Prevalence Of Infected Herds Research Articles

Retrospective benefit-cost analysis of bovine brucellosis control in the state of Mato Grosso, Brazil.

From 2001, due to the launching of the National Program for the Control and Eradication of Brucellosis and Tuberculosis, Brazil began a series of studies aimed at the epidemiological characterization of bovine brucellosis in its federative units. In the state of Mato Grosso, studies conducted in 2003 and 2014 showed a reduction in the prevalence of infected herds from 41.2 % to 24 % and in the prevalence of seropositive animals from 10.2 % to 5.1 %. These results stemmed from the efficient heifer vaccination program with S19 implemented by the state. From this scenario, the present study quantified and compared the benefits and costs of bovine brucellosis control in the state through a financial analysis. When considering private and public costs, the Net Present Value (NPV) was estimated at US$ 37.5 million, the Internal Rate of Return (IRR) was calculated at 31 %, and the Benefit-Cost Ratio (BCR) was 2.3. When considering only the private costs, the NPV was US$ 51.3 million, the IRR was 46 % and the BCR was 3.43, indicating that the cattle producer in Mato Grosso had a return of US$ 3.43 for each US$ 1.00 invested. Therefore, the bovine brucellosis control actions carried out in the state of Mato Grosso between 2003 and 2014 were highly advantageous from the economic point of view. The most rational way to continue decreasing bovine brucellosis prevalences at low cost in the state is to maintain the heifer vaccination program, using the RB51 vaccine in addition to S19.

Epidemiological situation of bovine tuberculosis in the state of Tocantins, Brazil

The epidemiological situation of bovine tuberculosis was studied from October 2014 to August 2015 in the state of Tocantins, a traditional beef exporter. The state was divided into five regions and the farms were randomly selected in each region. A predetermined number of animals was randomly selected and diagnosed using the Comparative Cervical Tuberculin Test. A total of 11,926 animals from 757 farms were tested. Animals with inconclusive test results were retested with the same diagnostic procedure at least 60 days later. The prevalence of infected herds in the state was 0.16% [0.02-1.15] and the prevalence of infected animals 0.009% [0.001-0.063]. Only one positive animal was detected in the Araguaína region. The state of Tocantins has a very low prevalence of bovine tuberculosis and, therefore, should evaluate the need of structuring a surveillance system to eradicate the disease.

Epidemiological situation of bovine tuberculosis in the State of Mato Grosso, Brazil

In 2009, the epidemiological situation of bovine tuberculosis was studied in the state of Mato Grosso, which is a traditional beef exporter. The state was divided into four regions. In each region, properties were selected randomly. A predetermined random number of animals were chosen from these properties, and comparative cervical tuberculin tests were conducted. In total, 28,878 animals from 1,133 properties underwent examination. The animals with inconclusive results were reexamined with the same diagnostic procedure in a minimal interval of 60 days. In each sampled property, a questionnaire-based survey was conducted to identify possible risk factors for the disease. In the state, the prevalence of infected herds and animals was 1.3% [0.7; 2.4] and 0.12% [0.03; 0.44], respectively. Further, the prevalence of infected herds and animals were 0.0% [0.0; 2.0] and 0.0% [0.0; 0.08] in the Pantanal region, 1.3% [0.5; 3.1] and 0.04% [0.01; 0.17] in the dairy region, 0.7% [0.2; 2.7] and 0.01% [0.003; 0.04] in the fattening region, and 1.7% [0.7; 4.1] and 0.24% [0.06; 0.90] in the breeding region, respectively. It was observed that the condition of the herds infected with bovine tuberculosis was associated with milk production, European or mestizo breeds, degree of sophistication in the production mode, and herd size of up to 486 animals. Therefore, the implementation of a monitoring system for detection and elimination of the residual infected herds along with incorporation of risk-based monitoring elements is the best strategy for the state.

Prevalence and risk factors for bovine tuberculosis in the State of Bahia, Brazil

An epidemiological study was carried out in order to characterize the bovine tuberculosis situation and to support the planning and implementation of the National Program for the Control and Eradication of Bovine Tuberculosis in the State of Bahia, owing to the importance of the disease in causing economic burdens and its impact on public health. The State was divided into four regions. In each region, properties were randomly chosen and, a pre-established number of animals was also randomly selected; these animals then subjected to the intradermal comparative cervical tuberculin diagnostic test. Animals with inconclusive test results were retested with the same diagnostic procedure within a minimum interval of 60 days. Within each sampled property, a questionnaire was administered to verify possible risk factors for the disease. In the State, the prevalence of infected herds was 1.6% [1.0–2.6] and that of infected animals 0,21% [0,07; 0,60]. In the regions, the prevalence of infected herds and infected animals were, respectively, 2,0% [1,0; 4,2%] and 2,0% [1,0; 4,2%] in region 1; , 2,9% [1,5; 5,5] and 0,66% [0,20; 2,16] in region 2; 0,3% [0,04; 2,1] and 0,02% [0,002; 0,12] in region 3; and 0,6% [0,2; 2,5] and 0,05% [0,01; 0,20] in region 4. The risk factors associated with tuberculosis infection were dairy farm (odds ratio [OR] = 9.72) or mixed farm (OR = 6.66), and size of herd ? 18 cows ? 24 months of age (OR = 8.44). In conclusion, it is recommended that the State of Bahia implement a surveillance system for the detection of herds with bovine tuberculosis to certifying them in free herds, with special attention to dairy properties, and develop a solid program of health education so that producers test animals for bovine tuberculosis before introducing them into their herds.

Epidemiological status of bovine tuberculosis in the State of Rio Grande do Sul, Brazil

A study was conducted to determine the epidemiological status of bovine tuberculosis in the state of Rio Grande do Sul. The state was divided in seven regions, and in each of them, a pre-established number of farms was randomly sampled. In each farm, cows with age equal to or greater than 24 months were selected at random and submitted to the comparative cervical tuberculin test. The animals whose tests were inconclusive were retested with the same diagnostic procedure within a minimum interval of 60 days. In all, 9,895 animals from 1,067 farms were tested. An epidemiological questionnaire was applied in the farms in order to identify risk factors associated with bovine tuberculosis. The prevalence of infected herds in the state was 2.8% [1.8; 4.0] and that of infected animals was 0.7% [0.4; 1.0]. There was a trend towards a concentration of infected herds in the northern part of the state, with a predominance of dairy and mixed herds. The risk factors associated with the condition of infected herds were being a dairy herd (OR = 2.90 [1.40; 6.13]) and herds with 16 or more cows (OR = 2.61 [1.20; 5.49]). Thus, the best strategy to be adopted by the state is the implementation of surveillance systems to detect and remediate the infected herds, preferably incorporating elements of risk-based surveillance. In addition, the state must carry out a solid action of health education so that the producers test animals for bovine tuberculosis before introducing them in their herds.

Prevalence and risk factors for bovine tuberculosis in the State of Mato Grosso do Sul, Brazil

The objective of this study was to describe the epidemiological situation of bovine tuberculosis in Mato Grosso do Sul. The State was divided into three regions, Pantanal, Planalto Norte, and Planalto Sul. In each region, properties were randomly chosen and a pre-established number of animals were also randomly selected; these animals were submitted to the intradermal comparative cervical tuberculin diagnostic test. In total, 17,121 animals from 938 properties were tested. In cases of inconclusive results, the animals were retested with the same diagnostic procedure within a minimum interval of 60 days. An epidemiological questionnaire was administered in the properties sampled to investigate possible risk factors for the disease. In the State, the prevalence of infected herds was 1.3% (95% confidence interval [CI]: 0.72–2.37%) and that of infected animals was 0.035% (95% CI: 0.017–0.069%). Point estimates indicated a higher concentration of infected herds (2.61%; 95% CI: 1.31–5.15%) and infected animals (0.132%; 95% CI: 0.055–0.315%) in the Planalto Sul region, which has a predominance of dairy properties. The prevalence of herds infected with bovine tuberculosis was found to be associated with the production of milk, with technification in the mode of production represented by the use of mechanical milking. Thus, it is recommended that the State adopt strategies for the eradication of bovine tuberculosis, with the structuring of the surveillance system for detection and mitigation of infected herds, incorporating risk-based surveillance elements.

Prevalence and herd-level risk factors of bovine tuberculosis in the State of Santa Catarina

With the aim of supporting the strategic planning of the National Program for Control and Eradication of Brucellosis and Tuberculosis, different Brazilian states have been conducting cross-sectional studies, coordinated by the Ministry of Agriculture, Livestock, and Supply and with scientific support from the University of São Paulo and the University of Brasilia. In Santa Catarina, the State Animal Health Agency (CIDASC) conducted a study on bovine tuberculosis (TB) prevalence and assessment of risk factors in 2012. The state was divided into five regions and, in each region, independent sampling was performed in two steps: (i) cattle herds with reproductive activity were randomly selected; and (ii) in each herd, a sample of females aged 24 months or older underwent the intradermal comparative tuberculin test. A questionnaire was used to collect data on production characteristics and management practices that could be associated with the tuberculosis infection. Herd prevalence of bovine TB was 0.50% (95% confidence interval [CI]: 0.074–0.93%) while the prevalence of TB in adult females was 0.06% (95% CI: 0–0.12%). No significant difference in the prevalence of infected herds and of positive females was observed among the five regions. The logistic regression model revealed that herds with 19 or more females showed an odds ratio (OR) of 7.68 (95% CI: 1.22–48.39) compared to smaller herds, while dairy herds presented an OR of 10.43 (95% CI: 2.00–54.25) relative to beef or dual-purpose herds. The results suggest that dairy herds, in which animals are kept in partial or total confinement, and larger herds, which tend to acquire animals more often, are at a higher risk of bovine TB. Given the low prevalence and the type of higher-risk properties, a bovine TB surveillance system should be targeted at the state’s dairy basins, particularly the western region that accounts for the major industries and more intensive dairy farms.

An update on the epidemiologic situation of bovine brucellosis in the State of Espírito Santo, Brazil

A cross-sectional study was carried out between January 2012 and May 2014 to estimate the prevalence of bovine brucellosis in the state of Espírito Santo, Brazil. This study was carried out 11 years after the implementation of the immunization program for heifers with a vaccine derived from the S19 strain of Brucella abortus. The state was divided into two regions. Three hundred farms from each region, with reproductive activity, were randomly chosen and included as primary sample units. A fixed number of cows were randomly selected and tested for antibodies against Brucella spp. A farm was considered to be infected when at least one female tested positive for Brucella spp. In the selected farms, an epidemiological questionnaire based survey, focused on herd traits as well as husbandry and sanitary practices, was conducted, to evaluate the factors associated with the risk of infection. The overall prevalence of infected herds was 9.3% (95% confidence interval, 95% CI = 7.1–11.8%), varying from 8.7% (95% CI = 5.7–12.6%) in region 2 to 9.7% (95% CI = 6.8–13.4%) in region 1. There was no significant difference in the prevalence between the regions. The apparent prevalence of Brucella spp. positive farms across the regions and the state was similar to the prevalence observed 11 years earlier. The prevalence of positive animals was 3.8% (95% CI = 0.9–10.1%), varying from 1.5% (95% CI = 0.8–2.4%) in region 1 to 7.9% (95% CI = 1.9–20.3%) in region 2, without a significant difference between the regions. There was no difference in the number of Brucella spp. positive animals after 11 years of the immunization program. The risk factors associated with brucellosis were (i) more than 10 cows per herd (OR = 5.0; 95% CI =2.5–11.1) and (ii) equipment, feedstock, or personnel sharing (OR = 2.2; 95% CI = 1.1–4.2). The state of Espírito Santo should seek systematic vaccination coverage targeting more than 80% of the eligible heifers. An efficient animal health program, which educates the farmers to test replacement animals for brucellosis before introducing them to their herds, to avoid equipment, personnel or feedstock sharing with farms of unknown sanitary conditions, and to increase awareness of the importance of good sanitary procedures during artificial insemination, should be implemented.

Epidemiological situation of bovine brucellosis after implementation of a vaccination program in Rio Grande do Sul State, Brazil

This study aimed to evaluate the effectiveness of a bovine brucellosis vaccination program in Rio Grande do Sul, with prevalence as the indicator, and to identify risk factors for the disease. The state was divided into seven regions. For each region, a predetermined number of properties were randomly sampled, in which a pre-established number of randomly selected females aged over 24 months were tested. The serodiagnosis protocol consisted of a screening test using buffered acidified antigen, followed by a confirmatory test using 2-mercaptoethanol. An epidemiological questionnaire was utilized to identify possible risk factors associated with bovine brucellosis. In the state of Rio Grande do Sul, the prevalence of infected herds was found to be 3.54% [2.49-4.88], and the prevalence of infected animals was 0.98% [0.57-1.57]. In assessments of specific regions, the infected herd prevalence ranged from 0.66% to 3.09%, and among the animals, from 0.06% to 2.03%. In herds comprising 15 or more cows, beef type and pasture sharing emerged as risk factors for bovine brucellosis in the state. The epidemiological status of bovine brucellosis in Rio Grande do Sul has remained unchanged since 2004, even though adequate vaccination coverage has been recorded since 2009. Thus, the state should continue its vaccination program, with emphasis on the quality of the process and on encouraging the use of non-antibody inducing vaccines. In addition, the state must make a greater effort to educate producers on the importance of testing for brucellosis in breeding animals before introducing them onto their properties, and on the importance of avoiding shared grazing among herds whose health conditions are unknown.

Epidemiological situation of bovine tuberculosis in the State of Pernambuco, Brazil

The epidemiological situation of bovine tuberculosis was studied in the state of Pernambuco, Brazil. The state was divided into three regions, and a predetermined number of properties was randomly sampled in each region. In each property, females aged 24 months or older were randomly selected and subjected to the cervical comparative tuberculin test. Altogether, 5,728 animals from 906 properties were tested. In the evaluated properties, an epidemiological questionnaire was applied to identify risk factors related to bovine tuberculosis. The prevalence of infected herds and infected animals and in the state was 2.87% [1.82–4.50] and 0.62% [0.29–1.29], respectively. There was a predominance trend of infected herds in the properties located in the dry areas of Pernambuco, where most dairy properties are found. The risk factors related to the occurrence of positive herds were: presence of 18 or more cows in the herd, milking the cows two or three times a day, and sharing the grazing area. In conclusion, the prevalence of bovine tuberculosis in Pernambuco is low, and the best strategy to be adopted is the implementation of a surveillance system for detection and sanitation of infected herds, preferably by incorporating risk-based surveillance strategies. In addition, the State should implement an effective sanitary program to enable producers to test their animals for bovine tuberculosis before inserting them into the herds, as well as avoid sharing the grazing areas with properties that are not free of bovine tuberculosis.

Situação epidemiológica da brucelose bovina no Estado de Minas Gerais

Realizou-se um estudo para caracterizar a situação epidemiológica da brucelose bovina no Estado de Minas Gerais. O Estado foi estratificado em sete circuitos produtores. Em cada circuito foram amostradas aleatoriamente cerca de 300 propriedades e, dentro dessas, foi escolhido, de forma aleatória, um número pré-estabelecido de animais, dos quais foi obtida uma amostra de sangue. No total, foram amostrados 20.643 animais, provenientes de 2.204 propriedades. Em cada propriedade visitada aplicou-se um questionário epidemiológico para verificar o tipo de exploração e as práticas zootécnicas e sanitárias que poderiam estar associadas ao risco de infecção pela doença. O protocolo de testes utilizado foi o da triagem com o teste do antígeno acidificado tamponado e a confirmação dos positivos com o teste do 2-mercaptoetanol. O rebanho foi considerado positivo, se pelo menos um animal foi reagente às duas provas sorológicas. As prevalências de focos e de animais infectados do Estado foram de 6,0% [5,0-7,1%] e 1,1% [0,78-1,4%], respectivamente. Os resultados para os circuitos pecuários da prevalência de focos e de animais foram: circuito 1, 4,7% [2,7-7,7%] e 0,82% [0,06-1,6%]; circuito 2, 7,2% [4,6-10,6%] e 1,2% [0,53-1,8%]; circuito 3, 6,8% [4,3-10,0%] e 1,5% [0,47-2,4%]; circuito 4, 6,5% [4,1-9,8%] e 1,1% [0,39-1,7%]; circuito 5, 3,8% [2,0-6,5%] e 0,40% [0,11-0,69%]; circuito 6, 6,2% [3,8-9,6%] e 0,66% [0,29-1,0%]; circuito 7, 11,0% [7,7-15,0%] e 1,7% [0,92-2,6%], respectivamente. Os fatores de risco (odds ratio, OR) associados à condição de foco foram: compra de reprodutores (OR = 1,66 [1,13-2,44]), ocorrência de aborto nos últimos 12 meses (OR = 1,81 [1,26-2,60]) e presença de cervídeos na propriedade (OR = 1,56 [1,08-2,27]). A vacinação contra brucelose foi identificada como fator protetor (OR = 0,38 [0,19-0,79]). Concluiu-se que o programa obrigatório de vacinação de bezerras, iniciado na década de 1990, está sendo eficaz ao reduzir a prevalência em todo o Estado e em todos os sistemas de produção animal. As autoridades sanitárias devem priorizar o controle da compra de animais para reprodução, que não apresentem garantias sanitárias e incorporar essa medida às ações de educativas.

Situação epidemiológica da brucelose bovina no Estado da Bahia

O trabalho consistiu em estratificar o Estado da Bahia em quatro regiões com características homogêneas (circuitos produtores) para que fossem amostradas aleatoriamente, em cada uma delas, 300 propriedades. Em cada propriedade foram escolhidas, de forma aleatória, 10 a 15 fêmeas bovinas adultas, das quais foi obtida uma amostra de sangue. No total, foram amostrados 10.816 animais, provenientes de 1.413 propriedades. O protocolo de testes utilizado foi o da triagem com o teste do antígeno acidificado tamponado (Rosa Bengala) e a confirmação dos positivos com o teste do 2-mercaptoetanol. O rebanho foi considerado positivo se pelo menos um animal reagiu às duas provas sorológicas. As prevalências de focos e a de fêmeas adultas soropositivas do Estado foram de 4,2% [3,1-5,3%] e 0,66% [0,41-0,93%], respectivamente. Para os circuitos produtores foram: circuito 1, 5,8% [3,6-8,7%] e 0,86% [0,41-1,3%]; circuito 2, 3,1% [1,5-5,6%] e 1,2% [0,25-2,1%]; circuito 3, 6,3% [4,0-9,3%] e 1,7% [0,66-2,7%]; e circuito 4, 0,60% [0,07-2,2%] e 0,07 [0,00-0,21%]. Para a análise de fatores de riscos associados à doença foi aplicado um questionário epidemiológico em cada propriedade visitada. Os fatores de risco (odds ratio, OR) associados à condição de foco foram: compra de reprodutores (OR= 2,27) e presença de áreas alagadiças (OR= 1,76). A vacinação de fêmeas de três até oito meses de idade foi um fator de proteção (OR= 0,53).

Situação epidemiológica da brucelose bovina no Estado de Santa Catarina

Realizou-se um estudo para caracterizar a situação epidemiológica da brucelose bovina no Estado de Santa Catarina. O Estado foi estratificado em cinco circuitos produtores. Em cada circuito produtor foram amostradas aleatoriamente cerca de 300 propriedades e, dentro dessas, foi escolhido, de forma aleatória, um número pré-estabelecido de animais, dos quais foi obtida uma amostra de sangue. No total foram amostrados 7801 animais, provenientes de 1586 propriedades. O protocolo de testes utilizado foi o da triagem com o teste do antígeno acidificado tamponado e o reteste dos positivos com o do 2-mercaptoetanol. O rebanho foi considerado positivo se pelo menos um animal foi reagente às duas provas sorológicas. As prevalências de focos e de animais infectados no Estado foram de 0,32% [0,10-0,69%] e 0,06% [0,0-0,17%], respectivamente. A prevalência de focos nos circuitos pecuários foram: circuito 1, 0,33% [0,0-0,99%]; circuito 2, 0,33% [0,0-1,0%]; circuito 3, 0,25% [0,0-0,75%]; circuito 4, 0,66% [0,08-1,84%] e circuito 5, 0,33% [0,0-1,0%].

Situação epidemiológica da brucelose bovina no Estado de Mato Grosso

Caracterizou-se a brucelose bovina em Mato Grosso por meio de um estudo transversal realizado em 2003 para auxiliar na implementação do Programa Nacional de Controle e Erradicação da Brucelose e Tuberculose. No Estado, estratificado em quatro circuitos pecuários, foram amostrados 13.684 animais, provenientes de 1.152 rebanhos. O protocolo de testes utilizado foi o da triagem com o teste do antígeno acidificado tamponado e os soros reagentes foram testados pelo 2-mercaptoetanol (ME) e concomitantemente retestados pelo teste de Rosa Bengala para resultado conclusivo. As prevalências de focos e de animais infectados foram: 41,2% [38,0-44,4%] e 10,2% [7,4-13,1%], respectivamente. Nos circuitos produtivos, as prevalências de focos foram 36,9% [29,2-45,2%], 27,2% [22,8-32,1%], 40,4% [38,8-46,2%] e 50,3% [44,5-56,1%]; e as prevalências de animais 7,9% [3,0-12,9%], 4,1% [2,8-5,4%], 8,1% [5,2-11,1%] e 15,3% [9,2-21,3%], respectivamente, para os circuitos 1, 2, 3 e 4. Os fatores de risco (odds ratio, OR) associados à condição de foco no Estado foram: exploração de gado de corte (OR= 1,8 [1,2-2,5]), exploração mista (OR=1,8 [1,2-2,7]), número de fêmeas no rebanho de 11 a 50 (OR=4,8 [1,1-20,8]), número de fêmeas no rebanho acima de 51 (OR=6,8 [1,6-29,0]), ocorrência de aborto (OR=1,7 [1,3-2,2]). A brucelose está homogeneamente distribuída no Estado, o que permite uniformidade de medidas sanitárias. Adicionalmente, sugere-se a intensificação da vacinação de fêmeas para todo o Estado.

Prevalence and distribution of paratuberculosis (Johne's disease) in cattle herds in Ireland

A simple random survey was conducted in Ireland during 2005 to estimate the ELISA-prevalence of paratuberculosis, commonly called Johne's disease (JD), in the cattle population. Serum samples were collected from all 20,322 females/breeding bulls over 12 months-of-age in 639 herds. All samples were tested using a commercially available absorbed ELISA. The overall prevalence of infected herds, based on the presence of at least one ELISA-positive animal, was 21.4% (95% CI 18.4%-24.9%). Herd prevalence levels amongst dairy herds (mean 31.5%; 95% CI: 24.6%, 39.3%) was higher than among beef herds (mean 17.9%; 95% CI: 14.6%-21.8%). However, the animal level prevalence was similar. The true prevalence among all animals tested, was calculated to be 2.86% (95%CI: 2.76, 2.97) and for animals >= 2 yrs, it was 3.30% (95%CI: 3.17, 3.43). For animals in beef herds, true prevalence was 3.09% (95%CI: 2.93, 3.24), and for those in dairy herds, 2.74% (95%CI: 2.59, 2.90). The majority of herds had only one ELISA-positive infected animal. Only 6.4% (95% CI 4.7%-8.7%) of all herds had more than one ELISA-positive infected animal; 13.3% (CI 8.7%-19.7%) of dairy herds ranging from two to eight ELISA-positive infected animals; and, 3.9% beef herds (CI 2.4%-6.2%) ranging from two to five ELISA-positive infected animals. The true prevalence of herds infected and shedding Mycobacterium avium subspecies paratuberculosis is estimated to be 9.5% for all herd types; 20.6% for dairy herds; and 7.6% for beef herds. If ELISA positive animals <2-years-of-age are excluded, the true herd prevalene reduces to: 9.3% for all herd types; 19.6% for dairy herds; and 6.3% for beef herds based on a test specificity (Sp) of 99.8% and test sensitivity (Se) (i.e., ability to detect culture-positive, infected animals shedding at any level) of 27.8-28.9%.

Estimating the prevalence of Salmonella spp. in swine herds--influence of sensitivity and specificity of Salmonella detection.

Information about the proportion of truly Salmonella-free herds is required for an evaluation of the epidemiological situation, the development of control strategies and their implementation. Findings regarding the presence of salmonellas in faeces and intestinal lymph nodes as well as the presence of Salmonella antibodies in meat juice from slaughtered pigs were obtained in the context of a study conducted by a number of institutes. These data were used for an analysis of the validity of data on the prevalence of infected animals within herds and on the prevalence of infected herds. The proportion of batches or herds with exclusively negative individual findings was found to depend not only on the true proportion of truly Salmonella-free animals within herds but quite essentially also on the distribution of the proportion of infected animals within herds, the sensitivity of the methods of examination and sample sizes. When taking into account the existing dependencies, it was found that among the swine, the real numbers of Salmonella carriers were much higher than shown by bacteriological and serological examination. Regarding salmonellosis in swine, also a number of contaminated herds must be expected which is far higher than that shown by the number of herds with positive findings in at least one animal. Even a low contamination of all or almost all herds would result in the numbers of 'negative' batches observed, i.e. batches with exclusively negative individual findings. A rating of the salmonella exposure of herds as high, low, or very low is possible and may, and should be, used for measures of consumer protection, irrespective of the proportion of truly Salmonella-free herds.

Eradication of bovine brucellosis in the 10th Region de Los Lagos, Chile

The process of Bovine Brucellosis Eradication that began in 1996 in the 10th Region de Los Lagos of Chile will be reviewed. The region comprises the most important dairy area of the country and it has the largest concentration of brucellosis infected herds. Based on the information gathered by an epidemiological surveillance system, the results of the eradication process for the years 1996 till 2001 are presented as rates of Milk Ring Test (MRT) positive dairies, rates of brucellosis reactors (bovines) in livestock markets and slaughterhouses, and the annual incidence and prevalence of brucellosis infected herds. During the period the rates of positive dairies, bovine reactors in livestock markets and slaughterhouses, and the annual incidence and prevalence of infected herds have experienced a decrease, while the rate of bovine reactors in slaughterhouses has remained stable. Data on the preventive measures taken, such as vaccination of female bovines and Certification of Brucellosis Free Herds, are also shown. The surveillance system has allowed the detection of infected herds, while the measures of prevention and cleaning of infected herds have allowed a reduction in the incidence and prevalence of the infection by Brucella abortus.

Pre-slaughter control of Escherichia coli O157 in beef cattle: a simulation study

A stochastic simulation model was used to assess the benefit of measures implemented in the pre-slaughter period that are aimed at reducing the contamination of beef carcasses with Shiga-like-toxin-producing Escherichia coli O157. The scenario studied was based on an abattoir processing ≈1000 head of lot-fed cattle per day. Input assumptions were described using probability distributions to reflect uncertainty in their true values. Control measures that were assessed were based on either a reduction in herd prevalence of infection, reduction in opportunity for cross-contamination in the processing plant by re-ordering of the slaughter queue, reduction of concentration of E. coli O157 in fresh faeces, or a reduction in the amount of faeces, mud and bedding (`tag') transferred from the hide to the carcass. Some control measures evaluated were hypothetical in nature and were included to assist with the planning of research priorities. Simulations suggested that the greatest potential impact is associated with vaccination and with an agent that reduces shedding E. coli O157 in faeces. Knowledge of herd-test results obtained by testing a sample of animals from the herd provides only a minor advantage in control programmes, although application of a rapid test to all animals in all lots might be of some benefit. Under most scenarios, there is ample opportunity for cross-contamination to occur within the slaughter plant as a result of early entry of cattle contaminated with E. coli O157. An industry-wide reduction in the amount of tag attached to hides and addition of a source of cattle having a prolonged average fasting time were not predicted to have a large impact on mean amount of carcass contamination with E. coli O157.

Herd-level test performance based on uncertain estimates of individual test performance, individual true prevalence and herd true prevalence

A generalized model was derived for understanding the performance of herd-testing protocols when there is uncertainty and variability in individual-level sensitivity, specificity, prevalence of infection within infected herds, and prevalence of infected herds in the population. The model uses Monte-Carlo techniques to provide estimates of test performance for a dichotomous classification of herd-disease status. Uncertainty and variability in input assumptions are described using empirical and parametric probability distributions. The model permits both cluster-correlated behavior of inputs and sampling of animals without replacement. Disease due to obligate parasites is modeled differently from that due to organisms that persist for long periods in the environment. Dependence among model outcomes is assessed using Spearman's rank correlation. Model output is suitable for inclusion in risk-assessment models requiring probabilistic estimates of herd-level test performance, such as those developed for food-safety decision making and import–export risk assessment. The model was demonstrated using an example scenario based on Shiga-like toxin (SLT) producing Escherichia coli O157 in Ontario beef-cattle herds. Inputs were derived from the literature and Statistics Canada agricultural census data. Where appropriate, these data were subjected to distribution-fitting techniques. Otherwise, subjective interpretation was used to select input distributions and their parameters. Simulation revealed that the distribution of herd-level sensitivity for detecting herds infected with SLT producing E. coli O157 has a large range (0.003–0.99) and a median of 0.19. Herd-level specificity also had a large range (0.58–1) and a median of 0.94. Distributions of herd-level positive and negative predictive values exhibited similar degrees of uncertainty. In combination with poor likelihood ratios for positive and negative herd tests, results indicate that the testing protocol investigated has limited ability to discriminate between herds infected and not infected with SLT producing E. coli O157.

A risk-assessment model for foot and mouth disease (FMD) virus introduction through deboned beef importation

We present a risk-assessment model to assess the risk of introduction of foot and mouth disease (FMD) virus associated with deboned beef importation. The model was developed in accordance with the risk-reduction procedures proposed by the European Community for meat importation. The risk reduction procedures include farm-level inspection, ante-mortem inspection, post-mortem inspection, chilling and deboning. The risk assessment was based on the prevalence of FMD-infected cattle in herds as well as the prevalence of infected herds in the exporting country. Computer simulations were carried out to evaluate the probability of FMD virus introduction by importing 100 tons of deboned beef in relation to FMD prevalence, number of cattle selected from each herd, and sample sizes in ante-mortem and post-mortem inspections. The effects of the risk-reduction procedures on the probability of FMD virus introduction were examined.