**3. Development of AMR in veterinary practice**

The global antimicrobial resistance (AMR) crisis is predicted to kill roughly 10 million people annually by 2050 due to antibiotic-resistant infections, with Africa alone accounting for about 4.15 million [29]. This is estimated to cost the global economy about \$100 trillion [30] with about 28.3 million people pushed into extreme poverty [31]. The alarming rate of AMR in developing countries can be attributed to gross misuse of antimicrobials in human and animals [32]. Although resistance can still develop even at an appropriate antimicrobial use, however the situation can be made worse whenever there is excessive and unnecessary usage [33]. The global revolution in livestock and aquaculture is an underlying factor for frequent antimicrobial use and subsequent development of AMR. This is also driven by population increase, urbanization, improving economic conditions, and globalization. Countries like Brazil, China, and India are currently the hotspots for livestock intensification, while Nigeria, Myanmar, Peru, and Vietnam are future spots (Van [17]). In developing countries, most nonhuman-medical use of antimicrobials is almost certainly in livestock and farmed fish production and it is likely that most veterinary use is in intensive production rather than pastoralist or small-holder systems [34]. In Nigeria and other developing countries in sub-Saharan Africa, Asia and Middle East, there is paucity of information on antimicrobial drug resistance in farm animals, although little information exists on residue level [35–38]. However, there is information on antimicrobial drug resistant microbes isolated from human patients from different parts of Nigeria [39, 40]. Previous report by Adesokan et al. [41] on pattern of antimicrobial usage in livestock production in three states of South-Western Nigeria between the period of 2010 and 2012 showed an increased use of tetracyclines (33.6%) followed by fluoroquinolones (26.5%) and betalactams/aminoglycosides (20.4%). Similar trend was also reported in Africa for tetracycline & beta-lactams [42]. However, studies by Idowu et al. [35] showed level of tetracycline residues between the ranges of 0.1–1.0% in chicken eggs.

The process of AMR development is very complex, and all of the factors that contributed to the events are not fully understood. It is clear that genetic change or mutation in microbial DNA may often cause resistance to antimicrobial agents, and this change might also be passed to the offspring or transferred to other related or even unrelated microorganisms [43]. This is known as "selection pressure" where the use of antimicrobial drugs in health care, agriculture, or industrial settings favor the survival of resistant strains (or genes) over susceptible ones, thus leading to a relative increase in resistant bacteria within microbial communities [44]. This is because no matter how effective an antimicrobial is, it rarely kills 100% of the organisms, meaning some may still survive due to genetic change, which can be passed forward. Currently, science has not fully proved the causes of different types of AMR that are causing great public health risks. The widespread use of antimicrobials in food production system especially in food-producing animals is another cause of AMR [45]. The extensive use of antimicrobials in animal production as growth promoters widely exposes the microbes to the drugs, thus enhancing the development of microbial resistance causing health consequences in both animals and humans. However, the scientific evidence of how and to what extent such drug

exposure affects human health still remains unclear. It is interesting to note that antimicrobial resistance would not develop in animals if antimicrobial drugs were never used in them [12].

There is danger to public health if resistant organism from animals can also cause disease in human exposed by a way of food consumption or direct contact with food-producing animals, companion animals, or through environmental spread [46]. The threat to public health also exists even if the organisms do not cause disease in human, because they may still be able to transfer the resistant genes from food-producing animals to unrelated human pathogenic bacteria as well as normal commensals [47]. It is then clear that the increase use of antimicrobials in animal production for variety of purposes such as for therapeutic and nontherapeutic use has contributed to increasing AMR in bacteria affecting man and animals [48]. In Africa and other developing countries, studies have suggested a strong correlation between the use of antimicrobials in veterinary practice and the development of AMR [49], because it is shown that a larger proportion of antimicrobial medications have been used in animals than humans mainly for food production purposes [50]. There is presence of high antimicrobial residue in meat and milk meant for human consumption correlating with the detection of multidrug resistance (MDR) bacteria in animals and their products [51] as well as in humans in contact with the animals [52–54]. This is also because a large proportion of the population in developing countries lives in close proximity with livestock, which enhance the chances of transfer of resistant microorganisms from animals to humans [55, 56]. Similarly, the increasing use of antimicrobials as prophylaxis in aquaculture in developing countries further contributed to the emergence of AMR causing problems in human, animal, and environmental health [57]. The risk to humans further exists especially when similar antimicrobial is used in both animals and humans, or there is presence of cross resistance between antimicrobial used in human and veterinary practice. Using antimicrobials that are also used in human medicine for growth promotion is especially conducive to AMR because exposure of many animals to low dosages makes resistance more likely to emerge [34].

For some antimicrobials, there is development of resistance by bacteria through plasmid-mediated transferable resistance [58]. The minimum inhibitory concentrations (MIC) for a target pathogen might be considerably different from those of commensals, and thus, the resistance gene in commensals may be selected and transferred to humans and then to human pathogens leading to development of AMR [59]. Despite the fact that the exchange of genetic materials and the short generation time of organism contributed to the development of AMR by many bacteria [60], some drugs such as penicillin still retains excellent activity on certain organism (e.g., *Streptococcus agalactiae*) after about 6 decades of usage [61].

AMR development can often be caused by inhibition of specific antimicrobial pathways such as cell wall synthesis, nucleic acid synthesis, ribosome function, protein synthesis, foliate metabolism, and cell membrane function by the organism [62–64]. The various steps involved in the production, distribution, prescription, dispensing, and finally consumption of the drug by human patient or its use in animal production often contributed to the emergence of AMR especially when there is imprudent or irresponsible practice along the supply chain [65]. Part of veterinary medical education is to understand how antimicrobials affect microorganisms, and how they can be used responsibly to protect human and animal health [66]. In food production systems, veterinarians are on the frontline when it comes to keeping nation's food supply safe. Advances in animal health care and management have greatly improved food safety over the years and have reduced the need for antimicrobials in food production systems [67]. Nevertheless,

#### *Veterinary Pharmaceuticals and Antimicrobial Resistance in Developing Countries DOI: http://dx.doi.org/10.5772/intechopen.84888*

antimicrobials are an important part of the veterinarian's toolkit, and so veterinarians are aware that they should be used judiciously and in the best interest of animal and public health [66]. More importantly in the development of AMR is the quality of antimicrobials. Though difficult to implement, it has been suggested that incidence of microbial resistance can be reduced if the antimicrobials that are used in human health are not used in veterinary practice [68]. Moreover, the practices of mass treatment of all animals in a group when only one animal is sick (metaphylaxis) as well as the treatment of all animals when they are exposed to conditions that can make them likely to be ill (prophylaxis) will result in an increased antimicrobial use and as such would encourage the development of resistance [69].

Although the development of animal-related AMR is associated with the quality and quantity of antimicrobial usage in veterinary practice, there are other underlining factors that can influence AMR development:

