George W. Beran

The epidemiology of toxoplasmosis in Iowa swine farms with an emphasis on the roles of free-living mammals

Multiparous sows from 19 central Iowa swine farms were tested for antibodies against Toxoplasma gondii by the modified direct agglutination test. Antibody titers of 1:32 or greater were considered positive. Rodents, domestic cats, opossums (Didelphis virginiana), raccoons (Procyon lotor) and striped skunks (Mephitis mephitis) were live-trapped on each farm and similarly tested for antibodies. The overall prevalence of T. gondii antibodies in the species tested was 39/273 (14.3%) swine, 31/74 (41.9%) cats, 2/588 (0.3%) house mice (Mus musculus), 0/21 mice of the genus Peromyscus, 0/9 Norway rats (Rattus norvegicus), 1/34 (2.9%) opossums, 4/14 (28.6%) raccoons and 2/7 (28.6%) striped skunks. The overall prevalence was significantly greater in adult cats versus juvenile cats, adult male cats versus adult female cats, and adult raccoons versus juvenile raccoons. The prevalence of T. gondii antibodies in sows was compared with the prevalence in each non-swine species on a farm basis in order to identify existing associations. The prevalence in sows (and each of the non-swine species) was also analyzed on a farm basis for association with farm characteristics or swine management practices, including the degree of confinement of swine, population size and average parity of breeding female swine, estimated cat population size, and estimated mouse and rat abundance. Average titers of seropositive animals were compared on a species basis. The prevalence in sows which were totally and continuously confined was lower than that in sows which were not totally and continuously confined. The prevalence in sows from farms with an average parity of less than 2.0 was significantly lower than that in sows from farms with an average parity of 2.0 or greater. These results suggested that the prevalence of T. gondii antibodies in swine increased with age and that prevalence in swine could be reduced through total confinement. No associations could be established between prevalence in sows and prevalence in non-swine species or other farm characteristics/swine management practices. However, the high prevalence of T. gondii antibodies in cats suggested that fecal contamination of the environment by cats may be the most significant source of toxoplasmosis for swine. The extremely low prevalence of T. gondii antibodies in house mice suggested that this species was not an important source of T. gondii for swine in Iowa.

A current assessment of the role of porcine parvovirus as a cause of fetal porcine death.

One hundred one litters containing 1 or more dead porcine fetuses were collected at an Iowa abattoir during a 2-month interval and examined for evidence of viral infection. Each of 1,137 fetuses (302 dead, 835 alive) of these litters was tested for porcine parvovirus (PPV) antigens by direct immunofluorescence microscopy (FA) of fetal lung. Antigens of PPV were detected in the lungs of most of the fetuses of 11 of the litters. The 11 FA-positive litters contained 105 dead (100 FA-positive) and 14 live (12 FA-positive) fetuses. Infectious PPV was isolated from 10 of the 11 FA-positive litters and from 3 of the 90 FA-negative litters. No cytopathogenic agents other than PPV were isolated from any of the litters. Eleven of 101 (11%) litters examined and 100 of 302 (33%) dead fetuses examined were FA positive for viral antigen, indicating that PPV remains as a major cause of porcine fetal death.

Porcine Leptospirosis in Iowa

The epidemiology of leptospirosis in Iowa swine was examined on the basis of serologic results and herd data from 55 herds in the National Animal Health Monitoring System (NAHMS) program and culture results and histories from 578 cases of reproductive failure submitted to the Iowa Veterinary Diagnostic Laboratory during a 3-year period. Thirty-eight percent of sera from NAHMS herds contained antibodies against 1 or more of 12 leptospira antigens. Leptospires were isolated from 9 (1.6%) of 578 cases of reproductive failure. Seven (78%) of the isolates were identified as Leptospira interrogans serovar kennewicki and 2 (22%) as serovar grippotyphosa. In 7 herds from which leptospires were isolated, attack rates ranged from 1% to 84%. Clinical leptospirosis, characterized by reproductive failure and confirmed by isolation of leptospires, was sporadic. No significant differences in farrowing averages and reproductive problems were observed between vaccinated and nonvaccinated NAHMS herds or between herds with higher (43–63%) or lower (14–40%) percentages of animals that were serologically positive against serovar bratislava.

Serologic diagnosis of encephalomyocarditis virus infection in swine by the microtiter serum neutralization test.

ophilic cytoplasmic and sometimes intranuclear inclusions characteristic of canine distemper infection. No viral inclusions were seen in the brain and lungs. However, in lung there was moderately severe patchy interstitial alveolar thickening. Other incidental findings included moderate numbers of Sarcocystis in striated muscles (heart, tongue, diaphragm, esophagus, masseter, and extraorbital muscles), a few Capillaria sp. in the mucosa of the esophagus and urinary bladder, large numbers of Cryptosporidium sp. in the intestines, and a few unidentified helminthic eosinophilic granulomas in the lung and mesenteric lymph nodes. The eosinophilic meningitis observed in the present case appears to be an incidental finding not related to the protozoa1 infection. Based on these findings, the primary disease in the raccoon was distemper. The neurologic signs were attributed to the extensive multifocal lesions produced by the unidentified protozoa. Based on morphologic and antigenic differences, the organism was neither T. gondii nor N. caninum. Both N. caninum and T. gondii divide into two progeny by endodyogeny, whereas the present organism divided into numerous progeny by schizogony. The low T. gondii antibody titer (10) in the raccoon serum is considered nondiagnostic in the agglutination test. The organism causing encephalitis in the raccoon is morphologically similar to the organism associated with equine protozoa1 myeloencephalitis (EPM). The organism in the raccoon and that causing EPM resemble Sarcocystis in structure, react with Sarcocystis immunologically, are located free in the host cell cytoplasm, divide by schizogony, have no rhoptries, multiply in neurons, and cause malacia of the central nervous system. Acknowledgements. This research was supported in part by grants from the Pennsylvania Department of Agriculture. The authors thank Eva Kovacs, M. Coicou, S. Hindman, B. Lehmann, and J. Dieter for technical assistance, Charlie Brown for transmission electron microscopy, and Dr. D. E. GranStrom for providing Sarcocystis cruzi serum.

A Study Comparing the Immunologic Responses of Swine to Pseudorabies Viral Antigens Based on the ELISA, Serum Virus Neutralization, and Latex Agglutination Tests

A study of pseudorabies virus (PRV)-vaccinated pigs comparing the immune responses detected by the latex agglutination test (LAT) with responses detected by other routine tests for pseudorabies antibodies indicated that LAT was more sensitive than either the enzyme-linked immunosorbent assay (ELISA) or the serum virus neutralization test (SVNT). The LAT detected antibodies sooner than ELISA and SVNT in unvaccinated pigs after challenge with virulent PRV. The specificities of the 3 tests were found to be near 100%. The LAT is a good alternative to SVNT or ELISA for detection of PRV-specific antibodies.

Further Studies on the Susceptibility of Raccoons (Procyon lotor) to a Rabies Virus of Skunk Origin and Comparative Susceptibility of Striped Skunks (Mephitis mephitis)

Two raccoons (Procyon lotor) were inoculated in the masseter muscles with 1059 mouse intracerebral lethal dose50 (MICLD50) of a rabies virus isolated from a naturally infected Iowa (USA) striped skunk (Mephitis mephitis). Five striped skunks were inoculated with either 1007 or 1021 MICLD50 of the same isolate. All five skunks died within 35 days following inoculation. Both raccoons survived 273 days without adverse effects, and virus was not isolated from saliva samples taken at between 25 and 273 days following inoculation.

Relationship of Mycotoxins to Swine Reproductive Failure

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Disease and destiny–mystery and mastery

When early people made their appearance, zoonotic infectious diseases were already waiting, but epidemic diseases did not appear in human history until people began to live in large numbers under conditions of close contact, mainly during the last 10,000 years. Disease has decimated urban populations, conquered armies, and disrupted society. The focus here is on (1) the plague of Athens and the Black Death; (2) smallpox, influenza, and rabies; (3) avian influenza prion diseases, and foot & mouth disease; and (4) emerging and re-emerging diseases. All have veterinary public health associations. In Athens, Greece, in 430 BC, when the Spartans ravaged the countryside, hordes crowded into Athens so that orderly movements, space in which to live, and adequate supplies of food became impossible. Crowding of any population fosters disease transmission; chaos and disorder enhance it all the more. Out of northern Egypt came a terrible plague from across the Mediterranean Sea. The identity of the plague of Athens remains unsure, but the well-considered conclusion is Rift Valley Fever, a mosquito borne, viral zoonosis. The Black Death, also called the Plague, raged in Asia for centuries. In 1347, the Black Death was brought by a ship out of Asia to Sicily. The scenes of devastation were repeated throughout Europe, with 90% or more of the people dying in city after city. Influenza, too, has been a cause of periodic human epidemics, but the great pandemic of influenza occurred in the last months of World War I. In the years of highest occurrence, more than half the worlds population became clinically infected. If veterinary public health had been born earlier, it could have led to elucidating the epidemiology of influenza and the plagues of Athens, Europe, and Asia. In turn, smallpox had also caused continual tragedy. In 1796, Edward Jenner began to harvest pustules of cowpox from children or infected cows and inject them into susceptible children. In 1980, the World Health Organization declared that smallpox had been eliminated from the world. Rabies, though, still strikes terror. A number of animal diseases, broadly termed emerging and re-emerging diseases, need surveillance because they have the potential to impact human health. From late in 2003 to 2007, the highly pathogenic H5N1 influenza virus in poultry infected at least 121 people and caused 62 deaths in four countries. The prion diseases, too, all have very high numbers in concentrated contacts. To control these diseases, veterinary public health is essential, with diagnosis, epidemiological surveillance, clinical manifestations, and prevention as primary measures.

Trial of Heat Inactivation of Selected Viruses Following Irradiation

Four selected viruses were irradiated in ground pork with an electron beam at absorbed doses of 4.4 to 5.27 kG. Irradiated and nonirradiated viruses were heated at four temperatures for four time intervals and assayed for surviving virus. Data were examined for evidence of irradiation-heat interaction to determine whether absorbed irradiation would sensitize virus so that a lesser amount of heat would be required for inactivation. It was determined that irradiation does not increase lability to heat to a level that has practical application in virus inactivation.

The effect of storage time on isolation of Leptospira interrogans from bovine kidneys

Kidney tissues from 20 cattle infected with Leptospira interrogans serovars hardjo, pomona, or grippotyphosa were cultured on the day of slaughter and 3, 6, and 8 days later to examine the effect of storage time on the recovery of leptospires by conventional culture methods. Leptospires were isolated from 85% of infected bovine kidney tissues cultured on day 1, and from 95%, 90%, and 90% of kidney tissues stored in transport medium at 4 C for 3, 6, and 8 days, respectively, prior to inoculation of culture media.