Bordetella bronchiseptica and toxigenic type D Pasteurella multocida as agents of severe atrophic rhinitis of swine.

Bordetella bronchiseptica and toxigenic type-D Pasteurella multocida were cultured from pigs in each of five herds diagnosed as having severe atrophic rhinitis (AR). B. bronchiseptica alone, P. multocida alone, or both organisms isolated from four herds were inoculated intranasally into 1-week-old gnotobiotic pigs which were necropsied 4 weeks post-inoculation (PI). Nasal turbinate atrophy in B. bronchiseptica-inoculated pigs was moderate to severe, while P. multocida-inoculated pigs had slight to severe atrophy. Pigs inoculated with both organisms had moderate to complete turbinate atrophy. P. multocida was reisolated at necropsy from all pigs receiving the organism except those having no turbinate damage. B. bronchiseptica and P. multocida from a fifth herd were simultaneously inoculated into six naturally farrowed 6-day-old SPF pigs. Necropsy performed 4 weeks PI revealed severe to complete turbinate atrophy. Nasal turbinates were normal for control pigs in both experiments.

Serologic survey for Bordetella bronchiseptica in Nebraska specific-pathogen-free pigs.

The frequency of Bordetella bronchiseptica infection in Nebraska specific-pathogen-free (SPF) pigs was determined by serologic and bacteriologic cultural analysis. Serum samples from non-SPF herds were tested for comparison. A total of 1,282 of 1,397 (92%) of the SPF pigs tested had antibody to B bronchiseptica; 37 of 220 (17%) were culture-positive, and 67 of 4125 (1.6%) were considered suspicious for atrophic rhinitis during slaughter inspection. A higher percentage of the non-SPF pigs had titers to B bronchiseptica (642 of 659 pigs or 97% of the pigs tested). There was no relationship between the B bronchiseptica antibody titer, the isolation of B bronchiseptica, or the frequency of gross lesions of atrophic rhinitis from pigs within the herd. The serum agglutination test may be a more reliable procedure for determining the herd prevalence of B bronchiseptica than isolation of the organism by cultural methods.

The effect of feeding Streptococcus faecium upon Escherichia coli induced diarrhea in gnotobiotic pigs.

Streptococcus faecium (Sf) was fed to gnotobiotic pigs to control colibacillosis. Three strains of Escherichia coli (Ec) were used. Strain 0:K103,987p:NM of Ec fed to pigs without Sf developed severe diarrhea which persisted for several days. Those pigs given Sf and Ec had less diarrhea, recovered earlier, and had better weight gains than Ec only pigs. Two other strains of Ec (0157:K88ac:H19 and 08:K87,K88ab:H19) which were more virulent developed severe diarrhea and death in 5 of 8 pigs given Ec only. Those fed Sf and challenged with Ec developed some diarrhea, but the pigs gained weight and none of the pigs died. Bacterial counts of Ec and Sf from 3 different levels of small intestine and cecum were comparable. The counts were reduced for both organisms in those pigs with dual colonization. It would appear that feeding Sf reduced the toxic effect of Ec and prevented a generalized infection and death. Forty-eight litters of surgically-obtained colostrum-deprived specific-pathogen-free (SPF) pigs for repopulating swine production units were started on Sf probiotic; 48 preceding litters not fed Sf were used for comparison. Those fed Sf had a mortality rate of 8.5% as compared to 18% for those not fed Sf.

Effect of Streptococcus faecium C-68 in control of Escherichia coli-induced diarrhea in gnotobiotic pigs.

Streptococcus faecium was fed to prevent colibacillosis in gnotobiotic pigs. Three strains of Escherichia coli were used. With strain O:K103, 987P:NM in pigs fed S faecium before the E coli challenge exposure, the pigs exhibited less severe diarrhea, recovered earlier, and produced better weight gains than did pigs given E coli only. Escherichia coli strains O157:K88ac:H19 and O8:K87, K88ab:H19 were more virulent. Pigs fed S faecium and challenge exposed with these 2 strains of E coli developed mild diarrhea; however, none of the pigs died, and they continued to eat well and gained weight. Pigs given E coli only developed severe diarrhea and lost weight, and 5 of 8 infected pigs died. Bacterial counts of E coli and S faecium from 3 areas of the small intestine and the cecum were all comparable among experimental groups. Histopathologic examinations demonstrated abundant colonization of the intestinal tract with S faecium. Seemingly, S faecium reduced the toxic effects of E coli and prevented generalized infection and death.

Long-term effect of Bordetella bronchiseptica infection in neonatal pigs.

A total of 62 gnotobiotic pigs were inoculated with Bordetella bronchiseptica at 7 days of age. There were 25 noninoculated controls. Thirteen of the inoculated pigs were killed and 6 pigs which died were examined between 3 and 5 weeks after inoculations were done (group A). Of these 19 pigs, 16 had severe pneumonia and B bronchiseptica was isolated from the lungs of 17. The turbinates in most of the pigs appeared to have some atrophy. Four other pigs died of pneumonia after they were transferred to the floor in isolation rooms, and 9 inoculated pigs were examined at necropsy at about 112 days of age (group B). Bordetella bronchiseptica was isolated from 8 of the latter 9 pigs, and 7 of the pigs had pneumonic lesions. The turbinates all appeared normal. Thirty inoculated pigs (group C) were killed at 180 days of age. Of these, 22 had pneumonic lesions. Bordetella bronchiseptica was reisolated from the turbinates of 2 of 30 pigs, although the turbinates in all appeared normal. The noninoculated controls examined at necropsy at 3 to 5 weeks, 112 days, and 180 days of age did not have any pulmonic lesions, and their turbinates appeared normal. The inoculated pigs killed at 112 days of age gained an average of 0.25 kg/day, and the control pigs gained 0.31 kg. At 180 days of age, the inoculated pigs had gained 0.41 kg/day and the controls, 0.49 kg. Bordetella bronchiseptica infection in susceptible pigs can cause a severe pneumonia which can persist and reduce the growth rate.

Scanning electron microscopy of intestine of gnotobiotic piglets infected with porcine rotavirus.

The development of intestinal lesions caused by the porcine rotavirus were studied in six day old gnotobiotic piglets by scanning electron microscopy. The onset of diarrhea followed an incubation period of 17 to 31 hr. The first detectable lesion was observed in the ileum at 12 hr postinfection, a few hours before the onset of diarrhea. At this time enterocytes appeared swollen and began to separate from each other. Seventeen hours after the onset of diarrhea, lesions were quite severe jejunum and ileum. Enterocytes were detaching from the lamina propria leaving denuded areas. Microvilli were sparse on the cell surfaces and there was marked villous atrophy. Regeneration of ileal mucosa was evident at 4.8 days after the onset of diarrhea. Nine days after recovery from diarrhea the intestinal villi had returned to near its normal structure but there remained some evidence of mucosal damage.

Duration of Mycoplasma hyopneumoniae infection in gnotobiotic pigs.

Sixteen gnotobiotic pigs raised in flexible plastic isolators (four pigs per isolator) were inoculated with a culture of Mycoplasma hyopneumoniae. One pig was killed and underwent necropsy at weekly intervals for the following 16 weeks. Macroscopic lesions were observed in the lungs of 13 of 16 pigs and microscopic lesions were found in 14 of 16 pigs. Mycoplasma hyopneumoniae was cultured from the trachea or lungs from 10 of the 16 pigs. Scanning electron microscope studies showed areas of damage to the cilia, collections, of leucocytes and mucus, and mycoplasma in the trachea as well as the bronchi. These conditions were found in all the pigs seen at necropsy from nine to 16 weeks postinoculation and there was no evidence of noticeable regression or recovery during this 16 week period.

Neonatal calf diarrhea caused by a virus that induces villous epithelial cell syncytia.

Intestinal lesions caused by a virus serologically unrelated to the calf diarrheal rotavirus or coronavirus were studied in gnotobiotic calves. The virion purified from feces from infected calves was a fringed particle with a diameter of about 100 nm. The incubation period from time of inoculation per orum to onset of diarrhea in calves was as short as 8 hours. The viral infection in bacteria-free calves or calves not contaminated with pathogenic bacteria caused severe illness for only 24 hours. When bacteria such as the K99 antigen Escherichia coli were present, the combined infection caused mortality. Lesions occurred only in the small intestinal villous epithelium. Calves euthanatized shortly before or after the onset of diarrhea had developed villous epithelial cell syncytia that contained numberous virions in the cytoplasm. Within 2 to 3 hours after onset of diarrhea, the infected cells were shed and the villi had denuded tips or had cuboidal to squamous epithelial cells.

Scanning electron microscopy of trachea and bronchi from gnotobiotic pigs inoculated with Mycoplasma hyopneumoniae.

Areas of trachea and right apical and right dorsal diaphragmatic bronchi from gnotobiotic neonatal pigs were examined by scanning electron and transmission electron microscopy at 7, 13, and 21 days after pigs were given intranasal inoculation of Mycoplasma hyopneumoniae. Similar areas were examined by scanning electron microscopy from 2 noninoculated neonatal pigs. Tracheal and bronchial lesions were observed in all inoculated pigs. Severe bronchial lesions were in grossly affected lobes. Early infection consisted of mycoplasmas on ciliated epithelial cells. As the interval between inoculation and euthanasia increased, mycoplasmas and leukocytes on the tracheal and bronchial surfaces became more numerous and fewer cilia remained.

Patterns of shedding of human reovirus-like agent in gnotobiotic newborn piglets with experimentally-induced diarrhea.

Virus shedding patterns of neonatal gnotobiotic piglets infected with the reovirus-like agent of human infantile gastroenteritis were studied. Fecal viral counts were highest before or at the onset of diarrhea. In diarrheic piglets, viral particles were usually observed for only 1-2 days after the onset of diarrhea, and total duration of shedding was 2-6 days. One infected piglet shed virus for 4 days but did not develop diarrhea. The presence of virus at or about the time of illness is consistent with the induction of diarrhea in piglets inoculated with the human reovirus-like agent.

Diarrhea caused in gnotobiotic piglets by the reovirus-like agent of human infantile gastroenteritis.

One- to four-day-old gnotobiotic piglets were inoculated orally with a reovirus-like agent obtained from human infants with acute gastroenteritis. Diarrhea developed in the piglets two to seven days after inoculation and was reproduced for five serial passages in one sequence and for three passages in another. Nineteen of 21 inoculated piglets developed diarrhea; reovirus-like particles were observed in intestinal contents and/or fecal samples from 17 animals with illness and from two inoculated piglets that did not develop diarrhea. One piglet, for which daily fecal samples were examined by electron microscopy, shed the largest number of virus particles at the onset of diarrhea. Immunofluorescent antibody responses to the reovirus-like agent were detected in sera from the seven inoculated animals that were tested.

Recovery of transmissible gastroenteritis virus from chronically infected experimental pigs.

Transmissible gastroenteritis (TGE) virus was reisolated from pulmonary and intestinal tissues from 6 of 9 chronically infected experimental pigs (principals) necropsied 30 to 104 days after inoculation. Tissue homogenates (lung and small intestine) from the principals were prepared and inoculated into 3- to 5-day-old gnotobiotic pigs. The virus reisolated from the tissue homogenates produced a milder disease on 1st passage and a more severe disease on 2nd passage. The chronically infected experimental pigs (principals) developed serum-neutralization titers to TGE of 1:30 to 1:525. There appeared to be no relationship between serum titers and reisolation of TGE virus from the 9 principals. The persistence of virus in lung or intestine to 104 days indicates the recovered (or carrier) pig may be considered the primary source of TGE virus infection.

Transferable drug resistance among Enterobacteriaceae isolated from cases of neonatal diarrhea in calves and piglets.

Fecal specimens were collected on 22 different Nebraska ranches and at the Department of Veterinary Science from young calves and pigs with neonatal diarrhea. Enterobacteriaceae isolated from these fecal specimens were screened for resistance to tetracycline, streptomycin, sulfamethizole, kanamycin, chloramphenicol, colistin, nitrofurantoin, and nalidixic acid. Of the 92 strains studied, 57 were resistant to one or more of these antimicrobial agents. Resistant strains were obtained from all herds involved in the study. The two most common resistance patterns were tetracycline streptomycin sulfamethizole (22 of 57) and tetracycline (13 of 57). None of the strains were resistant to chloramphenicol, colistin, nitrofurantoin, or nalidixic acid. The 57 resistant strains were studied to determine whether the resistance was transferable. Forty-three of the 57 resistant strains could transfer part or all of their resistance pattern to a drug-sensitive recipient. The 43 R(+) strains were obtained from 17 of the 23 herds studied. Considerable variation was observed between different R(+) strains in the frequency of transfer of resistance to a particular drug. In addition, variation in the frequency of transfer of different resistance determinants in individual R(+) strains was noted.