Remarks on an Increasing Resistance of Fishpathogenic and Facultative-fishpathogenic Bacteria in Lower Saxony (FRG)

Abstract

Increasing resistance of specific-fishpathogenic and facultative-fishpathogenic bacteria against the main drugs licensed in Germany. With an average of yearly 600 examined cases—including the whole range of additional virological-, bacteriological-, histological-, water quality and residual tests—the Fish Health Service (FHS) of Hannover of the Northern Federal State of LOWER SAXONY reached within the last years some representative experience dealing with the control and therapy of fish diseases in aquaculture. The control of the three notifiable viral epidemics of freshwater fish presently included in the pertinent legislation (Animal Epidemics Act) of the FRG—VHS, IPN and SVC—is the competence of the STATE FISH EPIDEMICS CONTROL SERVICE OF LOWER SAXONY from which the FHS mentioned above is a part. The therapy of bacterial diseases—essentially Aeromonas salmonicida infections (Furunculosis/Salmonids; Erythrodermatits/Cyprinids), vibriosis, from 1981 on increasingly Enteric Redmouth Disease/ERM (with an unexpected peak in late winter-, spring and summer 1984) as well as the mainly environment dependent—sometimes with septicemic development of the whole range of ubiquitous facultative-fishpathogenic bacteria from the aquatic environment—developed rather unproblematic and successful in Lower Saxony for many years. From 1981 on a change in this situation with concomitant increasing resistance of specific-fishpathogenic as well as facultative-fishpathogenic bacteria, against the main drugs licensed in the FRG and used in the control of freshwater fish diseases mainly through medicated feed is observed. The bacterological examination with antibiogramme proved indispensable. In the FRG the presently licensed drugs for treatment of bacterial infections in fish are Chloramphenicol, Chlor- and Oxitetracycline, Furazolidone, Trimethoprim/Sulfadimethoxine and Nifurpracine. In the FRG Chloramphenicol was forbidden for use in domestic animals (homoeotherms) for human consumption in April 1984. It is to assume that Chloramphenicol will be withdrawn for use in fish soon. Only in few individual cases and strictly controlled by the veterinary authorities some other drugs can be experimentally tested under prescription and strict supervision of a veterinarian specialized in fish diseases and aquaculture. Besides the substances mentioned above antibiogrammes are routinely carried out with Oxolinic acid, “Lincospectin” (Lincomycine + Spectinomycine 1:2), Ampicilline, Erythromycine and very recently Fluméquine. The results of 596 FHS-cases from which in 289 the bacteriological examination proceed necessary— from them in 162 cases the antibiogramme was feasible—carried out within the frame of the work of the FHS from January 1983 to May 1984 are discussed-, the increased resistance showed-, the effectivity and/or uselessness of some of the drugs presented. Fluméquine, Oxolinic acid, Lincospectine (not yet licensed in the FRG) and last but not least the tetracyclines showed promising. The finding of few Aeromonas salmonicida subsp. salmonicida isolates completely resistant against the drugs licensed in the FRG may involve further serious problems as well as cases of total failure of therapy carried out in strict accordance with the antibiogramme if a chronic viral infection is present in the background—as e.g. observed with ERM concomitant to VHS. The results of a first field trial with Oxolinic acid in a rainbow trout population during summer of 1984 are shown. As a main result of this trials it is recommended to enlarge the presently narrow frame of drugs licensed for fish in the FRG by at least two of the compounds tested: Oxolinic acid and Fluméquine, or Oxolinic acid and Lincospectin; and to delete Ampicilline which was included in a pertinent priority list in 1982. The limits of predicability in praxi of an in vitro test like the antibiogramme and later therapeutical results in vivo in the field are presented. The crucial importance of the environment (water quality and amount, temperature, stock, nutritional status and provenance of fish envolved) is discussed. Its optimation may contribute to health improvement which makes the use of drugs redundant and often unnecessary. © 1985, The Japanese Society of Fish Pathology. All rights reserved.