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The effect of sub-therapeutic uses of both animal and human drugs to manage diseases in poultry flocks

The effect of sub-therapeutic uses of both animal and human drugs to manage diseases in poultry flocks

Health management in poultry farms, whether commercial or small-scale, is of utmost importance because of the economic effect it has on the overall productivity of the flock. Even farms stocked with the best breeds that are properly housed and fed high quality feeds will not grow and produce efficiency under poor health management. For poultry health management to be effective, three principles have to be observed: Prevention of disease, early recognition of the disease and early treatment of the disease.

Most diseases in poultry farms are caused by infectious pathogens that quickly spread across the flock especially in commercial farms with high stocking density. These pathogens include bacteria, virus, protozoa and parasites in which some are easily controlled through vaccination while others require proper biosecurity measures be put in place. Bacterial diseases account for a higher proportion of health problems within poultry farms and as such most invest a lot of resources on antibiotics to control these diseases. Antibiotics belong to a category of drugs called "antimicrobials," and include penicillin (amoxillin), tetracyclines, fluoroquinolones (cipro-drugs) and other formulations that can kill or inhibit the growth of bacteria without causing significant harm to patients. The use of antibiotics for therapeutic reasons isn’t as controversial because few argue that sick birds should not be treated for the sake of organic poultry production. However, the biggest controversy centers on administering antibiotics used to treat human illness to poultry flocks. The effect of using human drugs to manage diseases in poultry flocks on human health, whether long-term or short-term remains unknown. The fact is that most approved animal pharmaceuticals are often made in the same manufacturing plants as human pharmaceuticals and will contain the same ingredients as human drugs.  These veterinary drugs have the same color, shape, and bare the same markings as human drugs. Therefore, given the similarities between the two categories of drugs the use of human drugs to treat livestock in general poses no threat to livestock neither to human health and they are just as effective as animal drugs.

However, apart from therapeutic purposes, most farmers administer antibiotics (whether human or animal antibiotics) to poultry in small doses on daily basis to enable the birds’ gain as much as three percent more weight than they otherwise would. Although it is still unclear why feeding small "sub-therapeutic" doses of antibiotics, like tetracycline, to birds makes them gain weight, research indicates that the antibiotics kill the flora that would normally thrive in the birds' intestines, thereby allowing the birds to utilize their food more effectively. The poultry industry doesn't publicize its use of antibiotics, so accurate information on the amount of antibiotics given to meat birds is hard to come by. Majority mix these drugs with poultry feed and water day after day as a substitute for healthier living conditions in crowded and unsanitary environment and to promote growth. The problem with feeding antibiotics to animals that are not sick is that it kills off weak bacteria and creates the perfect environment for antibiotic-resistant bacteria to multiply and thrive. When the poultry industry routinely misuses and overuses antibiotics in this way, it threatens public health when essential drugs no longer work to treat infections due to reduction in their efficacy hence makes us less safe. Due to public health risks associated with antibiotic resistance, there is need to end the use of low doses of medically important antibiotics in order to prevent the development of antibiotic resistant bacterial strains. When we get sick, we want medicine that works and through a doctors prescription we are able to control misuse of drugs. Therefore, by eliminating routine, non-therapeutic uses of antibiotics, the poultry industry can reduce the potential for antibiotic resistance and ensure these important drugs remain effective for treating human.

The livestock industry in general argues that there is no harm in sub-therapeutic uses and contributes little, if anything, to the burden of human antibiotic resistance. A key question is can antibiotic use in animals promote the development of hard-to-treat antibiotic-resistant bacteria that make people sick?  And if it can, are the illnesses rare occurrences, and the risks theoretical, or could current usage in animals pose a serious threat to human health. Research has indicated that there is a connection between antibiotic use in animals and the loss of effectiveness of these drugs in human medicine.  Take an example of salmonellosis, research indicated that the continuous sub-therapeutic use of amoxicillin in livestock led to the flow of a distinct salmonella strain to human through livestock products, who later on acquired clinical salmonellosis. The biological explanation behind this is that misuse and overuse of antibiotic drugs creates selective evolutionary pressure that enables antimicrobial resistant bacteria to increase in numbers more rapidly than antimicrobial susceptible bacteria and thus increases the opportunity for individuals to become infected by resistant bacteria.

So how does antibiotic resistant pathogenic bacteria develop? Similar to how immunization helps the human body fight disease by exposing the immune system to small amounts of a virus or bacteria, when bacteria are continually exposed to small amounts of antibiotics they can develop immunity to them. It’s a case of "survival of the fittest," with the strongest bacteria that are least susceptible to a specific antibiotic, surviving, adapting and multiplying. These are called "resistant bacteria" because they have adapted to the point where antibiotics are no longer an effective means of killing them. As a result, some antibiotics have lost their effectiveness against specific infectious diseases. Nevertheless, the livestock industry continues to argue that while antibiotic use may have something to do with antibiotic resistance in bacteria on the farm, it is not an important human health issue, and little change in current practices are needed. However, little is understood about the long-term effect of misuse of these drugs on human health. The frequency of ingesting drug resistant pathogen is not well documented and as such most people just ride out an infection and it fades into the background of the numerous cases of food borne illness reported annually in the Kenya.

Another antibiotic problem is cross-resistance to antibiotic in human illness, which comes as a result of an antagonistic relationship between drugs such as Baytril and Cipro (both belong to the flouroquinolone class of antibiotics). Baytril is used to treat sick birds infected with E. coli infection while Cipro is used to treat and prevent Campylobacteriosis and Salmonellosis in human. Overuse of Baytril in meat birds eventually compromises the power of Cipro to fight bacterial diseases in human. The problem comes in when a veterinarian diagnoses one infected bird then the farmer treats the whole flock by adding the drug to the flocks’ drinking water. General use of Baytril, therefore, falls in the gray area between therapeutic and sub-therapeutic.

Concerns about the growing level of drug-resistant bacteria have led to the World Health Organization (WHO) to declare its intention to "reduce the overuse and misuse of antimicrobials in food animals for the protection of human health." Specifically, the WHO recommended that prescriptions be required for all antibiotics used to treat sick food animals, and urged efforts to "terminate or rapidly phase out antimicrobials for growth promotion if they are used for human treatment." However, from the industry’s perspective removal of antibiotics whether for therapeutic or sub-therapeutic use from animals' feed and water would lead to increased animal disease, a reduction in food safety, little gain and serious economic effect on the livestock industry, in the effort to control resistance. In such cases, developing prudent drug use principles would be safer. An alternative that would serve as a sustainable measure would be to raise the birds under clean environments with adequate space to reduce stress and prevent the birds from being susceptible to infectious pathogens.  While this type of measure may use antibiotics, it only does so to treat acute infections in sick animals, just as they are used to treat infections in humans. Ending the routine use of antibiotics in animal agriculture is not only critical; it is possible and economically feasible.

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