Potential sites of virus latency associated with indigenous pseudorabies viruses in feral swine

Free-ranging feral swine (Sus scrofa) are known to be present in at least 32 states of the USA and are continuously expanding their range. Infection with pseudorabies virus (PRV) occurs in feral swine and the primary route of transmission in free-living conditions seems to be venereal. Between 1995 and 1999, naturally infected feral swine and experimentally infected hybrid progeny of feral and domestic swine, were kept in isolation and evaluated for occurrence of latent PRV indigenous to feral swine in sacral and trigeminal ganglia and tonsil. Sacral ganglia were shown, by polymerase chain reaction (PCR) amplification of the thymidine kinase (TK) gene of PRV, to be the most frequent sites of latency of PRV. Nine (56%) of 16 sacral ganglia, seven (44%) of 16 trigeminal ganglia, and five (39%) of 13 tonsils from naturally infected feral swine were positive for PCR amplification of TK sequences of PRV. These tissues were negative for PRV when viral isolation was attempted in Vero cells. DNA sequencing of cloned TK fragments from the sacral ganglia of two feral swine, showed only one nucleotide difference between the two fragments and extensive sequence homology to fragment sequences from various domestic swine PRV strains from China, Northern Ireland, and the USA. The hybrid feral domestic swine, experimentally inoculated with an indigenous feral swine PRV isolate by either the genital or respiratory route, acquired the infection but showed no clinical signs of pseudorabies. Virus inoculated into either the genital or respiratory tract could, at times, be isolated from both these sites. The most common latency sites were the sacral ganglia, regardless of the route and dose of infection in these experimentally infected hybrids. Nine of 10 sacral ganglia, six of 10 trigeminal ganglia, and three of 10 tonsils were positive for PCR amplification of TK sequences. No virus was isolated from these tissues in Vero cells. The demonstration of the sacral ganglia as the most common sites of latency of pseudorabies viruses indigenous to feral swine, supports the hypothesis that these viruses are primarily transmitted venereally, and not by the respiratory route as is common in domestic swine, in which the trigeminal ganglia are the predominant sites of virus latency.     

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.     

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.     

Absence of Mycobacterium bovis in feral swine (Sus scrofa) from the southern Texas border region

Free-ranging wildlife, such as feral swine (Sus scrofa), harbor a variety of diseases that are transmissible to livestock and could negatively impact agricultural production. Information is needed regarding the exposure and infection rates of Mycobacterium bovis and many other diseases and parasites in feral swine occurring in the Texas border region. Our main objective was to determine exposure rates and possible infection rates of M. bovis in feral swine by opportunistically sampling animals from the Texas border region. From June to September 2010, we obtained samples from 396 feral swine and tested 98 samples for M. bovis by histopathology and mycobacteriologic culture. We found no evidence of M. bovis infection. We believe that it is important to periodically and strategically sample feral swine for M. bovis in high-risk areas of the United States because they are capable of becoming reservoirs of the disease.     

Bait Preference of Free-Ranging Feral Swine for Delivery of a Novel Toxicant

Invasive feral swine (Sus scrofa) cause extensive damage to agricultural and wildlife resources throughout the United States. Development of sodium nitrite as a new, orally delivered toxicant is underway to provide an additional tool to curtail growth and expansion of feral swine populations. A micro-encapsulation coating around sodium nitrite is used to minimize detection by feral swine and maximize stability for the reactive molecule. To maximize uptake of this toxicant by feral swine, development a bait matrix is needed to 1) protect the micro-encapsulation coating so that sodium nitrite remains undetectable to feral swine, 2) achieve a high degree of acceptance by feral swine, and 3) be minimally appealing to non-target species. With these purposes, a field evaluation at 88 sites in south-central Texas was conducted using remote cameras to evaluate preferences by feral swine for several oil-based bait matrices including uncolored peanut paste, black-colored peanut paste, and peanut-based slurry mixed onto whole-kernel corn. These placebo baits were compared to a reference food, whole-kernel corn, known to be readily taken by feral swine (i.e., control). The amount of bait consumed by feral swine was also estimated using remote cameras and grid boards at 5 additional sites. On initial exposure, feral swine showed reduced visitations to the uncolored peanut paste and peanut slurry treatments. This reduced visitation subsided by the end of the treatment period, suggesting that feral swine needed time to accept these bait types. The black-colored peanut paste was visited equally to the control throughout the study, and enough of this matrix was consumed to deliver lethal doses of micro-encapsulated sodium nitrite to most feral swine during 1–2 feeding events. None of the treatment matrices reduced visitations by nontarget species, but feral swine dominated visitations for all matrices. It was concluded that black-colored peanut paste achieved satisfactory preference and consumption by feral swine, and no discernable preference by non-target species, compared to the other treatments.     

Influenza exposure in United States feral swine populations

Swine play an important role in the disease ecology of influenza. Having cellular receptors in common with birds and humans, swine provide opportunities for mixed infections and potential for genetic reassortment between avian, human, and porcine influenza. Feral swine populations are rapidly expanding in both numbers and range and are increasingly coming into contact with waterfowl, humans, and agricultural operations. In this study, over 875 feral swine were sampled from six states across the United States for serologic evidence of exposure to influenza. In Oklahoma, Florida, and Missouri, USA, no seropositive feral swine were detected. Seropositive swine were detected in California, Mississippi, and Texas, USA. Antibody prevalences in these states were 1% in Mississippi, 5% in California, and 14.4% in Texas. All seropositive swine were exposed to H3N2 subtype, the predominant subtype currently circulating in domestic swine. The only exceptions were in San Saba County, Texas, where of the 15 seropositive samples, four were positive for H1N1 and seven for both H1N1 and H3N2. In Texas, there was large geographical and temporal variation in antibody prevalence and no obvious connection to domestic swine operations. No evidence of exposure to avian influenza in feral swine was uncovered. From these results it is apparent that influenza in feral swine poses a risk primarily to swine production operations. However, because feral swine share habitat with waterfowl, prey on and scavenge dead and dying birds, are highly mobile, and are increasingly coming into contact with humans, the potential for these animals to become infected with avian or human influenza in addition to swine influenza is a distinct possibility.     

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.     

Prevalence of antibody to Toxoplasma gondii and Trichinella spp. in feral pigs (Sus scrofa) of eastern North Carolina

Feral pigs (Sus scrofa) survive in many climates, reproduce year-round, and are dietary generalists. In the United States, the size and range of the feral pig population has expanded, resulting in greater interaction with humans and domestic swine and increased potential for disease transmission. We conducted a serosurvey in feral pigs from eastern North Carolina to determine exposure to the zoonotic parasites, Toxoplasma gondii and Trichinella spp. Between September 2007 and March 2009, blood serum was collected from 83 feral pigs harvested at Howell Woods Environmental Learning Center, Four Oaks, North Carolina, USA. We used a modified agglutination test to test for T. gondii antibodies and an enzyme-linked immunosorbent assay to test for Trichinella spp. antibodies. The prevalences of antibodies to T. gondii and Trichinella spp. were 27.7% and 13.3%, respectively and 4% (n=3) had antibodies to both agents. We detected an increased risk of T. gondii antibodies with age, whereas the risk of exposure to T. gondii across years and between sexes was similar. In eastern North Carolina, feral pigs have been exposed to T. gondii and Trichinella spp. and may pose a health risk to domestic swine and humans.     

Prevalence and transmission of pseudorabies virus in an isolated population of feral swine

Six hundred sixty-one feral swine (Sus scrofa) from Ossabaw Island, Georgia (USA) were captured, bled, and their sera tested for pseudorabies virus (PRV) antibody during a 6 yr period. Prevalence of seroconversion in females was somewhat higher than in males (10% versus 7%), but the difference was not statistically significant. Adults had a significantly higher prevalence than juveniles (29% versus 1%). An important finding in this study was that seroconversion occurred primarily in the adult feral swine.     

A toxin fromPasteurella multocida serogroup D enhances swine herpesvirus 1 replication/lethality in vitro and in vivo

In swine, the nasal turbinate epithelium is both a site of swine herpesvirus 1 (pseudorabies virus, PRV) replication and a tissue affected by toxin fromPasteurella multocida serogroup D. We examined the effects of exposure to PRV and exposure to toxin in mice, swine, and nasal turbinate cell cultures. Increased mortality in mice was observed when nonlethal doses of PRV (1000 or 100 plaque-forming units, PFU) were administered along with nonlethal doses (60–200 ng/kg) of toxin. In swine, clinical disease and death in adult pigs was observed after an intradermal injection of toxin (20 ng/kg) and intranasal exposure to 1000 PFU/kg of PRV. Nasal turbinate cell cultures incubated with toxin and PRV had increased protein synthesis, DNA synthesis, and increased recovery of virus particles. These findings indicate that a toxin fromP. multocida serogroup D enhances swine herpesvirus 1 replication and lethality in cell cultures and animal models.     

Evaluation of fences for containing feral swine under simulated depopulation conditions

Populations of feral swine (Sus scrofa) are estimated to include >2 million animals in the state of Texas, USA, alone. Feral swine damage to property, crops, and livestock exceeds $50 million annually. These figures do not include the increased risks and costs associated with the potential for feral swine to spread disease to domestic livestock. Thus, effective bio-security measures will be needed to quickly isolate affected feral swine populations during disease outbreaks. We evaluated enclosures built of 0.86-m-tall traditional hog panels for containing feral swine during 35 trials, each involving 6 recently caught animals exposed to increasing levels of motivation. During trials, fences were 97% successful when enclosures were entered by humans for maintenance purposes; 83% effective when pursued by walking humans discharging paintball projectors; and in limited testing, 100% successful when pursued and removed by gunners in a helicopter. In addition to being effective in containing feral swine, enclosures constructed of hog panels required simple hand tools, took <5 min/m to erect, and were inexpensive ($5.73/m excluding labor) relative to other fencing options. As such, hog-panel fences are suitable for use by state and federal agencies for rapid deployment in disease response situations, but also exhibit utility for general control of other types of damage associated with feral swine. © 2011 The Wildlife Society.     

A modified bait for oral delivery of biological agents to raccoons and feral swine

A field study was conducted on Ossabaw Island (Georgia, USA) in March 1994 to evaluate four different types of bait for delivering orally effective biological agents to raccoons (Procyon lotor) and feral swine (Sus scrofa). A deep-fried corndog batter bait, which was previously shown to be ingested by both captive and free-ranging raccoons, and a polymer fishmeal bait which had been shown effective for both raccoons and feral swine were compared with a grain-based dog food meal polymer bait topically coated with corn oil and cornmeal or with fish oil and fishmeal. Tracking stations were used to determine the number of each bait type visited and removed by animals visiting stations. We found no significant differences in the numbers of different baits removed by either species. These data support the results of earlier studies which also indicated that an inexpensive grain-based matrix bait surface-coated with attractive flavors can be used to deliver oral biologics to problem species.     

Species-specific visitation and removal of baits for delivery of pharmaceuticals to feral swine

Within the domestic swine industry there is growing trepidation about the role feral swine (Sus scrofa) play in the maintenance and transmission of important swine diseases. Innovative disease management tools for feral swine are needed. We used field trials conducted in southern Texas from February to March 2006 to compare species-specific visitation and removal rates of fish-flavored and vegetable-flavored baits with and without commercially available raccoon (Procyon lotor) repellent (trial 1) and removal rates of baits deployed in a systematic and cluster arrangement (trial 2). During trial 1, 1) cumulative bait removal rates after four nights ranged from 93% to 98%; 2) bait removal rates by feral swine, raccoons, and collared peccaries (Pecari tajacu) did not differ by treatment; and 3) coyotes (Canis latrans) removed more fish-flavored baits without raccoon repellent and white-tailed deer removed more vegetable-flavored baits without raccoon repellent than expected. During trial 2, feral swine removed fish-flavored baits distributed in a cluster arrangement (eight baits within 5 m2) at a rate greater than expected. Our observed bait removal rates illustrate bait attractiveness to feral swine. However, the diverse assemblage of omnivores in the United States compared with Australia where the baits were manufactured adds complexity to the development of a feral swine-specific baiting system for pharmaceutical delivery.     

Seroprevalence of Toxoplasma gondii antibodies among Atayal aboriginal people and their hunting dogs in northeastern Taiwan

Atayal aborigines, living at an altitude of 1,500-1,600 m in northeastern Taiwan, still hunt for wild animals with the help of hunting dogs. In this study, the latex agglutination test (LAT) was used to detect sera anti-toxoplasma antibodies in this community as a measure of their exposure to Toxoplasma gondii. The positive rates for sera anti-toxoplasma antibodies were 21.8% and 19.6%, respectively, in 422 Atayal and 51 hunting dogs tested. Neither of the positive rates were found to be significantly different between male (22.1%) and female Atayal (21.4%), or between humans (21.8%) and dogs (19.6%) (P > 0.05) when compared by the Chi-Squared test (chi 2-test). A significant difference was observed between the positive rates in adults (28.3%) and children (18.7%) (P < 0.05), and the age pattern of prevalence is consistent with an increasing duration of exposure to Toxoplasma gondii with age. The consumption of raw liver of wild animals or insufficiently cooked meat may be the major mode of transmission of toxoplasmosis in Atayal.     

Alpha-herpesvirus glycoprotein D interaction with sensory neurons triggers formation of varicosities that serve as virus exit sites

Alpha-herpesviruses constitute closely related neurotropic viruses, including herpes simplex virus in man and pseudorabies virus (PRV) in pigs. Peripheral sensory neurons, such as trigeminal ganglion (TG) neurons, are predominant target cells for virus spread and lifelong latent infections. We report that in vitro infection of swine TG neurons with the homologous swine alpha-herpesvirus PRV results in the appearance of numerous synaptophysin-positive synaptic boutons (varicosities) along the axons. Nonneuronal cells that were juxtaposed to these varicosities became preferentially infected with PRV, suggesting that varicosities serve as axonal exit sites for the virus. Viral envelope glycoprotein D (gD) was found to be necessary and sufficient for the induction of varicosities. Inhibition of Cdc42 Rho GTPase and p38 mitogen-activated protein kinase signaling pathways strongly suppressed gD-induced varicosity formation. These data represent a novel aspect of the cell biology of alpha-herpesvirus infections of sensory neurons, demonstrating that virus attachment/entry is associated with signaling events and neuronal changes that may prepare efficient egress of progeny virus.     

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.     

Evaluation of a latex agglutination test for rapid detection of rotavirus in faecal specimens

Two methods for detecting rotaviruses (latex agglutination, electron microscopy) have been compared on 80 faecal samples. These samples were obtained from infants between the age of four and 30 months hospitalized for acute gastroenteritis in the Children's Hospital, Karl Marx University at Leipzig, in 1982. Complete agreement among the two techniques was found in 75 specimens. Sensitivity of latex agglutination could be estimated at 95%, the specificity also at 95%. Only one sample reacted nonspecifically. Performance of the latex agglutination proved quite simple. The results indicate that latex agglutination is suitable for rapid screening of rotavirus induced gastroenteritis in clinical practice thus enabling the rate of nosocomial rotavirus infections in children's hospitals to be reduced.     

西藏小型猪10种猪病血清学调查

目的对西藏小型猪进行10种猪病（猪瘟、伪狂犬病、篮耳病、猪流感、圆环病毒感染、细小病毒病、乙型脑炎、弓形体病、衣原体病和布氏杆菌病）的血清学调查。方法采用ELISA或凝集试验方法对10头已注射猪瘟疫苗的原代（F0代）母猪和40头20日龄乳猪、50头第一代（F1代）3～5月龄猪进行10种猪病的血清学检测。结果猪瘟病毒、细小病毒和乙型脑炎病毒抗体阳性率分别是母猪为80.0%、80.0%、70.0%;20日龄乳猪为45.0%、25.0%、45.0%;3～5月龄猪为4.0%、76.0%、80.0%。圆环病毒抗体阳性率母猪为60.0%,20日龄乳猪为5.0%。3～5月龄猪为0%;篮耳病病毒、伪狂犬病病毒、猪流感病毒、弓形体、衣原体、布氏杆菌在不同年龄西藏小型猪中抗体阳性率均为0%。结论不同年龄西藏小型猪未受篮耳病病毒、伪狂犬病病毒、猪流感病毒、弓形体病、衣原体病、布氏杆菌病感染。     

Induction and inhibition of apoptosis by pseudorabies virus in the trigeminal ganglion during acute infection of swine

We examined the ability of pseudorabies virus (PRV) to induce and suppress apoptosis in the trigeminal ganglion during acute infection of its natural host. Eight pigs were intranasally inoculated with a virulent field strain of PRV, and at various early times after inoculation, the trigeminal ganglia were assessed histologically. PRV-infected cells were detected by use of immunohistochemistry and in situ hybridization, and apoptosis was identified by in situ terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling. Light and electron microscopy was also used for morphological studies. Apoptosis was readily detected among infiltrating immune cells that were located surrounding PRV-infected neurons. The majority of PRV-infected neurons did not show morphological or histochemical evidence of apoptosis, even including those neurons that were surrounded by numerous inflammatory cells and exhibited profound pathological changes. However, neuronal virus-induced apoptosis also occurred but at a sporadic low level. These findings suggest that PRV is able to block apoptosis of infected trigeminal ganglionic neurons during acute infection of swine. Furthermore, our results also suggest that apoptosis of infiltrating inflammatory cells may represent an important viral mechanism of immune evasion.