Jerome C. Nietfeld

A field evaluation of mortality rate and growth performance in pigs vaccinated against porcine circovirus type 2

OBJECTIVE To evaluate, under field conditions, the effects of a commercial porcine circovirus type 2 (PCV2) vaccine on mortality rate and growth performance in a herd infected with PCV2 that had a history of porcine circovirus disease. DESIGN Randomized controlled clinical trial. ANIMALS 485 commercial, cross-bred, growing pigs. PROCEDURES Prior to weaning, pigs were randomly assigned within litter to a vaccination or unvaccinated control group. Pigs in the vaccination group were given a commercial PCV2 vaccine at weaning and 3 weeks later. Mortality rate was recorded, and pigs were weighed prior to vaccination, when moved from the nursery, and prior to marketing. Infection status was assessed by serologic testing and detection of viral DNA in serum. RESULTS Compared with control pigs, pigs vaccinated against PCV2 had a significantly lower mortality rate during the finishing phase, significantly higher average daily gain during the finishing phase, and significantly lower likelihood of being lightweight at the time of marketing. For vaccinated pigs, overall mortality rate was reduced by 50% and average daily gain during the finishing period was increased by 9.3%. At the time of marketing, vaccinated pigs weighed an average of 8.8 kg (19.4 lb) more than control pigs, without any difference in days to marketing. Serum PCV2 antibody titers increased in control pigs, and PCV2 DNA was detected, indicating active PCV2 infection. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that vaccination against PCV2 was effective at reducing mortality rate and improving growth performance among pigs in a herd infected with PCV2.

Comparison of Cultivation and PCR-Hybridization for Detection of Salmonella in Porcine Fecal and Water Samples

ABSTRACT A total of 150 fecal and water samples from four swine farms were tested for the presence of Salmonella enterica using different enrichment techniques as follows: (i) 92 fecal samples from nursery and farrowing barns at three swine farms were preenriched overnight in tryptic soy broth (TSB) at 37°C followed by overnight enrichment in Rappaport-Vassiliadis 10 broth (RV10) at 42°C; (ii) 24 water samples from the third farm were preenriched overnight in 3MC broth at 37°C followed by overnight enrichment in RV10 at 42°C; and (iii) 34 fecal samples from a fourth farm, a finishing farm, were enriched overnight in RV10 at 42°C with no additional enrichment. Following each of the enrichment techniques, samples were subcultured onto modified semisolid Rappaport-Vassiliadis (MSRV) agar prior to transfer to Hektoen Enteric agar plates for the recovery of viableSalmonella bacteria. Presumptive Salmonellaisolates were biochemically and serologically confirmed. For the PCR detection of Salmonella, a 1-ml portion was removed from each sample after the first overnight enrichment and the DNA was extracted using a Sepharose CL-6B spin column. Amplicons (457 bp) derived from primers to the invA and invE genes were confirmed as Salmonella specific on ethidium bromide-stained agarose gels by Southern hybridization with a 20-mer oligonucleotide probe specific for the Salmonella invAgene. Neither the standard microbiological method nor the molecular method detected all of the 65 samples that tested positive by both methods or either method alone. Salmonella bacteria were detected by both cultivation and PCR-hybridization in 68% (17 of 25) of the positive samples that were preenriched in TSB, in 73% (11 of 15) of the positive samples preenriched in 3MC broth, and in 24% (6 of 25) of the positive samples enriched in RV10. Agreement betweenSalmonella detection using cultivation with preenrichment and detection by PCR was 76% using the kappa statistic. However, agreement between Salmonella detection using cultivation without preenrichment and detection by PCR was about 6%; the PCR assay detected 80% (20 of 25) of the 25 positive samples, whileSalmonella bacteria were recovered from only 44% (11 of 25) by cultivation. Our results indicate that the PCR-hybridization approach is equivalent to or better than cultivation for detectingSalmonella in swine feces or water samples from swine farms when using the medium combinations evaluated in this study.

Neospora -like protozoan infection as a cause of abortion in dairy cattle

In 1989,29 of 240 drylot Holstein cows from a New Mexico dairy aborted over a 5-month period. Seven of the 9 fetuses examined had multifocal necrotizing encephalitis and multifocal myocarditis. Neospora-like protozoa were found in tissues from 3 of the fetuses. More recently, a protozoan that reacted positively with anti-N. caninum serum was identified as the most common cause of abortion in California dairy cattle. 1,2 Many of these abortions were epizootic, with multiple abortions over a 1 or 2-month period. 1 Abortions and congenital infections in calves infected by a Neosporalike protozoan have been reported in the United States, but these were isolated cases involving only a single calf in each herd. This protozoan has never been isolated, so its exact identity remains unknown. Recent studies indicate that the organism is closely related to N. caninum, but some ultrastructural and antigenic differences exist between the bovine parasite and N. caninum isolated from dogs. Except for a single case of abortion in a beef cow from Maryland, the cases of fetal and congenital neosporosis previously reported from the United States are from the western states of New Mexico, 11 Califomia and Washington. Nineteen additional cases of bovine abortion associated with Neosporalike infection that were submitted to the South Dakota Animal Disease Research and Diagnostic Laboratory (SDADRDL) are herein reported. Specimens from cases of bovine abortions that are submitted to the SDADRDL undergo a routine protocol of testing to determine the cause of the abortion. Entire animals are necropsied and samples of brain, heart, lung, liver, kidney, placenta, tissues with gross lesions, and, since February 1991, skeletal muscle are fixed for histopathologic examination. Abomasal fluid is cultured for aerobic and microaerophilic bacteria and fungi. Scrapings of placenta are digested with potassium hydroxide and examined for fungal hyphae by a direct, nonspecific fluorescent antibody (FA) technique. If hyphae are found, the placenta is cultured for fungi. Impression smears of kidney are examined by a direct FA technique for 6 serovars of Leptospira. Direct FA tests are performed on frozen sections of kidney and spleen for infectious bovine rhinotracheitis (IBR) virus and bovine viral diarrhea (BVD) virus. Pools of brain, lung, liver, kidney, and spleen are homogenized and inoculated onto primary cultures of fetal bovine lung and turbinate cells for virus isolation. When received, a homogenate of placenta is inoculated by itself onto the same cell lines. Formalin-fixed paraffin-embedded

Fatal Disease in Nursing Puppies Associated with Minute Virus of Canines

Thirteen cases of a previously undescribed parvoviral infection affecting puppies ranging in age from 5 to 21 days is described. The cases were originally thought to represent an unusual pathologic manifestation of canine parvovirus-2 (CPV-2) infection. However, failure to confirm CPV-2 infection in any of the cases suggested a different parvovirus was involved. Minute virus of canines (MVC) was subsequently isolated from a case by using the Walter Reed Canine Cell Line, the only cell line which will support the growth of MVC. The pathologic and virologic findings for these 13 cases are described in this report.

Comparison of Host Immune Responses to Homologous and Heterologous Type II Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) Challenge in Vaccinated and Unvaccinated Pigs

Porcine reproductive and respiratory syndrome (PRRS) is a high-consequence animal disease with current vaccines providing limited protection from infection due to the high degree of genetic variation of field PRRS virus. Therefore, understanding host immune responses elicited by different PRRSV strains will facilitate the development of more effective vaccines. Using IngelVac modified live PRRSV vaccine (MLV), its parental strain VR-2332, and the heterologous KS-06-72109 strain (a Kansas isolate of PRRSV), we compared immune responses induced by vaccination and/or PRRSV infection. Our results showed that MLV can provide complete protection from homologous virus (VR-2332) and partial protection from heterologous (KS-06) challenge. The protection was associated with the levels of PRRSV neutralizing antibodies at the time of challenge, with vaccinated pigs having higher titers to VR-2332 compared to KS-06 strain. Challenge strain did not alter the cytokine expression profiles in the serum of vaccinated pigs or subpopulations of T cells. However, higher frequencies of IFN-γ-secreting PBMCs were generated from pigs challenged with heterologous PRRSV in a recall response when PBMCs were re-stimulated with PRRSV. Thus, this study indicates that serum neutralizing antibody titers are associated with PRRSV vaccination-induced protection against homologous and heterologous challenge.

Investigation of a Microcystis aeruginosa cyanobacterial freshwater harmful algal bloom associated with acute microcystin toxicosis in a dog

Microcystin poisoning was diagnosed in a dog exposed to a Microcystis aeruginosa–dominated, freshwater, harmful algal bloom at Milford Lake, Kansas, which occurred during the summer of 2011. Lake water microcystin concentrations were determined at intervals during the summer, using competitive enzyme-linked immunosorbent assays, and indicated extremely high, localized microcystin concentrations of up to 126,000 ng/ml. Multiple extraction and analysis techniques were used in the determination of free and total microcystins in vomitus and liver samples from the poisoned dog. Vomitus and liver contained microcystins, as determined by enzyme-linked immunosorbent assays, and the presence of microcystin-LR was confirmed in vomitus and liver samples using liquid chromatography coupled with tandem mass spectrometry. Major toxic effects in a dog presented for treatment on the day following exposure included fulminant liver failure and coagulopathy. The patient deteriorated rapidly despite aggressive treatment and was euthanized. Postmortem lesions included diffuse, acute, massive hepatic necrosis and hemorrhage, as well as acute necrosis of the renal tubular epithelium. A diagnosis of microcystin poisoning was based on the demonstration of M. aeruginosa and microcystin-LR in the lake water, as well as in vomitus produced early in the course of the poisoning; the presence of microcystin-LR in liver tissue; and a typical clinical course including gastroenteritis and fulminant liver failure.

Characterization of a New Disease Syndrome Associated with Porcine Circovirus Type 2 in Previously Vaccinated Herds

ABSTRACT Porcine circovirus-associated disease (PCVAD) encompasses a group of wasting syndromes linked to porcine circovirus type 2 (PCV2). This paper describes a new PCV2 disease syndrome, called acute pulmonary edema (APE), which, unlike other PCVAD syndromes, has a peracute onset and is associated with herds vaccinated for PCV2.

Antibody responses following vaccination versus infection in a porcine circovirus-type 2 (PCV2) disease model show distinct differences in virus neutralization and epitope recognition.

Porcine circovirus associated disease (PCVAD) encompasses a group of syndromes linked to infection with porcine circovirus type 2 (PCV2). Based on the hypothesis that the immune responses to vaccination versus infection are quantitatively and qualitatively different, the objective of this study was to evaluate immunity, virus replication and disease protection in pigs vaccinated with PCV2 capsid protein (CP) and during infection. The disease model included dual infection with PCV2 and porcine reproductive and respiratory syndrome virus (PRRSV), a virus known to enhance disease progression and severity. The principal effect of PRRSV infection was to increase peak PCV2 viremia by almost 40-fold; however, PCV2 failed to show a reciprocal effect on PRRSV. In vaccinated pigs, there was no evidence of disease or PCV2 replication following dual virus challenge. Immunity following vaccination favored PCV2 neutralizing activity; whereas, PCV2 infection and disease produced high levels of non-neutralizing antibody, primarily directed against a polypeptide in the C-terminal region of CP. These results support the notion that the magnitude of the total antibody response cannot be used as a measure of protective immunity. Furthermore, protection versus disease lies in the immunodominance of specific epitopes. Epitope specificity should be taken into consideration when designing PCV2 vaccines.

Small Intestinal Chlamydia Infection in Piglets

Evidence of Chlamydia infection of small intestinal epithelial cells was found in 4 4-14-day-old nursing piglets and 2 22-30-day-old weaned piglets. Each nursing piglet was from a different South Dakota swine farm experiencing preweaning diarrhea. The first weaned piglet was 1 of 7 live piglets from a Minnesota swine farm that were having problems with postweaning weight loss and a mild cough; diarrhea had not been noted by the owner. The second weaned piglet was from an Iowa farm experiencing diarrhea beginning 5 days after weaning. Three piglets were submitted alive and necropsied at the diagnostic laboratory. Three piglets were necropsied by the herd veterinarians, who submitted fresh and formalinfixed samples to the laboratory. Increased fluidity of the colonic contents was the only macroscopic change in the intestinal tracts of 5 piglets. The submitting veterinarian reported that a pseudomembrane was adhered to the ileal mucosa of the sixth piglet. In 3 nursing piglets, the lymphatics in the cranial two-thirds of the small intestinal mesentery were filled with chyle, indicating absorption from the small intestine. Immunofluorescent antibody (IFA) staining detected porcine rotavirus antigen in small intestinal enterocytes of 1 nursing and 1 weaned piglet but not in sections ofintestine from the other 4 piglets. Transmissible gastroenteritis virus (TGE) antigen was not found in IFA-stained frozen sections of small intestine from all piglets. Viral particles were not found by electron microscopic examination of negatively stained colonic contents. Bacterial culture procedures for enteric pathogens and IFA staining for K88, K99, and 987P pilus antigens of enterotoxigenic Escherichia coli did not yield significant results. Microscopic examination revealed mild to moderate necrotizing enteritis in the distal jejunum and ileum of the 4 nursing piglets and 1 weaned piglet. Mild to moderate villous atrophy with attenuation, necrosis, and sloughing of the villous epithelium was present in affected areas of the small intestine (Figs. 1, 2). A variable amount of detritus and fibrin partially covered the mucosal surface, and abnormally high numbers of neutrophils were in the lamina propria of 3 piglets. Microscopic lesions in the small intestine from the rotavirus-positive weaned piglet consisted of moderate villous atrophy and attenuation of the villous epithelium; inflammation and epithelial necrosis were minimal. In hematoxylin and eosin (HE)-stained sections of distal jejunum and ileum from all piglets, the supranuclear region of many enterocytes contained large vacuoles. Basophilic round bodies < 1.0 μm in diameter were within these vacuoles (Fig. 2). Neither bacterial colonization of the brush border of enterocytes nor developmental stages of Isospora suis were found.

Colonization of the Tracheal Epithelium of Pigs by Filamentous Bacteria Resembling Cilia-Associated Respiratory Bacillus

Warthin Starry staining revealed filamentous bacteria colonizing the tracheal epithelium of 41 of 88 (46.6%) pigs submitted for necropsy at 2 midwestem veterinary diagnostic laboratories. The bacteria were interspersed between and oriented parallel to the cilia. In 4 of 4 colonized pig tracheas, filamentous bacteria were demonstrated by transmission electron microscopy. The bacteria were approximately the same length and diameter as cilia, and in areas of heavy colonization the bacteria outnumbered cilia. The filamentous bacteria were similar in location and morphologic characteristics to cilia-associated respiratory (CAR) bacilli of rats, mice, rabbits, and cattle. Results of immunoperoxidase staining and polymerase chain reaction analysis indicated that the pig CAR bacillus is a different bacterium than the rat CAR bacillus. Rat CAR bacillus causes chronic respiratory disease in rats and mice. The association, if any, between pig CAR bacillus and swine respiratory disease is unknown.