Cowdria ruminantium DNA is unstable in a SuperCos1 library

A Cowdria ruminantium genomic library was constructed in a cosmid vector to serve as a source of easily accessible and pure C. ruminantium DNA for molecular genetic studies. The cosmid library contained 846 clones which were arrayed into microtitre plates. Restriction enzyme digestion patterns indicated that these clones had an average insert size of 35 kb. Probing of the arrays did not detect any bovine clones and only one of the known C. ruminantium genes, pCS20, was detected. Due to the high AT content and the fact that C. ruminantium genes are active in the Escherichia coli host, the C. ruminantium clones were unstable in the SuperCos1 vector and most clones did not grow reproducibly. The library was contaminated with E. coli clones and these clones were maintained with greater fidelity than the C. ruminantium clones, resulting in a skewed representation over time. We have isolated seven C. ruminantium clones which we were able to serially culture reproducibly; two of these clones overlap. These clones constitute the first large regions of C. ruminantium DNA to be cloned and represent almost 10% of the C. ruminantium genome.

Heartwater in sheep and goats: a review

Heartwater (cowdriosis) is an important, often fatal, tick-borne disease of domestic and wild ruminants in sub-Saharan Africa and some Indian Ocean and Caribbean islands. The causal agent, Cowdria ruminantium (Cowdry 1925), is a rickettsia closely related to members of the genus Ehrlichia, and is probably a part of a complex of genomic species. Imported breeds of sheep and goats (especially Angoras) are highly susceptible, but indigenous populations of endemic areas may be resistant to infection. Very young stock (less than 9 d old) possess a natural resistance that is unrelated to the immune status of the dams. Symptoms of heartwater vary, but usually begin with fever and may involve neurological signs and respiratory distress. Clinical diagnosis is based on symptoms, history of tick-exposure and post-mortem findings, and is confirmed by demonstration of characteristic rickettsial organisms in vascular endothelial cells. Laboratory diagnosis is retrospective and includes fluorescent antibody and enzyme-linked immunosorbent assays. Serological tests are compromised by non-specific reactions with certain Ehrlichia spp. DNA and oligonucleotide probes have been developed, but are thus far unavailable in many countries affected by heartwater. Treatment with tetracyclines is effective if begun in the early stages of infection. Control is based on a knowledge of the disease cycle in nature, and is achieved through judicious tick control, vaccination or both. A virulent, blood-based vaccine is available. Existence of a carrier state in recovered animals, including wild ruminants, complicates control efforts, and eradication is feasible only in circumscribed foci. Problem areas in fundamental and applied research on heartwater, as it affects sheep and goats, are discussed.

Studies on the presence of endotoxin activity and inflammatory products (leukotrienes) in cases of experimentally induced heartwater in sheep

The presence of endotoxin was examined in seven sheep with experimentally induced heartwater. Elevations in endotoxin levels were recorded in one sampling in three of the seven sheep during the acute stage of the disease. The elevations in endotoxin levels were of short duration and decreased in the 24-h follow-up samples. There was no elevation of leukotrienes (B4, C4 and D4) in the blood, or the thoracic or pericardial fluid of any of the sheep.

Conconavalin A-stimulated bovine T-cell supernatants inhibit growth of Cowdria ruminantium in bovine endothelial cells in vitro

Conconavalin A-stimulated bovine T-cell supernatants inhibited the growth of Cowdria ruminantium in bovine endothelial cells in vitro but did not affect their entry. This finding represents one mechanism by which T cells may control C. ruminantium multiplication and hence affect the severity of disease.

The presence of endotoxin activity in cases of experimentally-induced heartwater in sheep

The presence of endotoxin was examined in 5 sheep with experimentally-induced heartwater. Two peaks in endotoxin levels were recorded in 4 out of the 5 sheep during the acute stage of the disease. The 1st peak coincided with or occurred shortly after the febrile reaction (over 40 degrees C). The 2nd peak occurred 3-5 days after the 1st, and in 2 sheep this 2nd elevation in endotoxin levels was associated with severe clinical signs (rapid and laboured breathing, cyanosis and recumbency), and 1 of the 2 sheep died on the day of the 2nd elevation. Both endotoxin peaks were of short duration and levels had decreased in the 24-h follow-up samples.

The pathogenesis of heartwater

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.

Abortion rate and mortality among exotic pregnant heifers imported to the Gezira in the central region of the Sudan

Despite the intensive management and husbandry precautions, exotic pregnant heifers imported to the Gezira, Sudan, suffered excessive stress. Four of five heifers aborted due to stress. Death was due to pasteurellosis, babesiosis and heart water.

Cowdria ruminantium (Rickettsiales) in primary goat kidney cell cultures

Fresh or cryopreserved kidney tissue from goats suffering from heart water (Cowdria ruminantium infection) was infective when inoculated intravenously into susceptible goats. Primary kidney cell cultures were established from 14 goats reacting to C ruminantium infection; they were tested for infectivity by intravenous injection into susceptible goats after periods varying from five to 31 days. Three cultures, five, 12 and 13 days old, induced heartwater in recipients. The other 11 cultures, varying in age from six to 31 days, did not cause any reaction and all 11 recipient goats died from heartwater on challenge. C ruminantium could not be detected microscopically in the cell cultures.

Heartwater in Nigeria. II. The isolation of Cowdria ruminantium from live and dead animals and the importance of routes of inoculation

A study was carried out to determine which materials from animals dying or dead of heartwater could initiate the disease in susceptible goats, using the intravenous and subcutaneous routes. C. ruminantium was consistently isolated by intravenous injection of the whole blood or of lung macrophages and by subcutaneous injection of brain homogenate. In animals dead of heartwater, it appeared that isolation of the organism was achieved only when extensive post-mortem autolysis had not supervened. Experiments with blood fractions showed that leucocytic and plasma fractions of infective blood transmitted heartwater; the erythrocytic fraction consistently failed to induce an infection.

Attempted artificaial infection or impala, blue wildebeest, buffalo, kudu, giraffe and warthog with heartwater

Intravenous injection of Cowdria ruminantium infected blood produced no sings of disease in four impala, Aepyceros melampus; three blue wildebeest, Connochaetes taurinus; a buffalo, Syncerus caffer; a kudu, Tragelaphus strepsiceros; a giraffe. Giraffa camelopardalis and a warthog, Phacochoerus aethiopicus. a control sheep injected with the same blood reacted severely and showed typical lesions of heartwater at autopsy.