International trade, animal health and veterinary epidemiology: challenges and opportunities.

The link between international trade, animal health and epidemiology has been recognized for a long time and has taken an additional importance in the aftermath of the Uruguay Round of Multilateral Trade Negotiations of the General Agreement on Tariffs and Trade (GATT) and of the inception of the World Trade Organization. The Agreement on the Application of Sanitary and Phytosanitary Measures of the World Trade Organization demands that sanitary and phytosanitary measures be scientifically based, placing epidemiology at the center of decisions related animal health and trade. This paper analyses the interactions between international trade of animals (and animal products) and epidemiology with discussion on the inputs of epidemiology in surveillance, risk analysis and regionalization.

Protection of mice and swine against infection with Actinobacillus pleuropneumoniae by vaccination.

CaCl2 and LiCl cell extracts and a crude hemolysin preparation were isolated from Actinobacillus pleuropneumoniae serotype 1 strain 4074 and tested for protection against A. pleuropneumoniae serotype 1 and 5 in mice. The LiCl cell extract adsorbed on AlPO4 and the crude hemolysin preparation adsorbed on Al(OH)3 showed a highly significant protection (P < 0.01) against both serotypes. Different vaccine preparations were used to immunize pigs by intra-muscular injection at days 0 and 14; the pigs were then challenged at day 21 by intra-tracheal inoculation of 1 x 10(8) colony forming units (CFU) of a serotype 1 strain 4074. A vaccine which combined the LiCl extract and the crude hemolysin preparation adsorbed on Al(OH)3 gave the best protection with no mortality and no sign of morbidity in the vaccinated pigs. In the other experimental groups which included a group immunized with a commercial bacterin, mortality, respiratory disease and extensive pulmonary lesions were noted. This mixture shows good potential as a vaccine against pleuropneumonia in pigs.

Antibacterial and antiviral activity of camel milk protective proteins.

Lysozyme (LZ), lactoferrin (LF), lactoperoxidase (LP), immunoglobulin G and secretory immunoglobulin A were extracted from camel milk. The activity of these protective proteins was assayed against Lactococcus lactis subsp. cremoris, Escherichia coli, Staphylococcus aureus, Salmonella typhimurium and rotavirus. Comparative activities of egg white LZ, bovine LZ and bovine LF are also presented. The antibacterial activity spectrum of camel milk LZ was similar to that of egg white LZ, and differed from bovine milk LZ. Bovine and camel milk LF antibacterial activity spectra were similar. The camel milk LP was bacteriostatic against the Gram-positive strains and was bactericidal against Gram-negative cultures. The immunoglobulins had little effect against the bacteria but high titres of antibodies against rotavirus were found in camel milk. The LP system was ineffective against rotavirus.

Disease outbreak investigation. Three case studies.

Three case studies of the investigation of outbreaks of disease or deviations from target performance are presented. The first is a study of a mastitis problem in a dairy herd, made evident by increased somatic cell counts. The pattern of the production problem is carefully analyzed and conclusions are reached that indicate an infection with environmental contaminant organisms, thus permitting control measures to be introduced. The second case study is an investigation of an outbreak of neonatal mortality in sheep. Analysis suggests a multiple etiology, with infection by border disease virus predominating. The third case study describes the investigation of foothill abortion in a beef herd in California and demonstrates the use of epidemiologic techniques to try to identify the source of infection in a subgroup of the study population, thus allowing specific control measures to be introduced.

Q fever vaccination of sheep: challenge of immunity in ewes.

Adult ewes (17 months of age) were vaccinated against Coxiella burnetii, using a formalin-inactivated whole cell (WC) phase I Henzerling strain vaccine or a chloroform methanol residue (CMR) vaccine. Nineteen pregnant ewes were placed in 3 categories [(i) unvaccinated, (ii) WC vaccine, and (iii) CMR vaccine] and were challenge exposed at approximately the 100th day of gestation with 210,000 plaque-forming units of C burnetii inoculated subcutaneously. Shedding of rickettsiae was measurably reduced, but was not prevented in vaccinated groups, as shown by inoculating ewes' placental tissues, amniotic fluid, and colostrum into mice, as well as by histopathologic lesions of placental tissues. The rickettsiae were shed in the placenta, amniotic fluid, or colostrum in 6 nonvaccinated ewes. In comparison, rickettsiae were detected in placental inoculations from 2 of 6 ewes in the WC vaccine group and 1 of 6 in the CMR group. In contrast to those in the vaccinated ewes, placentitis, high concentrations of rickettsiae in microscopic preparations, and weak lambs were typical for the nonvaccinated ewes.

Coronaviruses associated with outbreaks of transmissible enteritis of turkeys in Quebec: hemagglutination properties and cell cultivation.

Coronaviruses were observed by electron microscopy in the intestinal contents of turkeys in Quebec flocks where repeated outbreaks of enteritis occurred. Three isolates could be serially propagated in turkey embryos inoculated by the amniotic route with clarified intestinal contents. Purification and concentration of viral particles contained in intestinal contents of infected embryos were achieved by precipitation with polyethylene glycol and ultracentrifugation on sucrose density gradients. Three particle types were demonstrated: intact virions with a density of 1.18 to 1.20 g/ml and incomplete particles with densities of 1.14 and 1.24 g/ml. Hemagglutination of rabbit and guinea pig erythrocytes was demonstrated with the intact viral particles; the hemagglutinin was not dependent on incubation temperature. All the isolates were antigenically related, as shown by hemagglutination-inhibition. The turkey coronaviruses did not cross-react with antisera against coronaviruses of avian infectious bronchitis, porcine transmissible enteritis, bovine neonatal calf diarrhea, or mouse hepatitis. One of the Quebec isolates was shown to induce syncytia formation on its third passage in primary chicken-embryo kidney cell cultures. Electron-microscopic examination of infected cell-culture fluids revealed characteristics coronavirus particles identical to those found in intestinal contents of infected turkeys.

Enzyme immunoassay for surveillance of Q fever.

An enzyme-linked immunosorbent assay (ELISA) was developed to monitor antibodies against Coxiella burnetii among animal populations used in research and teaching facilities. Various antigenic components of C burnetii prepared from phase I and phase II whole cells and commercially available antigens were evaluated. A trichloroacetic acid extract was selected for routine use. There was a linear relationship between the transformed absorbance readings of the ELISA results and microagglutination (MA) titers. Comparison between positive or negative results of the MA test and ELISA gave 98.6% concordance. Using the MA test as the standard, ELISA results were 97.8% sensitive and 100% specific. The efficacy of ELISA was evaluated by testing ruminants with known histories of C burnetii infection. Antibody prevalence was 0 in 117 sheep with no history of C burnetii infection, 22% in 145 naturally infected sheep used for research, and 53% in 115 sheep used for vaccine field trials. Forty-eight percent of 120 dairy cows and 52% of 79 goats from endemically infected herds were seropositive. These results indicate that ELISA should be the test of choice for mass screening and surveillance of animals when Q fever is a suspected biohazard.

Epidemiologic study of toxoplasmosis on a sheep ranch.

An epidemiologic study was done on a ranch in northern California on a flock of ewes that had a history of abortions, mummified fetuses, weak or stillborn lambs, and failure to conceive. Of 56 ewes tested, 33 (59%) had serum agglutinating antibodies against Toxoplasma gondii, with an unusually high proportion of high titers. Over a 2-year-period, reproductive problems were higher (39% to 42%) among the seropositive ewes than among the seronegative ewes (9% to 33%). Of 89 sera received from persons and 7 species of animals on the ranch, 44 (49%) were found to be seropositive to T gondii, including seropositive members of a family of 6. The rancher's wife and teenage daughter, both of whom were involved with lambing, had serum titers exceeding 4,096. Other members of the family not involved with lambing were seronegative by the indirect hemagglutination test. The 2 infected persons are known to have come in contact with placentas, birth fluids, fetuses, and colostrums from these infected ewes.

Enzyme immunoassay of Chlamydia in birds.

Serum samples from 192 free-living birds (27 species) were tested for antibodies against Chlamydia using the enzyme-linked immunosorbent assay (ELISA); 97 (51%) were seropositive. The highest antibody prevalence was among pheasants (96%), ducks (88%), and blackbirds (86%). None of 41 starlings tested were seropositive. The serotesting of 42 confined pheasants indicated 100% exposure to the organism. The ELISA is a sensitive, rapid serologic method that can be of epidemiologic and diagnostic value for detecting exposure to Chlamydia. The ELISA could also be used for mass-screening of pet birds where chlamydiosis may be considered a potential public health hazard.

Serologic survey of California wild hogs for antibodies against selected zoonotic disease agents.

Blood samples were collected from trapped or hunter-killed wild hogs (Sus scrofa) in 4 areas of California. Sera were tested for antibodies against 7 zoonotic disease agents. Antibodies against Brucella sp were detected in 21 (15%) of 136 samples. Antibodies against Coxiella burnetii were found in 50% of the collected samples (67 of 135 tested). Of the 135 wild hogs screened for pseudorabies virus, 4 (3%) were seropositive. Leptospira interrogans antibodies were discovered in 118 (87%) of the 136 samples tested. Of the 130 samples screened for antibodies against Mycobacterium avium complex, 111 (85%) were seropositive. Antibodies against Toxoplasma gondii were detected in 17 (13%) of 135 wild hogs. Antibodies against Yersinia pestis were found in 9 (15%) of 59 sera tested.

Initial clinical and immunologic evaluation of a new phase I Q fever vaccine and skin test in humans.

A new phase I Q fever skin test was administered to 74 subjects. Thirty-eight had less than 8 mm and 36 had greater than or equal to 10 mm erythema at 24 hr. Only 14 had circulating antibody. Three skin test-positive and 17 skin test-negative, seronegative individuals subsequently received 6 or 30 micrograms of vaccine in a single dose. All skin test-positive individuals and one skin test-negative individual developed mild local reactions. Seventeen of 18 recipients developed fluorescent antibody to phase II antigen, and five developed positive phase II complement fixation titers. Serial assays of specific lymphocyte proliferation (LT) performed in 15 individuals revealed an increase in phase II LT in nine and an increase in phase I LT in six. All local reactions occurred in individuals with preexisting phase II LT. On the basis of these results, this vaccine and skin-test preparation appear safe, effective, and promising for eventual use in at-risk personnel.

A strategy for control of bovine leukemia virus infection: test and corrective management.

Test and corrective management was applied in one dairy herd (130 milking cows) to control bovine leukemia virus infection. It consisted of: raising uninfected calves in order to establish a pool of uninfected replacement heifers, preventing transmission of bovine leukemia virus through transfer of blood from animal to animal and closing the herd. Regular herd testing was combined with selected changes in herd management. These procedures have been followed since January 1979. Prevalence of antibodies (as determined by gel-immunodiffusion) has declined markedly since the program was implemented.

Serologic survey for certain zoonotic diseases in black bears in California.

Black bears (Ursus americanus) from 3 geographic areas of California were tested for antibodies against agents of 6 zoonotic diseases: toxoplasmosis (indirect hemagglutination), Q fever (microagglutination), trichinosis (latex particle agglutination), botulism (passive hemagglutination), leptospirosis (plate agglutination), and plague (enzyme-linked immunosorbent assay). Of 149 sera tested, 40 (27%) were positive for Toxoplasma gondii antibodies and 25 (17%) had antibodies against Coxiella burnetii. Of 141 bears tested for Trichinella spiralis, 18 (13%) were seropositive, and 19 (15%) of 125 tested had antibodies against the plague organism, Yersinia pestis. Only 2% (2 of 123 tested) had antibodies against Clostridium botulinum. Sera from 129 bears were tested against 4 pools of Leptospira interrogans representing 12 serovars, and 16% of the sera reacted with the pool containing the serovars australis, hyos, and mini georgia.

Why the dairy industry does not make greater use of veterinarians.

Interviews with 32 large-scale dairy operators in Tulare County, Calif, indicated that as large-scale dairies have replaced smaller dairies, the operator's reliance on the veterinarian as a primary source of advice about a wide range of dairy health management issues has declined. Large dairies require an integrated approach to herd management, ie, herd health, herd management, and production. Dairy operators do not look to veterinarians to provide this integrated approach, instead relying on feed representatives, nutritionists, accountants, and staff of dairy cooperatives. Operators perceive veterinarians as primary providers of clinical services only. As veterinarians have little conflict of interest or vested interest in giving advice about nutrition, proper facility design, and other general management issues, this perception of the veterinarian as a clinician only deprives the dairy operator of an objective appraisal of herd health, management, and production. Changing this perception will require a restructuring of many veterinary medical school curricula, with an emphasis on courses in epidemiology, preventive medicine, herd management, nutrition, and similar courses.

Metabolic and cellular profile testing in calves maintained under feedlot conditions: protein fractions and lactate dehydrogenase isoenzymes--changes over time.

Mean concentrations for total serum protein and serum protein fractions, and mean activities for total lactate dehydrogenase (LDH) and LDH isoenzymes were determined in 114 crossbred yearling cattle during a 56-day feeding trial. These values were to be used as predictors of performance (weight gain). The mean total serum protein concentration on day 0 was high (7.27 g/dl), reached a low on days 7 and 14 (6.47 and 6.50 g/dl), and then equilibrated toward the end of the study. The mean concentration for the albumin fraction also reached a low on days 7 and 14 (2.83 and 2.84 g/dl) and then increased, remaining steady until termination of the feeding trial. The alpha-, beta-, and gamma-globulin fractions fluctuated throughout the study. The mean for total LDH activity peaked on day 21 (1,363 IU) and then remained relatively constant through day 56. Mean serum activities for the LDH3 activity peaked on day 7 (27%) and then decreased progressively to day 56 (17%). The overall trend for LDH4 and LDH5 activities seemed to be a steady increase.

Q fever hazards from sheep and goats used in research.

Two recent outbreaks of Q fever in research institutions prompted the authors to review extant data, in an effort to delineate hazards to humans from small ruminants used in research. Prevalence of Q fever antibodies was 24% among 2097 sheep and 57% among 1475 goats from various sources. In a facility using sheep for prenatal research, in which an epidemic of human Q fever later occurred, antibody prevalence among sheep was 77%, with larger than usual proportions of high (greater than or equal to 128) titers. Antibody prevalence was 5% in a sample from the general human population and 11% among 347 persons at three research institutions (17% among students, 8% among the research staff). Except for animal caretakers routinely exposed to sheep, antibody prevalence among research staff approximated prevalence in the general population. Suggestions are made for surveillance and vaccination of sheep and goats used in medical research institutions.

Comparison of the enzyme-linked immunosorbent assay with other tests for brucellosis, using sera from experimentally infected heifers.

During an evaluation of H-38 Brucella melitensin vaccine, serum samples were collected from 24 Hereford-Angus heifers (nonvaccinated controls) before exposure and then 11 times between 12 and 102 days after exposure to Brucella abortus strain 2308. Antibody concentrations were determined by the enzyme-linked immunosorbent assay (ELISA) and by standard tube agglutination (STA), 2-mercaptoethanol agglutination (ME), microtitration complement-fixation (MCF), and automated complement-fixation (ACF) tests. The results were compared in terms of concordance, sensitivity, and specificity. Concordance between the ELISA and other tests were 100% (STA), 75.7% (ME), 97.8% (MCF), and 95.2% (ACF). On the 12th day after heifers were exposed, antibodies were detected in 18.2% of the infected heifers by the ELISA and in 11.1% with the STA test, in 0% with the ME test, in 33.3% with the MCF test, and in 44.4% with the ACF test. On the 25th day, ELISA and all serotests (except ME) detected antibodies in all infected heifers. All serum samples from the heifers before exposure were negative.

Metabolic and cellular profile testing in calves under feedlot conditions, using discriminant analysis to identify calves with low potential for weight gain.

Thirty-eight variables were measured in blood samples of 48 calves at the beginning (day 0) of a feed trial. After 56 days, the calves were assigned (according to weight gain) into three groups: high gainers, medium gainers, and low gainers. Discriminant analysis was used on the variables that were measured to classify the calves into three groups. When the mean values for three overlapping groups of 16 calves each were analyzed, blood urea nitrogen data alone correctly classified 68.7% of the low gainers. Overall, correct classification never exceeded 58.3%. When three nonoverlapping groups of nine calves each were used, inorganic phosphate data (used first and alone) correctly classified 66.7% of the low gainers. After seven steps, 81.5% of the animals were correctly classified, including 88.9% of the low gainers. The two-group discriminant analysis identified 78% of the nine lowest gainers, and 90% of the remaining animals were correctly classified.