Venereal transmission of pseudorabies viruses indigenous to feral swine

Between 1995 and 1998, we designed a series of studies in which we attempted to determine the main routes of transmission involved in the natural infection of pseudorabies virus (PRV) indigenous to free-ranging feral swine (Sus scrofa). Naturally infected feral sows transmitted the infection to uninfected feral boars, with which they had been commingled for a 6-wk period. Pseudorabies virus was isolated from boar preputial swabs, but not from nasal swabs. Three of the same PRV-infected feral sows did not transmit the infection to domestic boars during a 16 wk commingling period, despite the fact that they became pregnant. Feral boars, naturally infected with PRV transmitted the virus to domestic gilts while penned together during 6 wk. Pseudorabies virus was isolated from vaginal swabs, but not from nasal swabs of gilts, after 2 and 3 wk of commingling. When the same infected boars were commingled with either feral or domestic boars for 13 wk, PRV transmission did not occur. None of the exposed boars developed neutralizing antibodies or yielded virus from their preputial or nasal swabs. Our results indicate that PRV indigenous to feral swine is preferentially transmitted to feral or domestic swine of the opposite sex by the venereal route. This mode of transmission differs from that seen in the natural transmission of PRV prevalent in domestic swine, where contaminated secretions, excretions and aerosols are responsible for the spread of the virus. Based on these results, we feel that as long as feral swine do not come into direct contact with domestic swine, PRV-infected feral swine probably pose only a limited risk to the success of the National Pseudorabies Eradication Program. The fact that PRV is usually transmitted from feral to domestic swine at the time of mating would indicate that the isolation of domestic herds by the use of a "double fence," should be adequate protection against reinfection with PRV.     

Increased prevalence of Brucella suis and pseudorabies virus antibodies in adults of an isolated feral swine population in coastal South Carolina

Two hundred twenty seven adult (> 8 mo) feral swine (Sus scrofa) trapped from April through July 1999 at three locations on a coastal South Carolina (USA) peninsula with restricted ingress and egress were tested for Brucella suis and pseudorabies virus (PRV) antibodies. Approximately 44% of the animals tested positive for B. suis antibodies and 61% tested positive for antibodies to PRV. Previous surveys (1976 and 1992) of feral swine at the same location with similar methods indicated lower seroprevalences (28% and 18% for B. suis and 0% and 19% for PRV). We also found 39% of feral swine seropositive (n = 179) for Trichinella spiralis and 49% seropositive (n = 181) for Toxoplasma gondii. Results of repeated sampling demonstrated that seroprevalence to pathogens can increase with time in an isolated, unhunted population of feral swine suggesting an increased risk to local domestic livestock and potentially to human health.     

A serosurvey for Brucella suis, classical swine fever virus, porcine circovirus type 2, and pseudorabies virus in feral swine (Sus scrofa) of eastern North Carolina

As feral swine (Sus scrofa) populations expand their range and the opportunity for feral swine hunting increases, there is increased potential for disease transmission that may impact humans, domestic swine, and wildlife. From September 2007 to March 2010, in 13 North Carolina, USA, counties and at Howell Woods Environmental Learning Center, we conducted a serosurvey of feral swine for Brucella suis, pseudorabies virus (PRV), and classical swine fever virus (CSFV); the samples obtained at Howell Woods also were tested for porcine circovirus type 2 (PCV-2). Feral swine serum was collected from trapped and hunter-harvested swine. For the first time since 2004 when screening began, we detected B. suis antibodies in 9% (9/98) of feral swine at Howell Woods and <1% (1/415) in the North Carolina counties. Also, at Howell Woods, we detected PCV-2 antibodies in 59% (53/90) of feral swine. We did not detect antibodies to PRV (n=512) or CSFV (n=307) at Howell Woods or the 13 North Carolina counties, respectively. The detection of feral swine with antibodies to B. suis for the first time in North Carolina warrants increased surveillance of the feral swine population to evaluate speed of disease spread and to establish the potential risk to commercial swine and humans.     

Seroepidemiologic survey for Chlamydia suis in wild boar (Sus scrofa) populations in Italy

We used serology to estimate the prevalence of exposure to chlamydiae in Italian populations of wild boars (Sus scrofa). Sera from 173 hunter-killed wild boars harvested during the 2006-2009 hunting seasons in three Italian regions were tested for antibodies to Chlamydia suis, Chlamydophila pecorum, Chlamydophila abortus, and Chlamydophila psittaci by the microimmunofluorescence test. Antibody titers to chlamydiae ≥ 1:32 were detected in 110 of the 173 samples tested (63.6%). Specific reactivity could be assessed only in 44 sera with antibody titers to C. suis that were two- to threefold higher than antibody titers against the other chlamydial species; the other 66 sera had similar reactivity against all the chlamydia species tested. Antibody to C. suis was detected in sera from wild boar populations with rare or no known contact with domestic pigs. These results suggest that the wild boar could be a chlamydia reservoir and may acquire chlamydiae independent of contacts with the domestic pig.     

Prevalence of Streptococcus suis genotypes in wild boars of Northwestern Germany

Invasive serotype 2 (cps2+) strains of Streptococcus suis cause meningitis in pigs and humans. Four case reports of S. suis meningitis in hunters suggest transmission of S. suis through the butchering of wild boars. Therefore, the objective of this study was to investigate the prevalence of potentially human-pathogenic S. suis strains in wild boars. S. suis was isolated from 92% of all tested tonsils (n=200) from wild boars. A total of 244 S. suis isolates were genotyped using PCR assays for the detection of serotype-specific genes, the hemolysin gene sly, and the virulence-associated genes mrp and epf. The prevalence of the cps2+ genotype among strains from wild boars was comparable to that of control strains from domestic pig carriers. Ninety-five percent of the cps2+ wild boar strains were positive for mrp, sly, and epf*, the large variant of epf. Interestingly, epf* was significantly more frequently detected in cps2+ strains from wild boars than in those from domestic pigs; epf* is also typically found in European S. suis isolates from humans, including a meningitis isolate from a German hunter. These results suggest that at least 10% of wild boars in Northwestern Germany carry S. suis strains that are potentially virulent in humans. Additional amplified fragment length polymorphism analysis supported this hypothesis, since homogeneous clustering of the epf* mrp+ sly+ cps2+ strains from wild boars with invasive human and porcine strains was observed.     

Making Contact: Rooting Out the Potential for Exposure of Commercial Production Swine Facilities to Feral Swine in North Carolina

Despite North Carolina’s long history with feral swine, populations were low or absent in eastern counties until the 1990s. Feral swine populations have since grown in these counties which also contain a high density of commercial production swine (CPS) facilities. Sixteen of the highest swine producing U.S. counties also populated with feral swine are in North Carolina. Disconcertingly, since 2009, positive tests for exposure to swine brucellosis or pseudorabies virus have been found for feral swine. We surveyed 120 CSP facilities across four eastern counties to document the level and perception of feral swine activity around CSP facilities and to identify disease transmission potential to commercial stock. Nearly all facility operators (97%) recognized feral swine were in their counties. Far fewer said they had feral swine activity nearby (18%). Our inspections found higher presence than perceived with feral swine sign at 19% of facilities where operators said they had never observed feral swine or their sign. Nearly 90% expressed concern about feral to domestic disease transmission, yet only two facilities had grain bins or feeders fenced against wildlife access. Due to increasing feral swine populations, recent evidence of disease in feral populations, the importance of swine production to North Carolina’s economy and the national pork industry, and potential for feral-domestic contact, we believe feral swine pose an increasing disease transmission threat warranting a stringent look at biosecurity and feral swine management at North Carolina CPS facilities.     

Mixed ancestry from wild and domestic lineages contributes to the rapid expansion of invasive feral swine

Invasive alien species are a significant threat to both economic and ecological systems. Identifying the processes that give rise to invasive populations is essential for implementing effective control strategies. We conducted an ancestry analysis of invasive feral swine (Sus scrofa, Linnaeus, 1758), a highly destructive ungulate that is widely distributed throughout the contiguous United States, to describe introduction pathways, sources of newly emergent populations and processes contributing to an ongoing invasion. Comparisons of high‐density single nucleotide polymorphism genotypes for 6,566 invasive feral swine to a comprehensive reference set of S. scrofa revealed that the vast majority of feral swine were of mixed ancestry, with dominant genetic associations to Western heritage breeds of domestic pig and European populations of wild boar. Further, the rapid expansion of invasive feral swine over the past 30 years was attributable to secondary introductions from established populations of admixed ancestry as opposed to direct introductions of domestic breeds or wild boar. Spatially widespread genetic associations of invasive feral swine to European wild boar deviated strongly from historical S. scrofa introduction pressure, which was largely restricted to domestic pigs with infrequent, localized wild boar releases. The deviation between historical introduction pressure and contemporary genetic ancestry suggests wild boar‐hybridization may contribute to differential fitness in the environment and heightened invasive potential for individuals of admixed domestic pig–wild boar ancestry.     

Mitochondrial haplotypes of European wild boars with 2n = 36 are closely related to those of European domestic pigs with 2n = 38

Wild boars from Western Europe have a 2n = 36 karyotype, in contrast to a karyotype of 2n = 38 in wild boars from Central Europe and Asia and in all domestic pigs. The phylogenetic status of this wild boar population is unclear, and it is not known if it has contributed to pig domestication. We have now sequenced the mtDNA control region from 30 European wild boars (22 with a confirmed 2n = 36 karyotype) and six Asian wild boars (two Hainan and four Dongbei wild boars) to address this question. The results revealed a close genetic relationship between mtDNA haplotypes from wild boars with 2n = 36 to those from domestic pigs with 2n = 38. Thus, we cannot exclude the possibility that wild boars with 2n = 36 may have contributed to pig domestication despite the karyotype difference. One of the European wild boars carried an Asian mtDNA haplotype, and this most likely reflects gene flow from domestic pigs to European wild boars. However, this gene flow does not appear to be extensive because the frequency of Asian haplotypes detected among European wild boars (c. 3%) were 10-fold lower than among European domestic pigs (c. 30%). Previous studies of mtDNA haplotypes have indicated that pig populations in Europe and Asia have experienced a population expansion, but it is not clear if the expansion occurred before or after domestication. The results of the present study are consistent with an expansion that primarily occurred prior to domestication because the mtDNA haplotypes found in European and Asian wild boars did not form their own clusters but were intermingled with haplotypes found in domestic pigs, indicating that they originated from the same population expansion.     

Prevalence of infection and genetic diversity of porcine circovirus type 2 (PCV2) in wild boar (Sus scrofa) in Poland

Porcine circovirus type 2 (PCV2) is a widespread, important pathogen of domestic swine and the causative agent of postweaning multisystemic wasting syndrome and other diseases and conditions referred to as "porcine circovirus diseases." Specific antibodies and DNA to PCV2 have also been detected in European wild boars and North American feral pigs. We collected 312 tonsil samples from wild boars shot in 13 of 16 districts of Poland, and tested them for PCV2 DNA using a real-time PCR. We detected PCV2 DNA in 75.6% of tested tonsils, and in particular, in 60% of samples from the 2006-07 season, and 91% from 2007-08. The phylogenetic analysis that included 12 PCV2 sequences from wild boars revealed that they belonged to two genetic clusters, PCV2b and PCV2a. We present data on prevalence of PCV2 in Polish wild boars and for the first time report the PCV2a genotype in Poland.     

The wild boar of Egypt]

The wild boar, Sus scrofa, is not a typical member of the Egyptian wild fauna, although it appears to have lived in the Nile Delta and other suitable regions in the north of the country. However, historic populations were probably of mixed origin, including feral domestic pigs. It is incorrect, as is sometimes still done, to include the wild boar in the iconographic bestiary of Ancient Egypt and assume that the domestic pigs of Ancient Egypt derive from local wild boars.     

High domestic pig contribution to the local gene pool of free-living European wild boar: a case study in Poland

Rates of hybridization between wild and domesticated animals appear to be increasing worldwide. Recent results suggest that genetic introgression from domestic swine into European wild boar is much more common in local populations than expected, based on pan-European studies. Thus, we screened the genetic purity of 265 free-living wild boars from two hunting areas in Poland by genotyping the melanocortin receptor 1 gene (MC1R) for polymorphism. Unexpectedly, high numbers of individuals with domestic genes (24%) were identified. This suggests that mixed ancestry may be common in Polish wild boar. Among admixed individuals, backcrosses with domestic pig and/or introgressed wild boars were detected (2%). Multiple commercial domestic pig breeds are possibly involved in the introgression observed in the study populations. In addition, the absence of significant differences in the frequency of wild-type allele among two hunting areas suggests high dispersal of individuals and gene flow among populations. We conclude that further study is needed to better understand the mechanisms and sources of introgression in wild boars in Poland.     

A genetic method to distinguish crossbred Inobuta from Japanese wild boars

To distinguish pig-wild boar crossbred Inobuta from Japanese wild boar populations, a genetic method by using mitochondrial DNA (mtDNA) haplotypes and the nuclear glucosephosphate isomerase-processed pseudogene (GPIP) was developed. Sixteen mtDNA haplotypes from 152 wild boars from Kyushu, Shikoku and Honshu islands of Japan were distinct from those from Asian and European domestic pigs. Five alleles of GPIP were classified into two groups: 1). alleles GPIP*1, GPIP*3 and GPIP*3a from Japanese wild boars, Asian wild boars and domestic pigs; 2). alleles GPIP*4 and GPIP*4a from European wild boars and domestic pigs. An extensive genetic survey was done to distinguish the crossbred Inobuta from 60 wild boars hunted on Tsushima Island, Goto Islands, and Nagasaki and Ooita Prefectures. The mtDNA haplotypes from the 60 samples showed Japanese wild boars, but four wild boar samples from Nagasaki Prefecture had the European GPIP allele, GPIP*4. These results showed that nuclear DNA polymorphism analysis is useful, in addition to mtDNA haplotype assay, to detect "Inobuta" having the European genotype from Japanese wild boar populations.     

Renal structural flexibility in response to environmental water stress in feral hogs

Several morphological characteristics of the kidney were studied to determine the degree of acclimatization that may occur in three groups of feral hogs raised under different environmental conditions. Two groups of hogs were living in the wild, while another was raised in captivity for three generations and was directly descended from one of the wild-living groups. The two groups of wild hogs were living under two different types of water stress conditions. One group experienced periodic drought, and the other ate a high salt diet. The captive hogs were given food and water ad libitum. The captive-raised hogs had significantly lower relative medullary thickness (RMT) and relative medullary area (RMA) values (RMT of 2.35; RMA of 0.35) than either group of hogs living in the wild (RMT of 2.70 and 2.69; RMA of 0.41 and 0.44). Since the feral hogs living in the wild were exposed to a higher degree of water stress than the captive-raised hogs, it was concluded that the differences in observed kidney structure were due to acclimatization.     

Geographic population structure and sequence divergence in the mitochondrial DNA control region of the Japanese wild boar (Sus scrofa leucomystax), with reference to those of domestic pigs

Mitochondrial DNA (mtDNA) control regions from 40 Japanese wild boars were examined by direct sequencing after amplification by PCR. From the DNA sequences obtained, we found eight haplotypes, whose differences arose via transitions. The geographical distribution of these different haplotypes indicated that wild boar populations inhabited limited areas and that there was some restricted gene flow between local populations. Eight mtDNA haplotypes from Eastern and Western domestic pigs and the Ryukyu wild boar were also analyzed as references to those from Japanese wild boars. The cluster analyses of the control-region sequences showed that those from Japanese wild boards belong to the Asian type as do those from Eastern domestic pigs and the Ryukyu wild boar, which differed from the European type (Western domestic pigs).     

Genetic evidence for introgression between domestic pigs and wild boars (Sus scrofa) in Belgium and Luxembourg: a comparative approach with multiple marker systems

Hybridization between wild species and their domestic relatives can be an important conservation and management problem. Genetic purity of the wild species is desirable per se and the phenomenon can have unpredictable evolutionary consequences. Declining European wild boar populations were frequently restocked with farmed wild boars that sometimes had been crossed with domestic pigs. We used simple polymerase chain reaction‐based diagnostic tests to detect the presence of mitochondrial DNA and coat colour alleles of domestic origin in wild boars from Belgium, Luxembourg, and western Germany. Microsatellite genotypes were used to test for genetic admixture between the wild boars and domestic pigs. Although almost one‐third of all Luxembourg wild boars carried Asian mitochondrial DNA haplotypes originating from domestic pigs, microsatellite‐based clustering only identified four putatively admixed individuals in Luxembourg. By contrast, clustering identified wild boar × domestic hybrids in most sampling locations in Belgium. We interpret these results as evidence of releases of hybrid captive‐reared wild boars. Our results emphasize the need (if working with classical markers) to use different systems to obtain an understanding as to whether hybridization between wild and domestic relatives might have affected the genetic make‐up of a local population. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 104–115.     

Trichinella spiralis in an agricultural ecosystem. III. Epidemiological investigations of Trichinella spiralis in resident wild and feral animals

As part of a larger epidemiological study examining the transmission of Trichinella spiralis in an agricultural ecosystem, resident wild and feral animals were trapped to determine the extent of their involvement in the natural, on-farm cycling of the parasite among swine. During a 21-mo-study, seven of 15 skunks (Mephitis mephitis), one of three opossums (Didelphis virginiana), two of two feral domestic cats and a raccoon (Procyon lotor) were found to be infected, while five shrews (Blarina brevicauda) and 18 deer mice (Peromyscus spp.) were uninfected. Most of the former hosts probably became infected by scavenging dead infected swine or rats (Rattus norvegicus). However, infections obtained through predation of living rats, particularly with regard to the cats, cannot be excluded. Our observations do not suggest that there was transmission of T. spiralis from the wild animals to swine. Therefore, transmission of T. spiralis appeared to occur only from the farm's swine and rats to the associated wild and feral animals.     

Prevalence of antibodies to selected viral pathogens in wild boars (Sus scrofa) in Croatia in 2005-06 and 2009-10

We determined prevalence of antibody to selected viral pathogens important for domestic pigs and livestock in 556 wild boar (Sus scrofa) sera collected during 2005-06 and 2009-10 in four counties in Croatia. These counties account for an important part of the Croatian commercial pig production and have a high density of wild boars. Samples were tested for antibodies to porcine parvovirus (PPV), Aujeszky's disease virus (ADV), porcine circovirus type 2 (PCV2), swine influenza virus, porcine respiratory and reproductive syndrome virus (PRRSV), porcine respiratory coronavirus (PRCV), transmissible gastroenteritis virus, and swine vesicular disease virus (SVDV). Antibodies to all of the infectious pathogens except SVDV were detected. There was a statistically significant difference in prevalence between the two periods for PPV, ADV, PCV2, PRRSV, and PRCV, with a higher prevalence of PPV and ADV in the 2009-10 period (P<0.05). During the same period, the prevalence of PCV2, PRRSV, and PRCV was lower (P<0.05). Our results provide information on the current disease exposure and health status of wild boars in Croatia and suggest that wild boars may act as a reservoir for several pathogens and a source of infection for domestic pigs and other livestock as well as humans, especially for ADV.     

Serologic evidence of Venezuelan equine encephalitis in some wild and domestic populations of southern Texas.

More than 2,500 sera from approximately 30 wild and domestic species in southern Texas were tested for neutralizing antibodies to Venezuelan equine encephalitis (VEE). Virus isolations were also attempted from blood and tissue samples of many of the wild specimens. VEE neutralizing substances were present in a variety of species collected prior to the 1971 epizootic, suggesting that VEE was present and perhaps enzootic in this area before the recent epizootic. Serologic results of this study suggest that deer (Odocoileus virginianus) and feral swine (Sus scrofa) may serve as good indicators or sentinels of VEE transmission. The reservoir of VEE was not established, but results of the study suggest that a number of species or a combination of animal host populations including deer, feral swine, and peccaries (Pecari angulatus) may be involved in the eizootiologyof VEE in southern Texas.     

Variation in mitochondrial DNA of Vietnamese pigs: relationships with Asian domestic pigs and Ryukyu wild boars

Mitochondrial DNA (mtDNA) sequences (574 bp) of 30 Vietnamese pigs (large and small) were examined and compared with those of 61 haplotypes from wild boars and domestic pigs from various locations in Asia. The large Vietnamese pigs had genetic links to Ryukyu wild boars in southern Japan. The small Vietnamese pigs were closely related to other East Asian domestic pigs. These results indicate that Vietnamese pigs are genetically diverse and may be descendents of wild and domestic pigs from other regions of Asia.