1.1.1 Therapeutic uses of antimicrobials in animals

‘Therapeutic use means the administration of an antimicrobial agent to an individual or group of animals to treat, control or prevent infectious disease’

(WOAH, 2018a).

Even with good husbandry and biosecurity practices, many diseases that afflict animals require antimicrobials. Decisions on whether to use antimicrobials in sick animals are often more complicated than they are for sick people. Aside from the ethical and cultural implications of not treating sick animals, the economic value of animals to the farmer and the community often drives decisions to use antimicrobials.

Definitions for therapeutic uses of antimicrobials in animals are provided in Table 1.

Term Definition
Treatment

Administration of an antimicrobial to an individual or a group of animals showing clinical signs of an infectious disease.

Situations where antimicrobials may be used in clinically sick animals are many and varied. Common bacterial diseases in food animals that often require antimicrobials include mastitis, foot rot, and reproductive infections such as metritis.
Control

Administration of an antimicrobial to a group of animals including sick and healthy animals (presumed to be infected), to minimise or resolve clinical signs and to prevent further spread of the disease.

Situations where antimicrobials may be used for control include bacterial respiratory diseases in intensively reared animals, post-weaning diarrhoea, erysipelas in pigs.

The strategy of control can involve metaphylactic use or metaphylaxis, which involves treating the whole group of animals and not just the infected or those at high risk. This use is common in aquaculture systems, where a whole pond is medicated (commonly adding antimicrobials to the feed), even if only some fish are showing symptoms, or when applying medication to drinking water in poultry pens, and only few birds show symptoms.
Prevention

Administration of an antimicrobial to an individual or a group of animals at risk of acquiring a specific infection or in a particular situation where infectious disease is likely to occur if the drug is not administered.

Prevention is sometimes called prophylaxis or preventative use.

Situations where antimicrobials may be used when an animal is not currently diseased include giving an antimicrobial after surgery or traumatic injury, when animals are under a lot of stress such as being raised in a feedlot to prevent respiratory disease or foot infections, dry cow therapy for dairy animals, or to prevent liver abscesses caused by high-grain diets.
Table 1 Definitions of the therapeutic uses of antimicrobials in animals. (Source: Terrestrial Animal Health Code. Chapter 6.9. Monitoring of the quantities and usage of antimicrobial agents used in food-producing species (WOAH, 2018a))

Ideally, antimicrobials should only be prescribed for therapeutic purposes by a veterinarian or a trained person (e.g, veterinary paraprofessional) under the supervision of a veterinarian, according to national laws (WOAH, 2018a).

However, the reality in many low- and middle-income countries (LMICs) is that there is scarce access to veterinarians or veterinary paraprofessionals, providing a limited service to farming communities. This, coupled with weak regulatory controls, means people often access antimicrobials from other sources (e.g. pharmacies, feed mills, rural chemical stores) with limited government oversight. We will discuss this issue in more detail later in the course.

1 Use of antimicrobials in animal health

1.1.2 Non-therapeutic uses of antimicrobials in animals