Models for heartwater epidemiology: practical implications and suggestions for future research.
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 (R0 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.
Yonow
T
T
Department of infectious Diseases, College of Veterinary Medicine, University of Florida, Gainesville 32611-0880, USA. tania.yonow@tag.csior.au
Brewster
C C
CC
Allen
J C
JC
Meltzer
M I
MI
D000818:Animals; D001096:Arachnid Vectors / Q000502:physiology; D002353:Carrier State / Q000453:epidemiology / Q000662:veterinary; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000276:immunology / Q000635:transmission; D004198:Disease Susceptibility / Q000662:veterinary; D016995:Ehrlichia ruminantium / Q000502:physiology*; D006357:Heartwater Disease / Q000453:epidemiology* / Q000276:immunology / Q000635:transmission; D011157:Population Dynamics; D012098:Reproduction; D012680:Sensitivity and Specificity; D013019:South Africa / Q000453:epidemiology; D013987:Ticks / Q000502:physiology; D013997:Time Factors