Abstract:
Heartwater, a tick-borne disease caused by Ehrlichia ruminantium, is considered to be a
significant cause of mortality amongst domestic and wild ruminants in South Africa. The
main vector is Amblyomma hebraeum and although previous epidemiological studies have
outlined endemic areas based on mortalities, these have been limited by diagnostic
methods which relied mainly on positive brain smears. The indirect fluorescent antibody
test (IFA) has a low specificity for heartwater organisms as it cross-reacts with some other
species. Since the advent of biotechnology and genomics, molecular epidemiology
has evolved using the methodology of traditional epidemiology coupled with the new
molecular techniques. A new quantitative real-time polymerase chain reaction (qPCR) test
has been developed for rapid and accurate diagnosis of heartwater in the live animal. This
method can also be used to survey populations of A. hebraeum ticks for heartwater. Sampling
whole blood and ticks for this qPCR differs from routine serumsampling, which is used for
many serological tests. Veterinary field staff, particularly animal health technicians, are
involved in surveillance and monitoring of controlled and other diseases of animals in
South Africa. However, it was found that the sampling of whole blood was not done
correctly, probably because it is a new sampling technique specific for new technology,
where the heartwater organism is much more labile than the serumantibodies required for
other tests. This qPCR technique is highly sensitive and can diagnose heartwater in the
living animal within 2 hours, in time to treat it. Poor sampling techniques that decrease the
sensitivity of the test will, however, result in a false negative diagnosis. This paper describes
the development of a skills training programme for para-veterinary field staff, to facilitate
research into the molecular epidemiology of heartwater in ruminants and eliminate any
sampling bias due to collection errors. Humane handling techniques were also included in
the training, in line with the current focus on improved livestock welfare.
