Prevalence, Clinical Aspects, Diagnostic Conduct In Immunodeficiency (Fiv) And Leukemia (Felv) Of Domestic Cats

Feline immunodeficiency virus (FIV) and Feline leukemia virus are retroviruses that cause two of the most common and important infections in domestic cats (Felis catus). Diseases asscociated with these two entities can affect any organ.(3,7) Due to the immunosuppressive effect, infections with these viruses weaken the immune system of felines, resulting in opportunistic infections and side effects. These infections have a high mortality rate, directly or indirectly, by exacerbating symptoms of other diseases that are associated with these two viral infections.(4) For this study, a number of 197 of cats were tested for FIV and FeLV. The tests were performed on cats belonging to different breeds, with age between 6 months and 13 years, including 114 males and 83 females.,presented at the Faculty of Veterinary Medicine, Bucharest,Romania.

The study was conducted between 2015-2017 at the Clinic of the Faculty of Veterinary Medicine in Bucharest, study that was made by myself from my bachelor work.The tests were performed by the IDEXX SNAP®  FIV/FeLV Combo Test and supplemented by haematological, biochemical and imaging exams. Of the total number of cats tested, 12,18% were FIV positive and only 1,52% had a positive result for FeLV, indicating a low prevalence comparing to FIV. The relatively high prevalence of FIV infection observed in this study suggests the importance of establishing a correct diagnosis of retroviral infections and making a differencial diagnosis for other cats that may have similar forms of manifestation.

Feline immunodeficiency virus (FIV) and Feline leukemia virus (FeLV) affect both domestic cats (Felis catus) and wild cats from all over the world. The two viruses can be transmitted horizontally through saliva and other body fluids, and vertical transmission may also be a possible way of inoculating viruses. Following inoculation, the virus infects the immune cells of the host and their replication can compromise the immune system (Munro J. et al., 2013).In general terms, both infections produce similar clinical signs and a precise clinical diagnosis cannot be achieved.(1)

The most important sequelae of these infections are : immunodeficiency, followed by opportunistic infections, tumours and haematological abnormalities. Both FIV and FeLV show a high mortality rate having a global impact. (5,6)

 The FIV infection is present worldwide, the values of prevalence varying by location. The prevalence of infection in the European states is low (around 5%) even though it may reach 20% in some regions of Eastern Europe, due to lack of testing the animals for these diseases.(10) According to  international specialty studies, the prevalence of FeLV infection in healthy feline population is quite high, reaching 40% in some cases which may show signs of exposure to  Feline leukemia virus. (9,10)

The purpose of this study is to alert the attention of all veterinarians from around the world to be able to diagnose early these diseases by testing all cats regardless of breed, age or gender. The prevalence of FIV and FeLV in Bucharest, Romania can be now compared to other studies from all over the world.

Materials and methods

The research in this study was conducted between January 2015 and May 2017 in the Departament of Clinics of the Faculty of Veterinary Medicine in Bucharest, Romania. During this research, a total of 197 cats were tested for FIV and FeLV. The tests were performed on cats belonging to different breeds, and ages between 6 months and 13 years. Of the total of individuals tested, 114 were males and 83 were females.

The tests were performed using the IDEXX SNAP® FIV/FeLV Combo  Test (ELISA) method. This is a rapid immunoenzymatic assay for simultaneous detection of feline leukemia viral antigen (FeLV) and detection of antibodies to feline immunodeficiency virus (FIV) in serum, plasma or whole blood of feline.

For the research, were selected 27 positive cats for the two infections, of which 24 were FIV-positive (17 males and 7 females) and only 3 cats were FeLV-positive (2 males and 1 female). The prevalence of infections was studied on this positive cat count, analyzing the variations of diseases according to gender, age, clinical and haematological aspects. 

Results and discussions

Of the 197 cats tested, 27 (13,70%) were positive for the two infections, the remaining 160 felines were negative for FIV and FeLV, but this does not rule the existence of one of the infections due to testing the cats outside the phase of disease viremia, Also, other causes could be the lack of verification of the IDEXX SNAP® FIV/FeLV Combo  Test (ELISA) method with a PCR test because of subjective, financial reasons manifested by the owners of cats. (Figure 1)

The prevalence of FIV infection was relatively high, with 24 cats being FIV-positive (12,18%) compared to feline leukemia cases (3 cases, 1,52%). 

The tested cats belonged to several breeds: Scottish Fold, Sphynx, Norwegian Forest, Persian, British Shorthair, Maine Coon, Angora, Russian Blue, Domestic Shorthair (European). The 27 positive cats for the two diseases belonged exclusively to the Domestic Shorthair (European) breed. This result suggests that cat’s lifestyle can greatly influence the susceptibility to these infections. In Romania, European cats are often adopted by owners from the street compared to other breeds that are kept in stable homes, having a safer lifestyle for their health. However, infections are not excluded in other breeds, according to the results from international studies.(8)

The risk of FIV infection for males is higher due to their exposure because of their aggressiveness compared to females.(Figure 1). Studies show that FIV is mainly transmitted by biting or scratching. (2,10) The low prevalence of FeLV infection compared with FIV is due to testing outside the viremic period,when the virus is undetectable or because of not performing PCR tests to detect the provirus.

Graphic expression of tested and positive FIV and FeLV cases by gender. 
Graphic expression of the prevalence of FIV infection based on the age of cat at the time of testing.

Of the total number of cats infected with FIV (24 cases), the highest prevalence was recorded in the age range of 4-10 years (13 males and 4 females). Studies show that adult cats are more prone to exposure, the incidence increasing with age: 10% at one year, 20% at 4 years and 30% at 9 years then it slows down. (11), (Figure 2).

Haematological changes in cats with FIV and FeLV were non-regenerative anemia, neutropenia, trombocytopenia and trombocytosis. Anemia is common in both feline leukemia and feline immunodeficiency most often due to endoglobular parasites or bacteria.(10) Neutropenia occurs most often in the clinical phase of the disease, (especially in FIV infection) due to viral multiplication that weakens the body’s resistance. In this study, neutropenia was noted in 12,5% patiens with FIV and in all patients with FeLV (33,33%). (Figure 3) .

Graphic representation of major changes in CBC (blood count) indicating non-regenerative anemia, neutropenia, thrombocytopenia or thrombocytosis in infected cats.
Expression of the main predominant clinical signs associated to FIV and FeLV infections.

Cats tested for FIV and FeLV infections showed specific and non-specific clinical signs during the study. In the two diseases, there are no patognomonic signs of illness but there are certain manifestations that can lead to their suspicion. The most common clinical signs observed were: weight loss (present in 9 cases of FIV and one case oj leukemia), lymphadenopathy (3 felines with FIV, and 3 cases of FeLV), anemia appeared in 11 cats with FIV and 2 cats with FeLV, secondary infections due to immunosupresion manifested by 2 cats with FeLV and 11 cats with immunodeficiency. Neoplasia was found in 2 felines with Feline leukemia virus.(Figure 4).

Conclusions

 The relatively high prevalence of FIV infection (12,18%) found in Bucharest, Romania, suggests the importance of establishing a correct diagnosis of retroviral infections and making a differential diagnosis for other cats that may have similar manifestations.

Cats that were tested for these two retroviruses, during the study, had specific and non-specific clinical signs. None of the FIV/FeLV positive felines were detected in the asymptomatic phase of the disease.The clinical picture in these two conditions was dominated by the presence of secondary infections (55,55%) as a result of immunosupression. 

According to this study,cats of all categories are at increased risk for these infections and it is recommended to test all cats at the time of purchase, repeat tests in case of development of acute or chronic diseases and also test all cats for that have access to external environment as well as those in stable housing that may come in contact with other possible infected cats with FIV or FeLV.

Bibliography

  1. COLLADO V.M., DOMENECH A., MIRó G. (2012), Epidemiological aspects and clinicopathological findings in cats naturally infected with feline leukemia virus (FeLV) and/or feline immunodeficiency virus (FIV), Open Journal of Veterinary Medicine, 2012,2, 13-20
  2. CORNELL UNIVERSITY COLLEGE OF VETERINARY MEDICINE. (2014), Diagnostic Tests, New York 14853-6401
  3. DÉGI J., IMRE K., MORAR D., IANCU I. (2015), Prevalence of feline immunodeficiency virus (FIV) infection in cats – Preliminary study, Lucrări Științifice Medicină Veterinară, vol. XLVIII(3), 2015, Timișoara
  4. EROL N., PASA S., (2013), An investigation of the feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) infections in cats in Western Turkey, Acta Scientiae Vaterinariae, 41:1166
  5. HARTMANN K., GREENE C., SCHULZ B., VIDYASHANKAR A., JARRET O., EGBERINK H. (2007), Quality of different in-clinic test systems for feline immunodeficiency cirus and feline leukemia virus infection, Journal of Feline Medicine  and Surgery (2007) 9, 439e445
  6. LIEM B.P., DHAND N.K., PEPPER A.E, BARRS V.R., BEATTY J.A., (2013),  Clinical findings and survival in cats naturally infected with feline immunodeficiency virus, J Vet Intern Med, 27:798-805
  7. LITTLE S., BIENZLE D., CARIOTO L., CHRISHOLM H. (2011), Feline leukemia virus and feline immunodeficiency virus in Canada: Recommendations for testing and management, Can Vet 2011;52-849-855
  8. MUNRO H.J., BERGHUIS L., LANG A.S., ROGERS L., WHITNEY H. ( 2013), Seroprevalence of feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV)  in shelter cats on the island of Newfoundland, Canada, The Canadian Journal of Veterinary Research, 2014;78:140-144
  9. PERIANU T. (2012), Tratat de Boli Infecțioase ale Animalelor,Viroze și Boli Prionice,vol. II, Editura Universitas XXI, Iași
  10. RAMSEY I., TENNANT B. (2001), BSAVA Manual of Canine and Feline Infectious Diseases, Editura British Small Animal Veterinary Association, Hampshire, UK
  11. TILLEY P. L. , SMITH W.C. F. (2007), Blackwell’s Five-Minute Veterinary Consult: Canine and Feline,Editura Blackwell Publishing, Philadelphia,USA
DVM Oana Slate
DVM Oana Slate
Veterinary Physician, Bucharest, Romania.  Dr. Oana Slate, DVM, graduated from Faculty of Veterinary Medicine Bucharest, in 2017. Her postgraduate education continued through self-study; her passion, complementary/alternative medicine, led her to develop alternative therapies in veterinary medicine. She works at Urgențe Veterinare DI-VET MEDICAL, in Bucharest. Follow Dr. Slate and her great work on Instagram

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