A challenge-exposure model was developed for dose-dependent induction of subclinical (moderate) atrophic rhinitis (AR) in conventionally raised Dutch Landrace and Large White pigs, about 4 weeks old. Under favorable climatic and housing conditions, pigs were intranasally challenge-exposed with Pasteurella multocida-derived toxin (Pm-T) 3 days after pretreatment by inoculation with 1% acetic acid. Pigs were challenge-exposed with 1 of the following Pm-T doses: 0 (control), 5, 13, 20, or 40 microgram of Pm-T/ml of phosphate-buffered saline solution (PBSS), 0.5 ml/ nostril/d on 3 consecutive days. Five weeks after challenge exposure, subclinical moderate) AR status was defined as intermediate conchal atrophy (grade 2 for ventral conchae on a 0 to 4 scale and grade 1 or 2 for dorsal conchae on a 0 to 3 scale, respectively) and perceptible difference in change in brachygnathia superior (CBS) between control and challenge-exposed pigs between the beginning and end of the study. All Pm-T-exposed pigs had nasal damage that was dose-dependent. The higher Pm-T doses resulted in higher ventral conchae atrophy and dorsal conchae atrophy scores. The CBS increased with applied Pm-T dose, resulting in significant (P < 0.05) differences between controls (3.88 mm) and the 13-, 20-, and 40-microgram Pm-T-treated groups (7.77, 6.58, and 7.98 mm, respectively). In response to the applied dose, weight gain per week for Pm-T-exposed pigs was lower than that of controls after week 3 (P < 0.01). Difference from controls was 32, 54, 52, and 96 g/d/pig for 5-, 13-, 20-, and 40-microgram Pm-T-treated groups respectively, in the last 2 weeks. For Dutch Landrace and Large White pigs, intranasally administered Pm-T mimicked the pathogenic effect of in vivo infection with toxigenic Pm strains. The optimal model to induce subclinical AR appeared to be 13 microgram of Pm-T/ml (0.5 ml/nostril/d) on 3 consecutive days.

Pseudorabies virus (PRV) nucleic acids in the trigeminal ganglia and tonsils of swine latently infected with the virus were analyzed. By use of DNA-polymerase chain reaction (PCR), 14 of 14 trigeminal ganglia and 12 of 14 tonsils were positive for PRV genomes. By use of RNA-PCR, RNA containing the large latency transcript splice junction were detected in 4 of 4 trigeminal ganglia and 4 of 5 tonsils. In general, results of both PCR procedures indicated that the amounts of PRV DNA and RNA per microgram of cellular nucleic acids were higher in trigeminal ganglia than in tonsils. Identification of peripheral tissues that harbor latent PRV is an important asset for PRV research. The presence of large latency transcript in tonsil tissues, in the absence of virus replication, is a critical characteristic, which indicates that the tonsil is a site of PRV latency. For diagnostic purposes, animals need not be euthanatized to obtain their nervous tissue to determine latency; instead, tonsil biopsy specimens could be obtained from live animals for analysis. For pathogenesis studies, multiple specimens obtained sequentially from the same animal would be available for examination for the duration of the experiment.

The Rice strain of pseudorabies virus (PRV) was intranasally instilled in pigs that were seronegative to PRV. Cells were scraped or brushed from tonsillar surfaces biweekly until pigs were euthanatized at either 10 or 16 weeks after infection. The DNA extracted from tonsillar cells or parenchyma were subjected to polymerase chain reaction analysis, using either a single set of oligonucleotide primers or nested primers from the PRV gII glycoprotein gene. Pigs became seropositive to PRV by 3 weeks after infection. The virus was isolated from the trigeminal ganglia and tonsils of pigs that were euthanatized or died 1 to 2 weeks after infection, but not from pigs that were euthanatized 10 or 16 weeks after infection. The PRV gene products were consistently detected in trigeminal ganglia and tonsils of all pigs at 1, 10, and 16 weeks after infection, and sporadically in the nasal mucosa, lymph nodes, and lungs of pigs that were euthanatized or died during the first 2 weeks after infection. Cells collected biweekly from tonsillar surfaces were mostly nucleated, squamous epithelial cells with fewer lymphocytes and neutrophils. Polymerase chain reaction analysis of DNA extracted from these cells revealed PRV DNA in a large proportion of the samples when sufficient cells were collected to provide 1 microgram of extracted DNA for use in the reaction mixtures. A second group of pigs had PRV strain 4892 intranasally instilled. The virus was isolated from tonsillar swab specimens until 3 weeks after infection. Tonsillar brushing specimens were collected biweekly until 14 weeks after infection. Some brushing specimens contained all nucleated, squamous epithelial cells, whereas other specimens contained a mixture of epithelial cells and up to 15% neutrophils, lymphocytes, and small mononuclear cells. Results of polymerase chain reaction analysis of DNA extracted from tonsillar cells collected 5, 11, and 14 weeks after infection were consistently positive for PRV gene products. Intact cells collected from tonsillar surfaces were placed in polymerase chain reaction mixtures with nested oligonucleotide primers from the PRV gII glycoprotein gene and were subjected to multiple amplification cycles. Afterward, the specificity of the amplified PRV gene products was determined by hybridization procedures, using a virus-specific oligonucleotide probe. Most nucleated, squamous epithelial cells stained positive for PRV DNA, suggesting that these cells were the primary source of PRV gene products in tonsillar brushing specimens.

Various procedures of vaccination for pseudorabies were compared for their effects on shedding, latency, and reactivation of attenuated and virulent pseudorabies virus. The study included 6 groups: group 1 (10 swine neither vaccinated nor challenge-exposed), group 2 (20 swine not vaccinated, but challenge-exposed), and groups 3 through 6 (10 swine/group, all vaccinated and challenge-exposed). Swine were vaccinated with killed virus IM (group 3) or intranasally (group 4), or with live virus IM (group 5) or intranasally (group 6). The chronologic order of treatments was as follows: vaccination (week 0), challenge of immunity by oronasal exposure to virulent virus (week 4), biopsy of tonsillar tissue (week 12), treatment with dexamethasone in an attempt to reactivate latent virus (week 15), and necropsy (week 21). Vaccination IM with killed or live virus and vaccination intranasally with live virus mitigated clinical signs and markedly reduced the magnitude and duration of virus shedding after challenge exposure. Abatement of signs and shedding was most pronounced for swine that had been vaccinated intranasally with live virus. All swine, except 4 from group 2 and 1 from group 4, survived challenge exposure. Only vaccination intranasally with live virus was effective in reducing the magnitude and duration of virus shedding after virus reactivation. Vaccination intranasally with killed virus was without measurable effect on immunity. Of the 55 swine that survived challenge exposure, 54 were shown subsequently to have latent infections by use of dexamethasone-induced virus reactivation, and 53 were shown to have latent infections by use of polymerase chain reaction (PCR) with trigeminal ganglia specimens collected at necropsy. Fewer swine were identified by PCR as having latent infections when other tissues were examined; 20 were identified by testing specimens of olfactory bulbs, 4 by testing tonsil specimens collected at necropsy, and 4 by testing tonsillar biopsy specimens. Eighteen of the 20 specimens of olfactory bulbs and 3 of the 4 tonsil specimens collected at necropsy in which virus was detected by PCR were from swine without detectable virus-neutralizing antibody at the time of challenge exposure. One pig that had been vaccinated intranasally with live virus shed vaccine virus from the nose and virulent virus from the pharynx concurrently after dexamethasone treatment. Evaluation of both viral populations for unique strain characteristics failed to provide evidence of virus recombination.

An experimental model for subclinical edema disease was developed in weanling pigs. In multiple experiments, 3-week-old pigs were weaned, then inoculated intragastrically with 10(10) colony-forming units of an SLT-IIv-positive strain of Escherichia coli originally isolated from a pig with edema disease (principals). Control pigs were inoculated with a nonpathogenic E coli strain. Of 39 principals, 8 developed clinical edema disease within 14 days after inoculation. However, 20 of 21 principals that did not develop clinical signs of edema disease, but were submitted for necropsy examination at 14 days after inoculation, had characteristic vascular lesions of edema disease. Vascular lesions, found principally in ileum and brain, consisted of segmental necrosis of myocytes in the tunica media of small arteries and arterioles. None of the pigs inoculated with a nonpathogenic strain of E coli developed edema disease or vascular lesions. None of the principals necropsied at 2 days after inoculation had vascular lesions. Development of vascular lesions by 14 days after inoculation was used as the end point for detecting subclinical edema disease in the model.

Tracheobronchial aspirates obtained from 66 healthy Thoroughbred racehorses in training at the same track were examined. Twenty-seven percent of the horses had > 20% neutrophils in the aspirate. Eosinophils, mast cells, giant cells, and Curschmann's spirals of mucus were observed in 94, 83, 65, and 42% of the horses, respectively. Hemosiderophages were observed in 86% of the horses, half of which had previous confirmation of exercise-induced pulmonary hemorrhage. Although fungal elements were seen in 70% of the horses, bacteria were detected in only 3% of the horses. The authors conclude that inflammatory airway disease is widespread in the racing Thoroughbred population.

Pseudorabies virus (PRV) latency was investigated, using polymerase chain reaction (PCR). A PCR protocol was developed that specifically amplified a 217-base pair sequence within the gene encoding the essential glycoprotein gp50 of PRV. Using this PCR procedure, the gp50 sequence was amplified from tissues of pigs infected with various doses of PRV (Becker strain). At postinoculation day 64, viral isolation was performed on nasal swab specimens and homogenates of tonsils and trigeminal nerve ganglia obtained from 11 PRV-convalescent, seropositive pigs. Results were negative in all cases. By use of PCR, 11 of 11 pigs had PRV-positive trigeminal nerve ganglia and brain stem, 10 of 11 pigs had PRV-positive tonsils, and 9 of 11 pigs had PRV-positive olfactory bulbs.

The activity of leukocytes, determined by chemiluminescence (CL) emission, was compared with the somatic cell count (SCC) in 4,883 quarter-milk samples from 132 dairy cows. The presence of bacteria was determined by bacteriologic culture of samples in which SCC and CL were high. Chemiluminescence was measured with an automated illuminometer system at 37 C after separating the leukocytes from milk by allowing them to adhere to cotton-wool swabs. Chemiluminescence emission was induced by opsonized zymosan and enhanced by luminol. After luminol and zymosan were added to the measuring vials containing the swabs, CL emission increased rapidly, reaching its maximum usually at about 15 minutes of reaction time, and decreasing slowly thereafter. In general, good correlation was found between CL and SCC (r = 0.876; P less than or equal to 0.001; n = 4,883). Even milk samples with low SCC gave reliably measurable CL signals. Minor pathogens in the milk caused about a sevenfold increase in both SCC and CL, whereas major pathogens caused 14- and 25-fold increases in SCC and CL, respectively. The diagnostic situation that requires both sensitivity and specificity to be at least 90% was attained only by the CL assay for major pathogens. These results suggest that the measurement of milk leukocyte activity by CL assay applies well to the diagnosis of mastitis, and has the potential to become a large-scale laboratory test, as well as a simple cowside test.

Trypanosomiasis has been reported in dogs from Texas, Oklahoma, Louisiana, and South Carolina. We describe the first isolation and characterization of Trypanosoma cruzi from a Walker Hound pup in Virginia that also had postvaccinal distemper. The mother of the pup and 7 of its 8 siblings also were found to be infected with T cruzi, suggesting that the parasite had been transmitted transplacentally or through lactation. Parasitologic, serologic, histologic, and molecular methods were used to establish the diagnosis of T cruzi infection in these dogs. In a serologic survey of 12 dogs (including the sire of the pups) from the area in which the index case occurred, none were found to have antibodies to T cruzi. However, 2 of a further 52 dogs from different areas (to the index case), but in the same county, were sero-positive to T cruzi. These findings indicate that canine trypanosomiasis is present in an area of the United States not previously known to be enzootic.

Tissue specimens and serum samples obtained from adult budgerigars in various stages of reproduction housed in an aviary with enzootic avian polyomavirus (APV) disease were examined by means of polymerase chain reaction techniques for APV DNA. Although the birds were apparently healthy, APV DNA could be detected in all 40 birds examined (inapparent infection rate, 100%). Viral DNA was found in most organ systems examined. Analysis of data suggested that organ virus concentrations were lower in breeding than in nonbreeding birds. Serum samples from 144 birds were examined for virus-neutralizing (VN) antibody. All serum samples had detectable VN antibody titers. Determining VN titer had a sensitivity of 100% for detection of APV infection in birds and was more sensitive than analysis of droppings by use of polymerase chain reaction techniques to detect APV infection in 6-month-old birds. Analysis of the data suggested that lower VN antibody titers were associated with longer duration of continuous breeding.