Treatment of feline leukemia virus (FeLV) infection

K. Hartmanna,*, A. Blocka, G. Ferka, B. Beera, A. Vollmarb, H. Lutzc

aI. Medizinische Tierklinik, Ludwig-Maximilians-UniversitaÈt MuÈnchen, Munich, GermanybInstitut fuÈr Pharmakologie, Ludwig-Maximilians-UniversitaÈt MuÈnchen, Munich, Germany

cVeterinaÈrmedizinisches Labor, UniversitaÈt ZuÈrich, ZuÈrich, Switzerland

Abstract

FeLV infection is still considered to account for most disease-related deaths in pet cats. Different

treatment attempts with various drugs were performed in the past but none resulted in healing or

complete virus elimination. Therefore, it caused a sensation when HoÈrber and Mayr [HoÈrber, D.,

Mayr, B., 1991. Prax. 19, 311±314; HoÈrber, D., Schnabl, W., Mayr, B., 1992. TieraÈrztl. Umschau

47, 556±560; Mayr, B., HoÈrber, D., 1992. Kleintierprax. 37, 515±518] published that they were able

to cure 80 to 100% FeLV-infected cats from viremia by using an immunomodulating compound.

Articles in cat breeder and cat owner journals appeared assuming that obviously there is a rescue for

FeLV-infected cats suffering from this deadly infection. The immunomodulator [BuÈttner, M., 1993.

Comp. Immun. Microbiol. Infect. Dis. 18, 1±10] used in those studies was the so-called `paramunity

inducer' PIND-ORF (Baypamun1, Bayer, Leverkusen, Germany) consisting of inactivated parapox

ovis virus. Since that time, Baypamun1 is the most commonly used drug for treatment of FeLV

infection in Germany and other European countries. Four placebo-controlled double-blind trials

were performed to determine the therapeutic efficacy of Baypamun1 and other compounds in

naturally FeLV-infected cats under controlled conditions. # 1999 Elsevier Science B.V. All rights

reserved.

Keywords: Treatment; Feline leukemia virus infection; FeLV; Paramunity inducer; Baypamun1; Immunomo-

dulator

In the first study involving 120 cats, 60 cats were treated with Baypamun1, 60 with a

placebo preparation of virus-free cell culture medium. Dosage and administration of the

drug over a 7-week period were performed according to the instructions given by the

company. Seven of the 60 cats (11.7%) treated with Baypamun and 4 of the 60 cats

(6.7%) receiving placebo converted to a FeLV-negative state during the 6 week therapy

Veterinary Microbiology 69 (1999) 111±113

* Corresponding author. Tel.: +49-892180-2651/2697; fax: +49-892180-6240

E-mail address: k.hartmann@lrz.uni-muenchen.de (K. Hartmann)

0378-1135/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.

PII: S 0 3 7 8 - 1 1 3 5 ( 9 9 ) 0 0 0 9 7 - 8

interval (Table 1). The difference in the number of converting cats was not statistically

significant (p = 0.343).

In the second study involving 30 naturally infected cats, 15 cats received Baypamun1

and 15 placebo. The purpose of this study was to closely follow 20 clinical, laboratory,

immunological, and virological parameters. However, in none of these parameters, a

statistically significant difference could be demonstrated between Baypamun1 and

placebo application. Remission of viremia (Table 1) occurred in two cats of each group

(15.4%).

The results of these studies were compared to those of a placebo-controlled double-

blind study using the antiviral compounds 30-azido-20,30-dideoxythymidine (AZT) and 9-

(2-phosphonylmethoxyethyl)adenine (PMEA). Twelve cats received AZT, 11 PMEA, and

9 placebo. In contrast to Baypamun1 application, the treatment with antiviral compounds

caused a statistically significant improvement in some clinical and immunological

parameters and reduced FeLV antigenemia. However, none of the cats in this study

converted to FeLV-negative (Table 1).

In the fourth study, seven cats were treated with AZT, 10 cats with a-interferon (IFN-

a), seven cats with AZT in combination with IFN-a, and four cats with placebo. Again,

no cat however, became FeLV-negative.

As shown in these studies, there was no cure of FeLV infection by any of the used

treatments. In 11 cats of study I and in 4 cats of study II, there was a conversion from a

FeLV-positive to a FeLV-negative state but the difference in number of cats was not

statistically significant between the groups. These cats were generally younger than 1

year and had no clinical signs. It can be assumed that they were in a state of transient

viremia. There is no explanation of the divergent results of HoÈrber and Mayr (1991),

HoÈrber et al. (1992), Mayr and HoÈrber (1992) who stated to be able to cure 80 to 100%

FeLV-infected cats from viremia by using Baypamun1.

For an interpretation of treatment results, the comparison with a placebo group is

unavoidable. To prevent the subjective influence of the investigator, the study also has to

be double-blind. Otherwise a clinical improvement never can be judged objectively.

There was no statistically significant difference regarding any of the investigated

immunological, clinical, laboratory, or virological parameters between animals receiving

Baypamun1 or placebo neither in the first nor in the second study. In consequence,

Baypamun1 treatment cannot be recommended for treatment of FeLV infection. The

importance of conducting treatment studies as placebo-controlled double-blind trials was

demonstrated in this investigation.

Table 1

Percentage of cats converting to FeLV-negative during study I, II, III, and IV and p-value (statistical significance)

of the differences between the groups

Conversion to FeLV-negative (% of cats) p-value

Study I Baypamun1 11.7 Placebo 6.7 0.343

Study II Baypamun1 15.4 Placebo 15.4 1.000

Study III AZT 0 PMEA 0 Placebo 0 1.000

Study IV AZT0 INF- 0 AZT + IFN- 0 Placebo 0 1.000

112 K. Hartmann et al. / Veterinary Microbiology 69 (1999) 111±113

References

BuÈttner, M., 1993. Principles of paramunization, option and limits in veterinary medicine. Comp. Immun.

Microbiol. Infect. Dis. 18, 1±10.

HoÈrber, D., Mayr, B., 1991. Paramunisierung FeLV-positiver Katzen mit PIND-AVI. TieraÈrztl. Prax. 19, 311±

314.

HoÈrber, D., Schnabl, W., Mayr, B., 1992. Praxiserfahrungen bei der Paramunisierung FeLV-positiver Katzen mit

Baypamun HK. TieraÈrztl. Umschau 47, 556±560.

Mayr, B., HoÈrber, D., 1992. Paramunisierung FeLV-positiver Katzen ± ein Bericht aus der Praxis. Kleintierprax.

37, 515±518.

K. Hartmann et al. / Veterinary Microbiology 69 (1999) 111±113 113