The pathogeneses and clinical pathology of cowdriosis [Heartwater] in sheep

Abstract

Heartwater is a disease of ruminants transmitted by ticks. It is mainly found in the African continent and the surrounding islands but lately isolated cases have been reported elsewhere. The disease occurs in different forms ranging from peracute to inapparent forms. It is associated with a febrile reaction, acute gastroenteritis, hydropericardium and nervous symptoms. Heartwater is a killer disease and thus effective treatment and control of the disease are of utmost importance. Tetracylines used early have been found to be effective but for this, accurate diagnosis of the disease is important. The only definitive way of diagnosing the disease is at portmortem when the brain smears stained with giemsa reveal the rickettsial organisms. Lately, researchers have been doing a lot of serology work on the disease with the aim of coming up with diagnostic tests in the live animal. Clinical pathology tests can also help as diagnostic aids of the disease. This work was designed with this in mind, to observe the behaviour of particular blood components of sheep infected with Cowdria ruminantium and to correlate this with the pathogenesis of the cell fraction associated with the organisms in blood. Twenty sheep were used in this work. These were adults, non-pregnant and of Dopper breed (or Dopper cross). They were housed in the animal compound, Kabete, and fed on hay, bran and water. The sheep were mainly purchased from the Faculty Farm, Kabete. Fifteen sheep were infected while five were used as controls. Initially, blood was collected from all four sheep:- EDTA blood for hematology and clotted blood for biochemistry. This was done for 3 consecutive days before infection to get the baseline values. After this 3 experimental sheep were infected with' Cowdria ruminantium intravenously. A blood stabilate obtained from Veterinary Laboratories, Kabete was used as the infective agent. Body temperatures were monitored twice daily and after the onset of the febrile reaction, blood samples were taken for hematological and biochemical analysis. Blood samples were collected daily in the first 3 days and after that every other day upto death or recovery. In those sheep that died postmoretm was carried out. Some more work was done to try and identify the cell fraction in blood associated with Cowdria ruminatium. The animals manifested anorexia, depression, increased respiratory rate, increased pulse rate, harsh lung sounds with moist rales and muffled heart sounds. Nervous signs observed in some animals included circling, high stepping gait, chewing movements, ataxia and incoordination and then lateral recumbency and paddling movements. All animals which manifested nervous signs died of the disease. The major findings on postmortem were froth in the trachea, congested and oedematous lungs, hydropericardium, ascites, hyrdothorax and congested and oedematous brain. From the hematology results, sheep infected with Cowdria ruminantium showed anaemia, leukopenia during incubation period followed by a leukocytosis after fever onset. There was a neutrophilia, lymphopaenia and oesinophils disappeared completely from circulation. Statistical analysis using analysis of variance showed these findings were statistically significant. From the clinical biochemistry results there was an increase in glucose concentration especially terminally which was statistically significant. Of the enzymes analysed, lactate dehydrogenase, creatinine phosphokinase and aspartate aminotransferase showed the most signifcant change in that their activities increased. Alkaline phosphatase and alanine aminotransferase did not show significant changes. Blood urea nitrogen increased significantly after the febrile reaction. The study of the cell fraction associated wi th the organism revealed the neutrophil as the cell most likely to be associated with Cowdria ruminantium but this is, of course, subject to exhaustive research work.