Laboratory diagnosis and disease occurrence in the current African swine fever eradication program in Spain, 1989–1991

The purpose of this study was to determine the rate of decline and geographical distribution by municipality of clinical and subclinical African swine fever (ASF) in the affected areas of Spain. A second aim was to evaluate the performance of diagnostic tests in the Spanish ASF eradication program. Clinical outbreaks were confirmed using both the direct and indirect immunofluorescence test (and if both were negative, by the hemabsorption test). The serological status of swine was determined by an enzyme-linked immunosorbent assay (ELISA) and suspect serum samples were confirmed by the immunoblot assay.

The number of clinical outbreaks (herds) of ASF for 1989, 1990 and 1991 was 170, 347 and 207, respectively. The numbers of municipalities within each affected province experiencing acute outbreaks for the same time periods were 49, 69 and 48, respectively. Serologically diagnosed animals positive for ASF were 1.1% of animals tested in 1989, 0.5% in 1990 and 0.8% in 1991. The corresponding positive predictive values of the standard ELISA test used were 99.0, 97.9 and 98.8, respectively. Similarly, the number of municipalities within each affected province experiencing serologically positive subclinically infected animals was 269, 178 and 147 for each of the years 1989, 1990 and 1991, respectively.     

BHV-1 eradication program in Bavaria: a marker-independent strategy

In Bavaria a BHV-1 eradication program was initiated in 1986 and was changed to a compulsory program in 1998. The eradication success increased progressively from < 50% in 1986 to 87% of the farms in 2002. BHV 1-free farms are controlled by bulk milk serology twice a year along with blood serology in animals that are negative but from herds where positive field virus infected animals are present. All serological tests are performed with an indirect ELISA test, all positive results are confirmed by a gB ELISA. Currently about 100.000 virus infected cattle are in Bavarian herds, approximately 80% of these animals are in heavily infected herds (> 10 infected animals). These herds comprise about 5% of all Bavarian herds. The eradication of the virus in these heavily infected herds is the most diifficult, whereas the prevention of new infections appears controllable. In this review current problems in BHV1 eradication are named and possible improvements are discussed.     

Long-term lack of transmission of Aujeszky's disease virus (ADV) in a chronically infected Swedish weaner pig producing herd

A cohort of 53 swine seronegative to Aujeszky's disease virus (ADV) was monitored in a 1 year study of a chronically infected commercial Swedish weaner pig producing herd. Serum samples were acquired from all 134 adult swine and analyzed by enzyme-linked immmunosorbent assay (ELISA). Animals testing negative, along with introduced replacement gilts, were followed serologically every second month. Movements of animals were recorded for 319 days and exposure to seropositive animals was calculated for each seronegative pig in the cohort. The accumulated daily pig contact between the 53 ADV-non-infected swine and 43 infected swine was 35 660 days and the median number of days in contact for the non-infected swine with infected was 222. Despite the frequent contact with seropositive pigs, no seronegative animals seroconverted during the first 11 months of observation. Forty-six of 53 pigs seroconverted after a clinical outbreak during the twelfth month of observation.     

Surveillance and risk management during the latter stages of eradication: experiences from Australia

The paper reviews the eradication of bovine tuberculosis from Australia with special reference to surveillance and managing the risk of animals exposed to tuberculosis infected animals during the latter stages of eradication. The successful eradication was based on a sound technical program with strong industry and government support. The model of joint industry and government funding and decision-making first used during the brucellosis and tuberculosis eradication campaign (BTEC) has been successfully incorporated within subsequent livestock disease control programs in Australia. An overview of the history of tuberculosis eradication in Australia provides a background to the surveillance approach. Australia was fortunate that there were no wildlife reservoir hosts. Feral animal reservoir hosts were removed during the eradication program. Surveillance to detect rare diseases is recognised to be statistically challenging with high resource requirements. Australian veterinary authorities have a high level of confidence that the combination of increasing sensitivity of abattoir surveillance systems by the submission of all granulomas detected at slaughter with increasing risk management of animals exposed to tuberculosis infected animals during the final stages of eradication provides a high level of assurance that Mycobacterium bovis has been eradicated.     

Development of the Dutch Johne's disease control program supported by a simulation model

The development of a simulation model, "JohneSSim", was part of a research program aimed at designing a national Johne's disease control program for The Netherlands. Initially, the focus was mainly directed towards different compulsory "test-and-cull" strategies. However, the results from the JohneSSim model showed that eradication of Johne's disease based on such strategies would not be possible within 20 years and that it was also economically unattractive. However, improved calf management seemed to be more effective in reducing the prevalence within the same time period. Simulation of a strategy using an "ideal test" (80% sensitivity in all infected animals) showed a considerably faster decrease in prevalence. However, this strategy proved to be economically unattractive because of the high culling rate of (young) test-positive animals. The simulation model was also adapted to study beef cow herds. However, the results indicated that none of the strategies were able to reduce the mean true prevalence to almost zero for such herds. Only strategies based on "separation of calves and adult animals" proved to significantly reduce the prevalence but such a strategy is unpractical and uneconomic for Dutch beef cow herds. Due to this finding and the relative low number of Dutch beef cow farms, first priority has been given to the development of a Johne's disease control program for dairy farms. Based on the results of the "JohneSSim" model, the new national voluntary Johne's disease control program for dairy, Paratuberculosis Program Netherlands (PPN), started in September 2000. The PPN is based on a stepwise improvement of calf hygiene, with little dependency on "test and culling". The model results indicated that, if dairy farmers consistently carried out the necessary management adaptations, PPN considerably decreased prevalence and that it was economically more attractive than any previous plans.     

The control of infectious bovine rhinotracheitis (IBR) in Switzerland from 1978 to 1988

The eradication of Infectious bovine rhinotracheitis/Infectious pustular vulvovaginitis (IBR/IPV) in Switzerland is reviewed. In 1978 IBR was reported in dairy cattle in the Eastern part of Switzerland. No preexisting eradication program was available at that time. In 1983, following a period of hesitation, the legal basis for the eradication of IBR was issued. This aim was achieved by: i) Controls and restrictions of the traffic of susceptible animals in order to prevent further transmission of IBR. ii) Slaughter of seropositive cattle, based on the assumption that animals with antibodies to BHV 1 were virus carriers and therefore an IBR-virus-reservoir. iii) The fact that besides the cattle population no BHV 1 reservoir existed in Switzerland. iv) Never licensing IBR-vaccines because they were not able to prevent the infection and the establishment of latency. The costs of the eradication program amounted to approx. SFr. 114,000,000. A total of 51,911 animals were slaughtered in order to eradicate IBR. An amount of SFr. 5,000,000 per annum is estimated to be necessary in order to maintain the favourable situation concerning IBR. In the future, the experience concerning IBR is applied for the prevention and control of other infectious diseases in the Swiss cattle population.     

How do resources influence control measures during a simulated outbreak of foot and mouth disease in Australia?

An outbreak of foot and mouth disease (FMD) could seriously impact Australia's livestock sector and economy. As an FMD-free country, an outbreak would trigger a major disease control and eradication program that would include the culling of infected and at risk animals (‘stamping out’), movement restrictions and zoo-sanitary measures. Additional control measures may also include pre-emptive culling or vaccination. However, it is unclear what disease strategy would be most effective under Australian conditions and different resource levels. Using a stochastic simulation model that describes FMD transmission between farms in a livestock dense region of Australia, our results suggest that using current estimates of human resource capacity for surveillance, infected premises operations and vaccination, outbreaks were effectively controlled under a stamping out strategy. However, under more constrained resource allocations, ring vaccination was more likely to achieve eradication faster than stamping out or pre-emptive culling strategies.     

Eradication of Mycoplasma hyopneumoniae from infected swine herds joining the LSO 2000 health class

The study was conducted in order to determine if eradication of swine enzootic pneumoniae (SEP) had succeeded with different variants of partial depopulation during the eradication programme on swine farrowing farms joining a health class, LSO 2000. The farms in the health class need to be free from swine enzootic pneumoniae, swine dysentery, sarcoptic mange and atrophic rhinitis. Twenty-one eradication attempts for M. hyopneumoniae were carried out using different variants based on separating adult animals for 2 weeks from infected young pigs which were not returned to the herd. The infected young pigs were kept in the same building (variant 1) in 4 herds and on the same compound (variant 2) as disease-free pigs in 12 herds. The infected young pigs were finally all sold. In 5 herds only adult animals were present during the eradication (variant 3). The eradication attempt succeeded in 81% and failed or remained uncertain in 19% of the herds. The result was confirmed with 1) frequent clinical follow-up of the health status in the herds (both the farrowing and the finishing units) joining the LSO 2000 health class 2) milk and/or blood serology. Possible causes of the failure of the eradication attempt were described: a short distance between infected and uninfected animals, the time period between diagnosis of SEP and initiation of the programme, the age of the youngest animal kept on the farm, the period of time when animals with different status were reared close to each other, the medications used, the cleaning of the facilities during the programme and the season. Further, a good cooperation between the farmer, the local veterinarian and the animal health service of the slaughterhouse was an essential part of the initiation and the follow-up of the programme. The secondary aim of the study was to collect information about the expenses during the programme. Only 57% of the farmers gave some estimates for the expenses on their farms. For variants 1, 2 and 3 the expenses were 879, 1110 and 1274 FIM per sow (1 USD = 5.5 FIM), respectively (p > 0.1).     

Control and eradication programme of enzootic bovine leucosis (EBL) from selected dairy herds in Turkey

Serum samples of 15,909 cattle from 31 dairy herds located in various regions of Turkey were tested for the presence of antibodies against bovine leucosis virus (BLV) using Agar Gel Immuno-diffusion technique (AGID). 48.3% (15/31) of the herds had seropositive animals and positivity rates were detected from 0.5-34.4% in these herds. In an EBL control/eradication programme all seropositive animals were culled in the infected herds. Thereafter, a total of 74,347 sera were tested for the presence of BLV specific antibodies. The serological results and detail of EBL control/eradication programme were shown in this paper.     

Distribution and biology of Ornithodoros erraticus in parts of Spain affected by African swine fever

Ornithodoros erraticus was found in 30.7 per cent, 35.0 per cent and 71.0 per cent of the pig-pens sampled in the provinces of Salamanca, Badajoz and Huelva in which African swine fever is a problem in the rearing of Iberian pigs. Between 38 and 65 per cent of the pig-pens in these areas are now abandoned and their populations of O erraticus are extinct or becoming so because they can no longer feed on pigs, which in Spain are their main hosts. The abandonment of pig-pens has resulted in the elimination of most soft ticks infected with the virus of African swine fever, and means that the distribution of ticks is now irregular and focal. Another factor affecting their distribution is the kind of soil on which the pig-pens are located. In abandoned pig-pens, the adults and large nymphs survive for about five years or longer when animals occasionally enter them. Hungry tick populations may transmit African swine fever when feeding in winter, whereas the populations that have continuous access to pigs do not feed until the pig-pens reach a temperature of 13 to 15 degrees C. In the latter populations, each stage exhibits a single annual peak of activity, which implies that the development from larva to adult takes two to three years. Pigs may die as a result of the bites, but on no occasion were 100 per cent of the fasting ticks seen to feed, even though they had the opportunity of doing so. This may hinder the eradication of this soft tick from infested pig-pens.     

Epidemiology and control of an outbreak of classical swine fever in wild boar in Switzerland

An outbreak of classical swine fever in wild boar in the southern part of Switzerland (Canton of Ticino) was investigated after the implementation of control measures in a defined infected area (the risk zone), and in a surrounding surveillance zone (the non-risk zone). After the disease had been detected, hunting was not allowed in the risk zone for over six months, during which the disease was left to run its course, but hunting was continued in the non-risk zone for one month. After seven months, a hunting strategy targeted at young animals was implemented in both zones. Between May 1998 and January 2000,1294 wild boar were shot or found dead, and diagnostic and biological data were collected and analysed. Only one animal from the non-risk zone was found to be seropositive for antibodies to the virus, whereas 179 of 528 wild boar from the risk zone were virus positive and 162 were seropositive. The proportion of virus-positive animals decreased from 62.7 per cent to zero over one year. During the first hunting season, seropositive animals were found in all age groups, but 12 months later only animals more than one year old had antibodies against the virus.     

A scheme for the placement of rodenticide baits for rat eradication on confinement livestock farms

We investigated whether the allocation of rodenticide baiting points to specific structural elements would result in complete rat eradication on livestock farms, as opposed to assigning the baiting points only to places where there were obvious signs of rat activity. The goal was to establish an effective rodent-control program that is easy for untrained persons to conduct.

Rat-control strategies were examined on 25 farms in Velen (Muensterland), Germany, where an average of 20% of trapped rats were resistant for bromadiolone according to a blood-clotting response (BCR) test. All farms were investigated for signs of rat activity prior to and after the control measure. Differences in the percentage level of farmer compliance in setting up the baiting points as prescribed were analysed for each type of baiting point and in total, and were compared between the group of farms which achieved complete rat eradication and those which did not.

Farms achieving complete eradication had an average of 81% compliance with prescribed control plans, whereas a significantly lower compliance level of only 51% was recorded on farms that did not achieve eradication. A ≥75% level of implementation of the control plan always resulted in complete control success. The new method of bait-point allocation was incorporated into a self-explanatory computer program, which was verified to be effective during a rat-control campaign in the restricted area after an outbreak of classical swine fever near Soltau in northern Germany, in July 2001. This program, which is available on the Internet, enables the creation of individualised rat-control plans, including complete documentation of the control measure.     

Economic analysis of an epizootic of pseudorabies and subsequent production following the institution of a vaccination program in a Pennsylvania swine herd

The economic impact of pseudorabies was examined in a commercial swine herd. At the onset of clinical signs, a modified-live virus vaccine was administered to the sow herd and repeated at 3-month intervals. According to production data from the 320-sow farrow-to-feeder unit, preweaning mortality increased twofold, and subsequently, the number of pigs weaned per litter decreased by 19% (P less than 0.005) during the 5-week epizootic. Also, the number of pigs born alive decreased by 6% during the epizootic (P less than 0.05). No significant differences in production were observed between the 6-month periods before and after the epizootic. Actual cash flow analysis for the farm under isomarket conditions revealed a decreased net return of $2.40/inventoried sow/week, which was attributed to the disease during the epizootic, and a $0.46 decrease in net return/inventoried sow/week in the postepizootic period. Most seropositive herds have clinical signs less severe than those described in this herd, and the cost of eradication of the virus from a swine herd can be in excess of $200/inventoried sow. Thus, we believe that sufficient financial incentives are not available to all swine producers to ensure their enthusiastic cooperation in the effort to eradicate pseudorabies from the US swine population.     

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.     

Theoretical basis and empirical implications of the bovine brucellosis market slaughter testing program in the United States

With reductions in federal funding, the Market Slaughter Testing (MST) surveillance system might once again become the primary bovine brucellosis surveillance system for the beef-cow population in the United States. Thus, understanding the weaknesses and/or strengths of the MST surveillance system will be crucial in determining the most effective program in a limited funding control/eradication program.An estimation of a hypergeometric distribution used in previous studies to describe the effectiveness of the MST system is employed and parameters of this distribution are estimated from secondary data. Results analyzed by herd size, and within-herd infection level yield a distinct herd size bias in the MST surveillance system. For example, the probability of detection in a 9-cow herd is 24% compared to 85.4% for a 645 cow herd after 1 year of infection. This herd size bias implies that secondary testing may be efficiently u used by concentrating testing in the smaller herds when funds for secondary testing are limited.MST detection probabilities can vary 30% between the build-up and liquidation phases of the cattle cycle, i.e., secular upswings and downswings in cattle inventory numbers. First Point of Concentration testing (FPC) of purchased replacements can partially offset the effects of the cattle cycle. A 95% herd vaccination level can reduce the probability of detection as much as 40% when compared to a similar herd that is not vaccinated.     

The value of DNA paternity identification in beef cattle: examples from Nevada's free-range ranches

The feasibility and economic value of DNA paternity identification were investigated and illustrated using Nevada beef cattle operations. A panel of 15 microsatellites was genotyped in 2,196 animals from 8 ranches with a total of 31,571 genotypes. Probabilities of exclusion for each marker within ranch and across ranches were computed. Joint probabilities of exclusion for the 15 microsatellites were also determined, resulting in values over 0.99 for any individual ranch and across ranches. Dropping 1 or 2 microsatellites with the lowest probabilities of exclusion resulted in joint probabilities greater than 0.99 and with marginal reduction compared with the probabilities with 15 microsatellites. Formulas for benefit-cost analysis for a DNA paternity identification program in beef cattle were derived. Genotyping 15 microsatellites with 20 calves per sire resulted in benefits of $1.71 and $2.44 per dollar invested at bull culling rates of 0.20 and 0.30, respectively. The breakpoints for the program to be profitable occurred when the ratio of the price of 1 kg of calf liveweight over the cost of genotyping 1 microsatellite was greater than 1.1 for a bull culling rate of 0.30. Benefit-cost analysis was also derived under incomplete DNA paternity identification using a lower number of DNA markers than necessary to achieve joint probabilities of exclusion of 0.99. Approximately a 20% increase in the benefit-cost ratio was achieved using 10 vs. 12 microsatellites with incomplete paternity identification. The greater the number of bulls in the operation, the lower the benefit-cost ratio of the paternity testing program. Low probabilities of exclusion and a high number of bulls in the beef operation reduced the benefit-cost ratio dramatically. The DNA paternity identification programs are feasible and may be profitable for free-range beef cattle operations.     

BVDV infection risk in the course of the voluntary BVDV eradication program in Styria/Austria

A total of 1362 persistently BVDV-infected animals were identified in 850 herds during the first 3 years of the voluntary BVDV eradication program in Styria/Austria. Within the same period of time, the prevalence of BVDV-infected herds dropped from 7.3% to 2.2% of the 4412 herds covered by the program. The relative BVDV infection risk decreased at least four-fold in herds on common grazing and at least five-fold in herds which purchased cattle during the first 30 months of the BVD control program. Thus, the relative BVDV infection risk was reduced by between five to nine times of the initial risk following the implementation of the 3-year eradication program in all herds participating in the program.     

Foreign animal disease outbreaks, the animal welfare implications for Canada: risks apparent from international experience

Any outbreak of an Office International des Epizooties List A disease, such as classical swine fever or foot and mouth disease, has severe consequences for animal welfare, livestock production, exports of animals and animal products, and the environment. The public concern with the animal welfare effects of methods of disease eradication that result in the destruction of large numbers of uninfected animals has initiated a reconsideration of disease eradication policy in Europe. In many recent List A disease epizootics, the financial cost of addressing animal welfare concerns in healthy animals has greatly exceeded the cost of stamping out disease in infected herds. In the event of a similar incursion in Canada, the number of animals subject to welfare slaughter will be far greater than the number of infected animals killed. Current national disease eradication plans in Canada do not address the animal welfare component of disease control methods.     

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.