, H.M., Lachtara, J.L., Crawford, P.C., 2006. Seroprevalence of feline leukemia virus and feline immunodeficiency virus infection among cats in North America and risk factors for seropositivity. J. Am. Vet. Med. Assoc. 228, 371–376. Little, S., Sears, W., Lachtara, J., Bienzle, D., 2009. Seroprevalence of feline leukemia virus and feline immunodeficiency virus infection among cats in Canada. Can. Vet. J. 50, 644–648. Little, S.E., 2005. Feline immunodeficiency virus testing in stray, feral, and client-owned cats of Ottawa. Can. Vet. J. 46, 898–901. Lutz, H., Addie, D., Belak, S., Boucraut-Baralon, C., Egberink, H., Frymus, T., Gruffydd-Jones, T., Hartmann, K., Hosie, M.J., Lloret, A., Marsilio, F., Pennisi, M.G., Radford, A.D., Thiry, E., Truyen, U., Horzinek, M.C., 2009. Feline leukaemia ABCD guidelines on prevention and management. J. Feline Med. Surg. 11, 565–574. Ravi, M., Wobeser, G.A., Taylor, S.M., Jackson, M.L., 2010. Naturally acquired feline immunodeficiency virus (FIV) infection in cats from western Canada: prevalence, disease associations, and survival analysis. Can. Vet. J. 51, 271–276. Reggeti, F., Bienzle, D., 2004. Feline immunodeficiency virus subtypes A, B and C and intersubtype recombinants in Ontario. Can. J. Gen. Virol. 85, 1843–1852. Yamamoto, J.K., Hansen, H., Ho, E.W., Morishita, T.Y., Okuda, T., Sawa, T.R., Nakamura, R.M., Pedersen, N.C., 1989. 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.
Contents lists available at ScienceDirect
Veterinary Immunology and Immunopathology journal homepage: www.elsevier.com/locate/vetimm
Mini review
A review of feline leukemia virus and feline immunodeficiency virus seroprevalence in cats in Canada Susan Little ∗ Bytown Cat Hospital, 422 McArthur Ave., Ottawa, Ontario K1K 1G6, Canada
a r t i c l e
i n f o
Keywords: Feline FeLV seroprevalence FIV seroprevalence
a b s t r a c t Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are common and important infectious diseases of cats in Canada. Prevalence data are necessary to define prophylactic, management, and therapeutic measures for stray, feral and owned cats. Recently, comprehensive data on the seroprevalence of retrovirus infections of cats in Canada have become available and are reviewed. Further investigation into geographic variations in retrovirus seroprevalence within Canada is warranted, and may provide information to improve recommendations for testing and prevention. As well, more information is needed on FIV subtypes in Canada to improve diagnostics and vaccines, as well as to provide information on disease outcomes. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Seroprevalence of FeLV and FIV in Canada
Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are retroviruses causing two of the most common and important infectious diseases of cats. Diseases associated with FeLV and FIV may affect any organ, and include lymphoma, blood dyscrasias, central nervous system and ocular disease, gingivostomatitis, and secondary and opportunistic infections. Organizations such as the American Association of Feline Practitioners (Levy et al., 2008) and the European Advisory Board on Cat Diseases (Hosie et al., 2009; Lutz et al., 2009) have published guidelines for prevention and management of FeLV and FIV infections. Prevalence data are necessary to define prophylactic, management, and therapeutic measures for stray, feral and owned cats. Recently, comprehensive data on the seroprevalence of retrovirus infections of cats in Canada have become available.
The seroprevalence of FeLV and FIV infection in a variety of North American cat populations has been described in several publications, but until recently the available data applied predominantly to the United States. Presented here is a summary of FeLV and FIV seroprevalence for Canadian cats (Table 1). Yamamoto et al. (1989) evaluated the epidemiologic features of FIV infection, and categorized cats as high risk (n = 2254) or healthy with low or unknown risk (n = 511). In the high risk group, 14% were FIV seropositive compared to 1.2% in the healthy group. Further, in the high risk group, FIV seropositivity was more likely in males than females, in cats over 6 years of age than younger cats, and in free-roaming cats than confined cats. In the high risk group, FeLV seroprevalence among 1609 cats was 13%; 42 cats were reported to be from Canada, but no specific location was given. FIV seroprevalence was 19% among the Canadian cats. Within the healthy, low or unknown risk group of cats, 352 were reported to be from Canada, but no specific location was indicated. FIV seroprevalence for the healthy group as a whole was 1.2%, with no breakdown for origin from Canada versus the United States. More recently Levy et al. (2006), evaluated seroprevalence of FeLV and FIV among North American cats as well as
∗ Tel.: +1 613 741 2460; fax: +1 613 741 8463. E-mail address: [email protected] 0165-2427/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.vetimm.2011.06.018
244
S. Little / Veterinary Immunology and Immunopathology 143 (2011) 243–245
Table 1 Summary of FeLV and FIV seroprevalence studies in Canada. Study
Population Tested
Yamamoto et al. (1989)
Provinces not given High risk (n = 42) Low risk (n = 352) Atlantic Canada (90.5% PEI) PEI Adult feral males (n = 65) Adult feral females (n = 74) Ottawa Urban strays (n = 74) Owned cats (n = 152) AB, BC, NF, NS, ON, QC, SK (n = 325) All Canadian provinces (n = 11,144) NF shelter cats (n = 591) SK, MB, AB (n = 1205)
Hitt et al. (1992) Gibson et al. (2002)a
a
Little (2005)
Levy et al. (2006)a Little et al. (2009)a , b
Berghuis (2009)a Ravi et al. (2010)a a b
FIV
FeLV
19% 1.2% 7.6%
n/a n/a n/a
13.8%
7.7%
2.7%
5.4%
23% 5.9% 3.1%
6.7% 2.6% 2.5%
4.3%
3.4%
2.5%
6.1%
5.5%
3.5%
Testing performed with SNAP Combo FeLV antigen/FIV antibody, IDEXX Laboratories, Westbrook, Maine, USA. Testing performed with PetChek FIV antibody and FeLV antigen ELISA, IDEXX Laboratories, Westbrook, Maine, USA.
risk factors for seropositivity in a large prospective crosssectional survey. In this study, 18,038 cats were tested at 345 veterinary clinics (n = 9970) and 145 animal shelters (n = 8068). In this population of cats, seroprevalence of FeLV was 2.3% and seroprevalence of FIV was 2.5%, while 0.3% of cats were co-infected. The risk of seropositivity for either virus was higher in adult cats (>6 months) than juveniles, and in males than females. Other risk factors were access to outdoors and concurrent illness. The highest risk for retrovirus infection was associated with being sick and feral, followed by being sick with access to outdoors. The study included data on 325 cats from 7 Canadian provinces (AB, BC, NF, NS, ON, QC, SK), with 2.5% FeLV- and 3.1% FIVseropositivity among them. Little et al. (2009) conducted the first Canadian study of FeLV and FIV seroprevalence and risk factors. Signalment, lifestyle factors, and test results for FeLV antigen and FIV antibody were analyzed for 11,144 cats from the 10 Canadian provinces. More cats were tested at veterinary clinics (n = 9588) than at animal shelters/rescue organizations (n = 1556). Results showed seroprevalence for FeLV antigen was 3.4% and seroprevalence for FIV antibody was 4.3%. Fifty-eight cats (0.5%) were seropositive for both viruses. Significant risk factors for infection were age (>6 months), presence of current illness, and access to outdoors. FeLV seropositivity was highest in intact females (7.3%) and intact males (7.1%) and FIV seropositivity was highest in intact males (7.4%). An inactivated dual-subtype vaccine against FIV became available in Canada in 2003; however, FIV vaccination status was not recorded or known for cats in this study. It was assumed that veterinarians would be unlikely to test cats for FIV if they were known to be vaccinated, and that the population of cats tested by shelters and rescue groups is unlikely to have a high rate of FIV vaccination. Therefore, it seems likely that bias of FIV
prevalence estimates caused by vaccination in this study would be minimal. Other studies have evaluated seroprevalence of FeLV and FIV in specific populations of Canadian cats. Hitt et al. (1992) evaluated sera (n = 671) submitted to a diagnostic laboratory in Atlantic Canada, with 90.5% of samples from Prince Edward Island. FIV seroprevalence was 7.6%, and higher rates correlated with increased age and intact male status. FeLV seroprevalence was not reported. Of cats trapped in a neuter and release program in Prince Edward Island (n = 185), Gibson et al. (2002) found 6.5% and 7.6% were seropositive for FeLV antigen and FIV antibody, respectively. All kittens (n = 46) were negative for both viruses, and seroprevalence of FeLV was higher in adult males than adult females. Three male cats (1.6%) were seropositive for both FeLV and FIV. Little (2005) evaluated seroprevalence in 246 cats from three demographic populations in Ottawa, Ontario. Seroprevalence of FIV was highest in urban stray cats (23%) and lower in client-owned cats (5.9%) and in a feral cat colony (5%). The same groups of cats had 6.7, 2.6 and 0% seroprevalence of FeLV, respectively. Two male cats (0.8%) were seropositive for both FeLV and FIV infection. In a study of Newfoundland cats predominantly from shelters (n = 591), Berghuis (2009) found seroprevalence of 6.1% and 2.5% for FeLV and FIV, respectively. Coinfection was uncommon (0.1%). The majority of retrovirus positive cats were unneutered males with access to outdoors and signs of ill health. In a retrospective study of 1205 samples from Saskatchewan, Manitoba and Alberta, Ravi et al. (2010) found seroprevalence of FeLV and FIV was 3.5% and 5.5%, respectively. Coinfection was uncommon (0.66%), and males had higher rates of seroprevalence than females. FIV infection was also significantly associated with illness (bite wounds,
S. Little / Veterinary Immunology and Immunopathology 143 (2011) 243–245
lethargy, and inflammatory oral disease) and increasing age. Scant data exist on the prevalent FIV subtypes in Canada. A study of 35 FIV isolates from Ontario by Reggeti and Bienzle (2004) identified subtype A as the most common (23/35), even though subtype B was most common in the eastern and central United States. Also, 7 cats with subtype B, 1 cat with subtype C, and 4 cats with A/B or A/C inter-subtype recombinants were identified in the Canadian study. 3. Conclusion Retrovirus infections across Canada appear to be slightly more common than in the United States. FIV infection is more frequent than FeLV infection, co-infection is relatively uncommon, and factors such as sample origin, cat sex and outdoor access appear to influence infection rates. Further investigation into geographic variations in retrovirus seroprevalence within Canada is warranted, and may provide information to improve recommendations for testing and prevention. As well, further investigation of FIV subtypes in Canada is necessary not only for developing molecular assays, but also for possible vaccine design and understanding of subtype association with disease outcomes. Although testing for FeLV and FIV has been readily available in Canada for many years and vaccines against FeLV have been in widespread use for at least 15 years, feline retroviral infections remain common in Canada. Increased awareness of seroprevalence data and available guidelines for feline retrovirus testing and management among veterinarians, shelters, and pet owners may help improve testing and vaccination rates. Conflict of interest All authors declare that there is no conflict of interest.
245
References Berghuis, L., 2009. The prevalence of feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) in shelter cats of Newfoundland. B.Sc. (Honors) Thesis, Memorial University of Newfoundland. Gibson, K., Keizer, K., Golding, C., 2002. A trap, neuter, and release program for feral cats on Prince Edward Island. Can. Vet. J. 43, 695–698. Hitt, M., Spangler, L., McCarville, C., 1992. Prevalence of feline immunodeficiency virus in submissions of feline serum to a diagnostic laboratory in Atlantic Canada. Can. Vet. J. 33, 723–726. Hosie, M.J., Addie, D., Belak, S., Boucraut-Baralon, C., Egberink, H., Frymus, T., Gruffydd-Jones, T., Hartmann, K., Lloret, A., Lutz, H., Marsilio, F., Pennisi, M.G., Radford, A.D., Thiry, E., Truyen, U., Horzinek, M.C., 2009. Feline immunodeficiency ABCD guidelines on prevention and management. J. Feline Med. Surg. 11, 575–584. Levy, J., Crawford, C., Hartmann, K., Hofmann-Lehmann, R., Little, S., Sundahl, E., Thayer, V., 2008. 2008 American Association of Feline Practitioners’ feline retrovirus management guidelines. J. Feline Med. Surg. 10, 300–316. Levy, J.K., Scott, H.M., Lachtara, J.L., Crawford, P.C., 2006. Seroprevalence of feline leukemia virus and feline immunodeficiency virus infection among cats in North America and risk factors for seropositivity. J. Am. Vet. Med. Assoc. 228, 371–376. Little, S., Sears, W., Lachtara, J., Bienzle, D., 2009. Seroprevalence of feline leukemia virus and feline immunodeficiency virus infection among cats in Canada. Can. Vet. J. 50, 644–648. Little, S.E., 2005. Feline immunodeficiency virus testing in stray, feral, and client-owned cats of Ottawa. Can. Vet. J. 46, 898–901. Lutz, H., Addie, D., Belak, S., Boucraut-Baralon, C., Egberink, H., Frymus, T., Gruffydd-Jones, T., Hartmann, K., Hosie, M.J., Lloret, A., Marsilio, F., Pennisi, M.G., Radford, A.D., Thiry, E., Truyen, U., Horzinek, M.C., 2009. Feline leukaemia ABCD guidelines on prevention and management. J. Feline Med. Surg. 11, 565–574. Ravi, M., Wobeser, G.A., Taylor, S.M., Jackson, M.L., 2010. Naturally acquired feline immunodeficiency virus (FIV) infection in cats from western Canada: prevalence, disease associations, and survival analysis. Can. Vet. J. 51, 271–276. Reggeti, F., Bienzle, D., 2004. Feline immunodeficiency virus subtypes A, B and C and intersubtype recombinants in Ontario. Can. J. Gen. Virol. 85, 1843–1852. Yamamoto, J.K., Hansen, H., Ho, E.W., Morishita, T.Y., Okuda, T., Sawa, T.R., Nakamura, R.M., Pedersen, N.C., 1989. 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.