Swine Fever Virus Research Articles

Effect of infections with swine fever virus on immune functions III. Antibody response to lipopolysaccharide and sheep red blood cells

In order to determine the effect of infections with low-virulent swine fever virus (SFV) on antibody responses, pigs were administered lipopolysaccharide (LPS) or sheep red blood cells (SRBC), 2 days after injection. Infected pigs showed an enhanced primary response to LPS late during infection. The secondary response to LPS seemed to be unaffected. Both the primary and secondary antibody response to SRBC appeared to be enhanced rather than depressed in infected pigs. These in vivo findings that pigs infected with low-virulent SFV do not develop a depression of B lymphocyte function.

Effect of infections with swine fever virus on immune functions I. Response of lymphocytes from blood and lymphoid organs from infected and normal pigs to anti-immunoglobulin serum and protein A

Pigs exposed to a low-virulent strain of swine fever virus (SFV) developed an inapparent infection. At times when a transient leucopenia occurred, the peripheral blood lymphocytes (PBL) were unresponsive to the mitogenic stimulus of anti-immunoglobulin serum (anti-Ig) and protein A. Pigs lethally infected with a virulent SFV showed leucopenia and unresponsiveness of PBL to anti-Ig and protein A from 2 days post infection until death. This suggests a defect in B lymphocyte function in pigs infected with SFV. The unresponsiveness to anti-Ig appeared not to be caused by a reduced ability of lymphocytes to redistribute their receptors into caps, the presence of suppressor cells or absence of surface immunoglobulin bearing lymphocytes in the peripheral blood. A direct action of the virus itself also seemed unlikely. Lymphocytes from spleen reacted as PBL. However, lymph node cells did not lose their capability to respond to anti-Ig. These data suggest that a change in the migration pattern of anti-Ig responsive lymphocytes could account for the observed unresponsiveness of PBL and spleen lymphocytes to anti-Ig.

Experimental production of congenital persistent swine fever infections: II. Effect on functions of the immune system

Twelve pregnant sows were infected at various stages of gestation with a low-virulent field strain of swine fever (SF) virus. The sows developed neutralizing antibody in serum, colostrum and milk. Only one pig had antibody to SF virus at birth. Twenty-three congenitally infected pigs developed a persistent viraemia. In the plasma samples of these pigs, neither antibodies nor virus-antibody complexes were detected after the disappearance of maternal antibodies. The persistently infected pigs showed a normal antibody response against sheep red blood cells, except in the terminal stage of disease. These observations indicate immunological tolerance to SF virus in these pigs. Immunological tolerance was also induced in pigs which had been infected in utero after the onset of immune competence. The lymphocyte response to phytohaemagglutinin seemed to be slightly depressed in the persistently infected pigs, whereas the response to pokeweed mitogen was comparable with that of control pigs. A clear, cell-mediated immune response to SF virus could not be demonstrated by the lymphocyte stimulation test. Three pigs that were born uninfected did not produce neutralizing antibody following natural exposure from in-contacts, whereas the littermates did. These pigs appeared to be sensitized when challenged with virulent SF virus.

Experimental production of congenital persistent swine fever infections: I. Clinical, pathological and virological observations

Twelve sows were inoculated with a low-virulent field strain of swine fever (SF) virus at 40, 65 and 90 days of pregnancy. Transplacental infection occurred in eight sows and these farrowed 88 piglets. Prenatal mortality was highest in litters from sows infected at 40 days after service, and postnatal death was most frequent in litters from sows infected at 65 days. Three sows gave birth to completely infected litters, whereas the five others farrowed litters in which uninfected piglets were found. The later the sows were infected during pregnancy, the more uninfected piglets were born. Twelve piglets recovered from the infection and the percentage of recoveries increased with the stage of pregnancy at which inoculation took place. Twenty-three piglets developed a persistent infection. The earlier infection occurred during pregnancy, the more persistent infections were produced. The persistently infected pigs developed a runting syndrome from about one week after weaning. The clinical signs were more severe in pigs from sows infected at 65 days of pregnancy than in pigs from sows infected at 40 days. A persistent viraemia was present in these pigs with titres ranging between 10 5.7 and 10 7.0 plaque forming units/ml of plasma. At autopsy the most pronounced lesions were an atrophy of the thymus, and swollen and pale lymph nodes. Virus antigen was present in lymphoidal, reticulo-endothelial and epithelial tissues. One persistently infected pig survived superinfection with a virulent strain of SF virus for 45 days.

A Survey of the Viruses of Farm Animals in Northern Ireland

SUMMARY Continuing surveillance of the viral infections of farm animals in Northern Ireland since 1962, using virus isolation procedures, serological tests, direct electron microscopic examination of clinical material and clinical and histopathological investigations show that a wide range of viruses are present in Northern Ireland. The agents detected are recorded. There is evidence for the absence of several agents, viz foot and mouth disease virus; swine fever virus; and transmissible gastroenteritis of pigs. Newcastle disease virus was recovered but the disease is not now present in Northern Ireland, at least in a clinically recognizable form.

Recovery of caprinized and lapinized rinderpest viruses from condensed water vapour removed during desiccation.

Stein and Rogers1 demonstrated the presence of Newcastle disease virus in the condensed water vapour removed during desiccation of material containing that virus. They failed to demonstrate the presence of vesicular stomatitis, equine encephalomyelitis, equine infectious anæmia and swine fever viruses under similar conditions.