RESUMO
The likelihood ratio (LR) is a measure of association that quantifies how many more times likely a particular test result is from an infected animal compared to one that is uninfected. They are ratios of conditional probabilities and cannot be interpreted at the individual animal level without information concerning pretest probabilities. Their usefulness is that they can be used to update the prior belief that the individual has the outcome of interest through a modification of Bayes' theorem. Bayesian analytic techniques can be used for the evaluation of diagnostic tests and estimation of LRs when information concerning a gold standard is not available. As an example, these techniques were applied to the estimation of LRs for a competitive ELISA (c-ELISA) for diagnosis of Brucella abortus infection in cattle and water buffalo in Trinidad.Sera from four herds of cattle (n = 391) and four herds of water buffalo (n = 381) in Trinidad were evaluated for Brucella-specific antibodies using a c-ELISA. On the basis of previous serologic (agglutination) test results in the same animals, iterative simulation modeling was used to classify animals as positive or negative for Brucella infection. LRs were calculated for six categories of the c-ELISA proportion inhibition (PI) results pooled for cattle and water buffalo and yielded the following estimations (95% probability intervals): <0.10 PI, 0.05 (0ùC0.13); 0.10ùC0.249 PI, 0.11 (0.04ùC0.20); 0.25ùC0.349 PI, 0.77 (0.23ùC1.63); 0.35-0.499 PI, 3.22 (1.39ùC6.84); 0.50ùC0.749 PI, 17.9 (6.39ùC77.4); í0.75 PI, 423 (129ùCè). LRs are important for calculation of post-test probabilities and maintaining the quantitative nature of diagnostic test results.
Assuntos
Bovinos , Doenças dos Bovinos/diagnóstico , Bison , Brucelose/epidemiologia , Brucelose/etiologia , Relatos de Casos , Ensaio de Imunoadsorção Enzimática/métodos , Ensaio de Imunoadsorção Enzimática/estatística & dados numéricos , Trinidad e Tobago/epidemiologia , Região do CaribeRESUMO
The likelihood ratio (LR) is a measure of association that quantifies how many more times likely a particular test result is from an infected animal compared to one that is uninfected. They are ratios of conditional probabilities and cannot be interpreted at the individual animal level without information concerning pretest probabilities. Their usefulness is that they can be used to update the prior belief that the individual has the outcome of interest through a modification of Bayes' theorem. Bayesian analytic techniques can be used for the evaluation of diagnostic tests and estimation of LRs when information concerning a gold standard is not available. As an example, these techniques were applied to the estimation of LRs for a competitive ELISA (c-ELISA) for diagnosis of Brucella abortus infection in cattle and water buffalo in Trinidad. Sera from four herds of cattle (n=391) and four herds of water buffalo (n=381) in Trinidad were evaluated for Brucella-specific antibodies using a c-ELISA. On the basis of previous serologic (agglutination) test results in the same animals, iterative simulation modeling was used to classify animals as positive or negative for Brucella infection. LRs were calculated for six categories of the c-ELISA proportion inhibition (PI) results pooled for cattle and water buffalo and yielded the following estimations (95% probability intervals): <0.10 PI, 0.05 (0-0.13); 0.10-0.249 PI, 0.11 (0.04-0.20); 0.25-0.349 PI, 0.77 (0.23-1.63); 0.35-0.499 PI, 3.22 (1.39-6.84); 0.50-0.749 PI, 17.9 (6.39-77.4); > or =0.75 PI, 423 (129-infinity). LRs are important for calculation of post-test probabilities and maintaining the quantitative nature of diagnostic test results.
Assuntos
Anticorpos Antibacterianos/sangue , Brucelose Bovina/diagnóstico , Brucelose Bovina/epidemiologia , Brucelose/veterinária , Búfalos , Ensaio de Imunoadsorção Enzimática/veterinária , Animais , Teorema de Bayes , Brucella/imunologia , Brucelose/diagnóstico , Brucelose/epidemiologia , Bovinos , Ensaio de Imunoadsorção Enzimática/métodos , Funções Verossimilhança , Valor Preditivo dos Testes , Estudos Soroepidemiológicos , Trinidad e Tobago/epidemiologiaRESUMO
Thirty-two young domestic water buffalo were studied to evaluate ear-tag retention during an epidemiologic field trial. Plastic ear-tags were placed in both ears before the start of the trial, which was implemented in an extensively managed domestic water buffalo herd of approximately 1000 animals in Trinidad from 19992001. The presence or absence of ear-tags was recorded at the times of animal handling. The rate of ear-tag loss was modeled using a parametric survival analysis assuming an exponential rate of loss. A gamma distribution was used to estimate the amount of time that each animal would be positively identified based only on the presence or absence of one or more ear-tags. The overall median ear-tag retention was 272 days. The estimated rate of ear-tag loss was 0.0024 ear-tags lost per day. The use of ear-tags alone might not be sufficient for long-term identification of extensively managed animal populations.
Assuntos
Bovinos , Brucelose/epidemiologia , Búfalos , Sistemas de Identificação Animal , Sistemas de Identificação Animal/veterinária , Sobrevida , Projetos de Pesquisa/estatística & dados numéricos , Trinidad e TobagoRESUMO
Thirty-two young domestic water buffalo were studied to evaluate ear-tag retention during an epidemiologic field trial. Plastic ear-tags were placed in both ears before the start of the trial, which was implemented in an extensively managed domestic water buffalo herd of approximately 1000 animals in Trinidad from 1999-2001. The presence or absence of ear-tags was recorded at the times of animal handling. The rate of ear-tag loss was modeled using a parametric survival analysis assuming an exponential rate of loss. A gamma distribution was used to estimate the amount of time that each animal would be positively identified based only on the presence or absence of one or more ear-tags. The overall median ear-tag retention was 272 days. The estimated rate of ear-tag loss was 0.0024 ear-tags lost per day. The use of ear-tags alone might not be sufficient for long-term identification of extensively managed animal populations.
Assuntos
Bovinos , Animais , Sistemas de Identificação Animal/estatística & dados numéricos , Sistemas de Identificação Animal/veterinária , Sobrevida , Brucelose Bovina , Trinidad e Tobago , BúfalosRESUMO
Thirty-two young domestic water buffalo were studied to evaluate ear-tag retention during an epidemiologic field trial. Plastic ear-tags were placed in both ears before the start of the trial, which was implemented in an extensively managed domestic water buffalo herd of approximately 1000 animals in Trinidad from 1999-2001. The presence or absence of ear-tags was recorded at the times of animal handling. The rate of ear-tag loss was modeled using a parametric survival analysis assuming an exponential rate of loss. A gamma distribution was used to estimate the amount of time that each animal would be positively identified based only on the presence or absence of one or more ear-tags. The overall median ear-tag retention was 272 days. The estimated rate of ear-tag loss was 0.0024 ear-tags lost per day. The use of ear-tags alone might not be sufficient for long-term identification of extensively managed animal populations.
Assuntos
Sistemas de Identificação Animal/veterinária , Bem-Estar do Animal/estatística & dados numéricos , Brucelose/veterinária , Búfalos , Animais , Brucelose/epidemiologia , Orelha Externa , Feminino , Masculino , Trinidad e Tobago/epidemiologiaRESUMO
Thirty-two young domestic water buffalo (Bubalus bubalis) were obtained from a brucellosis-free farm to determine effectiveness of RB51 vaccination for prevention of Brucella infection under natural-exposure conditions in Trinidad. Study animals (20 males and 12 females 5-20 months old) were assigned to vaccination or control groups, using a block randomization design ensuring equal sex distributions between groups. The vaccination group received commercially available RB51 at the recommended calfhood dose of (1.0-3.4)x10(10) colony-forming units (CFU) and controls received 2ml sterile saline. Vaccination did not result in positive serologic results as measured by four traditional agglutination tests: standard tube agglutination test (STAT), standard plate agglutination test (SPAT), buffered plate agglutination test (BPAT), and card agglutination. Study animals were maintained in a brucellosis-positive herd in southern Trinidad with an estimated 56% prevalence to allow for natural exposure to B. abortus, which was evaluated using STAT, SPAT, BPAT, and card tests. Animals were sampled seven times over 2 years and were classified as positive if they had persistent agglutination titers or had Brucella isolated from specimens collected at completion of the study. Five of the original 32 study animals were lost to follow-up during the field trial. Six of the 14 (43%) vaccinated animals completing the study were classified as positive for Brucella infection-as were two of the 13 (15%) control animals (P=0.21). Isolates from four vaccinates and one control were confirmed as B. abortus biovar 1.
Assuntos
Vacinas Bacterianas/imunologia , Brucelose Bovina/imunologia , Brucelose Bovina/prevenção & controle , Búfalos/imunologia , Animais , Brucella abortus/imunologia , Bovinos , Feminino , Masculino , Trinidad e TobagoRESUMO
A cross-sectional study was conducted in southern Chile between January and March, 1996, to identify risk factors for papillomatous digital dermatitis (PDD) in lactating dairy and dual-purpose cows. A total of 3,265 cows from 22 farms were examined in the milking parlor for PDD lesions. Additional information was collected from dairies' computerized records and by direct interview of managers. Data were analyzed using logistic and logistic-binomial regression (with dairy as a random-effect term). German Red-Pied (dual-purpose) cows were significantly (P < 0.05) less likely (odds ratio (OR) = 0.3) to have PDD lesions than German Black-Pied and Holstein crossbreds. First-parity cows had the highest odds of PDD, and odds diminished, in a dose-effect manner, as parity increased. Odds of PDD increased with increasing days in lactation. Cows that calved during winter were more likely to have PDD (OR = 1.4) than those calving at any other season. Cows on farms that bought heifers in the past 10 years had a 3-fold increase in the odds of PDD compared to those on farms that never bought heifers. Loose-housed cows had a higher risk of PDD (OR = 7), followed by cows in free stalls or in open corrals (OR = 2.8 and 1.3, respectively), compared to cows on pasture all year. Cows on dairies that used a footbath during 1996 were less likely (OR = 0.3) to have PDD than those in dairies not using one. Parlor type was associated with PDD, but this was likely an effect of parlor design on ease of inspection of cows' feet. A policy of trimming all cows' vs. only lame cows' feet and a policy about buying adult cows did not have significant effects on PDD risk.
Assuntos
Doenças dos Bovinos/epidemiologia , Dermatite/veterinária , Dermatoses do Pé/veterinária , Casco e Garras/patologia , Papiloma/veterinária , Animais , Bovinos , Doenças dos Bovinos/patologia , Chile/epidemiologia , Estudos Transversais , Indústria de Laticínios/métodos , Dermatite/epidemiologia , Dermatite/patologia , Feminino , Dermatoses do Pé/epidemiologia , Dermatoses do Pé/patologia , Abrigo para Animais , Lactação , Coxeadura Animal/etiologia , Modelos Logísticos , Leite/metabolismo , Análise Multivariada , Papiloma/epidemiologia , Papiloma/patologia , Paridade , Fatores de Risco , Inquéritos e QuestionáriosRESUMO
Serum samples from 408 sheep from different regions of Chile and 447 alpacas (Llama pacos) from the north of the country were tested for Toxoplasma gondii antibodies. The indirect haemagglutination test (IHAT) was used in both species and the indirect immunofluorescence test (IIFT) was also used on the sheep samples in order to compare the performance of the tests in that species. In both tests, titers > or = 1:16 were considered diagnostically significant. Sera from 49 sheep (12%) were positive to T. gondii antibodies by the IHAT. When using the IIFT, 114 sheep sera (28%) were positive. The different results obtained in sheep sera between the tests were significant (p < 0.0001). No differences were observed between geographical locations or sex of the sampled sheep regarding serological detection of T. gondii antibodies in sheep. As expected, adult sheep showed higher T. gondii reactivity than young sheep (p = 0.0008). The corrected prevalence of toxoplasmosis in alpaca was 16.3% (32 positive out of 447). The rather low prevalence in alpacas may be associated with their extensive management as well as the extreme climatic conditions of The Andes which apparently would not be favorable for the transmission of the parasite.
Assuntos
Camelídeos Americanos , Doenças dos Ovinos/epidemiologia , Ovinos , Toxoplasma/imunologia , Toxoplasmose Animal/epidemiologia , Animais , Anticorpos Antiprotozoários/análise , Antígenos de Protozoários/imunologia , Chile/epidemiologia , Feminino , Técnica Indireta de Fluorescência para Anticorpo/veterinária , Testes de Hemaglutinação/veterinária , Masculino , Sensibilidade e Especificidade , Estudos Soroepidemiológicos , Doenças dos Ovinos/imunologia , Doenças dos Ovinos/parasitologia , Toxoplasmose Animal/imunologia , Toxoplasmose Animal/parasitologiaRESUMO
Outbreaks of papillomatous digital dermatitis (PDD) have been reported from many countries, but there is little information on prevalence and geographic distribution of the disease. Our objectives were to describe prevalence of PDD on dairies belonging to the two main dairy-producer associations in Chile, and to evaluate a milking-parlor screening method for detection of PDD in dairy cows. First, a self-administered questionnaire was sent to all 214 association dairy managers. Seventy percent of the 119 respondents had observed PDD on their dairies. About 83% of the 63 responding managers had first seen PDD during the previous 10 years. Subsequently, a random sample of 43 dairies stratified by association was selected from the total 214 for PDD screening. During milking, we inspected cows' feet for PDD lesions; 91% of dairies had cows affected by PDD; median PDD prevalence for milking cows in dairies was 6.1%. Finally, in one dairy, PDD screening at the parlor was compared to PDD diagnosis by inspecting restrained cows in a chute. The screening method had a sensitivity of 0.72, and a specificity of 0.99. This study demonstrated that PDD was widespread on study dairies in Chile. The screening test presented can be used as a cost efficient method to estimate prevalence of PDD either on individual dairies or in large-scale surveys.
Assuntos
Doenças dos Bovinos/epidemiologia , Dermatoses do Pé/veterinária , Coxeadura Animal/epidemiologia , Animais , Bovinos , Doenças dos Bovinos/diagnóstico , Chile/epidemiologia , Feminino , Dermatoses do Pé/diagnóstico , Dermatoses do Pé/epidemiologia , Programas de Rastreamento/métodos , Programas de Rastreamento/veterinária , Prevalência , Reprodutibilidade dos TestesRESUMO
This retrospective study of papillomatous digital dermatitis (PDD) was performed using data for cows that calved between July 1993 and June 1994 on a Mexicali, Mexico, dairy farm in order to calculate incidence rates, and to compare milk yield and reproduction data between affected and nonaffected dairy cows. A total of 190 out of 577 (33%) cows were affected during lactation and six (1%) during the dry period. Fifty-two of 77 (68%) cows that had lesions in the previous lactation and were also present on the farm in the current lactation had lesions in the current lactation. The highest risk for PDD occurred during the first month of lactation (9%). The yearly estimated cumulative incidence risk was 35% and the incidence density rate was 44.6 cases per 1000 cow-months. More animals were affected in summer and fall than in winter and spring. Purchased animals were 3.4 times more likely to be affected than animals born on the farm. Survival analyses indicated healthy cows conceived 93 days after calving (median), but affected cows conceived 113 days after calving (median) (P < 0.01). PDD-affected animals produced less milk than healthy cows, but the difference was not statistically significant in the multiple regression.
Assuntos
Doenças dos Bovinos/epidemiologia , Doenças dos Bovinos/fisiopatologia , Dermatite/veterinária , Casco e Garras , Lactação/fisiologia , Reprodução/fisiologia , Animais , Bovinos , Dermatite/epidemiologia , Dermatite/fisiopatologia , Feminino , Doenças do Pé/epidemiologia , Doenças do Pé/fisiopatologia , Doenças do Pé/veterinária , Incidência , México/epidemiologia , Gravidez , Modelos de Riscos Proporcionais , Análise de Regressão , Estudos Retrospectivos , Fatores de Risco , Estações do Ano , Análise de SobrevidaRESUMO
The reduction of domiciliary infestation by insect vectors, the key to controlling Chagas' disease, depends on identification of housing features associated with infestation. In this study, log-linear modeling was used to reanalyze data collected in 1964-1968 from 371 houses on characteristics potentially associated with infestation by the vector Triatoma dimidiata in a Costa Rican town with endemic Chagas' disease. A possible increased risk of infestation was observed for houses with a dirt floor (as compared with houses with another floor type) and for houses in poor sanitary condition (as compared with houses in good sanitary condition). A new risk factor for house infestation, the presence of roof tiles, was identified; the odds of infestation for houses with a tile roof were 2.4 times greater than the odds for houses with a galvanized metal roof. This significantly increased risk is probably due to the harboring of T. dimidiata in stacks of spare tiles next to house walls rather than to the tile roofs themselves.
Assuntos
Doença de Chagas/epidemiologia , Habitação , Doença de Chagas/etiologia , Costa Rica , Humanos , Fatores de Risco , SaneamentoRESUMO
In Los Angeles County, California, 142 cases of human listeriosis were reported from January 1 through August 15, 1985. Ninety-three cases (65.5 percent) occurred in pregnant women or their offspring, and 49 (34.5 percent) in nonpregnant adults. There were 48 deaths: 20 fetuses, 10 neonates, and 18 nonpregnant adults. Of the nonpregnant adults, 98 percent (48 of 49) had a known predisposing condition. Eighty-seven percent (81 of 93) of the maternal/neonatal cases were Hispanic. Of the Listeria monocytogenes isolates available for study, 82 percent (86 of 105) were serotype 4b, of which 63 of 86 (73 percent) were the same phage type. A case-control study implicated Mexican-style soft cheese (odds ratio, 5.5; 95 percent confidence interval, 1.2 to 24.8) as the vehicle of infection; a second case-control study showed an association with one brand (Brand A) of Mexican-style soft cheese (odds ratio, 8.5; 95 percent confidence interval, 2.4 to 26.2). Laboratory study confirmed the presence of L. monocytogenes serogroup 4b of the epidemic phage type in Brand A Mexican-style cheese. In mid-June, all Brand A cheese was recalled and the factory was closed. An investigation of the cheese plant suggested that the cheese was commonly contaminated with unpasteurized milk. We conclude that the epidemic of listeriosis was caused by ingestion of Brand A cheese contaminated by one phage type of L. monocytogenes serotype 4b.
Assuntos
Queijo , Surtos de Doenças , Microbiologia de Alimentos , Listeriose/transmissão , Adulto , Idoso , California , Métodos Epidemiológicos , Feminino , Hispânico ou Latino , Humanos , Recém-Nascido , Listeria monocytogenes/isolamento & purificação , Listeriose/epidemiologia , México/etnologia , Pessoa de Meia-Idade , Gravidez , Complicações Infecciosas na Gravidez/epidemiologia , Complicações Infecciosas na Gravidez/transmissãoRESUMO
Data for path analysis on the epidemiology of bovine brucellosis were gathered from 184 premises in Mexicali Valley, Mexico, that had dairy cattle, swine, and/or goats. Each farmer manager or owner was interviewed, using a pretested set of questions, and the livestock on the premises were serotested for Brucella antibodies. The focus in gathering these data was to identify the characteristics of premises with seropositive cattle in comparison with characteristics of premises with no seropositive cattle.