Public health and livestock: Emerging diseases in food animals

Despite public health and veterinary public health improvements within the past century, human and animal populations remain vulnerable to health threats caused by infectious diseases. Noticeably, the rate of emerging infectious diseases is increasing (one new emerging or re-emerging disease every eight months). Meanwhile, many endemic diseases have increased in incidence. Out of 1,400 microbes that could cause human infections, more than 60% are also pathogenic for wild or domestic animals (OIE, 2012). These zoonotic agents cause 75% of human emerging infections (OIE, 2012). Since they can be contagious to humans or compromise the food safety, the infectious diseases of animals represent a direct public health issue (OIE, 2012). They also carry an indirect threat since they account for the majority of the 20% losses that affect the livestock sector at the production level and since they could severely hamper the animal traction resources that are needed to produce or transport goods. These losses raise an issue of food security to sustain an increasing demand for proteins of animal origin. By 2020, the livestock sector is expected to represent 50% of the agriculture outputs in value. In developing countries, uncontrolled re-emergence of infectious diseases threatens the main asset of families, thus preventing them to escape from poverty. Additionally, the animal morbidity and mortality generated by infections represent an unjustified emission of greenhouse gases, thus raising an environmental issue. In a growing number of countries, infections are also perceived as a primary concern for animal welfare. The rapid pace of infection emergence is not only connected to more suitable conditions for pathogen appearance and spreading, it is also linked to improved methods and technologies for surveillance, pathogen detection, and identification. There are all kinds of pathogen agents of concern: prion, viruses, bacteria, and mono-cellular and pluri-cellular parasites. Several drivers of infectious diseases have been identified, many of which are of anthropogenic origin: i) Indeed, the role of the expansion and intensification of animal agriculture has been pointed out. Changes in nutritional and agricultural practices, associated to the second livestock revolution (1980s through 1990s), have led to intensive production systems, the frequent use of antimicrobial agents, high densities of animals with suboptimal husbandry conditions, and a decline in genetic diversity. ii) The ongoing global change and the resulting climate-driven environmental change, as well as natural disasters, have introduced ecological perturbations and flux shifts into finely tuned ecosystems consisting, for example, in modified interactions between pathogen vectors and hosts. iii) The population growth, associated with a facilitated access to travel means, has a strong impact. Socio-economical determinants such as political instability and the resulting migrations should be emphasized. iv) Fast and large-range trade of animal and food products have a major influence. Various kinds of changes in food-processing practices were also strongly influential. v) Several shifts in land use should be mentioned such as: accelerated urbanization, deforestation, and the encroachment on wildlife with extensive and closer contacts among humans, livestock animals, and wildlife. Species barriers crossing often occur at ecological interfaces. vi) Finally, it should be stressed that countries where a capacity breakdown occurs in the domains of public health and animal health management, become a weak link in the global effort to prevent, detect, and respond to disease outbreaks. Moreover, poor socio-economic conditions are generally associated with closer contacts between humans and animals, as well as greater exposure to vectors, thus increasing the risk of disease emergence in these countries.