Abstract:
We present a simple model of the dynamics of heartwater that we use to explore and better understand
various aspects of this disease. We adapted the Ross-Macdonald model for malaria epidemiology so
that we could consider both host and vector populations, and evaluate the interactions between the
two. We then use two more biologically detailed models to examine heartwater epidemiology. The first
includes a carrier state and host mortality, and the second includes density dependence. The results
from all three models indicate that a stable equilibrium with high disease levels is probably the standard
situation for heartwater (R<sub>0</sub> between 5,7 and 22,4). More than 80% of cattle become infected with
heartwater if only 12% of infected tick bites produce an infection in cattle, if tick burdens are as low as
only five ticks per host per day, or if tick lifespans are as short as 7 d. A host recovery rate of 30 d
results in over 50% of the cattle becoming infected with heartwater. Our analyses indicate that it is
quite difficult to prevent the establishment and maintenance of high levels of heartwater in a herd,
thereby supporting previous suggestions that any attempts at controlling this disease through stringent
tick control regimens are not warranted.
