Reliability evaluation of sampling plan fixed by Council Directive 91/68/EEC for the maintenance of officially brucellosis-free flock status

The European Union (EU) strategy with respect to sheep and goat brucellosis aims to eradicate the infection and achieve officially brucellosis-free (OBF) status in all EU holdings and territories. Council Directive 91/68/EEC of 28 January 1991 states that to maintain OBF status of ovine or caprine holdings located outside an OBF territory, only a representative number of animals need to be tested annually. However, depending on the number of animals in a holding, this testing method risks non-detection of the infection, thereby reducing the efficacy of the brucellosis control plan. The recommended sampling procedure has a low sensitivity for detecting infection in medium-sized flocks; furthermore, the risk of not detecting re-infection in OBF flocks, particularly in territories that have not yet gained OBF status, is also not acceptable. Moreover, in large-sized flocks, the Directive sampling procedure entails taking an excessive number of samples, which can be very expensive. The authors evaluated, by using statistical analyses and a simulation model based on field data, the possible consequences of the current EU strategy. It is suggested that the sampling criteria for the maintenance of OBF status in the EU should be modified and that a statistically based sampling method should be applied instead of the fixed percentage method that is currently in use.     

A Longitudinal Study of Salmonella Infection in Different Types of Turkey Flocks in Great Britain

Salmonella is, after Campylobacter, the most reported zoonotic pathogen in the EU. Poultry are a common source of infection to humans, and turkey flocks are commonly colonized with the organism. We investigated the prevalence and risk factors of Salmonella infection in 179 houses in 60 holdings representative of turkey meat and breeder production in Great Britain. From each holding, up to four houses were chosen, and two consecutive flocks per house were sampled/tested for Salmonella to investigate the persistence, elimination and introduction of Salmonella in consecutive crops. At the first sampling, the overall flock‐level Salmonella prevalence was 32.8% and 8.9% for meat and breeding flocks respectively. There was a higher prevalence of Salmonella in flocks in the rearing stage than in the fattening and breeding stages. At the first sampling, the flock‐level prevalence of Salmonella was 26.8% (95% CI: 20.7–33.7%), while the prevalence level in the subsequent flock was 20.5% (95% CI: 13.6–29.7%). No houses were positive for any of the EU‐regulated serovars. The most commonly encountered serovars were S. Kottbus and S. Kedougou. Carry‐over of infection was observed in 44.8% of the positive houses, and introduction of new infection occurred in 8.4% of houses. Data from the questionnaires and auditing of all holdings and houses were combined and used to calculate adjusted farm‐ and house‐adjusted risk factors. Significant risk factors were feed from a source other than a national compounder (OR = 2.4), feeder type other than pan feeders (OR = 2.4) and hygiene practices other than terminal cleaning and disinfection using power‐washing with sanitizer and anteroom with boot change (OR = 2.8). The study discusses the main challenges currently faced by the industry to control Salmonella in turkey production.     

A simulation model of brucellosis spread in British cattle under several testing regimes

Brucellosis is a widespread, economically devastating and highly infectious zoonosis. In cattle, infection predominantly is caused by Brucella abortus, and is usually detected in pregnant females through abortions. Great Britain (GB) has been declared free from brucellosis (officially brucellosis free (OBF)) since 1993 and as such is required by European Union (EU) regulations to test > or =20% of both beef and dairy cattle >24 months old routinely. Currently, however, GB serologically tests more cattle than required and the issue of reducing the level of testing has come under consideration. We developed a simulation model to determine the rate of spread of brucellosis under a variety of testing regimes. For dairy herds, we found that reducing the level of testing would have a major effect on the rate of spread of infection, should it be imported. For beef herds, reducing the level of testing would have much less effect. We also found that abortion notification is a very-important additional means of surveillance. As a result of our predictions, policy-makers decided not to reduce the level of testing and actively to promote abortion notification.     

A review of the use of B. melitensis Rev 1 vaccine in adult sheep and goats

The live Brucella melitensis Rev 1 strain is considered the best vaccine available for the prophylaxis of brucellosis in small ruminants. The classically recommended exclusive vaccination of young replacement animals has failed to control brucellosis in some developed countries and is frequently inapplicable in the developing world. Accordingly, whole-flock vaccination is the only feasible alternative to control B. melitensis infection in small ruminants under the extensive management conditions characteristic of these countries. This review describes the practical problems encountered and the experience acquired over the past decade (particularly in Spain) using the Rev 1 based control strategy. The vaccination of pregnant animals with full standard doses of Rev 1 administered subcutaneously is followed by abortion in most vaccinated animals. Reducing the dose of vaccine has been suggested as a method of avoiding this problem and, accordingly, a reduced-dose vaccination strategy has been widely used and has been reported as a safe and effective method of controlling small ruminant brucellosis. However, we reviewed field and experimental results supporting the fact that as a result of the induction of abortion in pregnant animals and the low degree of immunity conferred, reduced doses of Rev 1 should not be recommended as an alternative to the full standard doses.

When tested in a mouse model, differences in residual virulence and immunogenicity have been demonstrated between the different Rev 1 vaccines produced world-wide. These differences could account for the discrepancies in safety results obtained in mass vaccination trials in different countries. The induction of abortions when vaccinating pregnant animals means that there is no entirely safe strategy for Rev 1 vaccination. Conjunctival vaccination is safer than subcutaneous vaccination but is not safe enough to be applied regardless of the pregnancy status of the animals, and should be used only under restricted conditions. For sheep, conjunctival administration of standard doses of Rev 1 during the late lambing season or during lactation is recommended as a whole-flock vaccination strategy.     

A quantitative risk assessment for the importation of brucellosis-infected breeding cattle into Great Britain from selected European countries

Great Britain (GB) has been "Officially Brucellosis Free" (OBF) since 1991; because this disease has both public-health and international-trade implications, it is in the country's interest to maintain this freedom. A quantitative risk-assessment model was developed to determine the annual risk of importing brucellosis-infected breeding cattle into GB from Northern Ireland and the Republic of Ireland. (These countries exported the largest number of cattle into GB and were not brucellosis free during the development of the assessment in 2000.) We predicted that we can expect to import brucellosis from Northern Ireland every 2.63 years (1.89, 4.17) and from the Republic of Ireland, every 3.23 years (2.13, 5.88). The estimates of risk are sensitive to the assumed proportion of animals missed during routine surveillance that originate from OBF herds and the uncertainty associated with the surveillance test sensitivities. As a result of the assessment, the Department for Environment, Food and Rural Affairs (Defra) introduced post-calving testing for all cattle imported into British herds.     

Sero-prevalence and risk factors study of brucellosis in small ruminants in Southern Zone of Tigray Region, Northern Ethiopia

This study reports a prevalence and risk factor survey of brucellosis in small ruminants in Southern Zone of Tigray Region, Northern Ethiopia between October 2011 and April 2012 to determine the sero-prevalence of small-ruminant brucellosis and to identify associated risk factors for the occurrence of disease in small ruminants under extensive production system. Multistage random sampling was followed to select locations, flocks, and individual animals. Laboratory analysis of serum samples provided sero-prevalence estimates for flocks and geographic location. Information on risk factors at the individual and flock level was obtained by examination of individual animal and a questionnaire interview to flock owners. The overall individual animal-level sero-prevalence of brucellosis in small ruminants was 3.5 % and flock level sero-prevalence was 28.3 %, and the within-flock sero-prevalence was ranged from 0 % to 22.2 % based on the Complement Fixation Test. Multivariable logistic regression showed that the major risk factors for flock level sero-positivity were flock size and abortion history. This study showed that small-ruminant brucellosis is prevalent in the study area. Larger flock size and history of previous abortion in the flock were major risk factors identified for sero-positivity of small-ruminant brucellosis.     

Ovine brucellosis in alberta

Two parallel surveys of rams from Alberta sheep flocks were conducted to determine the presence of infection with Brucella ovis. In a retrospective study over a period of 24 months, using complement fixation test, 12 flocks out of 142 tested were considered infected. In another 17-month survey of slaughter rams by serology and culture methods 11 flocks out of 124 were found to be infected. The overall prevalence of ovine brucellosis was 8.6% of the flocks tested which represented 12.5% of the estimated sheep flocks in Alberta. Up to 67% of rams in infected flocks reacted to complement fixation test.

The complement fixation test was evaluated for its efficiency in the diagnosis of ovine brucellosis and compared with a limited number of an enzyme-linked immunosorbent assay (ELISA) results and clinical criteria. The complement fixation test as well as ELISA identified all culture positive rams. Both serological tests appeared satisfactory for the diagnosis of B. ovis epididymitis when the results could be interpreted in the light of flock history and clinical findings.

     

How to substantiate eradication of bovine brucellosis when aspecific serological reactions occur in the course of brucellosis testing

Collaborative work was financed by the EU to develop and assess new diagnostic tools that can differentiate between bovine brucellosis and bovine infections due to Yersinia enterocolitica O:9 either in conjunction with, or as an alternative to, the classical serological, bacteriological or allergic skin tests. Sixteen heifers were experimentally infected with Brucella abortus biovar 1 (five heifers), Brucella suis biovar 2 (two heifers), Y. enterocolitica O:9 (six heifers) and Y. enterocolitica O:3 (three heifers). Four heifers, naturally infected with Y. enterocolitica O:9 that presented aspecific brucellosis serological reactions were also included in the experiment. A self-limited infection was induced in cattle by B. suis biovar 2. All the brucellosis serological tests used, i.e. the slow agglutination test (SAW), the Rose Bengal test (RB), the complement fixation test (CFT), indirect and competitive ELISA’s, lacked specificity when used to analyze sera from Y. enterocolitica O:9 infected animals. A Yersinia outer membrane proteins (YOPs)-ELISA was also used and although the test is able to detect a Yersinia group infection, it provided no evidence of whether or not there is a possible brucellosis infection when dual infections are present. The brucellergen IFN-γ test showed a lack of specificity also. The only test that was proven to be specific is the brucellergen skin test. All brucellosis serological tests, except the indirect ELISA, were limited in their ability to detect B. abortus persistently infected animals.

Based on these experimental studies, a strategy was implemented as part of the year 2001 Belgian Brucellosis Eradication Program to substantiate the eradication of bovine brucellosis. Epidemiological inquiries have identified risk factors associated with aspecific serological reactions, possible transmission and infection of cattle by B. suis biovar 2 from infected wild boars; and both legal and administrative measures taken by the veterinary services. No cases of bovine brucellosis have been confirmed in Belgium since March 2000.     

Design and Results of an Intensive Monitoring Programme for Avian Influenza in Meat‐Type Turkey Flocks During Four Epidemics in Northern Italy

Surveillance programmes for low pathogenicity (LPAI) and high pathogenicity avian influenza (HPAI) infections in poultry are compulsory for EU Member States; yet, these programmes have rarely been evaluated. In Italy, following a 1999 HPAI epidemic, control measures, including vaccination and monitoring, were implemented in the densely populated poultry area (DPPA) where all epidemics in Italy have been concentrated. We evaluated the monitoring system for its capacity to detect outbreaks rapidly in meat‐type turkey flocks. The evaluation was performed in vaccination areas and high‐risk areas in the DPPA, in 2000–2005, during which four epidemics occurred. Serum samples and cloacal swabs were taken from vaccinated birds and unvaccinated (sentinel) birds. We compared the detection rate of active, passive and targeted surveillance, by vaccination status, using multinomial logistic regression. A total of 13 275 samplings for serological testing and 4889 samplings for virological testing were performed; 6315 production cycles of different bird species were tested. The outbreaks detection rate in meat‐type turkeys was 61% for active surveillance (n = 222/363 outbreaks), 32% for passive surveillance and 7% for targeted surveillance. The maximum likelihood predicted values for the detection rates differed by vaccination status: in unvaccinated flocks, it was 50% for active surveillance, 40% for passive surveillance and 10% for targeted surveillance, compared to respectively 79%, 17% and 4% for vaccinated flocks. Active surveillance seems to be most effective in detecting infection, especially when a vaccination programme is in place. This is the first evaluation of the effectiveness of different types of surveillance in monitoring LPAI infections in vaccinated poultry using field data.     

Increased Toxoplasma gondii positivity relative to age in 125 Scottish sheep flocks; evidence of frequent acquired infection

Toxoplasma gondii seroprevalence was determined in 3333 sheep sera from 125 distinct sheep flocks in Scotland, with the majority of flocks being represented by 27 samples, which were collected between July 2006 and August 2008. The selected farms give a representative sample of 14 400 sheep holdings identified in the Scottish Government census data from 2004. Overall T. gondii seroprevalence, at individual sheep level, was determined to be 56.6%; each flock tested, had at least a single positive animal and in four flocks all ewes tested positive. The seroprevalence of sheep increased from 37.7% in one year old stock to 73.8% in ewes that were older than six years, showing that acquired infections during the life of the animals is frequent and that environmental contamination by T. gondii oocysts must be significant. The median within-flock seroprevalence varied significantly across Scotland, with the lowest seroprevalence of 42.3% in the South and the highest seroprevalence of 69.2% in the far North of Scotland and the Scottish Islands, while the central part of Scotland had a seroprevalence of 57.7%. This distribution disequilibrium may be due to the spread and survival of oocysts on pasture and lambing areas. A questionnaire accompanying sampling of flocks identified farms that used Toxovax^®, a commercial vaccine that protects sheep from abortion due to T. gondii infection. Only 24.7% of farmers used the vaccine and the vaccine did not significantly affect the within flock seroprevalence for T. gondii. The implications for food safety and human infection are discussed.     

Comparison of milk-ELISA and serum-ELISA for the diagnosis of Brucella melitensis infection in sheep

Milk and blood samples from 704 lactating ewes were examined for the diagnosis of Brucella melitensis infection by milk-ELISA, serum-ELISA, RBPT, SAT and culture of milk. Of these ewes, 209 were from brucellosis free sheep flock, 443 from brucellosis infected sheep flock and 52 were from private sheep flocks of which status for brucellosis was not known. All the 209 ewes belonging to uninfected sheep flock were found negative in all the tests and of the remaining 495 ewes 105 were positive in serum-ELISA, 103 in milk-ELISA, 92 in RBPT, 85 in SAT, and B. melitensis biovar-1 was isolated from the milk of 29 ewes. Of the 105 serum-ELISA positive ewes, 99 were positive and 6 were negative in milk-ELISA, whereas of the 103 milk-ELISA positive ewes, 4 were negative in serum-ELISA. All together, 99 ewes were positive and 386 were negative in both the assays while 10 ewes yielded variable results. The specificity of milk-ELISA in brucellosis free flock was 100% and sensitivity and positive predictive value were 96.11% and 94.28%, respectively, in infected flocks. The Brucella antibody levels in milk and serum samples as determined by milk-ELISA and serum-ELISA were correlated significantly. The milk-ELISA for brucellosis appears to be an attractive alternative of serum-ELISA particularly in the lactating ewes.     

Brucellosis in the European Union and Norway at the turn of the twenty-first century

Control and eradication programs of brucellosis in cattle, sheep, goats and pigs have been more or less successfully implemented within the Member States (MS) of the European Union (EU) and Norway after Word War II. As a result, the epidemiological situation of animal brucellosis is extremely diverse among different MS or regions within a MS and among the different animal species. Some MS, mainly North European countries, and Norway are declared “officially bovine brucellosis free” and/or “officially ovine and caprine (Brucella melitensis) free”. The situation is less favorable in Southern European countries, particularly as far as sheep and goat brucellosis are concerned. This situation has important zoonotic consequences as reflected in the number of human brucellosis cases due to B. melitensis that are still encountered in those countries. Brucellosis in swine has re-emerged as a result of spillover from the wild boar brucellosis (Brucella suis biovar 2) reservoir, particularly in outdoor reared pigs. Besides the actual challenge to eradicate brucellosis, further issues have to be addressed: (1) the management of false positive serological results that occur in the course of brucellosis testing, particularly in cattle; (2) the impact of wildlife brucellosis, particularly wild boar brucellosis in domestic animals; and (3) the importance of B. melitensis infection in cattle that are in contact with infected sheep.     

PCR detection of lentiviral GAG segment DNA in the white blood cells of sheep and goats

A PCR assay for the detection of small ruminant lentiviral gag DNA (provirus) in the white blood cells of sheep and goats was developed and compared with a serological test (AGIDT). A sample of the DNA prepared from the white blood cells in 3 ml of blood from 208 sheep and goats from 18 different flocks was subjected to PCR assay. One of 85 animals from flocks accredited under the Dutch national MVV/CAEV control programme was positive by PCR while none was positive by AGIDT. In infected flocks, the AGIDT appeared slightly more sensitive, but preliminary results show that the sensitivity of the PCR assay may be further improved by increasing the number of monocytes tested. The PCR assay, however, was clearly more sensitive in detecting animals in the early stages of infection. With the use of a set of mixed primers and probes, the assay was able to detect the variety of CAEV and MVV strains occurring in the field.     

A serological study on Brucella abortus, caprine arthritis-encephalitis virus and Leptospira in dairy goats in Rio de Janeiro, Brazil

In spite of the large number of goats found in several developing tropical countries, milk production remains unsatisfactory. The occurrence of infectious diseases, such as leptospirosis, brucellosis and caprine arthritis-encephalitis (CAE) may in part be responsible for sub-optimal production. In this study, 1000 serum samples were tested for leptospirosis, 953 for brucellosis and 562 for CAE. All tested flocks presented at least one seroreactive animal for leptospirosis and for CAE. Reactivity to leptospirosis was 11.1%, and serovar hardjo was the most frequently found. Anti-B. abortus agglutinins were found in 0.5% of the samples presented and 14.1% were seroreactive to CAE. Leptospirosis was considered to represent the major infectious problem in the studied goat flocks. The occurrence of infectious diseases in the tested flocks may represent an important factor contributing to the decreased productivity of the animals. These findings may be similar to those observed in other developing countries and require further study to define the relationship between seropositivity and reduced production.     

Epidemiological studies on ovine brucellosis in selected ram flocks

SUMMARY The epidemiology of ovine brucellosis was investigated in 6 ram flocks in which anomalous reactions to the complement fixation test was recorded. It was shown that rams can become infected as young as 4 months of age. Naturally infected animals have an epididymitis and excrete Brucella ovis in their semen or they may only show a serological response for a short time then recover. The base line titres of chronically infected animals stay relatively constant. The importance of abortive infection and possible reinfection is discussed.     

Prevalence of Salmonella spp. in Austrian broiler flocks in the context of the EU-wide baseline survey 2005-2006

In Austria an EU-wide baseline survey on the prevalence of Salmonella spp. in broilers organized by the EU commission was conducted from October 2005 to September 2006. The aim of this study was to produce comparable data on the prevalence of Salmonella in broiler flocks and holdings for all member states and for the EU-Commission to set EU-wide targets for the control of Salmonella in the broiler populations. A randomised sampling plan was designed according to EU-commission parameters (p = 50%; CI = 95%, a = 5%). Sampling was carried out regularly throughout the whole year. On every farm one flock was sampled with five pairs of boot swabs and analysed in the lab according to appendix D of ISO 6579 (2002). In Austria, 363 flocks on farms consisting of at least 5000 broilers each were tested. 28 flocks (7.7%) showed infections with Salmonella spp., eight flocks (2.2%) had either S. Enteritidis (six flocks) or S. Typhimurium (two flocks). In detail, S. Enteritidis (1.7%), S. Typhimurium (0.6%), S. Montevideo (4.1%), S. Infantis 0.6%, S. Senftenberg, S. Tennessee and S. Virchow (0.3% each) have been found. Data indicated that the risk of vertical transmission of Salmonella spp. to broiler flocks has almost been kept at bay; however, the risk of horizontal transmission still needs attention. Contamination of feeding stuff, possible persistence, spreading between barns of a farm as well as introduction of Salmonella spp. through individuals or materials are important factors for future control strategies.     

Serology as an aid to diagnosis: uses and abuses

The importance of correct interpretation of serological test results, common sources of error and problems associated with tests are discussed. In bovine brucellosis, a disease which is ideally suited to serological diagnosis, foetal contact with infection may cause the calf to be a serologically negative carrier. The immune tolerant animal resulting from foetal contact with virus is a major problem in the serological detection of border disease. In Johnes' disease and to a lesser extent in Brucella ovis and leptospiral infections, problems associated with sensitivity and specificity of the tests are stressed. Serovar specificity, cumbersome test procedures and negative tests in the incubation period cause difficulty in the interpretation of serological test results for leptospirosis. The importance of clinical examination, herd histories and alternative diagnostic procedures is important in all diseases. Wherever possible, flocks or herds should be maintained in specific disease-free state. Selection of stock from accredited herds or flocks is the most certain method of buying non-infected animals.     

Evaluation of official eradication-campaigns data for investigating small-ruminant brucellosis in the province of León, Spain

Brucellosis official eradication-campaigns data were used to study the epidemiology of the small-ruminant brucellosis infection in the province of León (northwest Spain). Data from three consecutive campaigns (1997–1999) were retrieved from flock sheets from controlled flocks and from other official statistics. In general, flock information was scarce, with a small percentage of contradictory data and other deficiencies that might have affected the campaign results. Nevertheless, unconditional multivariable logistic regression showed four risk factors for brucellosis infection in 1999: larger flock size, higher percentage of flocks in the town that are seropositive and having been brucellosis positive in 1997 and 1998. Despite of the scarcity of data available from official records, they were useful to explain, in part, the extent of the SRB in the province of León in 1999.     

山西省大同市灵丘县养殖户布鲁菌病知识宣传干预调查

[目的]了解山西省大同市灵丘县养殖户对布鲁菌病相关知识知晓情况、可能的感染危险行为,为针对性开展布鲁菌病健康宣教提供参考。[方法]采用简单随机抽样方法,在灵丘县选取70户牛养殖户,通过设计的调查问卷对养殖户的布病防控知识和高危行为情况开展现状调查。[结果]在70名被调查对象中,有77.14%的养殖户没有对新购入牛进行单独饲喂的防疫隔离意识。有45.71%的养殖户对牛群未免疫布病疫苗。虽然灵丘县近年来多次开展过布鲁菌病的宣传干预,但该次调查结果显示,宣传干预仍有较大的改善空间。[结论]灵丘县养殖户对布鲁菌病的知识知晓率相对较高,但仍距离规划目标还存在较大差距,仍存在不小的感染布鲁菌病的风险。因此,在接下来的工作中应加强针对养殖户进行布鲁菌病宣传干预,提高该部分人群对布鲁菌病的防护意识。     

A Brucellosis Disease Control Strategy for the Kakheti Region of the Country of Georgia: An Agent‐Based Model

Brucellosis has been reported in livestock and humans in the country of Georgia with Brucella melitensis as the most common species causing disease. Georgia lacked sufficient data to assess effectiveness of the various potential control measures utilizing a reliable population‐based simulation model of animal‐to‐human transmission of this infection. Therefore, an agent‐based model was built using data from previous studies to evaluate the effect of an animal‐level infection control programme on human incidence and sheep flock and cattle herd prevalence of brucellosis in the Kakheti region of Georgia. This model simulated the patterns of interaction of human–animal workers, sheep flocks and cattle herds with various infection control measures and returned population‐based data. The model simulates the use of control measures needed for herd and flock prevalence to fall below 2%. As per the model output, shepherds had the greatest disease reduction as a result of the infection control programme. Cattle had the greatest influence on the incidence of human disease. Control strategies should include all susceptible animal species, sheep and cattle, identify the species of brucellosis present in the cattle population and should be conducted at the municipality level. This approach can be considered as a model to other countries and regions when assessment of control strategies is needed but data are scattered.