Likelihood ratio estimation without a gold standard: a case study evaluating a brucellosis c-ELISA in cattle and water buffalo of Trinidad.

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.

Risk factors associated with Neospora caninum abortion in Ontario Holstein dairy herds.

The objective of this epidemiological study was to identify risk factors for Neospora caninum-related abortions in Ontario Holstein dairy herds. A total of 88 herds, consisting of 5080 cattle, and utilizing Dairy Herd Improvement (DHI) services, were divided into three groups. Case (n = 30) and first control (n = 31) herds were selected from 1998 and 1999 fetal abortion submissions to the Animal Health Laboratory, University of Guelph, that were histopathologically positive or negative, respectively, for N. caninum. A second control group (n = 27) was selected from multiple sources of herds sampled within the previous 4 years that had a low seroprevalence (<7%) to N. caninum. Between May and December 1999, all available cows on all farms, in parity one or greater, were blood sampled. The sera were then analyzed for antibody to N. caninum using a kinetic ELISA. A survey administered at the time of sampling recorded information on housing, animal species present, manure management, reproduction, biosecurity practices, wildlife observations, peri-parturient cow management, herd disease history and nutrition. Production and other herd parameters were obtained from DHI records. Logistic regression indicated that the following parameters were positively associated with a N. caninum abortion in a herd: the N. caninum herd seroprevalence (OR = 1.1), the total number of dogs on a farm (OR = 2.8), the frequency that dogs were observed defecating in mangers (OR = 2.8), the number of horses on a farm (OR = 3.1), the observed annual rate of retained fetal membranes (OR = 1.2) and the observed annual rate of cows returning to estrus after pregnancy confirmation (OR = 1.2). Factors negatively associated were the frequency of stray cats and wild canids observed on a farm (OR = 0.4 and OR = 0.7, respectively) and the housing of heifers on loafing packs (a housing pen divided into feed manger, scrape alley and bedded pack areas, OR = 0.1).

The isolation of exotic Newcastle disease (END) virus from nonpoultry avian species associated with the epidemic of END in chickens in southern California: 2002-2003.

During the first 11 months of the 2002-2003 exotic Newcastle disease (END) epidemic in chickens in southern California, a total of 27,688 cloacal and tracheal (oropharyngeal) swab pools and/or tissue pools from 86 different avian species other than chickens and turkeys were submitted for Newcastle disease virus (NDV) isolation and characterization. Fifty-seven specimens (0.23%), representing 12 species of birds and 13 unspecified species, from a total of 24,409 accessions or submissions were positive for NDV. The NDV isolate was characterized as ENDV by real-time reverse transcription-polymerase chain reaction (RT-PCR). Of the 11,486 premises with other avian species, 1599 also had chickens. There were 1900 positive chicken samples from 164 premises, and 56 positive other avian species from 51 premises. Twelve premises had both positive chickens and positive other avian species. All positive other avian species were located on premises either on or within a 1 km radius of known infected premises. In this epidemic, premises with positive other avian species were significantly more likely to have chickens, and were significantly more likely to have positive chickens (OR = 3.7, P < 0.0001).

Cyclosporine pharmacokinetics in cats following topical ocular administration.

Topical ocular administration of two forms of cyclosporine were studied in the cat. Both forms were able to produce measurable whole-blood levels capable of suppressing in vitro lymphocyte stimulation. The kinetics of cyclosporine following administration of either oral solution or cyclosporine in olive oil were variable, with peak concentrations ranging from 450 to 1033 ng/ml and 288 to 648 ng/ml, respectively. Absorption lag time ranged from 0 to 1.34 hr for oral solution, and 0.27 to 1.2 hr for cyclosporine in olive oil. The half-life of elimination ranged from 2.41 to 10.04 hr, and 3.09 to 15.75 hr, respectively. When compared with the commercially available oral solution, cyclosporine dissolved in olive oil was better tolerated during administration. Topical ocular administration of cyclosporine in cats offers a possible alternative method of treatment for individuals intolerant of oral administration. Topical ocular administration might also replace the need for intravenous administration of cyclosporine during perioperative periods or during periods of vomiting and nausea associated with rejection or other illnesses. Due to individual variation in absorption and elimination of topically applied cyclosporine, dosages in each cat must be determined by monitoring blood, plasma, or serum levels.

Postnatal Neospora caninum transmission and transient serologic responses in two dairies.

Cattle on two typically managed drylot dairies were serologically monitored from birth through year 1 to year 4 of life to characterise congenital and postnatal Neospora caninum transmission. Of the 456 calves enrolled, 284 were classified as N. caninum negative and 172 were classified as N. caninum positive. Ninety-six percent of congenitally infected calves were seropositive for all samples tested. Seven (4%) of the 172 congenitally infected animals had a period that persisted for 9 to 18 months when they were seronegative; however, all returned to seropositive status by 25 months of age. In N. caninum-negative calves, colostral antibody decayed by 128 days, with an estimated half-life of 19.6 +/- 5.2 days. Of the 284 calves classified as negative, 18% had sporadic, isolated responses to N. caninum, typically between 29 and 35 months of age, without subsequent seroconversion or infection. During the study, 17 animals seroconverted and remained seropositive throughout the follow-up. Thirteen of the seroconversions occurred in the neonatal period; however, in nine of 10 where dam status was available, the dam was N. caninum positive, suggesting late gestation congenital infection rather than postnatal infection. Seroconversion was detected in an additional four animals, between 13 and 22 months of age. The estimate of postnatal infection rate was less than 1% per year despite a high N. caninum seroprevalence in the herds, and the presence of potential definitive and intermediate hosts on the dairy throughout the study. The extremely low rate of postnatal infection, as well as the lifelong persistence of congenital infection, emphasises the importance of congenital transmission in maintaining N. caninum infection in dairies.

Interaction of Rhodococcus equi with phagocytic cells from R. equi-exposed and non-exposed foals.

The interaction of Rhodococcus equi with alveolar macrophages from adult horses, foals experimentally exposed to R. equi (sensitized foals) and non-exposed foals was studied using in vitro bactericidal assays, cytochemical staining and transmission electron microscopy. It was demonstrated that R. equi is a facultative intracellular parasite, able to survive and multiply within the alveolar macrophages of the host by interfering with phagosome-lysosome fusion. Opsonization of R. equi with antibody against capsular components was associated with increased phagosome-lysosome fusion and significantly enhanced (P less than 0.05) killing of the organism by alveolar macrophages from non-exposed foals. Macrophages from non-exposed foals were able to ingest the non-opsonized organism, but unable to kill greater than 65% of the infective dose by 6 h post-exposure. Alveolar macrophages from sensitized foals behaved as adult macrophages, able to kill greater than 95% of the infective dose by 6 h. Lymphocyte factors, derived by in vitro incubation of sensitized peripheral blood lymphocytes with R. equi surface antigens, enhanced macrophage bactericidal activity. Macrophages from non-exposed foals incubated in the presence of the lymphocyte factors had a 50% increase in killing of R. equi, while sensitized macrophages incubated with lymphocyte factors had a greater than 100% increase in killing capacity.

Rhodococcus equi: equine neutrophil chemiluminescent and bactericidal responses to opsonizing antibody.

The opsonic capacity of serum containing R. equi-specific antibody was compared with antibody-deficient sera using luminol-dependent chemilumenscence (LDCL) and bactericidal assays. These assays incorporated peripheral blood polymorphonuclear neutrophilic leukocytes (PMNL) exposed to R. equi opsonized with neonatal equine pre-colostral serum (control) or serum from foals with R. equi infections (principal). All sera were complement inactivated at 56 degrees C for 30 min. Bacteria were obtained from the lung of a foal with R. equi pneumonia. Neutrophils were obtained from one adult horse for LDCL and another for bactericidal assays. Chemiluminescence of PMNL exposed to R. equi opsonized with control or principal sera was measured in a liquid scintillation counter. Mean peak LDCL within 1 h was significantly (P less than 0.01) higher with principal sera (2.4 X 10(5) cpm) than with control sera (0.018 X 10(5) cpm). A radioisotope bactericidal assay was used to determine the effect of control or principal sera on PMNL capacity to kill R. equi. Mean peak percent kill of R. equi by PMNL within 2 h was significantly (P less than 0.01) higher with principal sera (95.2%) than with control sera (54.6%). Enzyme-linked immunosorbent assay (ELISA) values for R. equi-specific antibody were determined on all sera. Mean ELISA values were significantly (P less than 0.01) higher for principal sera (71.8) than for controls (0.0). This investigation documents the presence and biological effectiveness of opsonic activity in complement-inactivated sera from foals with R. equi infections and R. equi-specific antibody.

Neutrophil phagocytic and serum opsonic response of the foal to Corynebacterium equi.

This study was undertaken to examine the neutrophil response to Corynebacterium (Rhodococcus) equi, and to assess the possibility of neutrophil immaturity or malfunction in predisposition to C. equi pneumonia in foals. Neutrophil phagocytosis of Corynebacterium (Rhodococcus) equi was studied in foals from birth to 6 months of age. Chemiluminescence (CL) and bactericidal assays were used to assay the phagocytic response of peripheral blood neutrophils to C. equi in vitro. Results of in vitro bactericidal and CL assays indicate that foal neutrophils are able to ingest and kill C. equi, however are significantly more efficient in the presence of opsonization with specific antibody, and less importantly complement. Neutrophil CL was significantly decreased (p greater than .05) or eliminated by antibody adsorption, heat-inactivation, or removal of serum from the assay. The ability of the neutrophil to kill C. equi, as measured by in vitro bactericidal assay, was greater than 90% killing by 6 hours, in the presence of C. equi antiserum. Bactericidal activity was reduced to less than 40% killing when C. equi adsorbed serum was used as the opsonin source. As CL results indicated complement involvement in the opsonization of C. equi, the temporal development of hemolytic and conglutinating complement was measured in normal and C. equi infected foals. Neither defects nor age-related suppression of neutrophil function or complement activity were detected in C. equi affected foals, suggesting that these are not pathogenic mechanisms involved in foal pneumonia.

An enzyme-linked immunosorbent assay (ELISA) for serological diagnosis of Neospora sp. infection in cattle.

A kinetic enzyme-linked immunosorbent assay (ELISA) was developed and optimized for detection of antibodies to Neospora sp. in cattle. Sonicated tachyzoites of Neospora sp. isolated from an aborted bovine fetus were used as antigen. Variability in immunoblot patterns among positive sera, and the fact that all life stages of the parasites are unknown, justified use of a multiple-antigen ELISA to allow for maximum sensitivity. Immunoblot analysis revealed negligible cross-reactions between Toxoplasma gondii antigen and Neospora sp. antisera and between Neospora sp. antigen and antisera from various apicomplexan parasites. The maximum positive-to-negative Vmax (average maximum slope of the optical density over time) ratio was obtained using 200 ng/well of sonicated tachyzoite antigen and a 1:200 serum dilution. Using logistic regression to determine the optimal cutoff point between known infected and noninfected cattle, a sample-to-positive control Vmax ratio of 0.45 was found to maximize the percent correct classification, with an estimated sensitivity of 88.6% and specificity of 96.5%. Use of Neospora caninum antigen following the same protocol demonstrated no difference in ELISA interpretation. Comparison with an existing indirect immunofluorescent antibody (IFA) test showed the ELISA to be the more sensitive and specific test for serodiagnosis of Neospora infection in cattle.

Prospective serology and analysis in diagnosis of dairy cow abortion.

A prospective serologic investigation was undertaken on 3 California dairies (herds 1, 3, and 4, as previously designated in a report on abortion surveillance) to determine if fetal loss was associated with infectious disease agents in cows. The diagnostic problem in these herds was typical of many dairies in that abortions were not discovered for several months and aborted fetuses were seldom recovered. Blood from approximately 100 pregnant cows in each herd was sampled at monthly intervals, beginning when the cows were palpated at approximately 40 days gestation. Sera were tested for antibodies to infectious bovine rhinotracheitis virus and bovine viral diarrhea virus (BVDV) and to the Leptospira serovars pomona, hardjo, grippotyphosa, icterohemorrhagiae, canicola, and szwajizak. Logn antibody titers were examined for an association with fetal loss, using multivariate methods of logistic regression and survival analysis. Of the 325 cows followed, 37 aborted, and no fetuses were recovered. Statistical analyses indicated that significant fetal loss was associated with high titers to L. hardjo and with low titers to L. szwajizak (herds 1 and 4) and BVDV (herd 1). Results for herd 3 revealed a connection between abortion and L. icterohemorrhagiae (P = 0.036) and L. canicola (P = 0.050) and possible vaccinal protection against abortion caused by L. grippotyphosa (P = 0.027 and 0.015). For herd 4, there was a marginally significant tendency for the first vaccination of the gestation against leptospirosis to have protected against fetal death (P = 0.077). Advantages of the diagnostic design were that it permitted comparison of titers of aborted cows with those of nonaborted cows and it considered vaccination-induced titers in analyses.(ABSTRACT TRUNCATED AT 250 WORDS)

Herd-based diagnosis of Neospora caninum-induced endemic and epidemic abortion in cows and evidence for congenital and postnatal transmission.

Aborting and nonaborting cows and their dams or daughters were studied to determine if herd abortion problems were associated with the presence of Neospora caninum antibodies and to estimate when aborting cows may have acquired the infection. Cows were sampled from 20 herds that had experienced an abortion epidemic presumed to have been caused by N. caninum and from 2 herds experiencing endemic abortion. Seroprevalence for 14 herds experiencing an epidemic ranged from 7% to 70%, as estimated by enzyme-linked immunosorbent assay. A strong association between seropositivity and abortion was found for only 5 of 14 herds with a presumed diagnosis of N. caninum abortion (P < or = 0.015, lower 95% confidence interval of odds ratio > or = 1.2), indicating N. caninum may be overdiagnosed as the cause of an abortion epidemic in some herds. No association was found between dam and daughter seropositivity for herds experiencing an epidemic (P > or = 0.17), suggesting that most cows aborting during an epidemic were infected postnatally. For the 2 herds with endemic abortion (A, B), odds of an aborting cow having N. caninum antibodies were 3.4-fold (herd A) and 7.0-fold (herd B) higher than odds for nonaborting cows (P < or = 0.05). Cows that aborted a fetus infected with N. caninum were more likely to have had a previous seropositive daughter than were nonaborting seronegative cows (P < or = 0.0025), suggesting that infection had been acquired before conception of the aborted fetus.

Pooled-sample testing as a herd-screening tool for detection of bovine viral diarrhea virus persistently infected cattle.

The study was conducted to develop methodology for least-cost strategies for using polymerase chain reaction (PCR)/probe testing of pooled blood samples to identify animals in a herd persistently infected with bovine viral diarrhea virus (BVDV). Cost was estimated for 5 protocols using Monte Carlo simulations for herd prevalences of BVDV persistent infection (BVDV-PI) ranging from 0.5% to 3%, assuming a cost for a PCR/probe test of $20. The protocol associated with the least cost per cow involved an initial testing of pools followed by repooling and testing of positive pools. For a herd prevalence of 1%, the least cost per cow was $2.64 (95% prediction interval = $1.72, $3.68), where pool sizes for the initial and repooled testing were 20 and 5 blood samples per pool, respectively. Optimization of the least cost for pooled-sample testing depended on how well a presumed prevalence of BVDV-PI approximated the true prevalence of BVDV infection in the herd. As prevalence increased beyond 3%, the least cost increased, thereby diminishing the competitive benefit of pooled testing. The protocols presented for sample pooling have general application to screening or surveillance using a sensitive diagnostic test to detect very low prevalence diseases or pathogens in flocks or herds.

Evidence suggesting a point source exposure in an outbreak of bovine abortion due to neosporosis.

A Holstein dairy farm suffered an abortion outbreak due to neosporosis. Abortion losses were > 18%. Cows with the highest Neospora antibody titers were at the greatest risk of aborting. Mummified fetuses were found after the 43rd day of the outbreak. The epidemic curve was suggestive of a point source exposure, which is consistent with the hypothesis that Neospora can be spread by a definitive host.

Reproducibility of a commercial enzyme-linked immunosorbent assay for bovine paratuberculosis among eight laboratories.

Interlaboratory reproducibility of an absorbed enzyme-linked immunosorbent assay (ELISA) kit for detection of bovine serum antibodies to Mycobacterium paratuberculosis was evaluated. A panel of 30 bovine sera (15 positives and 15 negatives) was tested in triplicate microtiter wells on each of 2 days at 8 different laboratories. One laboratory had invalid results because of positive or negative serum control optical density (OD) readings beyond the acceptable range specified by the kit. The coefficient of variation (CV) for mean OD values was influenced by low ODs on test negative sera at 2 laboratories, thus the CVs on positive sera were considered a more representative measure of kit reproducibility. Between-well CVs averaged 6.7% +/- 2.8% (mean +/- standard deviation), and between-day CVs averaged 14.5% +/- 9.8% among the 7 laboratories with valid assays on the 15 positive sera. The OD values were converted to positive or negative classifications for each assay well, and the results were compared. Among 1,392 assays in 7 laboratories, 98.6% were in agreement. Eleven of 18 discrepant results were due to a sample that consistently gave OD values near the cutoff for a positive test. Exclusion of that serum from the analysis resulted in a 99.8% rate of agreement among laboratories. Results indicated that the absorbed ELISA kit provided reproducible results within and between laboratories.

Risk factors for brucellosis seropositivity of goat herds in the Mexicali Valley of Baja California, Mexico.

A case-control study was conducted in the Mexicali Valley to identify risk factors for goat-herd seropositivity for Brucella melitensis. Nineteen case herds (> or = 2 positive results with the 8% rose bengal plate test (RBT)) and 55 control herds (zero positive results in RBT), matched for herdsize and geographic location, were enrolled. Conditional logistic regression was used to construct a multivariable model of the odds of seropositivity using variables assessed in a questionnaire administered to goat ranchers. The final model for herd seropositivity included increased risk from importation of goats from other Mexican states, the presence of La Mancha breed does, and the presence of does born outside the herd. Increasing herdsize was also highly significant (p < 0.01). In addition, a significant (p < 0.05) positive association was found between the presence of seropositive dogs (as assessed by RBT) and seropositive goats on the same ranch.

Evaluation of brucellosis RB51 vaccine for domestic water buffalo (Bubalus bubalis) in Trinidad.

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.

Neospora caninum antibodies in cows during pregnancy as a predictor of congenital infection and abortion.

A cohort study was undertaken on a dairy experiencing endemic Neospora caninum abortions, to characterize dam serologic variations during pregnancy, and to determine if dam N. caninum antibody levels during gestation predicted congenital infection or abortion. Blood samples were collected monthly during pregnancies of 254 cows and precolostrally from 87 of their calves. Antibody levels, as measured by an enzyme-linked immunosorbent assay, indicated 60.6% of cows were seropositive at some time during pregnancy and 87.4% of seropositive cows were seropositive throughout pregnancy. The rate of seroconversion was 8.5/100 cows/yr. The risk of abortion for seropositive cows at the time of pregnancy diagnosis and during gestation was twice that for seronegative cows (P = 0.025, P = 0.006). Calves born to seropositive cows were more likely to be seropositive at birth if the dam had high antibody levels at 240 days of gestation (P = 0.04) and an increase in antibody levels between 90 and 240 days (P = 0.08) than if the respective values of the dam were low or decreasing. Seropositive cows with high antibody levels at 180 and 210 days of gestation were less likely to abort than cows with low antibody levels at those times (P = 0.05, P = 0.03). Results support a causal effect between exposure to N. caninum and abortion, indicate that acquisition of infection during pregnancy is not necessary for congenital infection or abortion to occur, and suggest that maternal immune response influences congenitial infection and abortion.

Rhodococcus equi foal pneumonia: protective effects of immune plasma in experimentally infected foals.

The immunoprophylactic capacity of specific immune plasma was evaluated in pony foals infected experimentally with Rhodococcus equi. Immune plasma, produced by repeated parenteral administration of viable R. equi to adult horses, was harvested and frozen. Group I (six control foals) and Group II (six principal foals) received lactated Ringers solution and immune plasma respectively at three and five days of age. R. equi were aerosolised into a caudal lung lobe of all foals at seven days of age. Clinical signs, haematological alterations, immune responses, thoracic radiographs and technetium99m pulmonary perfusion scans were monitored. All foals were destroyed and complete post mortem examinations performed. All foals developed pneumonia as evidenced by clinical, radiographic and perfusion alterations, but the survival rate of principal foals was significantly (P less than 0.01) greater than that of control foals. Five control foals developed terminal disease, whereas all principal foals recovered. There was no significant (P greater than 0.05) difference in temperature response, or peripheral blood leucocyte, neutrophil or fibrinogen concentrations between groups. ELISA values for R. equi antibody were significantly (P less than 0.001) greater in principal foals following treatment, but there was no significant (P greater than 0.05) difference in IgG or IgM concentrations between groups. Results of the haemolysis inhibition assay indicated that equi factor neutralising antibodies were transferred by immune plasma to the principal foals. Post mortem examinations of five control foals destroyed at approximately three weeks post infection because of terminal disease, revealed severe pyogranulomatous pneumonia. One control and all principal foals were either free of lesions or had resolving lesions and/or minimal scar formation at three months post infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Congenital Neospora caninum infection in dairy cattle and associated calfhood mortality.

A prospective cohort study was undertaken on two central California dairies, A and B, to estimate prevalence of congenital infection with Neospora caninum, to characterize temporal variation in prevalence, to determine if occurrence of congenital infection was associated with specific dam and calf attributes, and to estimate the effect of congenital infection on calfhood mortality. Of the 405 calves enrolled over a period of 2 1/2 y on dairy A and dairy B, 30.6% (85/278) and 53.5% (68/127), respectively, were seropositive precolostrally to N. caninum, as determined by an ELISA test. Adult cow seroprevalence at calving was 36.0% (82/228) for dairy A, and 57.9% (33/57) for dairy B. No evidence was found for a significant increasing or decreasing trend in adult and precolostral seroprevalence through the study period (P > or = 0.26). For both herds combined, 81% of seropositive cows (93/115) and 5% of seronegative cows (8/170) had congenitally infected calves. Seroprevalence did not increase with cow age on either dairy (P > or = 0.47). The probability of a calf being congenitally infected was not associated with dam age, dam lactation number, dam history of abortion, calf gender, or length of gestation (P > or = 0.11). High dam ELISA values at calving were significantly associated (P < or = 0.001) with an increased probability of congenital infection in her calf. Results of survival analyses of female calves available for follow-up indicated a consistently greater survivorship to 90 d in congenitally infected calves than in noninfected calves on both dairies, which was significant for dairy A (P = 0.07, n = 186) but not for dairy B (P = 0.69, n = 72), thus indicating that congenital infection does not necessarily have a detrimental effect on calf health. The findings of a similar magnitude in congenital infection rate and adult cow prevalence, the lack of increasing seroprevalence with cow age, the lack of an effect of dam age on precolostral seropositivity, and the constant seroprevalences during the study period, suggest that, in the two dairies studied, congenital transmission constituted a substantial amount of infection and was likely the major mode of transmission of N. caninum.

Enzootic pneumonia: comparison of cough and lung lesions as predictors of weight gain in swine.

A prospective cohort study was undertaken in a commercial swine herd to determine the relationship between weight gain and the occurrence of enzootic pneumonia (EP). Estimates of the association between EP and weight gain were obtained from multiple linear regression models, using coughing episodes or slaughter checks as indicators of EP status. Models were estimated for pigs in 2 different age groups: roasters (n = 1084, sold at 32 to 50 kg) and market hogs (n = 1162, sold at 100 to 110 kg). The relationship between presence of lung lesions at slaughter and previous coughing episodes was also investigated. Throughout the study period, clinical evaluations were performed weekly, and coughing episodes recorded for each pig. Lungs were inspected at slaughter, and scores were expressed as the percentage of the lung with gross pneumonic lesions. Coughing and lung scores were significantly correlated, after adjusting for other covariates (R = 0.32 and 0.59, respectively, for market hogs and roasters). However, the agreement beyond chance between coughing history and lung lesions at slaughter was poor among both roasters and market hogs (kappa = 0.17 and 0.07, respectively). Although very specific, weekly assessment of coughing was not a sensitive indicator of lung lesions at slaughter. In multiple regression, lung score was a highly significant predictor of lower final weight in pigs of both age groups (P < 0.001 in the selected regression models).(ABSTRACT TRUNCATED AT 250 WORDS)