Seroprevalence of six reproductive pathogens in European wild boar (Sus scrofa) from Spain: The effect on wild boar female reproductive performance

Abstract

We studied the seroprevalence of six reproductive pathogens in Spanish hunter-harvested wild boar females. The sample was representative of the hunting harvest in the studied hunting estates. Mean antibody prevalences were: 60.6 ± 0.06% for Aujeszky's disease virus (ADV), 56.6 ± 0.09% for porcine parvovirus (PPV), 51.8 ± 0.06% for porcine circovirus type 2 (PCV2), 29.7 ± 0.09% for Brucella spp. and 36.3 ± 0.1% for Toxoplasma gondii. We did not detect antibodies against porcine reproductive and respiratory syndrome virus (PRRSv). ADV seroprevalence was associated with PPV and PCV2 seroprevalence in Spanish wild boar females. Ovulation rate in the studied wild boar females was 4.41 ± 0.16 (n = 120), mean litter size was 3.91 ± 0.16 (n = 82) and the partial resorption index 0.92 ± 0.17 (n = 66). Ovulation rate and litter size were statistically associated with age. T. gondii seroprevalence was negatively related to ovulation rate and partial resorption index. Wild boars from managed fenced estates had antibodies against more pathogens than wild boars from open estates. Potential relations between management of wild boar populations and exposure of individuals to different reproductive pathogens are discussed.

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.