This project focused on collecting field data to describe Salmonella transmission in commercial cattle in northern Australia (the Kimberley region) and the risk posed by the presence of feral pigs for Salmonella spread to cattle. The intra-herd genetics of feral pig herds associated with commercial cattle paddocks were also determined. Based on the field information collected and a disease spread model, inferences were made for potential foot-and-mouth disease (FMD) outbreaks to enhance emergency disease preparedness plans in northern pastoral regions.
Cattle sampling was completed in May 2011 on the three main pastoral leases comprising the study site. A total of 496 cattle faecal samples were collected from 47 different cattle herds in feral pig free and feral pig infested areas. Fecal samples were cultured for Salmonella using standard microbiological techniques. Approximately 2% of cattle samples were culture positive for Salmonella, a prevalence much lower than that of co-grazing feral pigs (~38%). Additionally, cattle Salmonella isolates were more commonly from areas without feral pigs, but conversely, from high density cattle populations on artificial water. No associations between the serotypes identified from cattle and those identified in the feral pig population were found. Fingerprint analysis (using pulsed‐field gel electrophoresis) confirmed the lack of an association.
The feral pig population in the study area was sampled and genotyping was completed. A total of 543 feral pig genotypes were analysed across 14 loci. The feral pig genetic population was found to be remarkably homogenous across the large catchment area of the Fitzroy River.
Feral pig and grazing cattle distributions were created based on aerial surveys of the study area and expert opinion. A susceptible-infected-resistant disease spread model was coded and parameterised based on published literature and expert opinion.
A baseline scenario in which infection was introduced via feral pigs, with transmission from pigs to cattle and no disease control, was simulated. Assumptions regarding disease transmission were investigated via sensitivity analyses. Predicted size and length of outbreaks were compared assuming different control strategies based on movement controls, surveillance and depopulation.
Based on field studies of the interaction between domestic cattle and feral pigs in the Kimberley region, the potential spread and control options for an FMD incursion in northern Australia were investigated, using a disease spread model. Depopulation of feral pigs only was not predicted to be successful. Movement standstill, surveillance and depopulation of cattle only would successfully eradicate the disease. However, control targeting both feral pigs and cattle would result in smaller outbreaks. If FMD is controlled in cattle, then it is likely to be self-limiting in feral pigs. To eradicate an FMD incursion as quickly as possible, both feral pigs and cattle should be targeted.