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Biomedical subjects

R F Cross

Publications and source records attributed to R F Cross.

At least 37 records · Page 2Linked to original sources
PubMed1978

Rotavirus as a cause of diarrhea in pigs.

A rotavirus (reovirus-like agent) was associated with diarrheal diseases occurring in 1- to 4-week-old suckling pigs in 8 herds and in weaned pigs in 2 herds. Transmissible gastroenteritis virus was also detected in 2 of these herds, as was enteropathogenic Escherichia coli in 5 herds. Morbidity was generally greater than 80% in pigs of the affected age group within these herds, and mortality from diarrhea ranged from 7 to 20%. The disease due to rotavirus in suckling pigs appeared similar to the syndrome commonly referred to as milk scours, white scours, or 3-week scours. Diarrhea and villous atrophy, resembling that seen in transmissible gastroenteritis, occurred in naturally infected pigs and in gnotobiotic pigs experimentally infected with rotavirus. Diagnosis was accomplished by immune electron microscopy of intestinal contents and by immunofluorescent staining of enterocytes. A massive infection of enterocytes with rotavirus was demonstrated by immunofluorescence, which helps explain the pathogenesis of this disease. The apparent rarity of clinical rotaviral infections in suckling pigs greater than 7 days old is probably due to the acquisition of passive immunity from immune sows.

Animals↗
PubMed1978

Pathogenesis of porcine rotaviral infection in experimentally inoculated gnotobiotic pigs.

Porcine rotavirus was shown to infect gnotobiotic pigs and induce an acute enteric disease clinically characterized by diarrhea, anorexia, depression, and occasional vomition. Onset of clinical signs correlated closely with the appearance of lesions within the small intestinal mucosa, and recovery from infection was associated with the regeneration of normal, functional villous epithelium. Villous atrophy, especially in the caudal two-thirds of the small intestine, was the consistent lesion observed in pigs with clinical signs of rotaviral infection. Villi were often short, blunt, and covered with cuboidal epithelial cells. Immunofluorescent microscopy methods demonstrated that the principal site of rotaviral replication was the villous columnar epithelial cells in the small intestine.

Animals↗
PubMed1978

Intrafetal inoculation of swine with transmissible gastroenteritis virus.

Fetuses in 3 sows were inoculated (intramuscularly) with transmissible gastroenteritis (TGE) virus on 95th, 77th, and 74th days of the gestation. At 15, 14, and 37 days later (or days when pigs were obtained by hysterectomy), there was evidence of intestinal localization of virus, with villous atrophy and subsequent repair. All intrafetal-inoculated pigs became serologic-positive for TGE. A noninoculated pig shown to be seropositive for TGE at 15 days of age (after hysterectomy) was resistant to challenge exposure with virulent TGE virus given on the 32nd day, in contrast to 3 seronegative littermates that developed typical disease when challenge exposed.

Animals↗
PubMed1976

Pathogenicity of an attenuated strain of transmissible gastroenteritis virus for newborn pigs.

The pathogenicity of a cell culture-attenuated strain of transmissible gastroenteritis virus for newborn pigs was investigated. Newborn (1- to 2-day-old) pigs were orally given 2 x 10(6) plaque-forming units of attenuated virus. All pigs developed mild diarrhea, but deaths did not occur. As determined by immunofluorescence and villous atropy, infection of the small intestine was limited to the caudal 50 to 66%. Fluorescing cells and atrophic villi were seen from 2 to 3 days until 6 to 7 days after exposure. Attenuated virus-exposed pigs produced circulating virus-neutralizing antibodies detectable as early as 5 days after exposure. By contrast, all pigs orally given 1 x 10(2) pig infective doses of virulent transmissible gastroenteritis virus developed severe diarrhea, and almost all of those not killed died within 2 to 5 days after exposure. In the latter pigs, the entire length of the small intestine, except for the first 4 to 5 cm, was infected with virus by 24 to 36 hours after exposure.

Alkaline Phosphatase↗
PubMed1975

Protection against neonatal enteric colibacillosis in pigs suckling orally vaccinated sows.

Pregnant swine were vaccinated with 1 of 2 enteropathogenic strains of Escherichia coli, and their pigs were challenge inoculated with the homologous strain 1.5 hours after the entire litter was born. Seventeen sows were vaccinated orally by feeding viable cultures on 3 consecutive days, 6 sows were given 2 intramuscular (IM) injections of viable cultures at 10- to 14-day intervals, 6 sows were given 2 IM injections fo formolized cultures at 10- to 14-day intervals, and 12 sows were not vaccinated. The pigs from sows which had been orally vaccinated with viable cultures were protected during the 10-day observation period against diarrhea, as well as against death, when the newborn pigs were challenge inoculated with the homologous strain. Most of the pigs from sows which had been vaccinated IM were protected against death, but few neonates were protected against the diarrheal effects of challenge exposure with the homologous strain. Challenge-inoculated pigs suckling nonvaccinated sows had diarrhea and became dehydrated, and many died. Fewer viable E coli were usually recovered from the homogenized intestinal contents or intestinal segments of newborn pigs which did not have diarrhea than from similar specimens of diarrheal pigs. Microscopic examination of segments of the small intestine revealed that large numbers of E coli were closely associated with the ileal mucosa of newborn pigs killed in the acute phase of neonatal enteric colibacillosis caused by either strain, but organisms were not detected in this location in the pigs which remained normal after challenge exposure. It is concluded that swine which have been vaccinated by feeding large numbers of viable E coli late in gestation can provide good protection to their suckling pigs against the effects of challenge inoculation with the homologous enteropathogenic strain.

Administration, Oral↗
PubMed1975

Vertical transmission of progressive pneumonia of sheep.

Forty-two lambs were derived by hysterectomy from 27 ewes. Eight ewes had lesions of chronic progressive pneumonia (CPP) and 19 did not. Eleven lambs were derived from ewes with lesions of CPP. These 11 lambs were maintained in isolators under germfree conditions until killed at 2 to 4 months of age. Lungs from each lamb were examined for gross and microscopic lesions of CPP and examined by microbiological cultural technique (blood, eosin methylene blue, and PPLO agar). The lungs of one 4-month-old lamb from a ewe infected with CPP had foci of gray consolidation in the apical and cardiac lobes. The microscopic changes were comparable to those in the dam. The lungs of a 2.5-month-old lamb from a ewe infected with CPP had lymphocytic accumulations in the alveolar walls and around blood vessels and bronchioles. The 9 other lambs were free of lesions. Neither bacteria nor mycoplasmas were isolated from any of the 11 lambs. Lesions of CPP were not found in 31 lambs from the 19 noninfected ewes.

Animals↗
PubMed1971

Observations on Trypanosoma theileri infection in cattle.

Naturally occurring Trypanosoma theileri infection was studied in two cattle herds. Herd A was a dairy herd of approximately 250. Herd B was an isolated herd of 32 and contained both dairy and beef breeds. Blood samples were collected from all animals in Herd A during July and August on two successive years. Samples were collected from Herd B at monthly intervals. Total leukocyte and differential counts packed cell volume determinations, and trypanosome cultures were made on each sample. Infection was detected in all age groups between seven months and fifteen years but it was rare in calves. Infected animals were not consistently positive for trypanosomes on consecutive blood cultures and there was considerable variation between infected individuals. Positive cultures were usually obtained from some animals while others were positive intermittently. No correlation was found between trypanosome isolations and the season of the year.A correlation was found between trypanosome isolation and lymphocytosis. Of the 920 blood samples examined, approximately one in every five trypanosome positive samples had lymphocyte levels in the Bendixen positive range. Approximately one in every twenty trypanosome negative samples had lymphocyte numbers in the Bendixen positive range. Evidence indicated that trypanosome isolation from animals with lymphocytosis was not caused by increased numbers of infected buffy coat cells in the inoculum cultured. Eight calves were inoculated intravenously with trypanosome-infected blood. Lymphocyte numbers increased an average of 3549 per cumm above pre-inoculation levels in seven and remained essentially unchanged in one. Prior to inoculation with infective blood, two of the calves were intravenously inoculated with trypanosome-infected blood that had been frozen and thawed to kill the trypanosomes contained in it. Neither developed lymphocytosis following this inoculation. No clinical disease problems which could be attributed to trypanosome infection were found.

Age Factors↗