Characterisation of Cowdria ruminantium (agent of heartwater infection) isolates from Kenya

• Main Author: Ngumi, Priscilla Nyambura
• Published: University of Edinburgh 1997
• Subjects: 591.9857
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.659964

A description of the isolation of new <I>Cowdria </I>isolates by different methods and from different vectors and geographical locations in Kenya is given. These included <I>Amblyomma variegatum, A. gemma and A. lepidum. </I>Isolates from the later two species were also by feeding adults moulted from nymphs collected in the field and is the first report on transtadial transmission by <I>A. gemma </I>ticks. A spectrum of virulence ranging from highly virulent to mildly virulent for sheep was found among the <I>Cowdria </I>isolates. The majority of isolates were highly virulent. There was a range of mouse infectivity among the isolates from inapparent to lethal. The Asembo and Baragoi isolates were pathogenic and lethal, the Kiswani, was infective and non pathogenic for Balb-C mice while the other 8 were avirulent or refractile to mice inducing only antibody production in various proportions of mice. There was a difference in the infectivity for neutrophils both in the frequency of infected cultures and in their level of infection. The different isolates were classified as of low infectivity where even the few positive cultures rarely reached 1% infection rate, medium infectivity if a good number of cultures regularly attained 1% infected neutrophils, or high infectivity if a large proportion of the cultures which became positive regularly attained 1% infected neutrophils and at least some of then attained more than 10% infected neutrophils. The isolates also had a range of infectivity for the brain endothelial cells, from no detectable colonies to greater than 16% infected endothelial cells in individual animals. The author concludes that the agent of heartwater is endemically widespread in many districts in Kenya and poses a potential threat of outbreaks to areas newly invaded by vector ticks and also to areas where immunity due to the local agent may not protect against an invading one. The author recommends that the Baragoi or Marigat isolate should be adopted for possible vaccine development in Kenya.