CRITICAL ENVIRONMENTAL AND PUBLIC HEALTH IMPLICATIONS OF IRRATIONAL USE OF ANTIMICROBIAL AGENTS IN VETERINARY PRACTICE.

Antimicrobial agents are precious and are among the most used drugs in veterinary practice. They are utilized for the therapy and prophylaxis of infectious diseases and as feed additives to growth. As pointed out by Van Den Bogaard (1993), antibiotics are among the most safe drugs and this attribute has provoked the liberal and even the use of these substances in man and animals, the argument being that if they do not do any good, they will do no harm either . The use of antimicrobial agents in Veterinary practice has no doubt resulted in a drastic reduction in mortality rate of infectious diseases. However, the indiscriminate use of these precious agents is not without serious adverse effects on the animal, environment and the public. This paper highlights some of the relevant aspects of antimicrobial drugs in Veterinary practice.
ANTIMICROBIAL AGENTS AND THE NORMAL BACTERIAL FLORA OF ANIMALS.
One of the major importance of the normal microbial flora is to keep invaders at bay (Schaechter, 1989). Two principal ways by which the normal flora prevent colonization and multiplication of invading pathogens are: (1). The normal flora is well adapted to the environment of the host and thus competes the invading pathogen for food and space. (2) some members of the normal flora produced antibacterial substances known as bacteriocins which are inimical to the pathogens. Proliferation on endogenous microorganisms like Clostridium difficile and Candida albicans is suppressed by the commensal bacteria of the intestinal tract. Antimicrobial agents are effective against both pathogens and normal bacterial flora of the animals. Irrational dosing of these animals with antimicrobial drugs especially broad spectrum oral antibiotics may result in:- (i) Total elimination of the typical bacterial flora of the intestinal tract  (ii) Emergence of resistance bacteria among the endogenous flora. Destruction of the normal flora with antibiotics increases the changes of exogenous bacteria to establish and multiply within the host and cause disease. Prolonged antibiotics therapy in animals may give rise to superinfection with resistant endogenous microorganisms such as Candida albicans (in dogs) and Clostridium difficile (in rabbits and guinea pigs). One of the most outstanding issues is associated with indiscriminate use of antibiotic resistant bacteria among the indigenous flora particularly those of the digestive system (Espinasse, 1993). Bacteria develop resistance to antibiotics through any of the following means:- (i) Productions of enzymes that destroy the active drug e.g. Penicillinase produced by Staphylococci. (ii) Alteration in permeability of bacteria to the drug eg. Resistance to polymyxins, (iii) Alteration of structural target for the drug e.g. resistance to sulphonamide. (iv) Alteration of bacterial enzymes which are less sensitive to the active drug e.g. resistance to sulphonamide genetic resistance (Chromosomal) can be conveyed from the resistant bacteria to sensitive ones (Frank, 1916; Espinasse, 1993). Greenwood (1989) observed that resistance to antimicrobial drugs develops in rough relation to the extent of use drug use. Hence lavish use of antimicrobial agents in animal may favour the emergence of resistance to different bacteria species or even genera in the same ecological niche. These resistant strains may also spread to other animals. The clinical implications of such a development are therapeutic failure and high cost of alternative treatments.

ANTIMICROBIAL DRUGS AND THE ENVIRONMENT
Large quantities of animal excretions especially faeces can be found in the environment. Millions of bacteria organisms are discharged into the environment through animal faeces. There are presence of resistant genes to pathogenic bacteria. Such pathogens may eventually establish in human or animal populations.
ANTIMICROBIAL AGENTS AND PUBLIC HEALTH.
Food animals constitute main source of animal proteins for man. Improper use of antimicrobial agents in animal may have hazardous effects on human health. Two main public health risks associated with antibiotic use in animals are:
(i)Risk related to the effect of antibiotic residues in animal products consumed by man.
(ii) Risk associated with antibiotic resistant bacteria in animals which contaminate man. Antibiotic residues in animal products such as meat and milk may produce direct toxic or hypersensitive reactions on the consumer for examples neurotoxicity associated with streptomycin; hepatotoxicity due to chloramphenicol residues; and haemolytic anaemia, a hupersensitivity reaction to sulphonamide residues. Antibiotic residues in animal products when ingested may favour the multiplication of microorganisms resistant to the particular antibiotic residues. The proliferation of such microorganisms (even non-pathogenic bacteria), particularly those with conveyable antibiotic resistant factor (R-Factor) constitutes a health problem. Transfer of such resistance to pathogenic bacteria will result in non-response to therapy when clinical infection sets in. Irrational use of antimicrobial drugs in food animals can select pathogenic bacteria such as salmonella in these animals which will contaminate the consumer. Resistant non-pathogenic strains or R-factor containing bacteria especially E. Coli when ingested through contaminated food may transfer the antibiotic resistance to pathogenic bacteria (e.g. Shigella) that may be present in the consumer digestive tract.
CONCLUSION
Antimicrobial agents are indispensable tools in veterinary practice. However, to preserve and safeguard the continuous efficacy of veterinary antimicrobial therapy now and in the future, and to protect human and environmental contamination with resistant bacterial strains, there is need for responsible use of antimicrobial drugs in veterinary practice. A WHO expert committee (WHO, 1961) had pointed out that estimation of bacterial sensitivity or resistance to antibiotics is an important requirement for the rational utilization of antibiotics and for preserving their efficacy. Since antimicrobial therapy is more effective if started early in disease, antibiotic treatment can be initiated when a bacterial infection is suspected pending results of sensitivity test. However, the choice of the antibiotic should be based up to date information on drug susceptibilities in previous cases in the farm and the neighbourhood. Rational use of antibiotics also entails respecting the dose route, frequency and duration of administration of the drug as indicated by the manufacturer.