Viral RNA oligonucleotide fingerprinting was used to compare genetic relationships among pestiviruses originating from ovine or bovine host species. Ovine pestiviruses, including reference border disease virus and 2 border disease isolates originating from natural pestivirus infections of sheep, appeared to have a more distant genetic relationship among themselves than with certain bovine pestiviruses. A closer genetic relatedness was evident between border disease virus and 3 noncytopathic bovine pestiviruses, including Draper bovine viral diarrhea virus (BVDV), a BVDV isolate that originated from aborted bovine fetuses, and a virus that was isolated from the serum of a calf that had a chronic BVDV infection. Four noncytopathic bovine viruses, including Draper BVDV and 3 field isolates, were closely related. Reference Oregon C24V BVDV, a cytopathic virus, was closely related to only 1 of the 7 noncytopathic viruses in this study.

Twenty-four isolates representing 6 species of Campylobacter were screened for plasmids. A large plasmid with an approximate molecular weight of 38 Mdal was detected in 5 C jejuni isolates originally recovered from diarrheic human beings, in one isolate of C coli recovered from diarrheic pigs, and in 1 isolate of C sputorum ssp mucosalis and 2 isolates of C hyointestinalis recovered from pigs with proliferative enteritis. One isolate of C coli and 1 isolate of C hyointestinalis contained an additional smaller plasmid with an approximate molecular weight of 1.6 Mdal; this plasmid was partially mapped by restriction endonuclease digestion. Fifteen Campylobacter isolates contained no detectable plasmids: 2 C coli, 2 C sputorum ssp mucosalis, 2 C fecalis, 1 C fetus ssp fetus, and 8 C hyointestinalis isolates. In summary, 37.5% of the Campylobacter isolates contained a 38-Mdal plasmid, with 8% having both 38 Mdal and 1.6-Mdal plasmids; 62.5% contained no detectable plasmids.

The performance of the serum complement fixation (CF) test was compared with that of a serum agar gel immunodiffusion (AGID) test on 74 subclinically infected and 154 uninfected cattle in 6 commercial midwestern dairy herds with Mycobacterium paratuberculosis infection and on 30 cattle in a herd that was free of infection. Infection status of cattle within herds was established by performance of a series of 3 or more fecal cultures and of ileocecal lymph node cultures of culled cattle. In cattle with subclinical infection detected by culturing, the sensitivity estimates of the CF and AGID tests were 10.8% (3.6% SE) and 18.9% (4.5% SE), respectively. In the cattle classified as disease free, the specificity estimates of the CF and AGID tests were 97.4% (1.3% SE) and 99.4% (0.6% SE), respectively. Neither set of estimates was significantly different. Negative test results obtained with the use of either test in apparently normal cattle from suspect herds should be interpreted with caution because both tests suffer from low sensitivities in subclinically infected animals. However, the AGID test may be more useful in regulatory situations in which the CF test is currently used because the AGID test is easier to perform and to interpret.

Eleven adult goats and 32 adult outbred mice were inoculated IV with Cowdria ruminantium-infected blood (Kwanyanga isolate), monitored clinically, then serially euthanatized. Predominant clinical signs of disease in goats were depression, head tremors, seizures, and dyspnea. In mice, dyspnea and depression were the only clinical signs of disease noticed. Tissues were examined histologically and immunohistochemically for C ruminantium colonies or antigen. In goats, C ruminantium was detected only in endothelial cells of the brain, even though gross and microscopic lesions were confined to the thorax. In mice, C ruminantium was detected only in endothelial cells of the heart and lungs.

Effects of immunosuppression were compared in newly hatched chickens given cyclophosphamide (CY) after inoculation with avian nephritis virus (ANV). All CY-treated infected chickens died within 13 days after inoculation of the virus and had heavy urate deposits throughout the body. However, non-CY-treated infected, CY-treated noninfected, and non-CY-treated noninfected control chickens survived through the observation period. In a chronologic study, the value of serum uric acid in CY-treated infected chickens was more than 3 times higher than that in non-CY-treated infected chickens, and more than 9 times higher than in noninfected chickens. Serum uric acid values were coincident with the positive degree of ANV antigen in the tubular epithelial cells in the kidneys and with the severity of renal degeneration. Serologic and immunohistologic examinations did not reveal detectable antibody and IgG- and IgM-containing cells in the spleen and kidneys of CY-treated infected chickens. However, non-CY-treated infected chickens had an increased number of IgM- and IgG-containing cells and antibody against ANV on postinoculation day 6. These findings demonstrated that CY treatment enhanced the susceptibility of chickens to ANV infection.

Sera and tracheal washings (TW) were used to identify antigens of Bordetella avium recognized during experimentally induced bordetellosis in young turkeys. Pooled sera and TW were examined for antibody by a microtitration agglutination test and by western immunoblotting. In addition, comparable samples collected from 1-day-old turkeys and uninoculated control turkeys also were examined. At least 8 outer membrane proteins of B avium were recognized in immunoblots of sera and TW from infected turkeys. Reactivity of TW in immunoblots was qualitatively similar but less intense, compared with reactivity of corresponding sera collected on postinoculation (PI) weeks 2, 3, and 4. Molecular weights of the major outer membrane proteins of B avium recognized by sera and TW at PI week 4 were 100,000, 97,000, 36,000, 31,000, 21,000, 18,000, 14,000, and < 14,000. A protein with a molecular weight of 55,000 reacted nonspecifically in all samples tested. Antibody, detectable by microtitration agglutination, was in sera of 1-day-old turkeys and in sera and TW of B avium-infected turkeys during PI weeks 2 to 4.

Fifty-six samples of feces and intestinal contents from nonvaccinated diarrheal pigs with rotavirus infections were tested, using a subgroup (SGP)-specific ELISA, to determine rotavirus SGP classification. Forty-one percent (23/56) were SGP 1, 25% (14/56) were SGP 2, and 34% (19/56) were not classifiable. For classifiable samples, the geographic distribution for SGP 1 and SGP 2, respectively was: 60%/40% from Ohio (n = 15), 63%/37% from other midwestern states (Iowa, Minnesota, Nebraska, South Dakota: n = 16), and 67%/33% from Canada (n = 6). Thirty-seven SGP-classifiable samples were categorized according to age of pigs. Of pigs less than or equal to 1 week old, 22% of samples were SGP 1 (n = 8), and 14% (n = 5) were SGP 2. Of samples from 1- to 2-week-old pigs, 8% were SGP 1 (n = 3), and 5% were SGP 2 (n = 2). Of samples from 2- to 3-week-old pigs, 5% were SGP 1 (n = 2), and 8% were SGP 2 (n = 3). Of samples from 3- to 4-week-old pigs, 5% were SGP 1 (n = 2), and 3% were SGP 2 (n = 1). Of samples from pigs > 4 weeks old, 22% were SGP 1 (n = 8) and 8% were SGP 2 (n = 3). Double-stranded RNA extracted from positive controls and from 10 selected field samples (5 from SGP 1 and 5 from SGP 2) was electrophoresed in polyacrylamide gels to detect correlation between subgroup classification by ELISA and long or short double-stranded RNA electrophoretic-migration patterns. All SGP-1 and -2 rotavirus samples tested had typical long double-stranded RNA electrophoretic-migration patterns.

The kinetics of specific IgM and IgG antibody response was characterized in four 9-month-old Beagles after inoculation of 2 x 10(2) plaque-forming units (PFU) of Sheila Smith strain of Rickettsia rickettsii. Immunoglobulin M antibodies were first detected by indirect immunoflorescence on postinoculation (PI) day 9, peaked by PI day 20, and were no longer detectable by PI day 80. Immunoglobulin G antibodies became detectable between PI days 22 and 28, peaked by PI day 42, and decreased gradually through PI day 130. Subsequent challenges with R rickettsii on PI days 216 (2 x 10(2) PFU/dog) and 1,029 (5 x 10(4) tissue culture infective dose [TCID50]/dog) resulted in slightly different serologic responses. The initial challenge exposure failed to increase the concentration of IgG antibodies and induced only low concentrations of IgM antibodies. After the second challenge inoculation, IgM antibodies were not detectable and the concentration IgG antibodies increased slightly. Clinical abnormalities and seroconversion were documented in control dogs following each challenge exposure. Examination of acute and convalescent serum samples from 55 dogs in which Rocky Mountain spotted fever was suspected clinically suggested that sole evaluation of IgM antibodies in acute-phase serum would result in inaccurate diagnoses because of false-positive and -negative results. Use of a composite conjugate that detects IgM and IgG antibodies to R rickettsii appears to be satisfactory for diagnostic purposes; however, concurrent quantitation of IgM antibodies may facilitate serodiagnosis in a select group of dogs in which a four-fold increase in convalescent antibody titer is not detected by use of the composite conjugate. With the exception of a dog with a serum antibody titer of 1:8,192, we were unable to detect IgM or IgG antibodies in CSF samples from 9 dogs with experimentally and 3 dogs with naturally acquired infections.

A deterministic mathematical model of the population biology of pseudorabies in swine was used to clarify some of the basic features of the host-virus relationship and to inquire into the circumstances that promote or impede virus persistence in a single herd. When the basic reproductive rate of the infection (ie, the number of secondary infections resulting from the introduction of a single infective animal into a wholly susceptible herd) is greater than unity, the model suggests that the number of infective individuals in the herd will undergo highly damped oscillations to a final equilibrium level. The most important determinants of virus persistence are herd size and the density at which sows are maintained. There is a threshold density of susceptible individuals below which the virus will eventually be eliminated from the herd, even when specific control measures are lacking. Test and removal strategies hasten virus elimination when herd density is already below threshold, but are otherwise likely to succeed only when the removal of latent infections reduces the basic reproductive rate of the infection below unity. Vaccination strategies may also result in virus elimination, but only in relatively small herds.

The infectivity and pathogenicity of selected bovine viral diarrhea virus (BVDV) isolates were determined in gnotobiotic, colostrum-deprived neonatal lambs. Five-day-old cesarean-derived gnotobiotic lambs were exposed to 1 of 10 BVDV isolates via aerosol suspension. These isolates were from tissues or secretions of calves or lambs affected with respiratory tract disease, weak neonatal calves, aborted bovine fetuses, or reference Singer or Draper BVDV. The pathogenicity of each isolate, relative to the others, was evaluated in lambs by measurement of the neutralizing antibody response, virus isolation from nasal secretions or tissues, and postmortem lesions. The BVDV isolates varied in their infectivity and pathogenicity. Singer, the cytopathic reference strain, was the most lymphotrophic isolate and stimulated the greatest neutralizing antibody response. Encephalitis was the most consistent lesion observed and was used as the final determinant of relative pathogenicity of the viruses. The most neuropathogenic isolates were the 2 viruses originating from lambs affected with respiratory tract disease, the 2 weak neonatal calf isolates, and 1 isolate from an aborted bovine fetus. The least pathogenic isolates were the 2 reference isolates, Draper and Singer; the 2 mucosal disease isolates; and 1 isolate originating from an aborted bovine fetus.