Use of long acting tetracycline for CBPP: preliminary results

A. Yaya^[30], H. Wesonga^[31] and F. Thiaucourt^[32]

Introduction

The use of antibiotics for CBPP control has always been controversial. For some “experts in development”, antibiotic therapy could be a valid alternative to vaccination. According to them, the advantage of antibiotics over vaccines is that these drugs are already available in the field and their use may have a direct impact on poverty alleviation. On the contrary, vaccines are often distributed by state veterinary services exclusively and may therefore fail to reach all the cattle owners that need them, as very few veterinary services in Africa are wealthy enough to organize comprehensive vaccination campaigns. On the other hand, there are many arguments that can be put forward that oppose the widespread use of antibiotics, such as the inevitable spread of residues that favour the emergence of resistant bacteria in the environment and the possible long-term carrier state that is allegedly attributed to animals treated with antibiotics.

For these reasons, African veterinary services have some difficulties in defining an official strategy concerning the use of antibiotics. This was exemplified during the recent CBPP AU/IBAR meeting in Accra, Ghana in February 2002. Some Directors of Veterinary Services were of the opinion that the use of antibiotics for the treatment of CBPP must be forbidden (although it is a very common practice in the field); others were eventually considering their use as a possible tool to control the disease. The difficulty is that there are very few data concerning the efficiency of these antibiotic treatments. Many antibiotics have been shown to be active in in vitro assays. This is the case of tetracyclines, macrolides, lincosamines, streptogramines and quinolones (Ayling, 2000). In the field, such antibiotics were used successfully to treat post-vaccinal reactions when using strain T1 44 (Lindley, 1971). This is the reason why it was decided to conduct some preliminary trials in order to assess the efficacy of long-acting tetracycline to treat CBPP-infected cattle.

Methods

The first trial was performed at KARI, Muguga. Groups of 5 animals were inoculated subcutaneously, either with a local virulent Mmm SC isolate or with a T1 44 vaccine strain that had apparently reverted to virulence. This inoculation was followed by the development of an invading oedema and animals were treated with a single dose of long-acting tetracycline according to the manufacturer's instructions.

The second trial was performed at LANAVET, Garoua. Twenty animals were added to the control group in a T1 vaccine trial. The assay started when the transmission of CBPP to the control group was well established. At this stage, 20 animals were randomly selected for the antibiotic assay and 12 of them displaying CBPP symptoms were subjected to treatment with long-acting tetracycline. Treated animals were housed in a different building in order to prevent reinfection by untreated controls. At the end of the experiment, all animals were slaughtered and their lesion score was evaluated. Comparisons were then established between the treated group and the corresponding controls (animals present at the beginning of the treatment).

Results

In the first trial, out of 10 animals, 2 samples of cutaneous tissue yielded a positive Mmm SC culture and, in addition, 2 other animals were positive for isolation of Mmm SC from other samples. Therefore, the antibiotic treatment did not prevent 4 animals out of 10 from becoming Mmm SC carriers, although the antibiotic treatment definitively stopped the extension of lesions.

In the second trial, in the treated group (12 animals) none died of CBPP, whereas 3 of them did in the untreated group. Furthermore, there was a difference in the distribution of lesion scores between the two groups. However, Mmm SC was isolated out of 5 animals (from the 12 treated ones). Preliminary data suggest that Mmm SC strains did not develop any resistance to tetracycline. Given that the lung lesions did not consist of well-formed sequestra, the persistence of Mmm SC cannot be explained by a problem of antibiotic diffusion to necrotic material within the fibrous capsule.

Discussion

Both trials indicated that tetracyclines had a positive effect on the clinical course of the disease. However, treated animals still suffered from CBPP lesions and some animals that were not treated because they did not display any obvious CBPP signs were nevertheless found to harbour CBPP lesions. These findings clearly show that antibiotic treatments in the field will not allow the disappearance of the infection. Antibiotics will certainly reduce the economic impact of CBPP in affected herds and in addition, they will reduce the infective pressure on susceptible animals. According to these preliminary results, antibiotics may be used in a combined strategy involving vaccinations, bearing in mind the possible drawbacks of the uncontrolled and widespread use of antibiotics.

References

Ayling, R. D., Baker, S. E., Nicholas, R.A., Peek, M. L. and Simon, A. J. (2000). Comparison of in vitro activity of danofloxacin, florfenicol, oxytetracycline, spectinomycin and tilmicosin against MmmSC. Veterinary Record 146, 243-246.

Lindley, E. P. (1971) La spiramycine et les lésions post-vaccinales au vaccin lyophilisé, "MmmSC souche T1/44" contre la péripneumonie contagieuse des bovidés (PPCB). Cah méd. vét. 40, 233-236.