Susceptibility to heartwater of calves born to non-immune cows

The resistance to artificical infection with Cowdria ruminantium of calves born to cows fully susceptible to heartwater is no different from that of calves bred in heartwater endemic areas where the tick challenge is negligible to considerable. The sub-inoculation into mice of blood collected 14-26 days after infection proved the presence of the heartwater agent in the blood of 8 out of 10 calves with no other clinical signs than mild to moderate fever. The combined use of a mouse model and the indirect fluorescent antibody test revealed considerable variation in the degrees to which calves become infected and react to artifical infection.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.lmchunu2014mn201

Heartwater : past, present and future : proceedings of a workshop held at Berg en Dal, Kruger National Park, on 8-16 September 1986

The preparation of the antigen, details of the reagents, the titration of the antispecies conjugates and the execution of the indirect fluorescent antibody test are described. The sensitivity and specificity of the test and its applicability to the detection of antibodies to Cowdria ruminantium are recorded. The test is both highly specific and sensitive and can be applied to a wide range of studies on heartwater, including epidemiology, determination of the C. ruminantium infection rate of Amblyomma ticks and the evaluation of immunization against heartwater. The test can also be used to detect antibodies to the heartwater agent in the sera of game.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.lmchunu2014mn201

Heartwater : past, present and future : proceedings of a workshop held at Berg en Dal, Kruger National Park, on 8-16 September 1986

A critical evaluation is made of reports in the literature on the block method of vaccination and the relevant factors that play a role in the immunization against heartwater are also discussed. The most important of these is the fact that in heartwater immunogenicity parallels pathogenicity. It is shown that the more severe the reaction of the host to the immunizing infection, the stronger its immunity to subsequent challenge. The importance of this principle in the block method is emphasized. Other factors that play a role are the average incubation periods recorded in the different domestic ruminants after experimental infection and differences in age and breed susceptibility. The survival rate of experimentally infected Bonsmara cattle and Merino sheep that were treated on different days of the febrile reaction also serve as a guideline to determine the day after infection on which block treatment can be applied. The danger of a fatal recrudescent infection if block treatment is given too early, necessitating additional treatment and close observation, is indicated. In conclusion, recommendations on the day of block treatment are made for each domestic ruminant species. It is emphasized that the other methods of immunization of large groups of animals, such as treatment only after the commencement of the febrile reaction determined by the daily recording of early morning temperatures, or the prolonged prophylactic chemotherapy of susceptible stock exposed to heavy tick challenge, are preferable to the block method. The block method does, however, find application in certain instances where these procedures are impractical or inappropriate.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

Heartwater : past, present and future : proceedings of a workshop held at Berg en Dal, Kruger National Park, on 8-16 September 1986

In an epidemiological study undertaken on 23 farms where heartwater occurs endemically, it was found that on an overall average, antibodies to Cowdria ruminantium were detected in 64,3 % of the cattle, 6 adult Amblyomma hebraeum ticks were counted per animal and 7,0 % of ticks were infected with the heartwater agent. It was found that the seropositivity of the animals was determined largely by the tick loads to which they were subjected and that the influence of the tick C. ruminantium infection rate was less evident. There was no parallel between the prevalence of heartwater on the farms and the immune status of the animals. In general, higher tick counts were recorded in herds where strategic tick control is practised than on farms with a total tick control programme. The method of tick control did not, however, appear to influence the immune status of the cattle, the tick infection rate, or the prevalence of heartwater.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.lmchunu2014mn201

Heartwater : past, present and future : proceedings of a workshop held at Berg en Dal, Kruger National Park, on 8-16 September 1986

Hypotheses on the pathogenesis of heartwater, which have been published so far, are briefly reviewed. Attempts were made at counteracting the effects of vaso-active substances released by mast cells by treating mice infected with Cowdria ruminantium with antagonists to histamin and serotonin on one hand, and with mast cell stabilizers on the other, but were not successful. Preliminary findings suggest that a hypersensitive type of reaction, triggered by the release of pharmacologically active substances, may possibly be basic to the pathogenesis of heartwater. Complement, and the products of arachidonic acid metabolism, possibly play a role in the release of the vaso-active substances.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.lmchunu2014mn201

Heartwater : past, present and future : proceedings of a workshop held at Berg en Dal, Kruger National Park, on 8-16 September 1986

Antibodies in the sera of domestic ruminants that have been infected with Ehrlichia bovis and other ehrlichial agents cross-react with the Kümm strain of Cowdria ruminantium used in the indirect fluorescent antibody test as antigen. These cross-reactions are also shown by the Elisa test in which the Ball 3 strain of the heartwater agent is used as antigen.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.lmchunu2014mn201

Heartwater : past, present and future : proceedings of a workshop held at Berg en Dal, Kruger National Park, on 8-16 September 1986

Techniques for the rearing of Amblyomma species to be used in heartwater (Cowdria ruminantium) transmission experiments are discussed. These involve the breeding and maintenance of infected and noninfected strains of ticks. They include the feeding of ticks on sheep, rabbits, mice, tortoises and guinea fowl.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.lmchunu2014mn201