A Mark–Recapture Technique for Monitoring Feral Swine Populations

Techniques to monitor populations of feral swine (Sus scrofa) relative to damage control activities are needed on rangelands. Our objectives were to describe and assess a mark–recapture technique using tetracycline hydrochloride (TH) for monitoring feral swine populations. We established bait stations at study sites in southern and central Texas. During 1 d, we replaced normal soured corn bait with bait containing TH and counted the number of feral swine that consumed bait with observers. We conducted feral swine removal using box-style traps and helicopters, at which time we collected teeth for TH analysis. In southern Texas, we estimated population reduction to be 43%. In central Texas, we estimated population reduction of 31%. Our mark–recapture population monitoring technique would complement programs to manage feral swine populations and damage through lethal control.     

Efficacy of the Boar-Operated-System to deliver baits to feral swine

Feral swine (Sus scrofa) pose a significant disease threat to livestock and humans. Emerging technologies to reduce feral swine disease transmission risks include fertility control, vaccination, and toxicants. However, for these technologies to be appropriate for field application, a feral swine-specific oral delivery system is needed. We used two field trials to generate information related to appropriate field application of the Boar-Operated-System (BOS?), an oral delivery system designed to provide bait access only to feral swine. Our objectives were to determine whether pre-baiting BOS? units increased bait removal and to evaluate the proportion of feral swine and non-target animals that ingest baits designed to deliver pharmaceuticals through the BOS?. During both trials we used baits housed within 10 BOS? units. We monitored wildlife visitation, bait removal, and ingestion using motion sensing digital photography and baits containing the bait marker tetracycline hydrochloride (TH). During trial 1 we found three of five pre-baited BOS? units were used by feral swine only. Additionally, we found the five BOS? units that were not pre-baited were not used by feral swine or non-target wildlife. During trial 2 we determined bait removal from the BOS? to be reduced by only 10% for feral swine when activated, whereas bait removal from the BOS? by all other wildlife was reduced by 100% when activated. We captured 81 feral swine and 23 raccoons and found 90% and 13% to have TH-marked teeth, respectively. With minor modifications, the BOS? should be considered a valuable tool to be used in feral swine disease management in conjunction with existing technologies.     

Vaccination of feral pigs (Sus scrofa) using iophenoxic acid as a simulated vaccine

OBJECTIVES: To develop an encapsulation method for delivery of vaccines to feral pigs, and quantify the effect of iophenoxic acid on captive feral pig blood iodine concentrations to assist in investigation of factors affecting vaccine uptake. DESIGN AND METHODS: Feral pigs were administered iophenoxic acid by oral gavage, and consumption was assessed for different encapsulation methods in baits. Blood iodine concentrations were monitored for eight days after consumption. The relationship between dose rate, time since dosing and blood iodine concentration was assessed for gavaged and baited captive feral pigs. Wild feral pigs were baited with PIGOUT baits containing 20 mg of encapsulated iophenoxic acid to simulate a vaccination program. Using knowledge from the pen studies, bait uptake and factors affecting bait uptake were investigated. RESULTS: Bait-delivered iophenoxic acid led to variable and inconsistent changes in blood iodine concentrations, in contrast to pigs receiving iophenoxic acid by gavage. This precluded accurate assessment of the quantity consumed, but still allowed a conservative determination of bait uptake. Iophenoxic acid in smaller capsules was consumed readily. Increasing baiting intensity appeared to increase bait uptake by wild feral pigs, and pigs of varying sexes, ages and weights appeared equally likely to consume baits. CONCLUSIONS: Encapsulated liquids can be delivered to feral pigs within baits, should the need to vaccinate feral pigs for fertility or disease management arise. High baiting intensities may be required.     

Grain,pellet and wax block bait take by the house mouse (Mus musculus) and non‐target species: implications for mouse eradications on coral cay islands

Introduced rodents have been eradicated from large numbers of offshore islands using toxic baits; however, toxic baits have been linked with negative impacts on non‐target species. The present study assessed the bait take of target (house mouse, Mus musculus) and non‐target (buff banded rail, Rallus philippensis) animals on Northwest and Heron Islands in the Great Barrier Reef. Three non‐toxic bait formulations (wax block, pellet and grain) were tested and each was applied at 1 kg ha^?1 in six treatment grids. The tracks of animals visiting the baits were identified using 30 tracking stations per treatment grid. A tracking station consisted of a track‐board placed in the centre of a sand‐pad. Mean bait take differed significantly between the formulations: birds took more grain bait than wax block bait; mice took more wax block than grain bait. Both mice and birds were equally selective of pellet bait. Thus, the findings indicate that wax blocks are the most suitable formulation for future baiting programs to eradicate mice on these and other islands.     

Diagnostic characterization of a feral swine herd enzootically infected with Brucella.

Eighty feral swine were trapped from a herd that had been documented to be seropositive for Brucella and which had been used for Brucella abortus RB51 vaccine trials on a 7,100-hectare tract of land in South Carolina. The animals were euthanized and complete necropsies were performed. Samples were taken for histopathology, Brucella culture, and Brucella serology. Brucella was cultured from 62 (77.5%) animals. Brucella suis was isolated from 55 animals (68.8%), and all isolates were biovar 1. Brucella abortus was isolated from 28 animals (35.0%), and isolates included field strain biovar 1 (21 animals; 26.3%), vaccine strain Brucella abortus S19 (8 animals, 10.0%), and vaccine strain Brucella abortus RB51 (6 animals, 7.5%). Males were significantly more likely to be culture positive than females (92.9% vs. 60.6%). Thirty-nine animals (48.8%) were seropositive. Males also had a significantly higher seropositivity rate than females (61.9% vs. 34.2%). The relative sensitivity rates were significantly higher for the standard tube test (44.6%) and fluorescence polarization assay (42.6%) than the card agglutination test (13.1%). Lesions consistent with Brucella infection were commonly found in the animals surveyed and included inflammatory lesions of the lymph nodes, liver, kidney, and male reproductive organs, which ranged from lymphoplasmacytic to pyogranulomatous with necrosis. This is the first report of an apparent enzootic Brucella abortus infection in a feral swine herd suggesting that feral swine may serve as a reservoir of infection for Brucella abortus as well as Brucella suis for domestic livestock.     

Description of empirical movement data from Canadian swine herds with an application to a disease spread simulation model

We report the methods and findings of a survey of Canadian swine producers summarizing farm-types at-risk of foreign animal disease (FAD) and the routine movement of animals, semen and workers among swine farms, as observed during a 42-day period. Of the 311 producers who returned completed questionnaires, 17% represented swine-herds with no swine or semen movement on or off the farm during the 42 days, 57% were sow herds or farrow-to-finish herds with limited movement onto the farm but movement off the farm, and 26% were swine-herds with movements on and off the farm. A substantial number of premises (>50% in some provinces) with swine also kept other animal species on the same premises. We applied the empirical movement data from the survey in a stochastic simulation model to estimate the number of herds infected and the basic regional distribution of infection that could be expected to occur if the FAD was not detected and routine movements were permitted to occur up to 42 days after infection with a FAD of a single randomly selected herd. Forty-five percent of the simulations did not involve spread beyond the index farm, whereas 34.8% involved spread among five or more farms after 42 days of routine movement.     

The role of movement restrictions and pre-emptive destruction in the emergency control strategy against CSF outbreaks in domestic pigs

Classical swine fever (CSF) outbreaks in domestic pig herds lead to the implementation of standard control measures according to legislative regulations. Ideal outbreak control entails the swift and efficient culling of all pigs on premises detected positive for CSF virus. Often all pig holdings around the detected cases are pre-emptively destroyed to exclude transmission into the neighbourhood. In addition to these measures, zones are defined in which surveillance and protection measures are intensified to prevent further distant disease spread. In particular, all movements are prohibited within standstill areas. Standstill also excludes the transport of fattened pigs to slaughter. Historical outbreaks provide evidence of the success of this control strategy. However, the extent to which the individual strategy elements contribute to this success is unknown. Therefore, we applied a spatially and temporally explicit epidemic model to the problem. Its rule-based formulation is tailored to a one-by-one model implementation of existing control concepts. Using a comparative model analysis the individual contributions of single measures to overall control success were revealed. From the results of the model we concluded that movement restrictions had the dominant impact on strategy performance suggesting a reversal of the current conceptual thinking. Additional measures such as pre-emptive culling only became relevant under imperfect compliance with movement restrictions. The importance of movement restrictions for the overall control success illustrates the need for explicit consideration of this measure when contingency strategies are being amended (e.g. emergency vaccination) and associated risks assessed.     

Risk based culling for highly infectious diseases of livestock

ABSTRACT: The control of highly infectious diseases of livestock such as classical swine fever, foot-and-mouth disease, and avian influenza is fraught with ethical, economic, and public health dilemmas. Attempts to control outbreaks of these pathogens rely on massive culling of infected farms, and farms deemed to be at risk of infection. Conventional approaches usually involve the preventive culling of all farms within a certain radius of an infected farm. Here we propose a novel culling strategy that is based on the idea that farms that have the highest expected number of secondary infections should be culled first. We show that, in comparison with conventional approaches (ring culling), our new method of risk based culling can reduce the total number of farms that need to be culled, the number of culled infected farms (and thus the expected number of human infections in case of a zoonosis), and the duration of the epidemic. Our novel risk based culling strategy requires three pieces of information, viz. the location of all farms in the area at risk, the moments when infected farms are detected, and an estimate of the distance-dependent probability of transmission.     

Seroepidemiology of trichinellosis in Florida swine

Surveys for swine trichinellosis, conducted in Florida using a commercial enzyme-linked immunosorbent assay (ELISA) kit with a modified protocol for screening and Western blot as a definitive test, revealed significantly different seroprevalences of 0.3% (four of 1294 samples) and 2.8% (five of 179 samples) in domestic breeding swine and feral swine, respectively.

Seropositive swine were identified in four of 114 (3.5%) domestic swine herds and in three of six feral swine regions. The location of two domestic herds with seropositive swine within approximately 2 miles of one another, and adjacent to a region where a seropositive feral hog was identified, suggests that a focus of trichinellosis exists in this area. The occurrence of singleton reactors in domestic herds may be explained by the absence of the common modes of transmission and suggests that swine were infected incidentally by feeding on the infected carcasses of small wild mammals or rodents. Although the presence of Trichinella spiralis spiralis isolates cannot be excluded, it is more likely that a sylvatic Trichinella isolate occurs in Florida swine. This conclusion is supported by the low seroprevalence in domestic swine, the failure to detect larvae in domestic or feral swine and the high prevalence in Florida panthers.     

Cost of distributing oral raccoon-variant rabies vaccine in Ohio: 1997-2000

OBJECTIVE: Analysis of the cost of 8 distributions of oral rabies vaccine (ORV) with strains known to infect raccoons in Ohio between 1997 and 2000. DESIGN: Original study. PROCEDURE: Fishmeal bait containing ORV was distributed on foot, by vehicle, and by helicopter and fixed-wing aircraft. The cost of personnel, vehicles, and helicopter and aircraft use and other associated expenses were obtained from field records and interviews with personnel and agencies involved in the ORV program. RESULTS: Each bait distribution lasted approximately 1 week. Areas baited ranged from 1,701 km2 to 6,497 km2. Density varied for each distribution, with means of 79 baits/km2 for ground baiting and 93 baits/km2 for aerial baiting. Typically, 72 people participated in the ground portion of each distribution and 32 in the aerial portion. The cost of ground baiting (mean +/- SD, 19.24 dollars/km2 +/- 6.35 dollars/km2) was consistently less than that for air baiting (mean +/- SD, 24.71 dollars/km2 +/- 4.65 dollars/kml) for each distribution. The total cost of distribution varied from 30,568 dollars to 145,842 dollars (mean, 96,791 dollars), and bait cost varied from 150,714 dollars to 1,029,423 dollars (mean, 543,839 dollars). The total cost of ORV distributions ranged from 102 dollars/km2 to 261 dollars/km2 (mean, 153 dollars/km2). CONCLUSIONS: In the United States, rabies strains that infect raccoons have been responsible for the largest increase in rabies in animals in the past 3 decades. Use of ORV is a promising new tool that can be used to control rabies in raccoons. Documenting the estimated cost of implementing an ORV program may lead to more efficient use of resources to control and limit the spread of rabies. In addition, accurately measured distribution costs can be used to perform an economic cost-benefit analysis for an ORV program.     

A review of feral cat control

Animal overpopulation including feral cats is an important global problem. There are many stakeholders involved in the feral cat debate over 'what to do about the problem', including those who consider them a nuisance, the public at risk from zoonotic disease, people who are concerned about the welfare of feral cats, those concerned with wildlife impacts, and the cats themselves. How best to control this population is controversial and has ranged from culling, relocation, and more recently 'trap neuter return' (TNR) methods. Data support the success of TNR in reducing cat populations, but to have a large impact it will have to be adopted on a far greater scale than it is currently practised. Non-surgical contraception is a realistic future goal. Because the feral cat problem was created by humans, concerted educational efforts on responsible pet ownership and the intrinsic value of animals is an integral part of a solution.     

Isolation of Campylobacter from feral swine (Sus scrofa) on the ranch associated with the 2006 Escherichia coli O157:H7 spinach outbreak investigation in California

We report the isolation of Campylobacter species from the same population of feral swine that was investigated in San Benito County, California, during the 2006 spinach-related Escherichia coli O157:H7 outbreak. This is the first survey of Campylobacter in a free-ranging feral swine population in the United States. Campylobacter species were cultured from buccal and rectal-anal swabs, colonic faeces and tonsils using a combination of selective enrichment and antibiotic-free membrane filtration methods. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS, Bruker Daltonics, Inc., Billerica, MA, USA) was used to identify species followed by confirmatory multiplex PCR or 16S rRNA sequencing. Genetic relatedness of Campylobacter jejuni and Campylobacter coli strains was determined by multilocus sequence typing (MLST) and porA allele sequencing. Altogether, 12 (40%) of 30 feral swine gastrointestinal and oral cavity specimens were positive, and six species were isolated: Campylobacter coli, Campylobacter fetus, Campylobacter hyointestinalsis, Campylobacter jejuni, Campylobacter lanienae and Campylobacter sputorum. Campylobacter jejuni subtypes were closely related to MLST sequence type 21 (ST-21) and had identical porA sequences. Campylobacter coli subtypes were unrelated to isolates in the pubMLST/porA database. This feral swine population lived in close association with a 'grassfed' beef cattle herd adjacent to spinach and other leafy green row crop fields. The findings underscore the importance of protecting raw vegetable crops from faecal contamination by wild or feral animals. The study also illustrates a potential risk of Campylobacter exposure for hunters during handling and processing of wild swine meat.     

Exposure of feral swine (Sus scrofa) in the United States to selected pathogens

Feral swine (Sus scrofa) are widely distributed in the United States. In 2011 and 2012, serum samples and tonsils were recovered from 162 and 37 feral swine, respectively, in the US to evaluate exposure to important swine endemic pathogens. Antibodies against porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) were found in 2.5% and 25.3% of tested sera, respectively. Positive serological reactions against Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae have been detected in 19.7% and 69.7% of animals. More than 15% of animals presented antibodies against these 2 pathogens simultaneously. Most animals were also seropositive for Lawsonia intracellularis. Feral swine can also be involved in transmission of zoonotic agents. Almost 50% of animals possessed antibodies against Salmonella. In addition, 94.4% of animals were carriers of Streptococcus suis in their tonsils. In conclusion, feral swine may be considered as a potential reservoir for different endemic diseases in domestic pigs, as well as for important zoonotic agents.     

Mixed models applied to the study of variation of grower-finisher mortality and culling rates of a large swine production system

Large scale production systems for swine are frequently organized in a hierarchical structure. Consequently, important production parameters, such as mortality and culling, can be analyzed at different levels. The major aims of this study were to assess variance components (VC) of mortality and culling rates attributed to sites and to barns within a site, and subsequently to investigate the impact of average entry weight, days on feed (length of the production turn), and season on the magnitude of the VC. Then, data from a large farm with 3 sites were collected during 5 y. In total, 1720040 pigs distributed in 1502 all-in/all-out grower-finisher groups were included. Linear mixed models were fitted for mortality and culling rates. The barn was modeled as the residual component (barn-to-barn variations) with production turn and site nested within production turn as random intercept variance components. Barn-to-barn pig group variation was the largest VC for mortality (63.08%), when no predictors were included in the models. Predictors, such as pigs placed on quarters 2 and 3, low average entry weight, and shorter production turn length, were associated together with higher mortality. The explained proportion of variance due to these predictors was about 12.05% and the VC for barn, site, and production turn were 67.6%, 17.6%, and 14.8%, respectively. Barn-to-barn variation was also the largest VC for culling rate (46.2%), but the same predictor mentioned above explained only about 1.4% of the variation. The VC for barn, site, and production turn were 46.8%, 21.3%, and 31.8%, respectively. Since the variability among barns far exceeded the variability among sites, the barn should be used as experimental unit in studies with grower-finisher mortality, culling rate, or both, as outcome variables.     

Fluoroacetate poisoning in seven domestic dogs

Sodium monofluoroacetate, also known as compound 1080, is used in Australia for control of feral and pest species. Poisoning of non-target species by sodium monofluoroacetate can be difficult to diagnose if there is no history of exposure because clinical signs are non-specific. This communication describes the poisoning by sodium monofluoroacetate of seven dogs from one property over a period of 3 days. Poisoning by sodium monofluoroacetate was confirmed by toxicological analysis of stomach contents, gastric lavage fluid and vomitus from three of the dogs, but the source of the toxin was not found. Six of the seven dogs were Maremmas, and livestock guard animals may be at particular risk of exposure to pest control baiting programs.     

Natural history of influenza in swine in Hawaii: swine influenza virus (Hsw1N1) in herds not infected with lungworms

To obtain more information on mechanisms by which influenza virus is perpetuated in swine, retrospective and prospective seroepizootiologic observations were made in swine herds in Hawaii, beginning in 1974. An epizootic of swine influenza (Hsw1N1) virus was observed in November and December 1976, involving 31 of 41 herds. Features of the epizootic included (1) infection of all herds within one geographic location, during a short period; (2) no obvious introduction of virus from the outside in most herds; (3) epizootics mainly in herds with serologic history of infection; (4) no evidence that lungworms were involved; and (5) little clinical disease associated with infection. There was evidence of viral activity in some herds before the epizootic period and afterward in two of three herds monitored. Evidence of viral transmission by feral animals was not obtained. Data indicated that swine influenza virus persists through latently or chronically infected swine, with epizootics occurring when herd immunity reaches a critically low degree.     

The recreational and commercial importance of feral swine in Florida: Relevance to the possible introduction of African swine fever into the U.S.A.

Florida has the largest population of feral swine in the U.S.A. Feral swine have recreational and economic importance to hunters, trappers, taxidermists, and also to dealers who sell feral swine to hunting clubs. Hunters spent over 522 00 man-days hunting feral swine during the 1980–1981 hunting year. They killed nearly 103 000 hogs which they valued at over $58 each, for a total value of nearly $6 million. Trappers caught 25 000 head valued at about $ 700 000, and landowners collected about $1.2 million in hunting lease fees. Taxidermists received about $389 000 in gross income from mounting feral swine. Sales of feral swine to hunting clubs amounted to about $81 000.

Sales of feral swine through commercial livestock auctions were limited to 1620 head valued at only $16 800 in 1980. Thus, feral swine are important to Florida from a recreational standpoint, but not from the perspective of commercial agriculture.

If African swine fever were to enter Florida, there are many socio-economic factors associated with feral swine that must be carefully evaluated for eradication to be successful.     

Identification of Brucella spp. in feral swine (Sus scrofa) at abattoirs in Texas,USA

Various tissues, nasal swabs, urine and blood samples were collected from 376 feral swine at two federally inspected abattoirs in Texas during six separate sampling periods in 2015. Samples were tested for Brucella spp. by culture and serology. Brucella spp. were cultured from 13.0% of feral swine, and antibodies were detected in 9.8%. Only 32.7% of culture‐positive feral swine were also antibody positive, and 43.2% of antibody‐positive feral swine were culture positive. Approximately, the same number of males (14.0%) and females (12.1%) were culture positive, and slightly more males (10.5%) than females (8.7%) were antibody positive. Our results indicate that serology likely underestimates the prevalence of feral swine infected, and that those who come in contact with feral swine should be aware of the symptoms of infection with Brucella spp. to ensure prompt treatment.     

The use of tetracycline in anthelmintic baits to assess baiting rate and drug efficacy against Echinococcus multilocularis in foxes

Anthelmintic (praziquantel) baiting of wild red foxes against Echinococcus multilocularis infection was studied in a highly epizootic suburban area of Otaru, Hokkaido (the northern island of Japan) during the summer and autumn in the years 1999-2004. Acceptance of baits containing the biomarker tetracycline (TC) was evaluated. The prevalence of E. multilocularis infection in foxes before baiting (1999-2000) was 58% (88/153), whereas in the fourth year of bait distribution year (2004), it decreased to 11% (5/45). Analysis of TC marking in the teeth of foxes showed that 39% (77/195) of those captured after baiting were estimated to have consumed baits in the year of capture. Importantly, more juvenile (56%, 49/87) than adult foxes (26%, 28/108) were marked, indicating efficient baiting of juveniles, which tended to have a higher worm burden of E. multilocularis. Of 77 marked foxes, E. multilocularis and Alaria alata (monitored as the second indicator species of deworming) were not detected in 70 (90%) and 76 (99%) foxes, respectively. The results suggest effective deworming by bait consumption. However, it was also demonstrated that 9% of the marked foxes were infected or re-infected after bait consumption, suggesting high infection pressure and the importance of frequent baiting.     

Culling of animals in large herds, experiences from the Netherlands

The outbreaks of classical swine fever in 1997-1998 and foot- and mouth-disease in 2001 provided a lot of experiences in the culling of animals. These experiences, as well as the aspects of animal welfare and public acceptance are described. In the future these experiences will help to carry out culling in a more efficient way including improved aspects of animal welfare and public acceptance.