Seroprevalence of six reproductive pathogens in European wild boar (Sus scrofa) from Spain: The effect on wild boar female reproductive performance
Introduction
Populations of the European wild boar (Sus scrofa) have largely increased in Spain during the past 30 years [1], [2]. In terms of hunting harvest, the Iberian red deer (Cervus elaphus hispanicus) and European wild boar are at present the most important big game species in Spain. Due to its economic relevance, many of the Spanish wild boar populations are subject to management in order to increase hunting harvest. Practices, such as high-wire fencing, artificial feeding and restocking, are becoming more common, while sanitary measures are not implemented to match this development. As a result, elevated boar densities are found that have already been shown to imply consequences for the control of infectious diseases [3], [4], [5], [6].
The European wild boar is a polygynous species with an autumnal breeding season influenced by environmental conditions. The Spanish wild boar breeding season occurs between September and December, with a main peak in October [7]. Farrowing takes place after 120 days in January–March, although some boars farrow in August–September.
The domestic pig and wild boar share common pathogens [8], [9]. The European wild boar could constitute a disease reservoir for the domestic pig [10]. Some of these pathogens produce reproductive failure in pregnant sows, reducing litter size or killing the whole litter. Return to estrus, resorption, mummification, abortion and fetal death are described in S. scrofa as the main features of diseases that affect reproduction. However, the knowledge about the epidemiology of reproductive diseases in wild boars is still limited.
The most relevant viral diseases that produce reproductive failure in domestic pigs are porcine reproductive and respiratory syndrome (PRRS) and porcine parvovirosis (PPV) [11]. Other pathogens affect the reproductive biology of suids, including viral, bacterial and parasitic agents. Aujeszky's disease virus (ADV) or pseudorabies virus infects the domestic pig, wild boar and feral pig. Although Aujeszky's disease clinical signs are primarily nervous and respiratory, the virus has a tropism for the reproductive tract and causes reproductive losses in pregnant domestic sows [12]. PPV is an ubiquitous and resistant virus with a worldwide distribution. While in immune adult animals reproductive effects are generally not detected, the tropism of the virus for the reproductive tract may lead to mummified fetuses and resorptions in naïve females, especially in their first pregnancy [11]. Porcine circovirus type 2 (PCV2) is considered the cause for postweaning multisystemic wasting syndrome (PMWS) [13]. A reproductive effect of PCV2 has been described in domestic sows [14], with abortion, infected stillborn and non-viable neonate piglets. Porcine reproductive and respiratory syndrome virus (PRRSv) is also widely distributed among domestic pigs and has been associated with reproductive failure in domestic gilts. PRRSv infection can cause resorption, late-term abortions, stillborn and weak piglets in pregnant sows [15]. Brucella is a worldwide distributed bacterial genus which produces reproductive failure in mammals [16]. Porcine brucellosis in Europe is mainly caused by Brucella suis biovar 2 while the disease is caused by biovars 1 and 3 in Asia and America [17], [18], [19], [20]. Brucellosis due to B. suis biovar 2 has been considered a re-emerging disease in domestic pigs in Europe, caused by spillover from the wild boar [16]. B. suis biovar 2 has been isolated from European wild boars [10], [21] in which no clinical disease was observed. Finally, Toxoplasma gondii is a pathogenic protozoan that infects a wide range of hosts, causing reproductive failure in females which contract the parasite for the first time during pregnancy. Its implication in abortion in domestic sows, however, is uncommon [22]. To our knowledge, few serological studies exist on the prevalence of antibodies against T. gondii in the wild boar [23], [24], [25].
Our goals were to describe risk factors that explain the presence of antibodies against these six significant pathogens among wild boars in Spain and to determine, by means of a correlational study, the potential influence that these diseases may have on reproductive parameters in wild boar females.
Section snippets
Sampling sites and field necropsies
Data were collected from hunter-harvested wild boars in 54 Spanish hunting estates during the hunting seasons from 2000 to 2003. The sampling effort was biased towards the main hunting season (October–February).
Every animal was morphometrically characterized, weighed and necropsied in detail. We determined the age of the wild boars on the basis of tooth eruption patterns [26]. Wild boars between 7 and 12 months were classified as juveniles, those between 12 and 24 months as sub-adults, and
Results
Reproductive parameters and antibody prevalences against the tested pathogens according to age class and estate type, as well as the significance of their variations, are shown in Table 1. No PRRSv antibodies were detected in any of the 123 sera analysed.
Discussion
Many pathogens are able to infect both, wild and domestic animals, and may be transmitted between them, which has been demonstrated specifically for the wild boar and the domestic pig [36]. Some of the diseases suffered by swine have effects on the reproductive function, leading to important economic losses in pig production [37]. In this study, we tested the seroprevalence of antibodies against some of the most significant pathogens known to be responsible for reproductive failure in domestic
Acknowledgements
The authors wish to thank Paqui Talavera, Pelayo Acevedo, Isabel G. Fernández de Mera, M. Paz Martín and Mónica Pérez for their help in field and laboratory work. Fran Ruiz-Fons has a grant of the “Ministerio de Educación y Ciencia”. The study was supported by projects AGL2001-3947, Ministerio de Ciencia y Tecnología and FEDER and PREG-04-004, “Junta de Comunidades de Castilla-La Mancha”. This is a contribution to the agreements between Yolanda Fierro and UCLM, and between CSIC and Principado
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