My principal research interest is in the community ecology of wildlife disease, and the implications for conservation and public health.
My PhD dissertation work at James Cook University examined the ecology of a host-parasite system involving lizards and blood parasites, as a model for understanding disease in wildlife systems in general. Since then I have worked as a postdoctoral researcher in partnership between IUCN – The World Conservation Union and several universities.
The research component of my work over the last 4 years has focused on two distinct systems, plague in shortgrass prairie communities, and Lyme disease in oak woodland communities of California. My work on the dynamics of plague (Yersinia pestis) and prairie dog colonies in northern Colorado was done in collaboration with Colorado State University and California State University – Fullerton. Prairie dogs are important members of prairie ecosystems, but entire colonies that inhabit hundreds of hectares of prairie can be decimated within a matter of weeks by sporadic outbreaks of the plague. Understanding the dynamics of the disease is therefore crucial to management plans for the conservation of this species. Previous research has focused on prairie dogs, but our team investigated the broader ecological community and surveyed rates of plague exposure and flea infestation patterns in other small mammals in this grassland habitat. We determined that plague outbreaks appear to be associated with the abundance of a syntopic mammal, the northern grasshopper mouse. Furthermore we have been able to describe a plausible mechanism for increased disease spread when these mammals are in high numbers: they are more resistant to plague than prairie dogs, can infect fleas with the disease, and importantly, appear to act as mobile carriers of large numbers of prairie dog fleas when prairie dogs begin to die off. We also investigated the interactions of plague with swift foxes, a species of conservation importance, and examined the possible roles of carnivores in plague ecology.
The second piece of research, at the University of California – Berkeley, has worked to understand the community ecology of Lyme disease, caused by the spirochete Borrelia burgdorferi, which is the most common arthropod-borne bacterial disease in North America. I have focused on the role of western gray squirrels and have demonstrated a good geographical correlation between rates of human infection and prevalence rates of squirrels in counties of northern California. Also, I have performed laboratory experiments to show that squirrels are indeed viable reservoir hosts of the disease agent B. burgdorferi. Using simple models that incorporate host densities, their tick burdens, and reservoir potential, it appears that in Californian oak woodlands, western gray squirrels are the predominant Lyme disease reservoir. This implies that public health initiatives to control Lyme disease risk should target anti-tick treatment on western gray squirrels to maximize management impacts.
Currently, I am working upon the impacts of landuse change upon the ecology and emergence of infectious diseases. I aim to examine deforestation and vector-borne diseases in south-east Asia, and traditional burning practices in Australia and the impact on mosquito-borne viruses.
Salkeld DJ & RS Lane (2009) Community ecology and disease risk: lizards, squirrels and the Lyme disease spirochete in California. Ecology in press Stapp P, DJ Salkeld, HA Franklin, JP Kraft, RJ Eisen, DW Tripp, MF Antolin & K Gage (2009) Evidence for the involvement of an alternative rodent host in the dynamics of plague in prairie dog colonies. Journal of Animal Ecology in press Stapp P & DJ Salkeld (2009) Inferring host-parasite feeding relationships using stable isotopes: implications for disease transmission and host specificity. Ecology in press Salkeld DJ & P Stapp (2009) The effects of weather and plague-induced die-offs of prairie dogs (Cynomys ludovicianus Ord) on the fleas (Siphonaptera) of northern grasshopper mice (Onychomys leucogaster Wied). Journal of Medical Entomology in press. Salkeld, DJ., S Leonhard, YA Girard, N Hahn, J Mun, KA Padgett & RS Lane (2008) Identifying the reservoir hosts of the Lyme disease spirochete Borrelia burgdorferi in California: the role of western gray squirrels (Sciurus griseus). American Journal of Tropical Medicine & Hygiene 79: 535-540. Salkeld, DJ, M Trivedi & L Schwarzkopf (2008) Parasite loads are higher in the tropics: temperate to tropical variation in a single host-parasite system. Ecography 31: 538-544. Stapp P, DJ Salkeld, RJ Eisen, DW Tripp, R Pappert, K Gage & MF Antolin (2008) Exposure of small rodents to plague during prairie dog epizootics. Journal of Wildlife Diseases 44: 724-730. Salkeld DJ, RJ Eisen, P Stapp, AP Wilder, J Lowell, DW Tripp, D Albertson & MF Antolin (2007) The potential role of swift foxes (Vulpes velox) and their fleas in plague outbreaks in prairie dogs. Journal of Wildlife Diseases 43: 425-431. Salkeld DJ & P Stapp (2006) Seroprevalence rates and transmission of plague (Yersinia pestis) in mammalian carnivores. Vector-borne and Zoonotic Diseases 6: 231-239. Salkeld DJ & L Schwarzkopf (2005) Epizootiology of blood parasites in an Australian lizard: a mark-recapture study of a natural population. International Journal for Parasitology 35: 11-18. Braithwaite VA, DJ Salkeld, HM McAdam, CG Hockings, AM Ludlow & AF Read (1998) Spatial and discrimination learning in rodents infected with the nematode Strongyloides ratti. Parasitology 117: 145-154.