Feature Article - Rabbit Calicivirus in Tasmania
Feature article published in the Tasmanian Year Book, 1998 (cat. no. 1301.6)
The European rabbit is one of Australia’s worst vertebrate pests. Previous attempts at biological control of this species-using the myxoma virus-have been only temporarily successful. In 1980 the rabbit calicivirus-another rabbit-specific pathogen-was brought to Australia for evaluation as a control method. In October 1995, during field testing, the virus escaped from the quarantine station on Wardang Island to mainland South Australia.
After spreading rapidly, the presence of calicivirus in Tasmania was confirmed in early January 1997. It is thought that infected insects introduced the virus to the State at some time in either late winter or spring 1996. First detected at Meander in the central north, the disease spread during the summer and autumn east to Perth and west to Lorinna at an average rate of about 3 km per week. North-south spread was limited, probably reflecting the prevailing wind patterns. In much of the infected area, rabbit numbers plummeted and were still very low in August 1997, although there was some reinvasion around the edges from uninfected rabbits.
Two other small outbreaks were also detected later, one near Rocky Cape and the other east of the Tamar River. These may have spread either from the first outbreak or have been separate introductions from the mainland.
Approval to actively spread calicivirus was given by the Minister for Primary Industry and Fisheries on April 23rd 1997. The first release was made one week later at a site on South Arm peninsula where rabbit numbers had been monitored for several months. With its dry climate and sandy soils, this area supports the densest rabbit populations in Tasmania. Due to low winter-time insect population, the virus spread slowly from the infection site covering a radius of approximately 1 km within 2 months. Within 3 months 75% of the rabbits near the release site had died. The virus was released at a number of other sites in southern and north-western Tasmania during winter 1997.
These winter releases were made partly to study the survival of calicivirus in Tasmania’s winter conditions and partly to try to ensure a supply of virus in the environment to allow rapid spread when conditions become favourable in spring.