founder animals to a crisis situation with related animals, a poor sex ratio, and few
mature, experienced breeder males.”
Captive-bred animals released into the wild may spread disease or pick up para-
sites and pathogens from endemic wildlife. A potential example of the former is Jones’s
(1982) report of the release of Arabian oryx captive-raised in the USA for a national
park in Oman, which was delayed when the animals tested positive for antibodies to
bluetongue disease. The failure of reintroduced animals of woodland caribou to an
island within their historic range in Ontario, Canada is an example of lethal trans-
species parasites and the problems that can be encountered with reintroduced
animals becoming infected with a disease from the endemic wildlife. The area had
been colonized by white-tailed deer and the caribou became infected with meningeal
worm from the deer via a gastropod secondary host (Anderson 1972).
Another example comes from the captive breeding of whooping cranes (Grus
americana). An eastern equine encephalitis (EEE) virus fatally infected 7 of the 39
captive-bred population at the Patuxent Wildlife Research Center in Maryland, USA.
At that time, in 1985, the captive population accounted for about 25% of the world’s
population. EEE virus causes sporadic outbreaks of disease in mammals and birds
in the eastern USA and is spread by mosquitos. No deaths are usually seen in endemic
hosts, but introduced game birds such as ringneck pheasants (Phasianus colchicus)
are vulnerable. Among the some 200 sandhill cranes in neighboring pens to the whoop-
ing cranes some birds were serum positive for EEE virus but no clinical signs were
found. The discovery of the vulnerability of the whooping cranes to a common pathogen
was seen as an unrecognized risk and an obstacle to the species’ recovery (Carpenter
et al. 1989).Spratt (1990), in reviewing the possible use of helminths for controlling vertebrate
pest species, pointed out the marked contrast between the numerous successes in
biological control of insects and the almost universal failure of such methods to con-
trol vertebrates. The one unequivocal success has been the use of the Myxomavirus
to control European rabbits in Australia (Fig. 11.5).Myxomatosis is a benign disease in Syvilagus(cottontail) rabbits in South
America which is transmitted mechanically by mosquitoes. In the European rab-
bit (Oryctolagus), which is a pest in Australia and England, the virus from Sylvilagus194 Chapter 11
11.12 Parasites and control of pests
8 7 6 5 4 3 2 1 01900 1920 1940 1960 1980
YearSkins (million kg)Fig. 11.5Numbers of
rabbits trapped in
Australia (million kg of
skins) shows a rapid
decline after 1950 when
the Myxomavirus was
introduced to control
rabbits. (Data from
Fenner 1983.)