Genetic structure of the tick Ornithodoros coriaceus (Acari: Argasidae) in California, Nevada, and Oregon.

The argasid tick Ornithodoros coriaceus (Koch) is the only confirmed vector of epizootic bovine abortion (EBA) in the United States. The disease and its tick vector have historically been reported in the foothills of the Sierra Nevada Mountains and coast ranges of California. In the past two decades, the range of EBA has apparently expanded into southern Oregon and northern Nevada. Possible explanations for this expansion include 1) increased recognition and reporting of EBA in these regions; 2) widespread movement of tick-infested and EBA-infected hosts with subsequent colonization of these regions by infected ticks; and 3) widespread movement of the EBA agent, independent of tick movements, into extant tick populations in these new regions. The current study was performed to evaluate these hypotheses by examining patterns of variability in a 420-bp segment of the 16S mitochondrial rDNA gene sequence among 210 O. coriaceus individuals from 14 sites in California, Oregon, and Nevada. Sixty-three unique haplotypes were identified in the ticks tested, with 84% of the sequence variation attributable to among-population variation and 16% to within-population variation. A majority of the haplotypes were unique to their particular collection site, whereas only four collection sites shared haplotypes. Overall, very little evidence of gene flow among tick populations was detected, making it unlikely that widespread tick movement had introduced O. coriaceus and the EBA agent into new regions.

A simulation model of brucellosis spread in British cattle under several testing regimes.

Brucellosis is a widespread, economically devastating and highly infectious zoonosis. In cattle, infection predominantly is caused by Brucella abortus, and is usually detected in pregnant females through abortions. Great Britain (GB) has been declared free from brucellosis (officially brucellosis free (OBF)) since 1993 and as such is required by European Union (EU) regulations to test > or =20% of both beef and dairy cattle >24 months old routinely. Currently, however, GB serologically tests more cattle than required and the issue of reducing the level of testing has come under consideration. We developed a simulation model to determine the rate of spread of brucellosis under a variety of testing regimes. For dairy herds, we found that reducing the level of testing would have a major effect on the rate of spread of infection, should it be imported. For beef herds, reducing the level of testing would have much less effect. We also found that abortion notification is a very-important additional means of surveillance. As a result of our predictions, policy-makers decided not to reduce the level of testing and actively to promote abortion notification.

Application of the Neospora caninum IgG avidity ELISA in assessment of chronic reproductive losses after an outbreak of neosporosis in a herd of beef cattle.

Point-source infections are most likely the cause for Neospora caninum-induced abortion outbreaks in cattle, whereas an increased annual abortion rate may be a consequence of vertical transmission. The aims of the present study were to examine the reproductive effects of neosporosis in a beef herd for 3 years, after a point-source outbreak and to use IgG avidity serology to examine the chronicity of infections and patterns of transmission. During the study, 76-78% of animals were seropositive for N. caninum. The pregnancy rate varied from 88% to 94%, without any reduction in the pregnancy rate of seropositive cows compared with seronegative cows. The annual abortion rate was 2.5-5.5%, and all but 1 abortion occurred in seropositive dams. The efficiency of vertical transmission was estimated to be 85%. Several calves, born to seronegative dams, were seropositive at 6-13 months of age, indicating a 22% mean annual rate of horizontal transmission. The mean avidity in seropositive cows increased from 30 during the initial outbreak to 74 after 3 years. The mode of IgG avidity was 21-40 during the initial abortion outbreak, 41-60 after 1 year, and 61-80 after 2 and 3 years. The results reveal high annual rates of both vertical and horizontal transmission of N. caninum in a herd of beef cows and provide further validation on the ability of the N. caninum IgG avidity ELISA to accurately assess the chronicity of infection.

Experimental transmission of epizootic bovine abortion (foothill abortion).

Advances in defining the biology of epizootic bovine abortion (EBA), including identification of the etiologic agent, have been hampered by the inability to reproduce the disease with confidence. Experimental reproduction of EBA, by feeding the tick vector Ornithodoros coriaceus on susceptible pregnant heifers, is not reliable. The primary objectives of this study were to identify specific tissue(s) obtained from EBA-infected fetuses that could transmit the disease, and then utilize such an infectious challenge system to better define the pathogen, host immunity and geographic distribution of the agent. Described here is the ability to routinely reproduce EBA following inoculation of cryopreserved suspensions of homogenized thymus into susceptible pregnant heifers. This challenge system permitted experiments demonstrating the agent was non-filterable, inactivated upon sonication and susceptible to antibiotics. These findings suggest a prokaryotic microbe and represent a major advance in EBA research. Additional experiments demonstrated that inoculation of the cryopreserved EBA-infectious tissue into heifers, prior to breeding, conferred immunity. Furthermore, such immunized heifers were resistant to challenge with heterologous sources of infectious tissue, suggesting monovalent vaccine development might be feasible. Lastly, challenge studies employing animals from Central Nevada, an area considered free of EBA, demonstrated partial immunity, suggesting the pathogen, and possibly the disease, enjoy a broader distribution than previously thought.

Diagnosis of epizootic bovine abortion in Nevada and identification of the vector.

In the 43 years since the first description in California, epizootic bovine abortion (EBA) has been considered but not definitively diagnosed as a cause of late-term abortions on Nevada ranches. Examination of aborted full-term bovine fetuses obtained from Nevada ranches revealed gross abnormalities consistent with EBA (enlarged lymph nodes, petechial hemorrhages of the oral mucosa and conjunctiva, ascites, and splenohepatomegaly), and EBA was confirmed by histologic examination of fetal tissues. The histologic thymic changes were characteristic of EBA and included severe histocytic thymusitis with depletion of thymocytes, interlobular hemorrhage, and fibrinocellular exudation. The gross enlargement of lymph nodes was the result of cortical follicular hyperplasia and histiocytic lymphadenitis. In addition, widespread, predominately nonsuppurative histologic lesions typical of EBA were observed in most organs, including the brain, lung, heart, liver, and spleen. Furthermore, the presence of Ornithodorus coriaceus, the argasid tick vector of EBA, was established by tick collection using CO2 traps. The tick was identified on ranches and in geographic areas (northern and northwestern counties of Nevada) coincident with diagnosis of multiple cases of EBA. This study establishes the presence of EBA as a cause of late-term abortion in Nevada. Additionally, identification of the EBA tick vector, O. coriaceus, in the same areas as the abortions provides strong evidence that the disease is endemic.

[Salmonella abortus ovis carrier state in dogs and rats]. / Prouchvaniia vurkhu nositelstvoto na Salmonella abortus ovis pri kucheta i plukhove.

Serologic and bacteriologic investigations were carried out with 10 dogs, guarding sheep flocks with and without Salmonella abortions, and 17 grey rats. It was found that both species of animals could harbour Salmonella abortus ovis provided they swallowed infective material (aborted fetuses and fetal membranes). It was shown that although lasting but 2 to 3 months only the carrier state could play a definite part in the epizootiology of Salmonella abortions in sheep.