Effect of vaccinal and passive immunity on experimental infection of pigs with porcine parvovirus

One group of 5 pigs was vaccinated twice at 6 and 8 weeks of age with an inactivated porcine parvovirus (PPV) vaccine. A 2nd group of 5 pigs was passively immunized at 9 weeks of age, and a 3rd group of 5 pigs served as nonimmunized controls. The immunity of all pigs was challenged with live PPV at 10 weeks of age. Four vaccinated pigs with hemagglutinating-inhibiting (HI) antibody titer of 160 to 640 and 3 passively immunized pigs with HI titer of 80 to 160 were resistant to PPV infection. Neither infective virus nor viral antigen was detected in their tissues. However, virus replicated in tissues of 1 vaccinated and 2 passively immunized pigs with HI titers of 80, and viral antigen was detected in their lymphoid tissues. There was a 4-fold increase of HI titer in 1 passively immunized pig. Viremia and viral excretion were not detected in any of the vaccinated or passively immunized pigs. In contrast, PPV replicated in the tissues of nonimmunized pigs; both virus and viral antigen were detected in their tissues, and they produced HI antibodies to PPV. All nonimmunized pigs developed viremia and shed virus in oral secretions and feces. Our data show that a high level of humoral antibodies is required for protection from PPV infection.

Response of conventionally raised weanling pigs to experimental infection with a virulent strain of porcine parvovirus

Conventionally raised 6-week-old pigs were inoculated intranaslly and orally with porcine parvovirus. The pigs remained clinically normal for up to 17 days. They were viremic between 2 and 6 days after inoculation and had detectable hemagglutination-inhibiting titers to porcine parvovirus at 5 or 6 days after inoculation. Virus was isolated from multiple tissues of pigs killed between 3 and 17 days after inoculation. Viral antigen was demonstrated mainly in lymphoid tissues of these pigs. Gross and microscopic examination of tissues failed to reveal any notable pathologic changes. The numbers of thymus- and bone marrow-derived lymphocytes did not differ significantly in inoculated and noninoculated control pigs, and the response of peripheral blood lymphocytes to selected mitogens was not altered by infection.

Porcine fetuses with pulmonary hypoplasia resulting from experimental swine influenza virus infection

Porcine fetuses between 51 and 57 days of gestation were inoculated intraallantoically with swine influenza virus and examined 3, 7, 13, 28 and 58 days after inoculation. At 3 and 7 days, severe epithelial necrosis was seen in most bronchial buds and there was moderate epithelial necrosis in more fully differentiated major bronchi. As a result of the epithelial injury, bronchial buds did not develop further and the surrounding mesoderm failed to differentiate. By 28 days, the lungs of inoculated fetuses were about one-half the size of the normal control lungs. Microscopically, the lungs of the inoculated fetuses were composed of major bronchi surrounded by multiple islands of cartilage, medium to large arteries and a few small, incompletely developed lobules. Influenza virus was isolated most consistently and in greatest quantity from the lung, trachea and chorion of inoculated fetuses. Influenza viral antigen was shown in the epithelium of bronchial buds, bronchi and the trachea by direct fluorescent antibody staining. Hemagglutination inhibiting antibodies to influenza virus were first found in the serum of an inoculated fetus at 13 days and in the sera of all inoculated fetuses at 28 and 58 days.

Transplacental infection and embryonic death following maternal exposure to porcine parvovirus near the time of conception

Each of 20 gilts (principals) from a commercial swine herd free of antibody for porcine parvovirus (PPV) was exposed intranasally and orally to PPV at the onset of gestation. The gilts were killed and necropsied 22 +/- 1 days later to determine the effect of the virus on their embryos. An equal number of gilts (controls of the same status, from the same herd, and bred to the same boars, were treated similarly except for exposure to PPV. The following data were obtained at necropsy and from subsequent laboratory tests. Principals had 223 corpora lutea (8 to 16/gilt) and 203 embryos (6 to 16/litter). Porcine parvovirus-infected embryos (1 to 9/litter) were detected in 12 (60 per cent) of the 20 litters. Of the 203 embryos of principals, 169 were alive and 34 were dead and in various stages of decomposition and resorption. Both virus and viral antigen were detected in 7 of the live embryos (1, 1, 2, and 3 in 4 litters) and in 32 of the dead embryos. With 1 exception, infected live embryos were next to infected dead littermates in the uterus suggesting the beginning of intrauterine spread of the virus. Controls had 234 corpora lutea (9 to 15/gilt) and 217 embryos (9 to 14/litter). None of their embryos were infected with PPV and all but 3 were alive.

Replication of porcine parvovirus in peripheral blood lymphocytes, monocytes, and peritoneal macrophages

Porcine peripheral blood lymphocytes (PBL), peripheral blood monocytes, and peritoneal macrophages were examined for their ability to support porcine parvovirus (PPV) replication. The cell cultures were infected with the NADL-2 strain of PPV at 0.1 multiplicity of infection. PBL cultures were stimulated with the following phytomitogens: phytohemagglutinin M, concanavalin A, and pokeweed mitogen. Unstimulated PBL cultures infected with PPV and uninfected PBL stimulated with phytomitogens served as controls. All cultures were examined daily for PPV-specific immunofluorescence and hemagglutinin. PPV replicated in PBL cultures stimulated with all phytomitogens. Both viral hemagglutinin in culture fluids and nuclear immunofluorescence in cells were detected. In contrast, unstimulated PBL did not support viral replication; however, PPV antigen was detected in the cytoplasm. PPV persisted in unstimulated PBL for 21 days (duration of the experiment) without replication, but replicated each time with the addition of phytohemagglutinin M at 0, 3, 7, 14, and 21 days after infection. Uninfected PBL stimulated with phytomitogens lacked both viral hemagglutinin and immunofluorescence. Simultaneous detection of lymphocyte surface marker and viral antigens in pokeweed mitogen-stimulated PBL revealed that both T and non-T cells (B and null cells) are able to support PPV replication. Peripheral blood monocytes and peritoneal macrophages phagocytized PPV but did not support virus replication.

Serological response of the bovine fetus to bovine viral diarrhea virus

Susceptible pregnant heifers were inoculated with bovine viral diarrhea virus at 150 days of gestation and earlier. Fetuses were surgically collected at selected times after inoculation. Serum immunoglobulins were quantitated, and the presence of specific antibodies was determined. In fetuses from heifers inoculated at 150 days, immunoglobulin M (IgM) appeared approximately 2 weeks after inoculation and was followed in 7 days by IgG1. Later IgG2 was detected in the sera of three fetuses. Serum-neutralizing and complement-fixing antibodies were first detected in a fetus taken at 206 days of gestation. Fetuses taken at later times also had specific serum antibodies. Possible explanations for the appearance of serum immunoglobulin substantially before specific bovine viral diarrhea antibodies include the viral alteration of host tissues rendering them antigenic viral activation of polyclonal B cells, and viral modulation of virus-specific lymphocytes causing specific interference with the appearance of antiviral antibodies. In one of the fetuses having IgG2, the serum also contained IgA. Placental leakage of material immunoglobulins was thought to be responsible for the presence of IgA and IgG2 in this fetus. Small quantities of IgM were found in the serum of two fetuses taken from heifers inoculated between 65 and 95 days of gestation, but specific antibodies were found in none.

Efficacy of an inactivated virus vaccine for prevention of porcine parvovirus-induced reproductive failure

Gilts vaccinated IM either once (4 gilts) or twice (2 gilts) with an acetylethyleneimine-inactivated porcine parvovirus (PPV) vaccine before they were bred were subsequently exposed intranasally and orally to virulent PPV at about the 40th day of gestation (from 37 to 43 days). At 2 weeks after vaccination, all had hemagglutination-inhibiting (HI) titers for PPV (from 20 to 80) which decreased by the time the immunity was challenged with virulent virus (from 10 to 40), but increased thereafter (from 160 to 1,280). Titers of singly and doubly vaccinated gilts were similar throughout the experiment. The gilts were killed at about the 84th day of gestation (from 80 to 87 days), and their litters were examined. Litters were comprised of 68 live fetuses and 1 dead fetus (7 to 14 fetuses/litter). Neither viral antigen, PPV, nor homologous HI antibody was found in any of the fetuses. In addition, 4 gilts were kept in contact with the vaccinated gilts and were treated similarly except for vaccination. These 4 gilts remained free of HI antibody until after they were exposed to virulent PPV during gestation. At the time the gilts were killed the titers were 1,280 to 2,560. Their litters were comprised of 11 live fetuses and 26 dead fetuses (8 to 11 fetuses/litter). Virus was isolated from fetuses of all litters. Viral antigen was found in 24 of the dead fetuses and 10 of the live fetuses. All infected live fetuses also had HI antibody for PPV. The 2 boars used to breed vaccinated and nonvaccinated gilts (usually each gilt was bred to each of the 2 boars), but not exposed to virulent PPV, remained free of HI antibody for PPV.

Cerebrospinal parelaphostronglylosis in llamas

Four of 11 llamas (Lama guanicoe) from a ranch near Houston, Texas developed clinical signs of a neurologic disease. Tissues from 2 of the 4 llamas were submitted for microscopic examination. Lesions in the central nervous system of both llamas appeared to have been caused by a migrating parasite. An adult nematode having morphologic features of the meningeal worm (Parelaphostrongylus tenuis) was found in the brain of one llama. The findings suggest that the neurologic disease in the llamas were caused by P. tenuis.

Male pseudohermaphroditism, cryptorchism, and Sertoli cell neoplasia in three miniature Schnauzers

A syndrome of male pseudohermaphroditism, cryptorchidism, and testicular neoplasia was diagnosed in 3 Miniature Schnauzers. The dogs had clinical signs of hyperestrogenism and were either unilateral or bilateral cryptorchids. At surgery, it was discovered that the dogs were male pseudohermaphrodites, having intra-abdominal testes containing Sertoli cell tumors and uteri that had undergone endometrial cystic hyperplasia.

Fetal and adult bovine interferon production during bovine viral diarrhea virus infection

Levels of interferon in adult bovine serum and in fetal bovine serum and tissues were examined during the course of transplacental bovine viral diarrhea virus infection. The cows produced circulating interferon between 2 and 9 days after viral inoculation, with mean peak levels in the serum on day 4. Interferon could be routinely detected in fetal tissues (e.g., thymus, spleen, and kidney) between days 4 and 21 after viral inoculation of the cows at 149 to 150 days of gestation (mid-second trimester) and in fetal serum from day 13 through day 21. Interferon was also detectable in the serum and tissues of fetuses from dams infected at day 95 of gestation (the beginning of the second trimester). In general, no differences were found between the ability of the adult and fetus to produce interferon. Fetal lamb kidney cells were more sensitive to the antiviral effects of bovine interferon than were fetal bovine kidney cells. The antiviral substance from the fetal and adult animals was characterized as interferon by standard criteria.

Pathogenetic studies of infection of the bovine fetus with bovine viral diarrhea virus. II. Ocular lesions

Twenty-three susceptible pregnant heifers were inoculated with bovine viral diarrhea virus at 150 +/- 1 days of gestation. Seven additional heifers were inoculated between 65 and 115 days of gestation. Acute ocular lesions were seen in fetuses taken 17-21 days after inoculation of the dams at 150 days. By the fourth week, the acute lesions were beginning to resolve, and in newborn animals focal to total retinal atrophy was seen. The acute lesions were characterized by a mild to moderate retinitis that resulted in various degrees of destruction of the different layers, mononuclear cuffing of inner retinal vessels, proliferation of pigment epithelium, and choroiditis. Residually there was an absence of cellular elements in the atrophied areas of the retina, frequently a loss of layering and various numbers of pigment-containing cells. Moderately severe acute inflammation was seen in the retina of the fetus taken at 22 days after inoculation of its dam at 95 days. Ocular lesions did not occur in the other fetuses taken from heifers inoculated at earlier stages of gestation.

Pathogenetic studies of infection of the bovine fetus with bovine viral diarrhea virus. I. Cerebellar atrophy

A cytopathogenic strain of bovine viral diarrhea virus was intravenously inoculated into 14 pregnant susceptible and two control heifers at 150 ± 1 days of gestation. Fetuses were surgically taken at sequential steps after inoculation. Acute cerebellar lesions consisting of leptomeningeal inflammation, necrosis of cells in the external germinal layer, focal hemorrhages and moderate to severe folial edema were seen in the fetuses taken at 17 and 21 days after inoculation. By 42 days, the cerebellar lesion had completely evolved, and the inflammatory reaction was subsiding. Moderate to severe folial degeneration with cavitation characterized the residual cerebellar lesion. Folial edema caused the major destruction of cerebellar tissue. Necrosis of cortical neurons and focal hemorrhages also contributed to the residual lesion.