Changing patterns of disease affecting pigs: Porcine Reproductive and Respiratory Syndrome (PRRS) and Porcine Epidemic Diarrhoea (PED)

Any disease in humans or animals has its own unique epidemiological pattern, that is, behaviour (occurrence, disappearance, re-occurrence as well as distribution of outbreaks and cases in space and time) (Blaha, 2000). The epidemiological behaviour is determined by the biological properties of the causative agent (such as pathogenicity and infectivity), the characteristics of the pathogen-host interaction (such as immune response, shedding and transmission pattern) and socio-economic conditions (such as structure of the industry, animal movements and herd size) (Thrusfield, 2005). The pig industry, like any other livestock sector, is not immune to disease, and recent examples of outbreaks that have affected the pig industry are the African Swine Fever outbreaks in Eastern European countries (Gogin et al., 2013), the Porcine Epidemic Diarrhoea (PED) outbreak in the United States (US) in 2013 (Stevenson et al., 2013) and the Porcine Circovirus Associated Disease (PCVAD) outbreak in Ontario, Canada, in 2004 (Carman et al., 2008). Some of these outbreaks have led to epidemics and then went on to become endemic in some countries, changing their disease epidemiological behaviour over time and space. Overall, in the last three decades, the pig industry worldwide has experienced several major disease epidemics – all caused by viruses: Swine Influenza, Porcine Circovirus (PCV), Porcine Reproductive and Respiratory Syndrome virus (PRRSv) and Porcine Epidemic Diarrhoea virus (PEDv). Some of these viruses are not host-specific and can spread to other hosts, including humans (H1N1 influenza); others are highly host-specific (PRRSv and PEDv). The latter agents also share remarkable features exhibiting rapid rates of mutation and appear to have been associated with pigs for years to decades before highly pathogenic disease syndromes were manifested (Davies, 2015). In this chapter we focus on these two agents (PRRSv and PEDv) due to their importance in pig production worldwide and their evolution over the years. We also discuss the agent, transmission, clinical presentation and evolution and spread of these two viruses in the pig population both worldwide, and more specifically, the United Kingdom, in detail. This will provide readers with an overview of the complexity of these two agents and how that influences their clinical presentation and evolution over time and space. However, this is not an exhaustive literature review and as these agents are two of the most widely studied viruses, current and future research may update some of the findings reported here. As PED outbreaks have only been seen quite recently in the Western world, the US epidemic of 2013 and the current situation in Europe (including surveillance) are summarised in more detail.

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